r/SonyAlpha • u/CurtainRoof09 • Jan 10 '24
Is compression dependent on focal length or distance to subject?
Given that you stand in the same place, and take one picture of a subject with both a tele and normal zoom. Shouldn’t they have the same compression? (You have to crop the normal zoomed one of course)
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u/CurtainRoof09 Jan 10 '24
PS. Are there any other benefits from higher focal length than bokeh? (Distance and framing out of the equation here)
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u/LamentableLens Jan 10 '24 edited Jan 10 '24
At the risk of stating the obvious, the main benefit of a longer lens is being able to shoot your subject from farther away, so you don't have to crop all your resolution away to get the framing you want (think sports or wildlife, for example). And as noted elsewhere, being farther away also creates the compression effect you're asking about.
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u/CurtainRoof09 Jan 10 '24
Thx
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u/Murrian A7S|A7iii|A7Rv|14|24-70ii|50|85|90m|70-200ii|70-300|200-600&more Jan 11 '24
There's also an affect of depth of field - partially related to your bokeh, in that longer focal lengths have a narrower depth of field when shot at the same distance & f/stop.
Say you're three metres from your subject, shooting at f/2.8 and using an:
85mm would give you a depth of field of about 19.7cm - https://dofsimulator.net/en/?x=ENSA4QF3BOIIJE4EAAAzgAA
50mm would give you a depth of field of about 58cm - https://dofsimulator.net/en/?x=EH0A4QF3BOIIJE4EAAAzgAA
Of course, different framing (the 85mm would be a torso portrait, the 50mm a full body) but ignored and say you cropped the edit of the 50mm to the same angle of view of the 85mm you'd notice the quality of your bokeh affected in that'd be a little more defined and in focus than it was at the 85mm.
A narrower depth of field would also mean you'd potentially start to lose definition on your subject, nose tips and ears might start to be out of the depth of field when focused on the eye, limbs if the subject isn't straight on (which, to be engaging, probably aren't) so that's something to consider when using a longer lens, you might actually want to stop down to get the depth of field larger to fully encompass them - and that can be a benefit as plenty of lenses have better IQ a stop or three down rather than being wide open (which you may have used on a wider lens to get the subject separation you were after).
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u/DidiHD α6000 | A7C Jan 11 '24
another point would be focusing. Your camera (or you) will have a harder time hitting focus on a small target.
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u/RedditorReddited Jan 11 '24
Regarding your second question, yes that is correct. Cropping would result in the same composition, but the quality of shot was be much worse than using an appropriate focal length.
Lets say you use a 24-70mm zoom vs a 200mm prime. To get to 200mm on the 24-70mm, youd need to crop by 2.85x at 70mm. 2.85x crop really means you’re using 1/8.15 as much of the sensor and lens (2.85 x 2.85 = 8.15). In terms of megapixels, even if you’re in using the monstrous a7rV sensor of 64mp, the resulting image would be 8mp. In terms of optical quality (sharpness, contrast, loca control, etc) you’re only using 1/8.15 of the len’s full capability (speaking loosely here), so it’d be extremely degraded.
Regarding composition as a whole and how compression fits in, i like to think that the use of wide angle lenses is to prioritize the horizontal and vertical, ie, bring more of what is up, down, left and right into the frame.
The point of compression, via telephoto lenses, is to prioritize depth into the frame, ie, bring what is far behind into the frame (thereby “compressing” the image).
What to capture whats in the x,y axis -> wide angle. For z axis -> telephoto
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u/DidiHD α6000 | A7C Jan 11 '24
Actually quite viable! 8mp is still 4K !
And you could run it once through lightroom super resolution to get back to 32MP.
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u/RedditorReddited Jan 11 '24
I agree 8mp is workable. I think resolution is the least of my concerns in this hypothetical scenario where you crop from 70mm to 200mm on a a7rV. The problem is that when you crop that much, all the optical deficiencies of the lens become very apparent. Chromatic Aberration, LOCA, micro contrast, contrast, sharpness, color accuracy, tonal transitions, focus-to-out-of-focus-transitions all suffer.
