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 Author Topic: DOF and Micro Four-Thirds Format  (Read 13293 times)
Er1kksen
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Quote from: BJL
That is very misleading, because the image used from the 14mm lens in 4/3 is only half the width and height of that from the 14mm lens in 35mm format, so when printed at the same size, it must be enlarged twice as much. That extra enlargement doubles out of focus effects too, and so gives half as much DOF as 14mm in the larger format, and also a very different FOV, if comparing with equal f-stop.

But on the other hand, doubling focal length from 14mm to 28mm at equal f-stop reduces DOF by a factor of four (it goes with the square of focal length.) And doubling f-stop doubles DOF (with same focal length same degree of enlargement.)

So, doing the comparison sanely, viewing equal sized images of the same subject from the same distance:
- 14mm in 4/3 has half the DOF of 14mm in 35mm at the same f-stop
- 28mm in 35mm format has one quarter the DOF of 14mm in 35mm format at the same f-stop
- 28mm in 35mm format has twice the DOF of 28mm in 35mm format at half the f-stop
and thus
- 14mm in 4/3 has twice the DOF of 28mm in 35mm at the same f-stop
- 14mm in 4/3 has the same DOF of 28mm in 35mm at twice the f-stop. E.g 14mm f/4 in 4/3 vs 28mm f/8 in 35mm.
The last is my rule of thumb, doubling focal length and f-stop for equal FOV and equal DOF (and equal diffraction effects.)

Hopefully we will not now return to debating whether it is more reasonable to compare images with completely different field of view from the different formats, or to compare crops to equally sized portions of the differently sized sensors!

I think you misunderstood my meaning. All I meant was that, quite simply, regardless of format or field of view, a 14mm lens is a 14mm lens and will have the same dof at a given aperture as any other 14mm lens. Naturally, format and field of view affect how that relates to the actual image captured, but that basic understanding is quite helpful to most (it certainly was to me) rather than misleading. It's an awareness to build from.

Also, Ray, in your goal to compare to the BEST zuiko lenses in their category, the 7-14 is certainly appropriate, but the 14-35 f2, undisputedly the top normal zoom for 4/3, is curiously absent? And are either of these top-end lenses you mention stabilized for optimal low-light performance? It's something to take into account.

As for my stake in all this, I shoot Pentax, still have an old, beaten up Oly E-330, and know that I get better low-light performance but have to be more careful with dof with my Pentax than I did with my Oly, and if I were shooting with a FF model that would be true of it over my Pentax. Like 250swb, I think just a little too much is being made here of dof calculations and equivalence. The real question is, does it allow you to get the images you want?
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BJL
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Quote from: Ray
My interest is in getting the best performance possible within the parameters of reasonable cost, reasonable weight and and reasonable convenience of use. I'm not interested in sacrificing a noticeable and significant loss of image quality for the benefit of a noticeable and significant loss of weight.
Fine: and for some one like you who is willing to buy and use heavier, more expensive lenses and bodies, larger formats have a natural advantage; there is no need for fancy, detailed comparisons to show the well-known benefits of larger aperture diameters and such in some situations! And there is also no point to comparing those heavy, expensive larger format options to a Four Thirds body equipped with cheapest, lightest f/3.5-4.5 entry level 4/3 lens options either! (For example, my 4/3 lenses are f/2.8-3.5.)

But do not pretend that you are "not interested in sacrificing a noticeable and significant loss of image quality for the benefit of a noticeable and significant loss of weight", especially when cost is also acknowledged as a factor. Some of your gear choices clearly involve trade-offs on quality. For example, getting your 400mm focal length using a zoom lens that offers only f/5.6 at 400mm rather than say a Canon 400/4 or 400/2.8, and struggling to get longer focal lengths with TC's that kill AF. And on the cost limit there is the understandable fact that you do not augment your 35mm format gear with DMF for the higher resolution and such.

It is just matter of where we draw the line on size, weight and cost, not pretending such factors are "beneath us" in our gear choices. And since getting a lot of my favorite images involves hauling telephoto-capable gear on hikes, my trade-offs are different than yours.
 « Last Edit: April 15, 2009, 11:13:29 AM by BJL » Logged
Ray
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Quote from: Er1kksen
Also, Ray, in your goal to compare to the BEST zuiko lenses in their category, the 7-14 is certainly appropriate, but the 14-35 f2, undisputedly the top normal zoom for 4/3, is curiously absent? And are either of these top-end lenses you mention stabilized for optimal low-light performance? It's something to take into account.

