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Author Topic: FOV Equivalences vs Magnification  (Read 57476 times)
Farkled
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« on: February 20, 2008, 06:52:45 PM »
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I understand why the same lens produces a smaller FOV on a small sensor.  I also understand that 250mm gives 5X magnification and 400mm gives 8X magnification (given that 50mm is normal) and that lens characteristics do not change regardless of sensor size.  Since I lack the lenses with which to test myself, I am asking the question:

Do images taken with a 250mm on a 1.6 crop factor sensor really appear identical to images taken with 400mm on a full frame?  I'm assuming that subject size in the frame is identical.  Stated another way, can I stand in the same place with those two lenses, shoot the same subject and get the same result?  I'm only talking about apparent magnification - all other IQ issues are irrelevant.

I have read so much conflicting blather all over the net that I thought I would ask here, where there seems to be more fact and reasoned opinion than in most places.

TIA
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Morgan_Moore
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« Reply #1 on: February 20, 2008, 11:55:57 PM »
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I understand why the same lens produces a smaller FOV on a small sensor. I also understand that 250mm gives 5X magnification and 400mm gives 8X magnification (given that 50mm is normal) and that lens characteristics do not change regardless of sensor size. Since I lack the lenses with which to test myself, I am asking the question:

Do images taken with a 250mm on a 1.6 crop factor sensor really appear identical to images taken with 400mm on a full frame? I'm assuming that subject size in the frame is identical. Stated another way, can I stand in the same place with those two lenses, shoot the same subject and get the same result? I'm only talking about apparent magnification - all other IQ issues are irrelevant.

I have read so much conflicting blather all over the net that I thought I would ask here, where there seems to be more fact and reasoned opinion than in most places.

TIA
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Its not just about subject size it is about the rendering out of focusness of subjects outside the field of focus ie the foreground or background

Larger sensors have less depth of field for a given aperture and field of view

or put another way using a  specific lens lenght  aperture and distance combo you get a fixed look, but with a larger chip you get more of that look

(ie a 50 is a tele on a D80, a normal on a D3 and a wide on an H1 but crop the H1 images in a quarter and the look is the same as the D80 shot)

Whether a large chip look can be replicated by using wider apertures on smaller chip cameras is really the debate

It is my opinion. that i am convinced is correct, that one can not recreate different looks from different sensor sizes by varying aperture because diffferent lenses and apertures drop in and out of focus at different RATES

ie you can perform a test on two sensor size aperture, combos and get point A sharp and point B equally defocussed with different chip sizes but if you bring a point C into the equation/test the amount of defocussing will not be holdable consistent across different sensor sizes

ANd in a three dimensional world there is nearly always a 'point C'

--------------

My real world summary,

big chip = smooth creamy look that is great for portraits but it can be difficult to get huge DOF for architecture or landscape when using a big chip

My personal preference - I hate small chip cameras exept for using long telephotos - where weight/size/cost is an issue

ps I own Hassy H1, D3, D80 (different chips)  and many lenses from 10.5 fisheye to 600F4 - so I might have more real world experience than some 'web blatherers'

If you are into long lenses a small chip camera is a good thing because it is much cheaper and more practical to buy and use if you are after as much magnification as possible

With longer lenses the differences become less noticable

A 14mm on a D80 is wildly different to a 35 on an H1 in terms of DOF

Whereas the look of 200 on the D80 is not wildly different to using a 300 on a D3

The sweet point of MF cameras seems to be when trying to shoot fashion - one typically needs the model to have sharp face and clothes but desires an out of focus background - hence many fashion shooters use MF cameras even when the target repro is only magazine size so MP is not really a factor

S
« Last Edit: February 21, 2008, 12:09:22 AM by Morgan_Moore » Logged

Sam Morgan Moore Cornwall
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« Reply #2 on: February 21, 2008, 04:34:12 AM »
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Do images taken with a 250mm on a 1.6 crop factor sensor really appear identical to images taken with 400mm on a full frame?  I'm assuming that subject size in the frame is identical.  Stated another way, can I stand in the same place with those two lenses, shoot the same subject and get the same result?  I'm only talking about apparent magnification - all other IQ issues are irrelevant.
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Theoretically, the answer is yes, provided you also increase the F stop (stop down)on the 400mm lens by a factor of 1.6x. Example, F8 on the 250mm lens is equivalent to f13 on the 400mm lens. (Actually f12.8 but let's not quibble).

