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07-31-2015, 01:19 AM   #16
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Although I am not entirely sure what issues the OP is trying to explore... this article may be related:
Lessons from a Legendary Lens Designer

07-31-2015, 04:27 AM   #17
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QuoteOriginally posted by rawr Quote
Although I am not entirely sure what issues the OP is trying to explore...

It is shooting the same scene with two entirely different focal lengths of lenses.

Would there be any differences in how the end photo turned out?

(I am asking because I don't know the answer)

21mm on a crop sensor like we all have now, and a 31mm on a full frame.

Would anything come out looking different in the photo, not because of the full frame sensor, but because of the 10mm differences in the two lenses used?

(What makes it interesting is that the two lenses have almost the same field of view on their format in this scenario)
07-31-2015, 05:10 AM - 1 Like   #18
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The DA21 on APS-C will produce images almost identical to the FA31 stopped down 1EV on full frame. That's how equivalence works.

There may be some subtle differences in the quality of the bokeh and other end-points; at least I hope so
07-31-2015, 05:14 AM   #19
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QuoteOriginally posted by Sandy Hancock Quote
The DA21 on APS-C will produce images almost identical to the FA31 stopped down 1EV on full frame. That's how equivalence works.

Will there be any perspective distortion or differences between the two seeing how the focal lengths are quite different? (which is a lot more prevalent on short lenses)

07-31-2015, 05:28 AM   #20
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QuoteOriginally posted by alamo5000 Quote
Will there be any perspective distortion or differences between the two seeing how the focal lengths are quite different? (which is a lot more prevalent on short lenses)
"Perspective distortion" is from where you are physically located relative to your subject... a few inches away from someones face and their nose will look massive relative to their ears, but step back 10 feet and the nose shrinks relative to the size of their ears. In your example nothing moves (camera, subject, or background), so the perspective is the same, and so is any perceived perspective distortion.

In general terms a change of 1.5x in focal length isn't going to shift you into new realms of lens distortions (<-products of the individual lens design, nothing to do with "perspective distortion"), i.e. you aren't going to go from the barrel distortion typically found in wide angle lenses into the pincushion type you typically see in telephoto lenses. This will of course depend heavily on the individual lenses used (and how well they correct these distortions).


You can do your own tests. Use both the 31mm and your 21mm from the same location on your aps-c camera. Crop the 21mm to the same field of view as the 31mm. This is essentially what your FF to APS-C test is asking for, just one step down the 1.5x crop ladder.
07-31-2015, 05:34 AM   #21
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QuoteOriginally posted by alamo5000 Quote
It is shooting the same scene with two entirely different focal lengths of lenses.
Would there be any differences in how the end photo turned out?
For faces, you can certainly see a difference, although between 21mm on APS-C and 31 mm on FF I would wager not so much, if equivalent apertures were used:
Lens distortion focal length - faces

07-31-2015, 06:14 AM   #22
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QuoteOriginally posted by alamo5000 Quote
Will there be any perspective distortion or differences between the two seeing how the focal lengths are quite different? (which is a lot more prevalent on short lenses)
Probably not. The DA21 *may* show a little more barrel distortion, and I'm sure there will be other minor differences, but they will be minor.
07-31-2015, 06:51 AM - 1 Like   #23
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People argue this a lot. There are plenty of folks who say that if you shoot 85mm on full frame and 55mm on crop, that the 85mm will be more flattering to the subject. But when I've actually seen the comparisons, as long as they are shot from the same place, they look so exceedingly similar that I can't tell them apart (except that the full frame will be capable of shallower depth of field).

07-31-2015, 09:00 AM   #24
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My answer is that no, there will not be a significant difference in the framing you see due to the focal lengths. Focal length is somewhat irrelevant - field of view is much more important.

Since you are asking only about the issue of framing, there should be very little difference between your images, in that regard.
07-31-2015, 09:06 AM   #25
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QuoteOriginally posted by fuent104 Quote
My answer is that no, there will not be a significant difference in the framing you see due to the focal lengths. Focal length is somewhat irrelevant - field of view is much more important.

Since you are asking only about the issue of framing, there should be very little difference between your images, in that regard.
And I think we see that in the images from the Canon test I posted.
07-31-2015, 12:42 PM   #26
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QuoteOriginally posted by UncleVanya Quote
And I think we see that in the images from the Canon test I posted.
I agree. Also, the 21mm and 31mm on the different formats should have even LESS of a difference than the Canon lenses in the test, as the fields of view will be more similar.
07-31-2015, 02:15 PM   #27
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If you scale the focal length of the lenses by cropping factor, the framing and perspective of the shot is exactly the same.

When you see a lot of these alarming comparisons, read the fine print and you'll see they moved the camera.
08-01-2015, 03:27 PM   #28
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QuoteOriginally posted by alamo5000 Quote
... My questions and/or topic of discussion is NOT about equivalence although I will reference angle of view to some degree.
...
My theory is ...
Your question is all about the equivalence theorem.
Please get over some of the opiniated discussions and actually learn what it is all about. All of your questions will be answered, and more. There is no need to have yet another theory about the topic.

I'll give you a pointer to an article I wrote about it but won't have time to participate beyond this point.
-> LumoLabs -- Camera Equivalence -- Whitepaper

Nevertheless, here is the answer to your question:

Yes, the FA31 (on FF) will bring out your subject "more prominently" than the DA21 (on APSC). But it isn't a property of the larger sensor or larger focal length per se.

E.g., the DA21 at F3.2 on APSC, and the FA31 at F4.8 (at twice ISO) on FF will produce indistinguishable images. However, at apertures between F1.8 and F4, the FA31 will render your images with more 3D "pop" (shallower depth of field) than the DA21 could provide. In the example you mentioned though, you did not reach the apertures where this matters, so you wouldn't have seen a benefit coming from FF there.

One more note, I know, you didn't ask, but ... When set to produce indistinguishable images, e.g., DA21 at F4 and FA31 at F5.6, then the FA31 (which is a stunning lens to start with) has much less aberrations. Even and contrary to common belief, in the corners. But the DA21 is a much smaller lens, so if only needed at above F4, I wonder if I wouldn't prefer the DA21 and an APSC body.

Last edited by falconeye; 08-01-2015 at 04:32 PM.
08-01-2015, 04:55 PM   #29
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QuoteOriginally posted by falconeye Quote
Nevertheless, here is the answer to your question:

Yes, the FA31 (on FF) will bring out your subject "more prominently" than the DA21 (on APSC). But it isn't a property of the larger sensor or larger focal length per se.

E.g., the DA21 at F3.2 on APSC, and the FA31 at F4.8 (at twice ISO) on FF will produce indistinguishable images. However, at apertures between F1.8 and F4, the FA31 will render your images with more 3D "pop" (shallower depth of field) than the DA21 could provide. In the example you mentioned though, you did not reach the apertures where this matters, so you wouldn't have seen a benefit coming from FF there.
A question here - (not an argument) are the OOF areas equally identical , ie is the potential for bokeh the same?
08-01-2015, 05:19 PM   #30
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QuoteOriginally posted by GUB Quote
A question here - (not an argument) are the OOF areas equally identical , ie is the potential for bokeh the same?
The canon links I shared seemed like it.
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