I'm not familiar with all Zuiko lenses, but the 14-35/F2 would seem to be a good match for the EF-S 17-55/F2.8 IS, having just done a Google search. Trouble is, an E-620 with Zuiko 14-24/F2 is just as heavy as a 50D and EF-S 17-55/2.8 IS. It's also slightly more expensive than the Canon set-up. One would therefore expect image quality to be at least as good, on balance.

I wonder if it is.
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BJL
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Quote from: Er1kksen
I think you misunderstood my meaning. All I meant was that, quite simply, regardless of format or field of view, a 14mm lens is a 14mm lens and will have the same dof at a given aperture as any other 14mm lens.
I understood perfectly: but that comparison only applies when one compares images with different angular FOV from the different lenses, and this is almost certainly not what people are asking about when they ask about how to compare DOF between different formats, which is why I called it "misleading" (not false). Especially since you did not mention the different FOV difference involved in that comparison.

DOF scales and tables are routinely compute using a "maximum acceptable circle of confusion" that increases roughly in proportion to format size, and for good reasons of allowing for the different degree of enlargement typically used with different formats. Without considering degree of enlargement in DOF reckoning, one is effectively debating the DOF to be seen on contact prints, or equivalently irrelevant stuff.

Your response is exactly what I was referring to in my final comment that
"Hopefully we will not now return to debating whether it is more reasonable to compare images with completely different field of view from the different formats ..."
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BJL
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For me, the f/2 zooms are an irrelevant indulgence of the 4/3 system: larger formats are probably a better solution when one needs aperture diameters that large. Meaning 24x36mm, not the baby step up to EF-S.

P.S. Not that I am saying there is no good reason for anyone to buy and use them, just that they are not relevant to my approach to choosing a camera system and format, and not to the vast majority of Four Thirds users, I suspect.
 « Last Edit: April 15, 2009, 12:41:44 PM by BJL » Logged
Ray
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Quote from: BJL
But do not pretend that you are "not interested in sacrificing a noticeable and significant loss of image quality for the benefit of a noticeable and significant loss of weight", especially when cost is also acknowledged as a factor. Some of your gear choices clearly involve trade-offs on quality. For example, getting your 400mm focal length using a zoom lens that offers only f/5.6 at 400mm rather than say a Canon 400/4 or 400/2.8, and struggling to get longer focal lengths with TC's that kill AF. And on the cost limit there is the understandable fact that you do not augment your 35mm format gear with DMF for the higher resolution and such.

BJL,
I'm not pretending. My attitude towards the 400mm problem is perfectly consistent with my previous statement, ie. "...best performance possible within the parameters of reasonable cost, reasonable weight and and reasonable convenience of use. I'm not interested in sacrificing a noticeable and significant loss of image quality for the benefit of a noticeable and significant loss of weight."

The 100-400/F5.6 IS is the only option avaialble that fits those parameters. There's simply no other lens available, whether Canon or Nikon. I might be prepared to accept the extra 1/2Kg weight of the 300/2.8 IS, but not the extra weight plus the extra cost (A\$6,500 street price). The Canon 400/F4 DO IS is no heavier than the 100-400/F5.6 and would be an ideal replacement and upgrade, but the cost is ridiculous (A\$8-9,000).

As regards 400mm options, I'm stuck.
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BJL
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Quote from: Ray
BJL,
My attitude towards the 400mm problem is perfectly consistent with my previous statement, ie. "...best performance possible within the parameters of reasonable cost, reasonable weight and and reasonable convenience of use.
...
As regards 400mm options, I'm stuck.
Right, so it comes down to different standards of reasonable, based on different standards of portability as well as cost. Which is why your insertion of the EF-S 17-55/2.8 into a comparison against far less expensive and lighter Four Thirds gear makes little sense: that is beyond the ``reasonable'' price limits of most DSLR users.

As to being stuck for 400m options: you need to think in terms of FOV, not focal lengths. Maybe a shorter, brighter[1] lens with a sensor of higher resolution[2] would be a better option! The sensor rather than the body might be your main barrier in telephoto performance.

