Gear Talk > Technical Support

Are you really getting all the benefits of wide apertures.....?

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GuyF:
There's an interesting article in the May issue of the British Journal of Photography that compares the low-light capabilities of the 5D mk3 and Nikon D4. Both cameras use their own 24mm f1.4 lenses in the article. As I've just bought a mk3 and Sigma 85mm f1.4 I thought the article would be pretty informative but was quite surprised to read:-

"Fast lenses are only part of the solution, as the microlens structure of sensors has the effect of limiting the maximum effective f stop - you get the reduced depth of field, but not the true lens speed. To compensate for this, camera firmware detects apertures faster than f2.8 and applies additional  gain. You must add the gain mapping applied at all apertures to compensate for vignetting."

It goes on to say that shooting at f1.4 and ISO 6400 will probably give you ISO 25600 in the corners. Yikes!

Well, you learn something new every day.

I guess those shooting Leica with a Noctilux f0.95 must feel robbed!

Mt Spokane Photography:

--- Quote from: GuyF on June 05, 2012, 11:39:57 AM ---There's an interesting article in the May issue of the British Journal of Photography that compares the low-light capabilities of the 5D mk3 and Nikon D4. Both cameras use their own 24mm f1.4 lenses in the article. As I've just bought a mk3 and Sigma 85mm f1.4 I thought the article would be pretty informative but was quite surprised to read:-

"Fast lenses are only part of the solution, as the microlens structure of sensors has the effect of limiting the maximum effective f stop - you get the reduced depth of field, but not the true lens speed. To compensate for this, camera firmware detects apertures faster than f2.8 and applies additional  gain. You must add the gain mapping applied at all apertures to compensate for vignetting."

It goes on to say that shooting at f1.4 and ISO 6400 will probably give you ISO 25600 in the corners. Yikes!

Well, you learn something new every day.

I guess those shooting Leica with a Noctilux f0.95 must feel robbed!

--- End quote ---

 
Here is another article on the effect.
 
http://www.luminous-landscape.com/essays/an_open_letter_to_the_major_camera_manufacturers.shtml

Forceflow:
That really sucks... that certainly is something I did not want to learn

neuroanatomist:
There are two issues at play here.


--- Quote from: GuyF on June 05, 2012, 11:39:57 AM ---You must add the gain mapping applied at all apertures to compensate for vignetting. ... It goes on to say that shooting at f1.4 and ISO 6400 will probably give you ISO 25600 in the corners. Yikes!

--- End quote ---

This sounds like it's referring to peripheral illumination correction, which is applied to jpgs if the setting is enabled, and by RAW converters if desired.  Or, you can live with the vignetting (which with the 24/1.4L II is actually closer to four stops at the edges, i.e. ISO 6400 gets pushed to the equivalent of ISO 102400 in the corners!!).  Vignetting affects most lenses to some degree, is apparent on both digital and film, fast lenses are generally worse (although some f/5.6 zooms are quite bad, too).


--- Quote from: Mt Spokane Photography on June 05, 2012, 12:01:03 PM ---Here is another article on the effect.
 
http://www.luminous-landscape.com/essays/an_open_letter_to_the_major_camera_manufacturers.shtml

--- End quote ---

This one, referencing the data from DxOMark, is a different issue.  This is specific to fast lenses, generally faster than f/2.  The clandestine exposure boost applies to the RAW image data, and is usually not more than 1/2 stop.  The effect is worse with smaller pixel sizes.

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