My take on: Does lens sharpness matter for video?

Samuel H

Samuel H

Major Contributor
I have run some tests in order to find out, and my conclusion is that yes, it does, big time.
http://www.similaar.com/foto/lenstests/lenstestsv.html


And what if I'm just recording for the web? Will vimeo's compression make that difference dissappear?
Well, it definitely makes it smaller, but I think I can still see a difference:
http://vimeo.com/16611175


This is what I did:

* I used my new 550D to record video in 1080p24 format.

* I used my "One Dollar Resolution Chart", but didn't frame it all, just about a third of the area; still, it was framed so that my top-left half-dollar sits right on the top-left corner of the frame.

* I shot several videos with the same camera settings and the same lens: a Carl Zeiss Jena "zebra" Pancolar 50mm f/1.8, which I know from my stills tests is exceptionally sharp, but looses a lot of that sharpness in the corners when aperture is wide.

* So I shot with three different settings, changing only aperture and shutter speed (there's no movement so keeping a 180º degree shutter was not too important), to alter the lens' sharpness.

* I took some 100% and 200% crops from the corners of those three clips.

http://vimeo.com/16611175
 
I don't understand the nature of the test.

If I smear vaseline over the lens or use a diffusing filter, it's certainly not going to resolve as well. This is expected. At some point, the lens will be sharp enough to give the full capabilities of the sensor. Beyond that, it's really not going to help a whole lot. I actually rather enjoy shooting with glass that isn't as razor sharp. I see fewer artifacts, and really enjoy the look.

But to each their own. :)
 
well, I was just trying to counter the argument that you don't need a good lens for shooting video because nearly anything will be good enough for 1920x1080

I can also see, in this very same test, that aliasing gets worse when sharpness increses; still, it's usually easier to take sharpness out (for example by going just slightly out of focus) than it is to put it in
 
NormanBates said:
well, I was just trying to counter the argument that you don't need a good lens for shooting video because nearly anything will be good enough for 1920x1080

I can also see, in this very same test, that aliasing gets worse when sharpness increses; still, it's usually easier to take sharpness out (for example by going just slightly out of focus) than it is to put it in
Click to expand...

It would be awfully hard to find a modern lens (or even a decent vintage lens) that didn't EASILY outresolve the APS-C sensor in video mode. Perhaps if you got just an AWFUL lens you'd see issues. But even the included $100 kit lens on a T2i resolves BEAUTIFULLY at 5K. 1080p is going to be trivial. You do gain other benefits from better glass (lower distortion, better contrast, better feel of the controls, etc.) but sharpness shouldn't even be a question.
 
I think the issue for most people isn't whether good lenses make a difference, its more about what are the cheapest lenses I can get that provide enough quality.
 
With SD video, this was sometimes the case. NTSC SD only has 486 lines of active video. And this is why older video lenses for Beta and DigiBeta look so soft on HD cameras.
 
Even as these cameras output 1080p into a highly compressed file the sharpness of a lens is what the sensor gets and of course it does matter if you have a soft or sharp lens. Sharpness isn't everything but I certainly prefer a well resolved image. Just look at the Canon 100L. It's a bitingly sharp lens and neither of my Zeiss primes has anything near that 100L sharpness but I still like them and prefer them in many situations. Same thing with my Canon 16-35 which at times can be softer than either Zeiss prime and I like that lens also. But I'll never get the sharpness like that 100L or the 70-200 by the way.

To look at it like the camera "only" does 1080p and that any still lens will resolve more than 1080p is to overlook what you actually feed the sensor with.
 
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