A matter of glass

[JOCO34]

Hi Ive got a question. I have been shooting with my M8 and IR cut filtered lenses. Now I have just obtained a really nice M-240. I usually keep a filter on my lenses for protection so do I need to replace the IR cut filters with UV or can I just go ahead and use the IR's? Will it degrade the image, cause color casts etc. Any advice will be appreciated.

 

[ferider]

Actually it will be better to continue using IR filters, the 240 is quite sensitive to it.

 

[Pete B]

I've heard skin tones are better with the IR on the M240.
Pete

 

[rscheffler]

I've heard skin tones are better with the IR on the M240.
Pete

Any idea if there are any online tests to confirm this? I haven't really searched for it, but so far haven't found anything, either.

I definitely see IR contamination in some M240 images with certain types of synthetic textiles (i.e. when shooting weddings) and have considered getting a few Leica IR cut filters to ease post production headaches...

 

[JOCO34]

Thanks for the replies! So the consensus is that the IR cut filters should stay on the lenses and it will be of some help. Thanks again for the advice.

 

[user237428934]

Actually it will be better to continue using IR filters, the 240 is quite sensitive to it.

So you say the 240 is more sensitive than the M9? With my step from M8 to M9 I got rid of all IR cut filters and have nothing to complain. I must admit that I never heard of an IR issue with the 240.

 

[krötenblender]

So you say the 240 is more sensitive than the M9? With my step from M8 to M9 I got rid of all IR cut filters and have nothing to complain. I must admit that I never heard of an IR issue with the 240.

Well, I have... And easily seen with my own. On a sunny day, when photographing people with black/dark grey synthetic fabric, the black comes out all violett. Even with filter it is there, but much better manageable.

 

[JOCO34]

So if I can understand the comments Infra Red is a common problem with all sensors but to varible degrees depending on the thickness of the cameras sensor shield. So, in other words, the M8 has basically none, the M9 is fairly thin and the M-240 is somewhat thicker, hence the different effects. In bright sunny weather it would be expected for more IR to be resident on the subject. The question that I have is that in the absence of any IR radiation will the IR cut filters have any negative effects on the image.

 

[ferider]

So you say the 240 is more sensitive than the M9? With my step from M8 to M9 I got rid of all IR cut filters and have nothing to complain. I must admit that I never heard of an IR issue with the 240.

Not really an issue, but IR filters certainly don't hurt the 240 for skin tones and deep blacks. From a discussion with Jaap last year, once I saw magentas with my - back then - new 240: Next to the M8, the M (240) is the most IR sensitive short register camera. M8 50%, M9 80%, M240 70% of IR suppression. Like 1, 3, and 2 stops, when you think in terms of DR.

 

[JOCO34]

Great advice guys. You have saved me from buying around $300 in UV filters and I will get better IQ with the IR filters in place. I am really glad that I found this Forum!

 

[rscheffler]

So if I can understand the comments Infra Red is a common problem with all sensors but to varible degrees depending on the thickness of the cameras sensor shield. So, in other words, the M8 has basically none, the M9 is fairly thin and the M-240 is somewhat thicker, hence the different effects. In bright sunny weather it would be expected for more IR to be resident on the subject. The question that I have is that in the absence of any IR radiation will the IR cut filters have any negative effects on the image.

I don't think it will have a negative effect, but can't promise it. IIRC, there might be some consequences to using these filters with ultra wide angle lenses in that it could mesh poorly with the in-camera color shift correction, resulting in over-correction of the color shift. But that would be something to test in order to confirm.

The amount of IR suppression by the glass in front of the sensor is very much a factor of the type of glass/filter used, in addition to thickness. The tricky situation for Leica is that the cover glass needs to be as thin as possible to reduced image quality degradation (smearing of details towards the periphery in images, especially with wide angle lenses), but thin glass passes more IR. From past discussions on another forum, apparently the glass type used for the M9 sensor cover is not that great quality, which might also be a factor in the current sensor (cover glass) corrosion problem Leica is fixing for M9 owners. There has been speculation the M240's cover glass is slightly thicker than the M9's, IIRC. IR contamination is definitely also present in M9 images, having experienced this enough times with my images before moving to the M240, where as I mentioned, I also see the effect from time to time. It's primarily a problem with synthetic fabrics and most noticeable in those that are neutral, such as black and gray. Shooting weddings with these cameras, I've had situations where gray suits that reproduced well with Canon cameras resulted in a magenta lapel with the M240, while the rest of the suit remained neutral. Also happened with a groom wearing a very expensive deep navy tux... lapel shifted purple. Day to day I see it a lot with fleeces and the nylon material used in backpacks and other kinds of bags. I've been thinking of getting some of these filters to try. Might be worthwhile. Biggest problem is my 21 Lux with the stupid Series VIII filter.

 

[JOCO34]

Thanks for the in depth response! I have been shooting with my M8 for the last 10 years or so and I am very familiar with the purple demon lurking within the sensor. Usually it has been very controllable if you do a little extra planning and use the IR cut filters. I was hoping that with my new to me used M240 I could put this behind me. It seems the cut filters will have to stay. It is interesting though that I have seen more purple with my Leica lenses than with my Zeiss. The difference must be in the glass chemical formulation or maybe just coincidence since I didn't do any scientific study.

I am now using my M8 as a mini-monochrom and have been getting good B&W without using an IR filter attached and the camera set to B&W only. I guess the IR that gets through adds a little more depth to the "color" plus greater detail. It's pretty nice having two great cameras and I hardly return to my Nikon Df kit for everyday non-paid work.