UV/IR Cut filters unnecessary or unwanted for b/w?

[Rayt]

I have read some posts on the LUG and on the other M8 forum and I believe Sean Reid mentioned it also though I can't find anything concrete thus this question: Files taken without the UV/IR Cut filter convert better to black and white. For example a black fabric now is purple looks better when converted to b/w that it lifts the lower tones. Can any M8 user explain this? Thanks.

 

[grduprey]

I have read some posts on the LUG and on the other M8 forum and I believe Sean Reid mentioned it also though I can't find anything concrete thus this question: Files taken without the UV/IR Cut filter convert better to black and white. For example a black fabric now is purple looks better when converted to b/w that it lifts the lower tones. Can any M8 user explain this? Thanks.

You do not need the IR filters if you plan on shooting B&W only. Some do not use them for color either, as the IR problem only effects about 10% or so. I decided to use them for all of my shooting, but that is just my decision.

Gene

 

[Artorius]

I have read some posts on the LUG and on the other M8 forum and I believe Sean Reid mentioned it also though I can't find anything concrete thus this question: Files taken without the UV/IR Cut filter convert better to black and white. For example a black fabric now is purple looks better when converted to b/w that it lifts the lower tones. Can any M8 user explain this? Thanks.

I don't use them if I am shooting in B&W. If I am shooting color for a possible conversion to B&W, I use the filter. If you want true conversions from color, magenta does not equate to black.

 

[jaapv]

If shooting for B&W without filter there will be an unsharp (IR light focusses in a different plane with most lenses!) image overlaying your sharp image at about -4 stops. This makes for slightly less microcontrast and crispness. Otoh some like the different greyscale this produces. So it is largely a matter of taste whether you shoot B&W with or without filters. But it DOES make a difference.
Monochrome conversion in Photoshop has so much control over the contrast gradient, one mimics red,yellow, blue or green filters in the channel mixer, contrast and gradient can be adjusted infinetly, white,black and gray points can be set, etc, that I will go for the higher sharpness by leaving the filters on.

 

[bottley1]

"If shooting for B&W without filter there will be an unsharp (IR light focusses in a different plane with most lenses!) image overlaying your sharp image at about -4 stops. This makes for slightly less microcontrast and crispness"

Eh? There will NOT be another image "overlaying" the main image! This is rubbish! All images are a amalgum of RGB light with a small amount of UV and IR on the fringes of the visible spectrum - with or without a filter. If this were true, purists looking for the ultimate sharpness would photograph green subjects only..........

 

[jaapv]

No you are wrong. Put an IR pass filter on and you will see the image at minus (about) four stops. Without adjusting the focus it will be out of focus. And yes, your remark about green light is more or less correct. For non-apochromatically corrected lenses only green (and red when partially corrected, as are nearly all) will be in full focus; there will be colour fringes on the outlines of your subject, called chromatic aberration. On an IR sensitive camera IR light causes chromatic aberration too, only worse than with visible light. As most film and sensors are not sensitive to IR light this is of no importance there. With a highly IR sensitive camera like the the M8 is this phenomen comes into the picture (sorry for the pun..) At minus four stops, of course, the effect is not so pronounced that it will immediately be of great influence on small prints, especially with the shorter focal lengths. As chromatic aberration is less magnified with short lenses, it is far more important with longer focal lengths. And other causes of unsharpness, like motion blur or misfocussing may well "drown" it. So it will be up to the photographer to decide whether he/she is bothered.

One lens that is not affected is the 90 mm Apo-Asph, which is corrected deep into IR. But that is an exception.

Btw, it was quite usual to use a blue or green filter when copying critical documents onto high-resolving slow film in the past for this very reason.