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02/15/2013 07:52:36 AM · #1 |
I have a feeling this may have been asked in the past...sorry if I bring this up again.
2 lenses, say a Canon 50mm f1.2 and a Canon 50 f1.4, same subject, same lighting...would the overall sharpness be different when you stopped down to 2.8 or 5.6? What creates this difference? What if you did the same with 50mm f1.2 and 85mm f1.2? Do the starting lower apertures equal better sharpness than lenses of the same focal length (Or close to it) even with a starting aperture of 2.8?
If I've not managed to articulate this very well (Tired, but wanted to post before bed), I'll be back to edit for clarification.
I often use my 70-200 f/4 @ 5.6 when shooting portraits in my little home studio. However, I also have the 100mm 2.8 and wondered if I should put that lens on instead, @ 5.6 and just move in closer or further away. I haven't tested anything...was hoping someone already knows. Sleeepppp calllls....zzzzzzz |
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02/15/2013 08:07:01 AM · #2 |
This really just varies from one lens to another. Sharpness isn't absolute, meaning, you don't have a "sharpness score" of 50 at 1.2 for all lenses, nor for maximum aperture +1 stop.
GENERALLY, a lens will be sharper the more it's stopped down, up until diffraction starts, so one could ASSUME that a 1.2 @ 4 would be sharper than a 2.8 @ 4. But that's just a generality and there are plenty of times where that wouldn't necessarily hold true. And different lenses will behave differently at different focus distances, as well.
In short, you need to be more specific in what you are comparing before it can be answered.
The difference is just caused by the construction. You'll also get different behavior from each lens on each different body due to slight variations in the build of both the lens and the body. |
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02/16/2013 05:47:05 AM · #3 |
If I'm shooting a portrait, I like the 70-200 because I have room to play with. I normally shoot at f5.6. However, I never thought of putting my 100mm f2.8 on and just moving around. Stopping that down to 5.6 I wondered if it would be just as sharp...
Or...if one has 2 lenses, both 70-200, but one is f/2.8 and the other is f/4. When both are stopped down to 5.6 or 8...would the f/2.8 always be sharper? Or is my brain just not working properly in understanding this. |
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02/16/2013 06:38:09 AM · #4 |
| There is no general rule. You will need to compare the specific lenses. Fortunately, this site does exactly that. In the case of the 50mm f1.2 vs. f1.4 stopped down to f5.6 - the 1.4 seems to be on top. As for the 70-200 f4 IS, its sharpness is exceptional, and can compete with most lenses on that level. Its only disadvantage is that it can't go faster than f4. |
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02/16/2013 09:03:55 AM · #5 |
Another generalization would be that the prime would be a bit sharper/perform better than a zoom, but this certainly isn't always true.
Based on what  mitalapo just posted, this page specifically compares the lenses you're asking about at 100mm focal length. (Mouse pointer off the image is the 70-200mm; mouse hovering over the image is the 100mm.)
Based on that, the 100mm 2.8 seems a tad crisper at 5.6, though both look excellent. It is just one test, obviously, and your own tests under your studio conditions would be more meaningful.
Personally, if I had the room to move around while shooting, I would use the 100mm. Not just because it looks minimally sharper, but because the consistent focal length will keep the perspective the same, and I think this is beneficial when doing portraits as it keeps the shape of faces/bodies consistent. And an added benefit to the 100mm 2.8 is the ability to shoot wide open for creativity.
I haven't checked your lenses, but here's another site that does a nice review of lens performance throughout their aperture range. |
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