This characteristic is one of the advantages of the smaller format. You can get the same FoV with a shorter lens and the same DoF with a wider aperture on that shorter lens. But the reverse is also true. You can get a shallower DoF with a larger format at the same f stop, shooting from the same position with a lens that gives you the same FoV.

There is a myth about lens performance at really wide apertures. The shallow DoF tends to give the impression that the part that's in focus is sharper than it really is, at least with 35mm lenses. MF lenses on a DB can be used at about a one stop numerically larger aperture to produce a similarly OoF background, but the part that's in focus (the lady's eyeball) can be really sharp if it's a good MF lens designed for the DB. Example, a good MF 120mm lens at f4 can be sharper than a good 85mm lens on 35mm format at f2.8. As a consequence of the greater sharpness at the plane of focus, the DB shot appears to have greater 3-dimensionality.
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Ray
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« Reply #3 on: February 21, 2008, 10:45:53 PM »
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Its not just about subject size it is about the rendering out of focusness of subjects outside the field of focus ie the foreground or background

Larger sensors have less depth of field for a given aperture and field of view

or put another way using a  specific lens lenght  aperture and distance combo you get a fixed look, but with a larger chip you get more of that look

(ie a 50 is a tele on a D80, a normal on a D3 and a wide on an H1 but crop the H1 images in a quarter and the look is the same as the D80 shot)

Whether a large chip look can be replicated by using wider apertures on smaller chip cameras is really the debate

It is my opinion. that i am convinced is correct, that one can not recreate different looks from different sensor sizes by varying aperture because diffferent lenses and apertures drop in and out of focus at different RATES

ie you can perform a test on two sensor size aperture, combos and get point A sharp and point B equally defocussed with different chip sizes but if you bring a point C into the equation/test the amount of defocussing will not be holdable consistent across different sensor sizes

ANd in a three dimensional world there is nearly always a 'point C'

--------------

My real world summary,

big chip = smooth creamy look that is great for portraits but it can be difficult to get huge DOF for architecture or landscape when using a big chip

My personal preference - I hate small chip cameras exept for using long telephotos - where weight/size/cost is an issue

ps I own Hassy H1, D3, D80 (different chips)  and many lenses from 10.5 fisheye to 600F4 - so I might have more real world experience than some 'web blatherers'

If you are into long lenses a small chip camera is a good thing because it is much cheaper and more practical to buy and use if you are after as much magnification as possible

With longer lenses the differences become less noticable

A 14mm on a D80 is wildly different to a 35 on an H1 in terms of DOF

Whereas the look of 200 on the D80 is not wildly different to using a 300 on a D3

The sweet point of MF cameras seems to be when trying to shoot fashion - one typically needs the model to have sharp face and clothes but desires an out of focus background - hence many fashion shooters use MF cameras even when the target repro is only magazine size so MP is not really a factor

S
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Morgan,
I have to say, but without any intention of insulting you, I hope you understand   , that I find your answer very convoluted and confusing.

There is no doubt that larger sensors tend to have an image quality advantage because they collect more photons. The greater the difference in format size, the more pronounced such differences as 'creaminess of texture' can be and the greater the pixel count the greater the likelihood that what's in focus will be sharper, although it's perhaps illuminating to read in Michael's review of the Canon G7, that he occasionally confused (momentarily at least) G7 prints with Leica M8 prints.

To try and add some clarification here, I would say that one has to be aware of the differences between system performance and lens performance. Larger formats have the advantage that they require less resolution from the lens (ie. lower lp/mm at the same MTF). Conversely, smaller formats need higher resolving lenses to equal the system resolution of larger formats.