Notes:
(1) "brighter" is the wonderful name used in parts of Europe for a lens of lower minimum f-stop: more accurate than "faster" when comparing different formats.
(2) resolution of the "electronic emulsion", in l/mm or pixels per mm or whatever.
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Er1kksen
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Quote from: BJL
I understood perfectly: but that comparison only applies when one compares images with different angular FOV from the different lenses, and this is almost certainly not what people are asking about when they ask about how to compare DOF between different formats, which is why I called it "misleading" (not false). Especially since you did not mention the different FOV difference involved in that comparison.

DOF scales and tables are routinely compute using a "maximum acceptable circle of confusion" that increases roughly in proportion to format size, and for good reasons of allowing for the different degree of enlargement typically used with different formats. Without considering degree of enlargement in DOF reckoning, one is effectively debating the DOF to be seen on contact prints, or equivalently irrelevant stuff.

Your response is exactly what I was referring to in my final comment that
"Hopefully we will not now return to debating whether it is more reasonable to compare images with completely different field of view from the different formats ..."

That's the thing: I'm not talking about comparing between different fields of view and formats or not. I'm not talking about comparing anything. I'm talking about a law of optics. A 14mm lens is a 14mm lens and has a given dof for a given aperture at a given focussing distance and that's that. I think you would agree with that. Your points about fov and degree of enlargement are perfectly valid as far as I can tell, and I'm happy to agree with them. But that basic law is, as stated, constant between formats. Things like acceptable circle of confusion and degree of enlargement come after that basic fact. No comparisons needed.

It's easy to use it to make a comparison, if you wish: you say "well, my 50mm lens on my 35mm camera gives me a certain amount of dof at f2.8. Since I would use a 25mm lens on 4/3 to get the same angle of view, and 25mm lenses have more dof at f2.8 than 50mm lenses have at f2.8 due to their shorter focal length, I will have more dof using the 25mm lens at f2.8 on 4/3 than the 50mm at f2.8 on 35mm." It's that simple, and it's true, as I can attest having used both formats extensively and observed the results. If something in your arguments about degree of enlargement and "acceptable circle of confusion" applies to prints smaller than poster-size, I have yet to see it, having made great looking 11x14s from 4/3 with lenses at a variety of focal lengths and apertures, and having seen poster prints that look quite good as well. Hardly contact sheets.

It's also useful if you want to compare how much increase in dof you'd get by putting that 50mm lens on your 4/3 camera and shooting it at f2.8: the short answer is, at the same focusing distance, you wouldn't, since according to the simple law I described it's constant. Of course, given that you'd then have a much narrower fov, you'd have to back up to get a similar composition to what you had before, and therefore your focusing distance increases, resulting in greater dof. So there is no increase in dof if focusing distance is kept constant, but there is if the composition is kept approximately constant (obviously perspective will be altered).

I don't know how you're expecting your technical side-arguments to help the OP. The things I'm saying here are not misleading or hard to understand. They're quite simple and based on my direct experience in conjunction with a basic understanding of how optics work. I've never bothered with a dof calculator (I can see with my own eyes whether or not I have sufficient dof at a given aperture) but I have made plenty of prints.
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Ray
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Quote from: BJL
As to being stuck for 400m options: you need to think in terms of FOV, not focal lengths. Maybe a shorter, brighter[1] lens with a sensor of higher resolution[2] would be a better option! The sensor rather than the body might be your main barrier in telephoto performance.

I do think in terms of FoV. My current 100-400 has the FoV of a 640mm lens on FF 35mm, and my 50D is amongst the highest pixel densitiy DSLRs available, with the exception of the 12mp 4/3rds cameras.

I'm not aware of any Zuiko options that would either equal the performance of the 100-400/F5.6 with a substantial savings in weight, or exceed the performance of the 100-400 without a substantial increase in both weight and cost.

The Zuiko ED 90-250/2.8 certainly has the advantage with regard to speed, but it's doubful that a 12mp image from a 500mm (35mm equivalent) lens would be sharper than a 15mp image from a 640mm lens. Even if the Zuiko were marginally sharper, the additional weight and cost (compared with the 100-400) could not be justified. (3.2Kg and A\$7-8,000 as opposed to 2Kg and A\$2,000).

As I said, I'm stuck

Quote
Right, so it comes down to different standards of reasonable, based on different standards of portability as well as cost. Which is why your insertion of the EF-S 17-55/2.8 into a comparison against far less expensive and lighter Four Thirds gear makes little sense: that is beyond the ``reasonable'' price limits of most DSLR users.

