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Author Topic: New Camera for Africa  (Read 6507 times)
stever
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« Reply #40 on: September 04, 2012, 08:51:39 AM »
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using Imatest target and software, it appears that a crop from the 5D2 and 100-400 (at 400mm) is of equal resolution to the 7D and 100-400 at between 500 and 550mm

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Ray
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« Reply #41 on: September 04, 2012, 04:49:56 PM »
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using Imatest target and software, it appears that a crop from the 5D2 and 100-400 (at 400mm) is of equal resolution to the 7D and 100-400 at between 500 and 550mm


That sounds about right if I've understood what you mean. Do you mean that an 8mp crop from the 5D2 at 400mm, which matches the same FoV that the 18mp 7D sensor would produce with a 400mm lens, that is 640mm equivalent, would be equal in resolution to the 7D used at an actual 312-340mm, instead of 400mm, producing an effective focal length of 500-550mm?

In other words, using a 7D instead of a 5D2 would allow one to extend the reach of, say, a 328mm lens to 400mm whilst maintaining the same level of resolution, and therefore, proportionally, would allow one to extend a 400mm lens to effectively a 488mm lens.

If this is what you mean, I wouldn't disagree because image resolution is always a combination of sensor resolution and lens resolution. If one doubles the pixel count of a sensor, as the 7D is  approximately double the pixel count of a 5D3 cropped to the 7D's field of view, then the resolution of the sensor will increase by the sq rt of 2, ie 1.4x.

However, in order to get that full increase in resolution of 1.4x, that the increased pixel density of the 7D provides, one would have to proportionally increase the quality of the lens. If one uses the same lens, such as the 100-400, one might expect that increase to be halved; instead of 1.4x one might expect a 1.2x increase in resolution. 640/525= 1.22.

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stever
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« Reply #42 on: September 04, 2012, 10:38:10 PM »
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i think we agree, the practical focal length multiplier for equivalent resolution between the 7D and 5D2 (or 3) is about 1.2, not 1.6.

with better lenses, e.g. 100 macro, 400 f5.6, 300 f2.8 the multiplier (at equivalent resolution) may be more like 1.3-1.4 (but never gets to 1.6)

the practical result for me is that with decent technique i can get images from the 5D2 or 3 with the 100-400 (and most other Canon lenses) that will print to 17x25 at most focal lengths with reasonable technique (and larger with better primes).  then i can crop 30% and print 13 x19 (or more with good primes) for a focal length multiplier.

that's why i don't use the 7D so much -- what we need is a 7D that will autofocus at f8 (my EOS 3 will autofocus at F8, what's the big deal) and a 400 f5.6 IS and 500 f5.6 IS
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Ray
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« Reply #43 on: September 05, 2012, 07:15:26 AM »
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Well, I'd agree that the multiplier for the Field of View is not the same as that for resolution.

The multipliers of 1.6x for Canon and 1.5x for Nikon, have always applied to the FoV and equivalent F stop when using the same lens from the same position with full-frame as opposed to cropped format. Changes in resolution when the same lens is attached to different cameras is largely dependent on the pixel density of the sensor in whatever camera is used, and to some lesser extent on the strength of the AA filter.

As a consequence, the old 20D and 30D are basically redundant for owners of a 5D2 or 5D3 because the pixel density is about the same on all 4 sensors. Likewise, my Nikon D7000 is redundant now that I have a D800E which has very close to the same pixel density as the D7000. I get effectively 2 cameras for the price of one.

However the pixel density of the 7D is much greater than the pixel density of the 5D3.  A 1.2x increase in resolution from the same lens is not trivial. My Canon 100-400 at 400mm is sharpest at F8. The Photozone tests of this lens with the Canon 8mp 350D (same pixel density as the 5D2) show that centre resolution at F8 is 1.07x the centre resolution at F5.6.

Supposing Canon were to produce an updated model of this lens which was 1.2x sharper at F5.6 than the current lens is at F8. I think it would be a huge success.