Another issue is that standard DoF calculators do not take lens quality factors into consideration. There is an implied assumption that all lenses are equal in quality. Now we know that is just not true. All lenses are not equal (in sharpness) and to the extent they are not equal, the DoF formulas and calculators are imprecise.

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A 14mm on a D80 is wildly different to a 35 on an H1 in terms of DOF

An H1 is a film camera body, isn't it? What DB did you have on that H1 when you discovered that a 14mm lens on a 10mp D80 is wildly different to a 35mm lens on the H1 in terms of DoF? What is the quality of the 14mm lens on the D80? What is the quality of the 35mm lens on the H1?

The OP's question related to the difference between a 1.6 cropped format and FF 35mm. The D80 in relation to a DB represents a 2.25x crop factor and the difference in pixel count is likely huge. That's a different ball game entirely.

To get back to a more realistic comparison, for example the recently announced 12mp Canon 450D with a 250mm lens compared with a 5D with 400mm lens, the answer is that the 450D with 250mm lens at f8 will provide very similar DoF and over all quality to the 5D with 400mm lens at f13.

The smaller sensor of the 450D requires a higher resolving lens and it's got it at f8, which is the aperture at which most 35mm lenses are usually sharpest. All lenses are roughly equal at f13.

On the other hand, if you change the conditions and compare a 450D using a Canon 50/1.4 at f1.4, with a 5D and 85/1.2 at f2.2, the results could be wildly different. The 50/1.4 needs to be sharper at f1.4 than the 85/1.2 is at f2.2, in order for the 450D to produce similar quality results. I think it would be no understatement to say that the opposite is true. I think there is no doubt that the 85/1.2 is much sharper at f2.2 than the 50/1.4 is at f1.4 and this fact will skew the results.
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Morgan_Moore
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« Reply #4 on: February 22, 2008, 12:40:20 AM »
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Morgan,
I find your answer very convoluted and confusing.


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Which bit of my post dont you understand ?


ps I have a sinar 54LV digital back on my H1 camera and a nikkor 14/2.8

S
« Last Edit: February 22, 2008, 12:55:15 AM by Morgan_Moore » Logged

Sam Morgan Moore Cornwall
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« Reply #5 on: February 22, 2008, 04:45:41 AM »
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Which bit of my post dont you understand ?
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This bit:

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It is my opinion. that i am convinced is correct, that one can not recreate different looks from different sensor sizes by varying aperture because diffferent lenses and apertures drop in and out of focus at different RATES

ie you can perform a test on two sensor size aperture, combos and get point A sharp and point B equally defocussed with different chip sizes but if you bring a point C into the equation/test the amount of defocussing will not be holdable consistent across different sensor sizes

ANd in a three dimensional world there is nearly always a 'point C'

What on earth does that mean?  
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Morgan_Moore
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« Reply #6 on: February 22, 2008, 06:18:29 AM »
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This bit:
What on earth does that mean?
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Ok for this example figures are approximate

Right. stand at a point with two cameras lets say for simplicity a FUll  frame with a 300mm and a Crop with a 200m lets say we have f8

Your subject say a person is far enough to be framed head to toe

(the cameras are upright)

Take two image anc compare them -

both images are at first glance identical - a person framed head to toe in focus.

Then you look more carefully and realise that there is a telegraph pole 5 meters behind the person

It is distracting

But you notice that the FF shot on the 300 the pole is more out of focus - less distracting

Five meters behind the first pole is a second pole even more out of focus but still a distraction

You go back to the scene and re-shoot the image with the small sensor camera, having chosen a wdier aperture than the inital f8

You play with the aperture until the first pole has an equal 'confusion' to the FF image by opening the aperture

You then print the new wider aperture image

Still it is not the same as the FF image, yes the first pole and the subject look the same but the second pole is differently rendered still from the FF image -