The differences in price and weight between the EF-S 17-55/2.8 and the cheaper Zuiko zooms of equivalent focal length are trivial compared to the differences between the Zuiko 90-250/2.8 and the Canon 100-400 IS. I could be wrong, because there's a dearth of rigorously conducted comparisons on the internet, but I get a clear impression that the cheaper and lighter 4/3rds equivalents never quite match the image quality of the slightly heavier and more expensive Canon combinations. If you want to equal and, hopefully, even exceed the quality of the Canon equivalent, you end up with a 4/3rds system which is heavier and more expensive than the Canon equivalent. Right?
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Ray
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Quote from: Er1kksen
That's the thing: I'm not talking about comparing between different fields of view and formats or not. I'm not talking about comparing anything. I'm talking about a law of optics. A 14mm lens is a 14mm lens and has a given dof for a given aperture at a given focussing distance and that's that. I think you would agree with that.

Your point is a point worth making for the sake of clarity, and it's a point that needs to be understood before embarking upon any DoF/FoV/FL comparisons. But the fact remains, for the practicing photographer, the resulting print or displayed image, is always, without exception, a specific composition which, of necessity, has a specific field of view.

Whether you acheive that FoV by selecting a lens of an appropriate focal length, or cropping during post-processing, is up to you. If maximum detail and sharpness is your priority, then maximising the 'real estate' of your sensor through use of the most appropriate FL, is the way to go; hence the popularity of zoom lenses.

Another point worth mentioning in relation to this, is that of image circle. Whilst a 14mm lens is a 14mm lens, the diameter of the usable image circle may vary considerably. If one were to fit the Canon EF-S 10-22mm to the Nikon D700 and take a shot at 14mm, then compare it with a shot of the same scene taken with the Nikkor 14-24 at 14mm (same aperture), you'd probably get a shock   .

The images might appear to be about equally sharp in the centre of the frame (with equal DoF if you're lucky), but long before you'd reached the edge of the 35mm frame, the EF-S 10-22 would look like crap. DoF considerations in those areas close to the edge of the frame are irrelevant. Image quality is so poor.
 « Last Edit: April 16, 2009, 08:38:17 PM by Ray » Logged
Er1kksen
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The differences in price and weight between the EF-S 17-55/2.8 and the cheaper Zuiko zooms of equivalent focal length are trivial compared to the differences between the Zuiko 90-250/2.8 and the Canon 100-400 IS. I could be wrong, because there's a dearth of rigorously conducted comparisons on the internet, but I get a clear impression that the cheaper and lighter 4/3rds equivalents never quite match the image quality of the slightly heavier and more expensive Canon combinations. If you want to equal and, hopefully, even exceed the quality of the Canon equivalent, you end up with a 4/3rds system which is heavier and more expensive than the Canon equivalent. Right?

Not on the budget end, you don't. The Olympus kit zooms (14-42 and 40-150) are easily some of the best kit zooms available, and they're tiny. I'd pit them against the current Canon kit zoom (admittedly pretty nice) any day, and there's really no comparison with the older non-IS 18-55. Then there's the Olympus 70-300, which is pretty competent even if not amazing, as opposed to the Canon 75-300, which I've only ever heard moaning and complaining about.

Another interesting comparison, at the other end of the price spectrum, might be the Zuiko 300mm f2.8 against the Canon 400mm 2.8.

Quote from: Ray
Your point is a point worth making for the sake of clarity, and it's a point that needs to be understood before embarking upon any DoF/FoV/FL comparisons. But the fact remains, for the practicing photographer, the resulting print or displayed image, is always, without exception, a specific composition which, of necessity, has a specific field of view.

Whether you acheive that FoV by selecting a lens of an appropriate focal length, or cropping during post-processing, is up to you. If maximum detail and sharpness is your priority, then maximising the 'real estate' of your sensor through use of the most appropriate FL, is the way to go; hence the popularity of zoom lenses.

Another point worth mentioning in relation to this, is that of image circle. Whilst a 14mm lens is a 14mm lens, the diameter of the usable image circle may vary considerably. If one were to fit the Canon EF-S 10-22mm to the Nikon D700 and take a shot at 14mm, then compare it with a shot of the same scene taken with the Nikkor 14-24 at 14mm (same aperture), you'd probably get a shock   .