Out of curiosity I compared the resolution of some cheap zooms with expensive primes at Photozone, on the same camera body, either the 8mp 350D or the 15mp 50D. The results were quite revealing. It was rare to find differences greater than 1.2x in centre resolution at the sharpest aperture of each lens compared. Most differences were in the region of 1.1x, comparing primes with cheap zooms of the same focal length.

With lenses that were tested by Photozone up to F16, such as the 100/F2.8 macro, I was surprised to find that often the resolution at the sharpest aperture, such as F4 in a good prime, was little more than 1.2x the resolution at F16, and less than 1.2x the resolution at F11.

I'd say, if any owner of a 5D3 can get 1.2x more resolution from a lens by using a 7D when a longer reach is required, go for it.  Grin
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stever
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« Reply #44 on: September 05, 2012, 09:08:50 AM »
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agree - however thinking about the same number of pixels on subject as a 20D with the 5D3 cropped to APSC size - and lower per pixel noise, the 100-400 at 400 will make images printable to 13x19 as did and does the 20D (although, as with the 20D desirably be stopped down to f8)

this useful discussion has clarified my decision to pretty much leave the 100-400 on the 5D3 and the 400 5.6 and 1.4x on the 7D for the occasional long shot

i'm leaving for Madagascar and Namibia next week

p.s. i tried the Tamron 70-300 and Canon 70-300 along with the 70-300L and 70-200 f4 and found that although the center resolution isn't down to much for the "cheap" zooms, they're not very good (to be polite) away from center - usually with severe loss of resolution on one side or the other from de-centering.  this may be okay if you're going to do a "center focus" crop, but if you want the full frame and the main subject is off center you may be in trouble.  Similarly, they're not much good for "landscape with wildlife".
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Ray
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« Reply #45 on: September 05, 2012, 09:28:35 PM »
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I can see the problem here. I remember years ago investigating the Canon 400/F5.6 prime after hearing reports it was sharper than the 100-400 zoom at 400mm. The copy I bought turned out not to sharper than my 100-400. In fact, at 100% on screen it appeared less sharp, so I returned the lens for a refund.

I notice that the copy of this lens that Photozone tested on the Canon 350D is also very marginally less sharp than the 100-400 at 400mm, but to a degree that's not significant in relation to the other disadvantages of a prime without image stabilization.

In retrospect, I'm rather glad that the copy of the 400 prime I tested wasn't as sharp. If it had been just marginally sharper I might have kept the lens but now suspect I would probably have rarely used it because any benefit from that marginal increase in sharpness would probably have been lost due to the frequent need for a higher ISO because the lens has no IS.

The lack of autofocus and autofocus tracking with 1.4x extender attached, plus the disadvantage of that inherent inflexibility of not being able to use, say, 350mm when that suits the composition better, are all serious disadvantages in my opinion.

I generally find that a shutter speed equal to "1/effective FL" (ie.1/640th) is required for a sharp image, when I use the 100-400 with my 50D. Using a slower shutter speed, sometimes as slow as 1/250th, can sometimes produce acceptable results, but is not reliable. If there's any significant movement of the subject, a shutter speed faster than 1/FL is required of course..

If one accepts that the IS on the 100-400 provides a 2 stop advantage, and that a reliably sharp image without IS would therefore require a shutter speed of 1/4FL, I can't see how  that 400/F5.6 prime with 1.4x extender is going to provide much benefit, unless you intend using a tripod or at least a monopod, and even then I would be doubtful. The 640mm FL equivalent becomes a 900mm equivalent. With IS in place that would require a shutter speed of 1/800th or 1/1000th. Without IS, we're looking at 1/3200 or 1/4000th.

To attain such a shutter speed, it would appear to me one would probably need to frequently use ISO 3200, and sometimes ISO 6400. But maybe I'm exaggerating. It's your equipment.

Are you able to provide any comparison images showing, for example, the 5D3 with 100-400 plus 1.4 converter used at ISO 800, the 7D with 400 prime plus 1.4x converter used at ISO 3200 to compensate for its lack of IS, and the 7D with 100-400 without converter, used at ISO 400. It would be interesting to see the differences comparing equal size and equal FoV crops. However, if you're leaving for Madagascar next week, I will understand if you haven't got the time.