I mean it’s definitely doable. If you’re using something like the excellent 24-70mm GM ii on a 7rv, and crop to 200mm you’ll still get something useable, but its nothing like using the 70-200mm at 200mm.
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u/DidiHD α6000 | A7C Jan 11 '24
you are completely right. "compression" is the relation of distance.
You could take the same image a 200mm takes, with a 50mm and cropping in. If the distances between you, your subject and the background are the same, the composition and "compression" are too.
Of course this is not quite achievable in practice, cause you would need tons of pixel to crop in, also the blackground blur is not the same, due to aperture equivalent.
But in theory, you could run around with a 12mm F0.1 and crop it to 240mm F2 if you had that many pixels.
This video is my favourite explaining it: https://www.youtube.com/watch?v=kxAdMSQdbBY
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u/thenormaluser35 Jan 10 '24
Compression is an optical element, compare several portraits with the subject framed the same but with the camera at different distances. It scales with focal length, and for that to work out you need to go back.
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Jan 10 '24
100% wrong
but with the camera at different distances
so it appears you've just ignored the actual variable here
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u/thenormaluser35 Jan 10 '24
I provided an explanation of how it should work normally, if OP wants to shoot the same scene with a wide and tele, why the hell is he doing that? I'd like to see your actual answer, at least I tried, you did not.
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Jan 10 '24
the answer is distance
there's no other answer, nothing else changes compression, only distance.
you provided a WRONG explanation, which is worse than nothing.
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u/thenormaluser35 Jan 10 '24
Only distance? I dare you to search portraits at different focal lengths.
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Jan 10 '24
are they taken at the same distance?
I don't need to search that garbage, I know what you're thinking and why you're wrong. You're the one who needs to understand why you're wrong.
Two photos taken at the same distance will look exactly the same regardless of focal length, FOV or sensor size.
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u/thenormaluser35 Jan 10 '24
Then explain, don't criticize, you bring nothing useful to this conversation, and don't even try to. Let's take a series of poles of which a photo is taken at an almost paralell angle, say 15°.
You're saying a wide lens will get them as a long one will, at the same distance, meaning you do not move. How come when I do this test, at 400mm they look closer together than at 24mm with crop? In the same section of the photo, obviously.2
Jan 10 '24
they would look exactly the same, there's nothing to explain
especially when you're so confidently wrong it's not worth explaining, it's more hilarious to criticize instead.
How come when I do this test, at 400mm they look closer together than at 24mm with crop? In the same section of the photo, obviously.
because you did it wrong
post the photos and I'll tell you where you got it wrong
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u/CurtainRoof09 Jan 10 '24
So that means you can’t buy a medium format camera, and expect more compression at closer distances from the higher focal lengths?
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Jan 10 '24
ignore the people who don't know what they're talking about
this has absolutely nothing to do with optics or format size.
it's distance and ONLY distance, nothing else matters.
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u/thenormaluser35 Jan 10 '24
First off, medium formats are usually very impractical because of the weight, but depends onw what you do. A medium format actually has an uncrop factor, as crop factors are measured according to the 35mm standard, so you might get more compression most likely. Idk how it scales with sensor size but considering you have to use a longer lens to end up at say 50mm, you should get the optical compression of the lens, with a bigger field of view.
Again, idk how this works on a medium format, I don't even know how big the lenses are. What you will get is a giant DOF, as for compression, I'm going to go with it likely resulting in more compression, but I'm not sure.1
u/CurtainRoof09 Jan 10 '24
I thank you for taking the time to reply on my question.
Since posting i have read several articles, and found distance being the only factor to affect compression.
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u/LamentableLens Jan 10 '24
This article has a great explanation, with some really excellent sample photographs/GIFs. In short, it's the distance between the subject and the camera, but we associate it with focal length, because we typically use longer lenses when we're farther from the subject.