You then go back and shoot loads of aperture combinations and realise that what ever you do you cant get the small chip image to look the same as the FF image

because the focus is dropping off at different RATES with the different chip sizes, irrelevant of aperture

You may be able to get more blur with the Small chip by using the wider aperture but you will never get the same blur RATIOS between the different subjects

-----------

Anyone knows that  the DOF drops off faster with a lens of a longer focal lenght - look at the grass on the pitch in  a sports photo say shot with a 300 2.8

If one had a 300 2.8 10 plate camera lens (Yes that lens would be the siaze of a car)

One could photograph a good chunk of the stadium (300 is quite wide on a 10.8 plate) but would still have that 'focus cut' though the grass same as the sports picture

a totally differnt look to a shot of the stadium shot say with a 35mm on a canon

S
« Last Edit: February 22, 2008, 06:22:02 AM by Morgan_Moore » Logged

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« Reply #7 on: February 22, 2008, 07:59:07 AM »
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Ok for this example figures are approximate

Right. stand at a point with two cameras lets say for simplicity a FUll  frame with a 300mm and a Crop with a 200m lets say we have f8

Your subject say a person is far enough to be framed head to toe

(the cameras are upright)

Take two image anc compare them -

both images are at first glance identical - a person framed head to toe in focus.

Then you look more carefully and realise that there is a telegraph pole 5 meters behind the person

It is distracting

But you notice that the FF shot on the 300 the pole is more out of focus - less distracting

Five meters behind the first pole is a second pole even more out of focus but still a distraction

You go back to the scene and re-shoot the image with the small sensor camera, having chosen a wdier aperture than the inital f8

You play with the aperture until the first pole has an equal 'confusion' to the FF image by opening the aperture

You then print the new wider aperture image

Still it is not the same as the FF image, yes the first pole and the subject look the same but the second pole is differently rendered still from the FF image -

You then go back and shoot loads of aperture combinations and realise that what ever you do you cant get the small chip image to look the same as the FF image

because the focus is dropping off at different RATES with the different chip sizes, irrelevant of aperture

You may be able to get more blur with the Small chip by using the wider aperture but you will never get the same blur RATIOS between the different subjects

-----------

Anyone knows that  the DOF drops off faster with a lens of a longer focal lenght - look at the grass on the pitch in  a sports photo say shot with a 300 2.8

If one had a 300 2.8 10 plate camera lens (Yes that lens would be the siaze of a car)

One could photograph a good chunk of the stadium (300 is quite wide on a 10.8 plate) but would still have that 'focus cut' though the grass same as the sports picture

a totally differnt look to a shot of the stadium shot say with a 35mm on a canon

S
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Morgan,
This sounds to me like lens quality variation and nothing necessarily to do with format. Lenses are very imperfect products. Just look at any real world MTF chart. The sharpness (contrast at a specific spatial frequency) is often all over the place. In the centre of its image circle a lens is usually sharpest, but not always. It might sometimes be sharpest 2mm from its centre, fall in sharpness towards a point 10mm from its centre, rise in sharpness from 10mm to 18mm from the centre then fall drastically towards the corner at 22mm (in the case of a 35mm lens). And this pattern is likely to be different at different apertures and different spatial frequencies.

There's an interesting comparison of the Canon 14/2.8, Nikkor 14/2.8 and Sigma 12-24 zoom at [a href=\"http://www.16-9.net/lens_tests/14mm/14mm_test_2.html]http://www.16-9.net/lens_tests/14mm/14mm_test_2.html[/url]

The Nikkor 14/2.8 has some very weird performance at wide apertures, in this test, which gradually disappear, however, as the lens is stopped down.