The images might appear to be about equally sharp in the centre of the frame (with equal DoF if you're lucky), but long before you'd reached the edge of the 35mm frame, the EF-S 10-22 would look like crap. DoF considerations in those areas close to the edge of the frame are irrelevant. Image quality is so poor.

Have I ever said anything to the contrary? You could simply have added your point for further clarification. Making it sound like you're correcting something I said is unnecessary.
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Ray
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Quote from: Er1kksen
Not on the budget end, you don't. The Olympus kit zooms (14-42 and 40-150) are easily some of the best kit zooms available, and they're tiny. I'd pit them against the current Canon kit zoom (admittedly pretty nice) any day, and there's really no comparison with the older non-IS 18-55. Then there's the Olympus 70-300, which is pretty competent even if not amazing, as opposed to the Canon 75-300, which I've only ever heard moaning and complaining about.

Another interesting comparison, at the other end of the price spectrum, might be the Zuiko 300mm f2.8 against the Canon 400mm 2.8.

It's very rare to see any comparisons between 4/3rds camera-and-lens combinations and the Canon equivalents. The Canon 70-300 is designed for full frame 35mm, isn't it? A better comparison might be between the Panasonic Lumix 45-200 for the G1 and the Canon EF-S 55-250 IS.

I'm sure it's possible to find a 4/3rds camera/lens combination which is not only lighter and cheaper than the nearest Canon equivalent, but delivers image quality on a par with the Canon and perhaps even slightly better. However, at this stage, the highest pixel density Canon, the 50D, has a slight resolution advantage. Photozone results show the EF-S 55-250 IS, tested on the 50D, as being sharper, in terms of LW/PH at 50% MTF, than the Lumix 45-200 on the G1, particularly at it's widest angle of 55mm, which is fairly close to 45mm on a 4/3rds sensor.

One should also bear in mind that 4/3rds DSLRs in general seem to have up to a stop worse performance at high ISO (than Canon APS-C). This can be a disadvantage with a long telephoto. I often find that I need to increase ISO to 1600, and even ISO 3200, when using my 100-400 IS at 400mm.

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BJL
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Quote from: Er1kksen
A 14mm lens is a 14mm lens and has a given dof for a given aperture at a given focussing distance and that's that.
DOF is not a property of a lens alone, or of a focal length and f-stop combination alone. DOF is a property of final viewed images, like prints of a given size viewed at a given distance, and so varies with degree of enlargement and such. The same image enlarged to different degrees and then viewed from the same distance (which is quite likely if different crops are used and then enlarged by different degrees so as to get equal print sizes) will have different DOF. So when the the use of different format makes it likely that a different degree of enlargement will be made, that cannot be ignored in reckoning about DOF.

As an extreme case, have you ever tried to judge DOF from a contact sheet made from 35mm film? Usually, those tiny prints look to be in focus everywhere, but final prints look otherwise.

All that you know from focal length, f-stop and focus distance is how large the circle of confusion (OOF blurring) will be on the sensor or film for the part of the image coming from an object at a certain distance in front of or behind the plane of critical focus. How large that CoC on-sensor can be before it causes a perception of being OOF for the viewer of a print cannot be determined from that information alone; extra information like the degree of enlargement and viewing distance (or at least the ratio of those two) are essential.
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BJL
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Quote from: Ray
My current 100-400 ... The Zuiko ED 90-250/2.8 ...
We seem to have wandered very far indeed from the lenses relevant to the original comparison, which were small, inexpensive kit zooms for Four Thirds and Micro Four Thirds! I am glad though that you are following my advice of using a smaller, higher resolution sensor instead of a TC with a f/5.6 lens!

P. S. In my kit, my closest match for the 100-400/4-5.6 would be my 50-200/2.8-3.5 used with and without 1.4x TC, though effectively 2/3 stop slower. But if you are comparing super-telephoto options for Four Thirds, you might want to check out the Sigma options too. The Sigma 70-200/2.8 with and without 1.4x or 2x TC's offers similar speed/FOV options to the 100-400/4-5.6. There are also some extreme options like a 50-500/4-6.3 for about US\$1100, or a 300-800/5.6 for the price of a small car. What would be more interesting for me though would be if the Sigma 100-300/4 (about US\$1100) were offered in Four Thirds mount. For now that is available for Four Thirds bodies only in a clumsy manual focus form, via the Nikon mount version used with a lens mount adaptor. (Never mind the need for stop-down metering; I would probably not be stopping down often with that "600mm, f/8 equivalent"!) To be more ambitious, the Sigma 120-300/2.8 (US\$2,900) would be tempting; it is supposedly as sharp as the Sigma 300/2.8 prime, and about the same price and weight.

