Blessing: Purple Cast lifts the shadows?

[rbrooks]

Could it be that this purple cast is what I/we want for black and white? Why do I say this? Because if we look at chemical developers we all strive to lift the shadows. We use tricks like double bath processing and pre-flash. Could it be that this IR coming through actually adds info and fill the shadows? Later if I want to force it to black (in b&w) I can always adjsut the curves. Just food for thought... Any others out there with experience in both this speciality area of chemical darkroom and in this new digital purple cast?

 

[jlw]

I also wondered if the extra IR sensitivity might contribute the digital equivalent of "latensification" to shadow areas. In principle it makes sense, since a CCD presumably would need to be hit by a certain minimum number of photons to reach the minimum level required to make it register a charge.

I have no idea how you'd test this hypothesis, though. Maybe somebody with an M8 and a strong IR-only light source (one of those lamps used with night vision devices?) could shoot some pictures with and without the additional IR source, and see if it contributes to extra shadow detail.

 

[Steve L]

Except the problem here is that the IR component is focused at a different point than the visible light, so it not only lifts the shadows, it creates an out-of-focus haze over them...(in high-IR areas).

Is that really what you want?

This effect is fairly easily seen in sunlit foliage (at least, I only had a foliage shot from Guy Mancuso available, I don't have an M8 yet, I don't know how obvious it would be on other content) - magnify and compare with- and without- 486 IR cut filters and you will see the filtered image is sharper....at least that is what I saw, and what the description of the 486 filter on the Schneider Optics says will happen.

 

[J. Borger]

I do not know if it is lifting shadows ... but tonality in B&W is 'OUTSTANDING' .....
Never noticed any soft spots Steve mentions ..... this is one of those issues that MIGHT come up in certain very specific situations or when you go looking for it and shoot pictures to simulate the effect...
If you shoot landscapes at f16 with a wider angled lens .. there is no IR focus-shift ........ because everything front to back will be in-focus!
So even for landscapes you have to use a very specific combination of focal length and apperture to notice any issues related to IR focusshift.

 

[jaapv]

It is exactly what Sean Reid is saying in his M8#4. he backs it up with comparative shots.

 

[varjag]

IR sensitivity can indeed open up shadows, but only if they reflect back IR. It might also add slightly to camera's "true" sensitivity under IR-rich lightsources, not unlike film emulsions with extended red sensibilization.

But I would chose absence of magenta cast over that any day, YMMV.

 

[Steve L]

J. borger-
I believe that where the image is focused *behind* the lens has nothing to do with how much depth of field you get in *front* of the lens. I got Guy's picures from his Leica board thread (he made them available for download in that thread) and saw a significant difference in contrast/resolution in the foliage (plus it was a much lighter green in the unfiltered shot).

So I think the unfocused haze is over any part of the picture that has strong IR relative to visible light - as you say, in many shots this is only a small part of the picture, but it shouldn't be ignored. And if you read the 486 filter description on the Schneider website, it even says that the filter is designed to reduce the blurring of a picture caused by having both IR and visible light present.....

For me it only means that I will keep filters on the lens all of the time.

I know I seem to be harping on this issue....but it does seem to be getting no attention - just like the magenta issue got no attention on the R-D1, because there were other issues that were more important...I don't know how important this one is, I can't really test without an M8....

 

[MarkM6]

I've briefly read a user's comment on LUG Forums that M8 should be available in 2 versions; a B&W and a Color versions. I thought it would be cool!