Best of luck on your trip.
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stever
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« Reply #46 on: September 05, 2012, 11:39:23 PM »
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sorry, think i mentioned in an earlier post that the 400 f5.6+ 1.4xiii is tripod only for subjects that remain in the same plane.  without the extender, it's sharp wide open - shutter speed is an issue early in the morning and late afternoon (and it's pretty useless in jungle) - but a reasonable long backup if something happens to the 100-400 (my short backup is the 70-200 +1.4x) with the high ISO capability of the 5D3

the 400 f5.6 is sharper with better contrast than the 400DO (and without the terrible sensitivity to flare) - much lighter, more compact (particulary considering the terribly heavy but essential lens hood on the DO, and cheaper -- but without IS it's seriously limited.  It's the best alternative i've found to getting longer (with good IQ) than the 100-400 at reasonable size and weight. 

Ray, i'm not sure where your 1/4fl comes from.  1/fl for a long hand-held lens without IS may be a bit optimistic, but with a sequence of multiple images there's a pretty good probability of some keepers.   the shutter speed required for action has nothing to do with the focal length - only the speed of motion of the subject which for wildlife is 1/500 to 1/1000 at most (except some small birds and amimals, and of course hummingbirds). in reasonable light, the problem of handholding the 400 + extender is more about getting focus on the subject than shutter speed and ISO

the 100-400, 400 5.6 and over-priced 400 DO are overdue for up-grade - maybe because Nikon still has no equivalent for any of these lenses
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Ray
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« Reply #47 on: September 06, 2012, 01:37:24 AM »
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Ray, i'm not sure where your 1/4fl comes from.  1/fl for a long hand-held lens without IS may be a bit optimistic, but with a sequence of multiple images there's a pretty good probability of some keepers.   the shutter speed required for action has nothing to do with the focal length - only the speed of motion of the subject which for wildlife is 1/500 to 1/1000 at most (except some small birds and amimals, and of course hummingbirds). in reasonable light, the problem of handholding the 400 + extender is more about getting focus on the subject than shutter speed and ISO

Steve,
The issue was raised recently in the review of the Nikon D800. The claim was made by Michael, and supported by others, that in order to benefit from the unusually high pixel density of such a camera, one may need to use a faster shutter than one is used to using with lower resolution cameras.

1/FL even with VR was considered to be inadequate to get that extra resolution the D800 is capable of. I claimed that it wasn't inadequate, and took a number of test shots, hand-held, using my D7000 with 24-120/F4 zoom to demonstrate my point. But I admit the test was flawed because I used a zoom lens instead of a first rate prime. I don't have any Nikkor primes.

No-one mentioned this, not even Slobodan. A bit slack really.  Grin

The pixel density of the 7D is equivalent to that of a 46mp full-frame sensor, a bit higher than that of the D800, so such reasoning would be even more relevant to the 7D.

Whilst it's true that there is always a certain degree of variability in the sharpness of results, due to the variability of camera shake, a shutter speed of 1/FL with the older versions of VR and IS, seemed about right to ensure a sharp image most of the time. With the newer versions of image stabilization, such as VRII, that claim up to a 3 stop advantage, one may get away with a shutter speed of 2/FL. I don't know. I haven't got any such lenses.

However, I agree that taking multiple shots in continuous mode will increase your chances of getting a sharp image, whatever the shutter speed.

As regards subject movement versus camera movement, I haven't carried out any tests. One might assume if the shutter speed required to freeze subject movement is faster than 1/FL then that will also take care of any camera shake, if the lens has IS or VR.

If the lens doesn't have IS, it may be a different kettle of fish. We have two competing sources of movement. If such movements are in opposite directions at the precise time the exposure is taken, we may get a blurred shot.

Quote
the 100-400, 400 5.6 and over-priced 400 DO are overdue for up-grade - maybe because Nikon still has no equivalent for any of these lenses

Absolutely! I would like Nikon to take the plunge and design a first-rate 200-400/F5.6 which is significantly sharper at F5.6 than at F8 and costs no more, or little more, than its 80-400/F5.6 which is a bit behind the Canon 100-400/F5.6.
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