I would expect that with the Four Thirds sensor using only the central 1/4 of the image area, IQ would be fairly good with these telephotos, except maybe the 50-500.
 « Last Edit: April 19, 2009, 02:03:09 PM by BJL » Logged
Ray
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Quote from: BJL
We seem to have wandered very far indeed from the lenses relevant to the original comparison, which were small, inexpensive kit zooms for Four Thirds and Micro Four Thirds! I am glad though that you are following my advice of using a smaller, higher resolution sensor instead of a TC with a f/5.6 lens!

I've been through this exercise before. In the absence of direct and competently executed comparisons, I find it difficult to make any decision when it comes to opting for a different system, or going to the expense of adding yet another system to what I currently use. I also think it's reasonable to suppose that the true reason why there are no comparisons between 4/3rds camera/lens combinations and Canon APS-C and FF systems (apart from Dpreview comparisons using a standard lens), is because there's nothing to shout about regarding 4/3rds' performance. In other words, you get what you pay for. If a particular 4/3rds camera and lens is lighter and cheaper than the Canon equivalent, it probably produces at least slightly worse image quality, on balance. If the performance is noticeably better than the Canon equivalent, the 4/3rds' system is likely to be more expensive and heavier.

I notice that Photozone have tested the Panasonic 14-45 & 45-200 with the G1. There's a very close Canon equivalent in terms of price, focal length range, maximum aperture, price and weight. It's the Canon 500D with EF-S 18-55 IS and EF-S 55-250 IS. Photozone have tested both of these EF-S lenses using the 50D which has the same pixel count as the new 500D. Photozone advises against comparing systems because of issues of AA filter strength, pixel count and choice of RAW converter. However, I think it would be reasonable to assume that the image quality from the 500D will be very similar to that of the 50D.

The Australian price of the G1 with both kit lenses is slightly greater than the kit price for the 500D with the two EF-S lenses, about A\$50-100 greater comparing a range of internet prices.

On the other hand, the G1 with both lenses is 115gms lighter than the 500D with its two kit lenses. Neither \$100 nor 100gms either way, is likely to influence my buying decision by itself.

Comparing the Photozone results for these 2 lenses using the G1, with the two EF-S lenses using the 50D, the Canon lenses, on balance, produce better results. There are a few intances where the EF-S lenses are significantly sharper (the 55-250 at 55mm), and a couple of instances where the Panasonic lenses are significantly sharper (at full aperture at 14mm and 18mm, but only in the centre). The EF-S 55-250 is sharper at all apertures and focal lengths tested, although not always significantly sharper. Both EF-S lenses are sharper at the edges at all apertures and focal lengths tested. The Panasonic lenses seem to have a fairly severe vignetting problem. At 200mm, edge performance is abysmal on the Lumix G 45-200, at all apertures tested, including F11.

Quote
In my kit, my closest match for the 100-400/4-5.6 would be my 50-200/2.8-3.5 used with and without 1.4x TC, though effectively 2/3 stop slower.

You mean, the 50-200/2.8-3.5 with 2x converter, don't you?

Quote
But if you are comparing super-telephoto options for Four Thirds, you might want to check out the Sigma options too. The Sigma 70-200/2.8 with and without 1.4x or 2x TC's offers similar speed/FOV options to the 100-400/4-5.6. There are also some extreme options like a 50-500/4-6.3 for about US\$1100, or a 300-800/5.6 for the price of a small car. What would be more interesting for me though would be if the Sigma 100-300/4 (about US\$1100) were offered in Four Thirds mount. For now that is available for Four Thirds bodies only in a clumsy manual focus form, via the Nikon mount version used with a lens mount adaptor. (Never mind the need for stop-down metering; I would probably not be stopping down often with that "600mm, f/8 equivalent"!) To be more ambitious, the Sigma 120-300/2.8 (US\$2,900) would be tempting; it is supposedly as sharp as the Sigma 300/2.8 prime, and about the same price and weight.