If your copy of the Nikkor 14/2.8 is anything like the one tested in the above review, it's no wonder you found it wildly different to your 35mm lens on the H1   .
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John Sheehy
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« Reply #8 on: February 22, 2008, 10:13:16 AM »
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Do images taken with a 250mm on a 1.6 crop factor sensor really appear identical to images taken with 400mm on a full frame?  I'm assuming that subject size in the frame is identical.  Stated another way, can I stand in the same place with those two lenses, shoot the same subject and get the same result?  I'm only talking about apparent magnification - all other IQ issues are irrelevant.
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(Original reply deleted after reading OP again)

Lenses are different enough in characteristics that it should never be exactly the same (ignoring resolution and noise, as you seem to have requested).  The bokeh is different with different lenses, and bokeh is something that people often get sensitive to when they look at more and more pictures from various lenses.  The bokeh on a lot of my photos when I use too many TCs, and of many images linked to by other people often makes me cringe; bad bokeh makes me feel uncomfortable with its spatial distortion.
« Last Edit: February 22, 2008, 10:22:00 AM by John Sheehy » Logged
Ray
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« Reply #9 on: February 22, 2008, 11:52:24 AM »
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(Original reply deleted after reading OP again)

Lenses are different enough in characteristics that it should never be exactly the same (ignoring resolution and noise, as you seem to have requested). The bokeh is different with different lenses, and bokeh is something that people often get sensitive to when they look at more and more pictures from various lenses. The bokeh on a lot of my photos when I use too many TCs, and of many images linked to by other people often makes me cringe; bad bokeh makes me feel uncomfortable with its spatial distortion.
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Actually, if you want to be really precise about this, you can never get the same effect with 2 different lenses irrespective of format differences. I'm sure that even the quality of bokeh can be different between two lenses of the same model.

I got the impression the OP didn't really mean, "do images really appear identical". No two things are identical. Not even two Blank DVD discs on the same spindle.

One has to allow for a certain interpretive license here. I interpreted the question as meaning, "Are the two images broadly identical in respect of FoV and DoF?", and I think the answer is yes.
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« Reply #10 on: February 22, 2008, 01:26:23 PM »
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"Are the two images broadly identical in respect of FoV and DoF?", and I think the answer is yes.
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And I think the answer is no !

But it only really becomes obvious when comparing a D80 to an H1 the second having about four times the recording area of the first

The practical differences between cameras is most important

like the pleasure of vieing though an H1, the AF on a D3 or the cheap telephoto options on crop cameras

S
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« Reply #11 on: February 22, 2008, 03:28:02 PM »
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Assuming "perfect" lenses and sensors, it is impossible to get identical photos in two different size formats.

You can get damn close, and if you take a photo of a 2-dimensional plane (perfectly aligned with the film plane), I suppose they would match.

I don't have the proof on me anymore, but you can prove it yourself with some basic algebra. It's actually in interesting exercise.

Find the equation for the circle of confusion based on aperture, focal length and focus distance and distance from the sensor. Let's assume that we're comparing 35mm with aps-c (1.6x crop factor).

First pick lenses for the sensor; how about a 160mm lens for the 35mm sensor and 100mm lens for the aps sensor. This will give them the same angle of view.

Now pick a focus distance. You could use a a constant "c" here or plug in a number (like ten meters).

We need to solve to find an aperture aperture that makes the CoC curves (image) the same, here's where it gets tricky. You have 2 three-dimensional functions. The variable is aperture, and the resultant is a function of distance and size of the CoC.

It is impossible to solve this equation without imputing a specific CoC (just like those DoF calculators do). This is because the CoC, as a function of distance from the sensor, curves are not the same.

These curves are very useful in photography. They allow you to calculate desired hyperfocal distances, Depth of Field, and blur. Exploring them can tell you a lot about your photos.
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« Reply #12 on: February 22, 2008, 03:38:26 PM »
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Actually, if you want to be really precise about this, you can never get the same effect with 2 different lenses irrespective of format differences. I'm sure that even the quality of bokeh can be different between two lenses of the same model.

I got the impression the OP didn't really mean, "do images really appear identical". No two things are identical. Not even two Blank DVD discs on the same spindle.

