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11-09-2016, 01:38 AM   #16
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QuoteOriginally posted by photoptimist Quote
FF designs are bulkier and costlier. They require larger glass elements and often require more complex designs to correct aberrations out to the farthest corners. To a first approximation an FF lens has about 3X the weight in glass of the equivalent angle-of-view APS-C lens (and probably about 1.5 to 2X in other materials).

It's hard to say anything general about the IQ differences of APS-C and FF lenses on APS-C sensor due to the wide variations in prices, brands, and design ages. The one IQ area where FF lenses may be generally inferior to APS-C lenses on an APS-C camera is flare from out-of-frame light sources. If you have an FF lens on an APS-C camera, you may think the sun is out of the frame but it's not. In general, the FF lens is capturing an FF frame worth of light but the sensor is only seeing the APS-C frame of it. All that extra FF light is bouncing around inside the lens and mirror box and potentially flaring or fogging the image.
An interesting point, however that issue can be easily resolved by using an APS-C-sized hood, i.e. a hood which would cause vignette on FF and manages to cover the unused part of the image circle on APS-C.

11-09-2016, 06:06 AM   #17
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QuoteOriginally posted by lightbox Quote
Some interesting points. I never considered the possibility of more flare in a FF lens on APS-C, for example.

Please continue the technical conversation (it's enlightening) but I'll now also pose a slightly different question: If we are not pixel peeping for sharpness, is there any artistic or compositional reason to choose one type of lens over the other on an APS-C camera?

Asked differently, if I were to take two identical portraits- one with a 50mm crop lens, and one with a 50mm FF lens- both on an APS-C camera and both at an equal f/4 (say), then what visual differences could I expect? Again, putting the resolution and sharpness aside for a moment.

(I think the answer is "none" to both questions, but I'm just guessing)
Ignoring technical merits takes us into the strange realm of subjective rendering and variations in how different specific lenses affect the look of a portrait.

There are some people who argue quite vehemently that older lenses (which tend to have fewer elements and are all FF because they date to the era of film) have a different and superior rendering compared to newer "designed-for-digital" lenses (which tend to have more elements and some of which are APS-C). As Sandy Hancock said, there's the subjective matter of "pixie dust" in some lenses.

There's others who say this is hogwash and that if you took five identical pairs of portraits, one portrait with an old FF lens and a second portrait of the same person and background with new DA lens, that no one could consistently say which portrait was taken with which lens or which lens was consistently superior.

Personally, I suspect there is something to the pixie dust argument but it's pretty subtle.

---------- Post added 11-09-16 at 07:13 AM ----------

QuoteOriginally posted by LensBeginner Quote
An interesting point, however that issue can be easily resolved by using an APS-C-sized hood, i.e. a hood which would cause vignette on FF and manages to cover the unused part of the image circle on APS-C.
That's a good point although it does require a rectangular or petal-hood that is optimized for the specific focal length, aperture, and filter ring geometry of the lens. Even a perfectly optimized round hood will let in 60% more excess light than would the right rectangle/petal hood. Round hoods let in a lot of excess light from above the frame where bright sky, sun, and overhead light tend to be.
11-09-2016, 07:01 AM - 1 Like   #18
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I have a small collection of SMC-M fixed FL lenses - 28 f/2.8, 50 f/1.4 & f/1.7, 55 f/1.8, 135 f/3.5. I don't normally use them as I am primarily a zoom user. However, I picked this bad habit of pursuing high resolution as a result of using Pixel Shift on my K-3II, I played with the above lenses just to see what they can offer. With aperture in the range of f/8 and f/11, these old SMC-M are unbelievably good. The best part is that the edges and corners are completely sharp with no distortion. I don't know if the performance is due to FF design or these old lenses are simply this good.
11-09-2016, 07:16 AM   #19
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QuoteOriginally posted by Pixelhdr Quote
With aperture in the range of f/8 and f/11, these old SMC-M are unbelievably good
Yes, you're right. I love my "old" legacy lenses, they're a pleasure to use and give good results compared to new glass. But I use them only on APSC - for the moment. no k1 in my bag . I really like the way they render subtle color transitions; it looks like they're less contrasted so more accurate regarding color rendition in some situations.

11-09-2016, 02:12 PM   #20
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Many people prefer the older glass, in tho case the SMC 35 ƒ3.5 and the FA 35-80. But every lens has those who prefer it, even the kit lenses. It's not about what "people" like it's about what you like.

https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/302815-35mm-find-prime.html
11-09-2016, 02:55 PM - 1 Like   #21
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QuoteOriginally posted by lightbox Quote
Please continue the technical conversation (it's enlightening) but I'll now also pose a slightly different question: If we are not pixel peeping for sharpness, is there any artistic or compositional reason to choose one type of lens over the other on an APS-C camera?

Asked differently, if I were to take two identical portraits- one with a 50mm crop lens, and one with a 50mm FF lens- both on an APS-C camera and both at an equal f/4 (say), then what visual differences could I expect? Again, putting the resolution and sharpness aside for a moment.

(I think the answer is "none" to both questions, but I'm just guessing)
If lenses are designed for compact size (and even if they aren't), they may have some vignetting. Similar to the edge sharpness case, a FF lens on an APC-C sensor might similarly have less vignetting (because you're using the center of the lens) than a APS-C designed lens of the same focal length. Whether vignetting is undesirable is up to your particular preference; some people remove it, some people like it, and some people even add it in post-production.
11-09-2016, 04:31 PM   #22
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dcshooter, the video only demonstrates one point. If you want to do proper comparison, keep the FOV constant. In the case 21mm, Cooke has a wider FOV and in the case of 100mm, Cooke has a narrower FOV. We all know wide angle exaggerated distance perspective. In the case of 100mm, Cooke has a narrower FOV. This is a bad example.
11-09-2016, 07:24 PM   #23
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As a very general observation, Nikon is noted for the image quality and build of its 50mm f/1.4 while the f/1.8 design is less highly regarded. The Pentax 50mm f/1.8 is optically similar to the f/1.7 design - and is at least as highly regarded as the f/1.4 Pentax lenses. All of these lenses are very sharp overall, so the crop factor is not a huge issue, IMO. Given that none of these lenses are especially bulky, I think the corner sharpness and contrast of the FF designs make them more desirable overall, even on APSc.

11-10-2016, 05:20 AM   #24
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QuoteOriginally posted by photoptimist Quote
That's a good point although it does require a rectangular or petal-hood that is optimized for the specific focal length, aperture, and filter ring geometry of the lens. Even a perfectly optimized round hood will let in 60% more excess light than would the right rectangle/petal hood. Round hoods let in a lot of excess light from above the frame where bright sky, sun, and overhead light tend to be.
Not only that, you'd need to find a hood for the equivalent focal length, which could or could not be availablr for the specific bayonet/thread size.
My point was purely theoretical.
11-10-2016, 06:50 PM   #25
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It took me a bit to go through the posts, the linked video (wow), and normhead's linked lens comparison thread (fantastic test). Thanks to everyone for the responses; I am starting to understand what is meant by "pixie dust," which I've seen used a few times on the forums.
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