All comparisons I've seen between different lenses with and without converter, suggest that the shorter focal length with the converter is not as good as the longer focal length without converter. For example, the excellent and highly regarded Canon EF 70-200/F2.8 IS with 2x converter is not as good as the humble 100-400 IS at 400mm.

I've come across lots of glowing reports of the Canon 300/2.8 IS, supposedly one of the best lenses that Canon produce. Yet I've never come across a direct comparison between the 300/2.8 IS with 1.4x extender and the 100-400 at 400mm. Why is that? Have I not been searching hard enough? Again, it's a reasonable assumption that the reason there are no comparisons is because there's nothing to shout about. The 300/2.8 with 1.4x extender is probably very marginally sharper in the centre than the 100-400 IS, and very marginally less sharp at the edges. No big deal either way. If you already own a 300/2.8 IS, then it's probably not worth getting a 100-400. However, if one already owns a 100-400, then going to the expense of getting a 300/2.8 in order to improve upon the 100-400, doesn't make much sense.

I'm really only interested in significant leaps in quality, such as that offered by the D700/14-24/2.8 combination compared with the 5D/Sigma 15-30.
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BJL
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Quote from: Ray
You mean, the 50-200/2.8-3.5 with 2x converter, don't you?
For the rough equivalence I was talking about, either 1.4X or 2X, depending on how one adjusts for the difference in format and sensor size. If there were a 1.7x TC for 4/3, I would have mentioned that instead!
400mm on EF-S gives the FOV of 640mm in 35mm format while 200mm with 1.4x on 4/3 gives "560mm  FOV" and with 2x it is "800mm FOV". Decide for yourself which is closer to equivalent.

And after all, we are "really only interested in significant leaps in quality", so the modest differences in pixel count and such should not matter!

As to the disadvantage of TC's; that is one reason why for telephoto work, I prefer using smaller pixels and cropping! Another is "loose framing" with moving subjects like birds in flight: deliberately choosing  a focal length too short to fill the frame with the desired image of a moving subject, so that even if subject movement prevents me from positioning the subject as I want it in the frame, cropping can tidy that up.

Anyway, you have certainly dragged this discussion very far from the original question of
"will there be an inherent increase in depth of field for a given f-stop" and
"Would there be such things as 'f-stop equivalents' between micro four-thirds and APS-C sensors?"
onto the irrelevant and "well-worn to the point of thread-bare" subject of why you personally prefer Canon DSLR gear to Four Thirds, with the usual subject-changing segue of "let's us ignore the desire for adequate DOF and look instead at the low DOF and low light advantages of using bigger, heavier, and typically more expensive lenses", often accompanied by the misrepresenting these as effects of larger sensors rather of larger aperture diameters." I will try to say nothing more on that topic ... in this thread at least!
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Er1kksen
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Quote from: BJL
DOF is not a property of a lens alone, or of a focal length and f-stop combination alone. DOF is a property of final viewed images, like prints of a given size viewed at a given distance, and so varies with degree of enlargement and such. The same image enlarged to different degrees and then viewed from the same distance (which is quite likely if different crops are used and then enlarged by different degrees so as to get equal print sizes) will have different DOF. So when the the use of different format makes it likely that a different degree of enlargement will be made, that cannot be ignored in reckoning about DOF.

As an extreme case, have you ever tried to judge DOF from a contact sheet made from 35mm film? Usually, those tiny prints look to be in focus everywhere, but final prints look otherwise.

All that you know from focal length, f-stop and focus distance is how large the circle of confusion (OOF blurring) will be on the sensor or film for the part of the image coming from an object at a certain distance in front of or behind the plane of critical focus. How large that CoC on-sensor can be before it causes a perception of being OOF for the viewer of a print cannot be determined from that information alone; extra information like the degree of enlargement and viewing distance (or at least the ratio of those two) are essential.

Is that not referred to as "apparent" depth of field? Given that we're not limited to printing at contact sheet size, or any other size for that matter, I'd say that that's less of an issue than the actual "circle of confusion" (I've never really bothered to learn the exact technical terms for any of these). So it's the "circle of confusion" and not the dof that will remain constant? Fine. That's still what I was talking about.