One has to allow for a certain interpretive license here. I interpreted the question as meaning, "Are the two images broadly identical in respect of FoV and DoF?", and I think the answer is yes.
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You said that the images would be theoretically identical. Which is definitely untrue. Practically similar, yes. Lens variability and other IQ issues would overshadow the effect of CoC curves. But projecting theoretically identical images on different sized media is impossible with current optical technology.
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« Reply #13 on: February 22, 2008, 08:33:10 PM »
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You said that the images would be theoretically identical. Which is definitely untrue. Practically similar, yes. Lens variability and other IQ issues would overshadow the effect of CoC curves. But projecting theoretically identical images on different sized media is impossible with current optical technology.
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When someone says something is theoretically true, I understand him to mean it's true according to some theory but not precisely or necessarily true in practice.

Are you saying it would be impossible to design a lens for a smaller format, which would behave with regard to DoF exactly the same as a longer focal length on a larger format after equalising physical aperture sizes on both lenses?

In other words, setting aside the difficulties of manufacturing a lens precisely according to design specifications, are you saying there's no theory which would support the design of two such lenses without contravening the laws of physics?

I don't know enough about optics or lens design to answer that question, but if this is indeed true, then of course I am wrong in asserting that the images are theoretically identical.

What would concern me here regarding a general principle of sound methodology, is that someone such as Morgan (and others) might have a bunch of lenses and a bunch of different format cameras, but not a bunch of lenses of the same focal length that fit the same format. I generally try to avoid duplicating focal lengths, but I will sometimes do that when I discover a lens which appears to be much better than what I already have.

If one does a lot of testing of lenses of equivalent FoV on different formats, equalising the physical aperture size used by adjusting  the f stop accordingly, and one finds that out-of-focus areas on the different formats are surprisingly different, how can one be sure that such differences are not due to the normal variation amongst lenses?

In order to check this properly, one would need to have a number of different lenses of the same focal length for the formats one was comparing, preferrably lenses that differed in quality and model or brand, say a Mamiya 80mm, a Hassy 80mm a Rodenstock 80mm and perhaps a few zooms for the DB, and a Nikon, Canon, Sigma and Tamron 50mm for the 35mm format.

If one then found that there was very little difference in the OoF areas amongst lenses of the same focal length on the same format, but found there was a significant difference when using lens FL and DoF equivalents with different formats, then you would have proved your point.

Perhaps I should add, just in case anyone has the lenses and can find the time to do such tests, that the lenses of equal FL should be tested at various apertures. Any variation in DoF behaviour is likely to be greatest at wide apertures.
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« Reply #14 on: February 23, 2008, 01:22:26 AM »
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Assuming "perfect" lenses and sensors, it is impossible to get identical photos in two different size formats.

..... you can prove it yourself with some basic algebra. [a href=\"index.php?act=findpost&pid=176749\"][{POST_SNAPBACK}][/a]

Great Explaination of what I have been trying to say



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then of course I am wrong in asserting that the images are theoretically identical.

Indeed


---------------

I actually happen to have an identical lens for for three formats..

A mamiya 80mm which I have a home made T/S adapter for nikon so the lens fits MF, D3 and APS size cameras

I terms of practicality I think there are real wrold visible benefits to using MF systems versus smaller formats if ones desire is a steep DOF curve -  the effect that makes the subject 'pop' off the background

Even if a close theoretical match can be found between different theoretical lenses one finds that with the smaller sensors you must be either shooting avbsolutely wide open or at an aperture that does not exist and is not available like F1.4 or F1

in the real world the only lenses that can come close to creating MF style look are the most expensive canon or nikon primes (35 1.4 50 1.2 85 1.2etc) used on a FF camera

I did a test yesterday with a model shooting some pretty tiddly apertures like F13 - when shooting tight faces one still sees a situation wher the eyeball is sharp and the nose and ears distinctly blurred (using the H1)

This reminded me that the effect is very real world

Conversly shooting kids the other day with a D3 on a commercial job I found the 80-200 didnt really have the reach I was used to compared with shooting on the D200 with that lens, really I needed a 300 2.8 on the D3, no zoom and much more money and weight, If jobs of that nature are ones bread and butter then APS can provide great practicality and value with no client dicernable differnces in the final product

Also the auto focus points on the H1 and the D3 are poorly spaced compared to nikon APS offerings like D2x and D300 which gives those camers a huge real world disadvantage over APS

SMM
« Last Edit: February 23, 2008, 01:37:06 AM by Morgan_Moore » Logged

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« Reply #15 on: February 23, 2008, 08:23:59 AM »
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Assuming "perfect" lenses and sensors, it is impossible to get identical photos in two different size formats.

