[popo]

I just had an idea that might be a little crazy, but I think might be worth a try.



Does anyone know their filter gel characteristics? I'm looking for one that passes red and blue, but blocks green. Something like Congo Blue is close, but that passes blue and IR. If there's one that shifts the red range up a bit that will be ideal.



Why do I want this? I wonder what the DSLR phase AF sensors are like to colour? I have to assume they're somewhat panchromic otherwise they wouldn't work with some monochromatic targets. I suspect that for a lot of "near misses" I get with tracking AF of smaller or darker subjects, the AF system is picking green items nearby in preference. If I can slide in a gel to modify the AF response (possibly needing minor offset correction) that might help.

[PuxaVida]

[quote name='popo' timestamp='1311981807' post='10324']

I just had an idea that might be a little crazy, but I think might be worth a try.



Does anyone know their filter gel characteristics? I'm looking for one that passes red and blue, but blocks green. Something like Congo Blue is close, but that passes blue and IR. If there's one that shifts the red range up a bit that will be ideal.



Why do I want this? I wonder what the DSLR phase AF sensors are like to colour? I have to assume they're somewhat panchromic otherwise they wouldn't work with some monochromatic targets. I suspect that for a lot of "near misses" I get with tracking AF of smaller or darker subjects, the AF system is picking green items nearby in preference. If I can slide in a gel to modify the AF response (possibly needing minor offset correction) that might help.

[/quote]



I'm not sure about other systems but in the latest Nikon DSLRs AF and metering work hand in hand for specific combinations. For example auto area mode gets the color information (e.g. the skin tone) from the metering module and uses it for correct choice of focus point(s). Also, dynamic area AF (AF tracking) is assisted by the metering module regarding the changes in color patterns to determine the movement of the subject.



But when it comes to single point AF, I'm not sure if the AF module utilizes the color information. Though, the luminance, shape, pattern and the size of the objects are definitely important for a precise AF.



Serkan

[popo]

I'm aware of the Nikon colour assist but that isn't exactly what I'm after. Within a single point area there are may be wanted and unwanted targets, and I think by cutting green sensitivity I can swing the chances in my favour. As mainly a nature and wildlife photographer I find the over-emphasis of green in most photographic technology implementations rather annoying! The really interesting stuff isn't green.

[PuxaVida]

[quote name='popo' timestamp='1312372356' post='10360']

...

Within a single point area there are may be wanted and unwanted targets, and I think by cutting green sensitivity I can swing the chances in my favour.

...

[/quote]



I doubt that the single point AF relies on (or effected by) the color info. That would be very annoying for cases where you want to nail the precise focus.



But rather than the color, the size of the target which is projected to the AF sensor cell is definitely important here. The size of the subject should not be smaller that the AF cell on the AF sensor. And these AF cells usually are not as big as they seem on the VF... Also their type can be different (e.g. D700 has 51 focus points but only the center 15 points are cross type).



But I'm afraid you've already eliminated these factors and I just sound like bla bla bla <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='' />....



Serkan