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A question for dSLR shooters


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#1 Stuart Brereton

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Posted 12 March 2014 - 08:31 PM

I generally try to avoid dSLR shooting. I don't have an issue with the images these cameras make, they're often very appealing, but the ergonomics of the cameras are a complete deal breaker for me.

 

That said, I seem to have had a number of dSLR shoots come my way recently, and so I've found myself further down the rabbit hole that I ever intended going. I've been testing a set of Asahi Takumar lenses on a Canon T2i today, and come across an issue.

 

I'm shooting various test subjects with each of the lenses in video mode, Neutral picture style, 23.98fps. At the same time I also take a high resolution still of the same frame. In the stills, the lenses are tack sharp, in the video, they are noticeably soft and exhibit other artefacts, like chromatic aberration.

 

I'm aware that a T2i hardly represents the cutting edge of modern dSLRs. I'm also aware that there are a number of compromises involved in these cameras shooting video at all, but my question is: Is this a problem with this particular camera, a problem with older/cheaper dSLRs, or a problem with all dSLRs?


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#2 Phil Rhodes

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Posted 12 March 2014 - 08:42 PM

The softness is entirely normal. Earlier DSLRs are really considerably less than 1080p cameras; the only reason they look sharper is because of the aliasing. This is made clear by the third-party, behind-the-lens antialiasing filters, which take out most of the jaggies but leave you with an image that looks permanently out of focus.

 

I think you can only be seeing aliasing - which can include cross-colour artefacts - as chromatic aberration. Like this 5D2 shot (saturation increased in the lower inset):

 

alias.jpg

 

Absent some sort of external physical influence, the sensor and lens aren't going anywhere, so there shouldn't be any way there's any actual optical offset getting involved, other than the usual aperture and focus configuration - and the camera presumably can't mess about with aperture on these non-EF lenses anyway. You are using a slightly smaller sensor area for video, which may be a minor issue in that any existing softness will be exacerbated, although the much greater resolution of the stills should make it easy to compare. You could evaluate the influence of this by comparing absolute field of view in video and stills modes.

 

A 5D Mk. 3 or GH3 will, as you suspect, do considerably better. The upcoming GH4 is supposed to be a 4K camera, for what it's worth. About the worst possible offender for non-chromatic aliasing is probably the 7D.

 

P

 

PS - I don't think anyone really wants to shoot DSLR. As you may have gathered, I've done quite a bit of shooting with cameras I'd rather not have shot with, but honestly it's so much better than even quite expensive alternatives it seems churlish to complain.


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#3 Stuart Brereton

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Posted 12 March 2014 - 08:54 PM

Thanks Phil, that's pretty much what I suspected. Most of the shoots I've done have been on a 5D mkIII, and have looked great. The T2i just happened to be around today so I thought I would test a few lenses on it and was horrified by how soft they appeared. Glad to know it's not the glass (or my eyesight...).


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#4 Sean Cunningham

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Posted 12 March 2014 - 10:55 PM

All of the Canons (including the MkIII) will exhibit aliasing and moire to some degree because the 1080P video image is arrived at through line skipping rather than supersampling from the however many megapixel sensor.  The built-in codec is also rather marginal with factory settings and Magic Lantern, in addition to RAW, has added higher quality compression of double or more the bit rate if you've got media fast enough.

 

I had to deal with the chroma moire on 7D footage and was able to virtually eliminate it by doing a small median filter to just the chroma while sharpening just the luminance.


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#5 Freya Black

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Posted 13 March 2014 - 04:08 AM

Phil is right, tho I think he is being quite polite to describe the cameras of being capable of "considerably less than 1080p". There are a lot of people in denial about

the cameras but I suspect it might be more accurate to suggest they struggle to resolve 720p. Even the more high end Canon 5D Mark III has been criticised for being able to "barely resolve 720p" in some quarters. Of course these cameras can take very nice images. Lovely colour science, interesting depth of field (in the case of the huge 5D sensor), generally nice video, except for all the occasional artifacts. I think this is why people believe that they are shooting 1080p video in spite of overwhelming evidence to the contrary.

 

This actually extends to a lot of things. Talking to someone at BVE I must have mentioned that IMAX was only 2K. He told me in know uncertain terms that IMAX must be at least 8K and went on to tell me about all the cinemas that were definitely 4K in London. I had to bow to his greater knowledge on the subject as I've never seen digital IMAX but certainly many people have told me that it looks better than the 4K digital projection they have seen. (assuming those people had really seen 4K digital projection and didn't believe that all cinema projectors are 4K which seems a common meme)

 

The point is that I think a lot of people still equate image quality with resolution, so if something seems to look better, it must have more pixels right?

 

Freya


Edited by Freya Black, 13 March 2014 - 04:09 AM.

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#6 Zac Fettig

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Posted 13 March 2014 - 09:40 AM

You were right, Freya. Digital IMAX (IDF) uses a 2k projector, through at least 2012. They do have 4k projectors too.

 

http://en.wikipedia....AX#Digital_IMAX


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#7 Freya Black

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Posted 13 March 2014 - 06:44 PM

Yeah I know but I didn't need to be right and when someone else is so completely sure about something, it's suddenly useful to play the dumb blonde and exit the discussion as quickly and easily as possible.

 

AFAIK the 4K IMAX projectors are still in development?

 

Freya


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#8 Sean Cunningham

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Posted 13 March 2014 - 09:09 PM

Of course there's also "real" IMAX to consider.  That's a helluva lot higher resolution than 4K.


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