You can get damn close, and if you take a photo of a 2-dimensional plane (perfectly aligned with the film plane), I suppose they would match.

I don't have the proof on me anymore, but you can prove it yourself with some basic algebra. It's actually in interesting exercise.
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Dobson,
That is interesting. I didn't know that. But how can I be sure you know what you are talking about  ?  Mathematicians tell me one can prove some very absurd notions at times and that such proofs seem very logical. Paul Dirac proved mathematically that anti-matter should theoretically exist, but kept quiet about for some time fearing ridicule and loss of reputation.

Can you provide a link to any authoritative source on the net that might explain in detail this algebraic proof and what the current status of such a proof might be amongst mathematicians? It seems a bit negative to me, like some of those attempts before airplanes were developed to prove that heavier-than-air objects could not fly.

On technical issue like this I sometimes refer to Roger Clark's website. He addresses the DoF/format issue at [a href=\"http://www.clarkvision.com/photoinfo/dof_myth/]http://www.clarkvision.com/photoinfo/dof_myth/[/url] and concludes the following:

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Given the identical photon noise, exposure time, enlargement size, and number of pixels giving the same spatial resolution (i.e. the same total image quality), digital cameras with different sized sensors will produce images with identical depths-of-field. (This assumes similar relative performance in the camera's electronics, blur filters, and lenses.) The larger format camera will use a higher f/ratio and an ISO equal to the ratio of the sensor sizes to achieve that equality. If the scene is static enough that a longer exposure time can be used, then the larger format camera will produce the same depth-of-field images as the smaller format camera, but will collect more photons and produce higher signal-to-noise images. Another way to look at the problem, is the larger format camera could use an even smaller aperture and a longer exposure to achieve a similar signal-to-noise ratio image with greater depth of field than a smaller format camera. Thus, the larger format camera has the advantage for producing equal or better images with equal or better depth-of-field as smaller format cameras.
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Ray
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« Reply #16 on: February 23, 2008, 09:11:57 AM »
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I actually happen to have an identical lens for for three formats..

A mamiya 80mm which I have a home made T/S adapter for nikon so the lens fits MF, D3 and APS size cameras
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Morgan,
If you were to use this lens on the 3 formats with the purpose of trying to get identical FoV and DoF, you'd be shooting from a different perspective and using different apertures. I think one would expect lenses to have at least a slightly different performance at different apertures. What I had in mind was testing say 3 different lenses of the same focal length, at the same aperture, and on the same format, to see if there was any differences in OoF effects. I suspect that there would be, depending on how critical you want to be about such differences.

For my own benefit, this afternoon I took a few test shots using my Canon 100-400 zoom with 40D and 5D. I was curious if such effects you refer to were noticeable with this lens. I used the 40D at 250mm and F8, and the 5D at 400mm and f13. I wasn't sure whether to use f13 or f11 on the 5D, but figured f13 was closer although not providing an exact DoF equivalence.

I did notice some slight differences in the degree of out-of-focusness behind the plane of focus in the two images. The 5D appeared to be showing very slightly shallower DoF. On the other hand, it could be that the 40D was not focussed as accurately as the 5D. Perhaps focussed just a little behind the focus point. I find it difficult to believe my 5D at f13 is sharper than the 40D at f8 with this zoom lens. It might be worth my redoing these tests using LiveView with the 40D.

