Light Sensitivity of the Leica M8 in nm?

Discussion in 'Leica and Rangefinders' started by carbon_dragon, Sep 28, 2018.

  1. Regarding the Leica M8's infrared sensitivity, does anyone know, or know how to find, how far into the infrared in nm the sensor is sensitive. To compare, according to my book, Kodak HIE was sensitive to 900nm. Konica went to 820. Ilford SFX to 740nm.

    In practice I can get noticeable infrared effects with a red filter or a Leica IR filter (frequency of the Leica IR is unknown, never been able to figure that out either but seems a little darker than a 25A). It seems to me to be more than SFX is capable of, but less than HIE significantly. If I had to guess (and I'd probably be wrong) I'd guess somewhere between 750 and 800nm.

    But what is the real answer? Does anyone know? Has Leica ever published this as part of the specs of the camera (bought mine used, don't even think I have a manual). Thanks!

    P.S. Like the frequency range of the Leica 39mm IR filter, I suspect this may be a question nobody knows the answer to, but if I'm wrong, I'd like to know.
     
  2. Last edited: Sep 28, 2018
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  3. If I'm reading it right, it looks like at 750, there isn't much sensitivity left, but that it at least a little sensitive to maybe 775nm. Since a 25A filter starts off about 580nm there's plenty of room there and if you're right about the Leica IR, then using that filter gives you 700nm-775nm. The M8 is capable of metering TTL with the Leica IR filter pretty accurately so this seems to make sense as well.

    So maybe the M8, if it were a film, would be perhaps closer to Ilford SFX with the right filter, maybe a touch more sensitive? Probably not as sensitive as Konica.
     
  4. The Leica IR filter is a cut-off filter, it does not give you 700-775 - it takes it away. You wouldn't use that filter if you wanted to do IR photography. There should be plenty of articles out there where people have used the M8 for IR photography.
     
  5. No, wrong filter. The IR cut filter was made at the time of the M8. The Leica IR filter is ANCIENT. It's listed in the oldest Leica handbook I have, but it's never explained other than to list its existence. That is a dark red filter. Nice chrome ring though. may date from the pre-M days, I'm not sure.
     
  6. My bad, sorry.
     
  7. No problem. If you say the words IR Filter, it does kind of imply that the filter is filtering out IR. In this case though, all I have to go on is that this silver chrome ring filter has the letters IR written on it! Language is so imprecise.
     
  8. https://www.datasheets360.com/pdf/4613689109339751409

    The Data Sheet for the KAF-10500 was published by Kodak, you can find it on the link above.

    Leica M8 Color Infrared

    And above is my experiemts with my custom DNG processor that is designed to use an Orange Filter over the lens and 16-Bit DNG files produced by M8RAW2DNG.

    The custom DNG processor is written in FORTRAN and Assembly, runs on DOS using the PharLap extenders,

    [​IMG]I1015897 by fiftyonepointsix, on Flickr

    The IR cut filter of the KAF-10500 has a 5% leakage, sensitive past 1um. With true Raw files as given by M8RAW2DNG, enough to pull up the Blue Channel as IR only when using the O56 Orange filter.
     
    Last edited: Sep 29, 2018
  9. When I use a darker red filter, like the IR filter I can do decent IR effects in black and white and when I use a 25A, I can do the channel swap to do false color. Maybe a fully converted camera with no IR cut filter at all could create even stronger effects. I've debated using my old canon 5D mk I as a candidate for conversion.

    L1000843.jpg

    L1000835.jpg
     
  10. I wish the IR cut filter of the KAF-10500 could be removed- would gladly have that done. I had an Olympus E-P2 converted to full-spectrum. I find the mirrorless cameras best for this job these days. The SLR viewfinder is limited to an R25 filter, going deeper is easier with the EVF. You can use "liveview", but I like looking through a viewfinder.

    Infrared and full-spectrum

    My first full-spectrum camera is THE first full-spectrum camera sold by Kodak. Called them up in 1993 to ask for it, before they sold them.
     
    Jochen likes this.
  11. Looks like a monster from a weight perspective.

    I see on eBay there are a lot of converted cameras for sale for various prices. I wonder if it would be better to buy a converted one or have an old one converted? I understand that the Canon 50mm/1.4 is supposed to have an IR hot spot though, so I guess if I did that, I’d have to use the 24-105. Not sure I can carry the weight anymore though. The Nex-7 might be an option too.

    Regarding the M8, I like the idea that I can use it EITHER for IR OR for regular color just by putting a different filter on the front, and with the rangefinder, an opaque filter (or at least a really dark red one) isn’t a downside as it would be in an SLR. For IR film I tend to either use an M2 or a Contax SLR. In the latter case I don’t usually use anything but a 25A filter because I can still see through it.

    I’m re-reading “Infra-Red Photography A Complete Workshop Guide” by Hugh Milsom. It’s the best book I ever found on the subject in the film era. He’s very methodical in his approach. I think most of it still applies except for the stuff about the films specifically.

    I would guess that a modern converted digital will probably have a frequency response similar to HIE with the filter installed? Except for the halation effect of the thin film in HIE that gives you the glow effect. And the grain effect you can also get with HIE (though you could probably do that digitally). I expect though you get a similar frequency response but a sharper, lower noise result.
     
  12. High Speed Infrared Ektachrome was designed to be used with a Yellow filter and used a false-color scheme for rendering the visible and Infrared spectrum. The color dye used in the color mosaic filter for red, green, and blue are all sensitive in Infrared. So a full-range/converted camera has a lot of IR in the Blue and Green channels, as well as red. HIE did not do this.

    With the M8+Orange filter, the Blue Channel is IR only, Green channel gets green and 5% IR, Red channel gets Red and 5% IR. So- boost the Blue channel by 4 stops to equalize it with Green and Red, a bit closer to HIE. This is where the true uncompressed DNG comes in.
     

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