So what you seem to be saying is that 4/3 format has no dof advantage at equal angles of view and apertures, and enlarged to equal print sizes? Hmm... I guess that would also seem to throw the idea that you can't achieve sufficient subject isolation with 4/3 due to excessive dof...
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BJL
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Quote from: Er1kksen
Is that not referred to as "apparent" depth of field? Given that we're not limited to printing at contact sheet size, or any other size for that matter, I'd say that that's less of an issue than the actual "circle of confusion" ...
It is the unique established meaning for "depth of field": look up "depth of field" up in any good reference work on photography, though the effect of degree of enlargement is sometimes hidden in the talk of adjusting the "maximum circle of confusion size deemed to be in focus" with format size. The sensor circle of confusion sizes tell us the degree of OOF effects at various parts of the image, but it does not give any dividing line between "in focus" and "out of focus"; DOF depends on print circle of sensor sizes.

One exception is those "digital DOF radicals" who deem an image to be OOF wherever the CoC is larger than the resolution scale of the sensor, so that OOF effects can be seen with sufficiently large prints or sufficiently close pixel peeping. But that is a very different criterion than the established one. For one thing, that radical version of DOF then varies if one uses films or sensors of different resolution with the same focal length and same aperture in the same format.

Quote from: Er1kksen
So what you seem to be saying is that 4/3 format has no dof advantage at equal angles of view and apertures, and enlarged to equal print sizes?

At equal angle of view, focus distance, aperture ratio and print size, the DOF is greater in 4/3 than in APS-C formats by about 2/3 of a stop, and about two stops greater than in 35mm format. At equal aperture ratio, the shorter focal length used to get equal angle of view in a smaller format decreases CoC sizes at the focal plane by more than enough to offset the greater degree of enlargement. Approximately, sensor CoC varies inversely with the square of focal length and in inverse proportion to aperture ratio, and then print CoC grows in proportion to degree of enlargement, judged from equal print viewing distance. This adds up to print CoC being approximately in proportion to the effective aperture diameter (focal length divided by aperture ratio) for any combination of focal length and degree of enlargement used to get a print of the same size covering the same angle of view.
 « Last Edit: April 20, 2009, 05:11:09 PM by BJL » Logged
Ray
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Quote from: BJL
.... with the usual subject-changing segue of "let's us ignore the desire for adequate DOF and look instead at the low DOF and low light advantages of using bigger, heavier, and typically more expensive lenses", often accompanied by the misrepresenting these as effects of larger sensors rather of larger aperture diameters."

I've never ignored the DoF implications in this thread or any other thread where DoF has been an issue. As a matter of fact, I usually prefer not to aim for the shallowest of DoFs where the larger format usually has the advantage. I use fast lenses mainly for low light situations and would prefer more DoF rather than less.

A point I didn't mention about the Photozone tests of the two comparable sets of lenses, is that the EF-S lenses at F8 and F11 always outperform the Panansonic lenses to some degree.

If one were to assume that the 4/3rds system would produce similar DoF at F8 to the EF-S lenses at F11 and therefore maybe slightly sharper results because F8 is usually a sharper aperture than F11, one would be wrong in the case of these examples. On balance the EF-S lenses at F11 are about as sharp in the centre as the Panasonic lenses are at F8 in the centre. That is partly due to the fact that we're comparing a 15mp sensor with a 12mp sensor. However, at F11 the EF-S lenses have significantly better edge performance than the Panasonic lenses have at F8.

If your goal is achieve the maximum DoF consistent with an acceptably sharp image from corner to corner, the 500D/EF-S 18-55/55-250 system will produce better results than the Micro 4/3rds G1/14-45/45-200 system, according to Photozone tests.

Just trying to get at the facts, BJL   .
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BJL
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Quote from: Ray
A point I didn't mention about the Photozone tests of the two comparable sets of lenses, is that the EF-S lenses at F8 and F11 always outperform the Panansonic lenses to some degree.
Ray, this thread was not about the IQ of those entry level Panasonic Micro Four Thirds lenses; it was about DOF comparisons, and the fact for example that equal DOF is achieved at apertures about 2/3 stop lower in 4/3 than with EF-S. The Panasonic lenses are by all accounts the least good of all Four Thirds standard zooms, so not of much interest to me for performance comparisons.

And I do wonder why you choose those atypically small apertures for your comparisons. Remember the lower f-stops typically used with smaller formats: with Four Thirds, the old slogan translates as "f/4 and be there"!
 « Last Edit: April 20, 2009, 05:30:29 PM by BJL » Logged
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