For what they're worth, here are the results with 100% crops. No processing other than auto adjustment in ACR, default sharpening of 25, and downsizing the 5D shot to the same size as the 40D for ease of comparison.

[attachment=5223:attachment]  [attachment=5224:attachment]  [attachment=5225:attachment]  [attachment=5226:attachment]  [attachment=5227:attachment]  [attachment=5228:attachment]

I took a few more shots later in the day using  f11 instead of f13 on the 5D, but the lighting was poor so I bumped up the 5D ISO to 800 leaving the 40D at ISO 400. The OoF parts in these shots seem very close to me. Are you referring to differences of this magnitude?

[attachment=5229:attachment]  [attachment=5230:attachment]

The focus point was supposed to be the power pole.
« Last Edit: February 23, 2008, 09:13:51 AM by Ray » Logged
Morgan_Moore
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« Reply #17 on: February 23, 2008, 05:26:45 PM »
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For my own benefit, this afternoon I took a few test shots

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Thses are geniunely  interesting tests

I am amazed you can be bothered with such an activity !

They would appear to completely disprove my theory because for what I can see the images look near enough the same

I think choosing a small aperture, focus near infinity you are maringalising the effect if it exists at all !

That doesnt mean a bigger sensor is not better (if your mission is shallow DOF)

At F13 you were able to open the small camera up to F8,

If however you were shooting with a H1 at f2.8 you could have to open up an APS camera about four  stops - this is not possible becuase no such lens exists

As I said before some fast DSLR prime lenses on FF DSLRs can get less DOF than MF cameras

I still think I can 'see' MF pictures as being different - particularly 67 and larger formats like 54 - of course there are no practical digital solutions for these formats

SMM

I have sketed a graph of circle of confusion verses distance from point of focus for two lenses,

obviouly changing the aperture will change the curve steepness

I still dont exactly know if..

changing aperture can suitably affect those curves to equalize them

OR

changing aperture can do this but only if those apertures are available

I hate to admit I would like to see some maths [a href=\"http://en.wikipedia.org/wiki/Circle_of_confusion]wiki[/url] is a start..
« Last Edit: February 23, 2008, 05:53:37 PM by Morgan_Moore » Logged

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Ray
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« Reply #18 on: February 23, 2008, 06:11:08 PM »
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If however you were shooting with a H1 at f2.8 you could have to open up an APS camera about four  stops - this is not possible becuase no such lens exists

As I said before some fast DSLR prime lenses on FF DSLRs can get less DOF than MF cameras

I still think I can 'see' MF pictures as being different - particularly 67 and larger formats like 54 - of course there are no practical digital solutions for these formats
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I agree completely with that. As regards shallow DoF, people using P&S cameras are stuck. Thre's no way of achieving it, except in macro shots. Some 35mm lenses seem to be faster than their MF counterparts, ( Do you have any F1.2 or F1.4 MF lenses?), so one might think it's possible to get equally shallow DoF with FF 35mm.

However, my experience is that fast 35mm lenses are simply not sharp at full aperture. Is the 85/1.2 an exception? Some people claim it is sharp at full aperture, but I suspect they mean it's surprisingly good considering how wide f1.2 really is. I know for sure my own copy of the Canon 50/1.4 is not sharp at full aperture.

I would not expect the 50mm lens on a 40D at F1.4 could produce the same effect as a 110mm lens at F3.2 on a DB, yet theoretically they should have the same FoV and DoF.
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« Reply #19 on: February 24, 2008, 11:33:35 AM »
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. . . can I stand in the same place with those two lenses, shoot the same subject and get the same result?  I'm only talking about apparent magnification - all other IQ issues are irrelevant.

I have read so much conflicting blather all over the net that I thought I would ask here, where there seems to be more fact and reasoned opinion than in most places.
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Hahaha. Conflicting blather can be found everywhere on the net. It seems Ray and Morgan missed or chose to ignore that you said, "all other IQ issues are irrelevant," which would include apparent DOF. To answer your question regarding apparent magnification: yes.
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