Don't Know Where To Start Exposure Bracketing

[rpcrowe]

I have been shooting infrared images for years and have used both an older Canon D60 (not 60D) DSLR and presently I use a Sony NEX7 camera converted to full time infrared.

It has been quite simple to shoot with these dedicated IR cameas. Since no filter is used in front of the lens - exposure times have been decently short and thus, I could easily hand hold the camera for daylight photography...

The D60 was not a good choice for conversion - even though it is an APSC camera, it did not accept EFS lenses and it was also quite large and heavy so I did not carry it with me on trips. The little NEX7 is a handy size and it will accept all of my Sony mount and Legacy lenses with Sony converters. This little camera allows me to view my images through the viewfinder and focus is right on. I always convert my images to B&W since I don't like the false color of infrared.

However, recently a friend gave me a 67mm screw-in, 950nm IR filter which will fit many of my lenses. He couldn't figure out the exposure to use with this filter. I know that exposures with IR filters can be long and should be bracketed, but, I can't figure out where to start the bracketing. Any hints as to the ISO and exposure to begin with???

I have tried a Google search with no success...

[Manfred M]

Back, a very long time ago when I shot B&W IR film, the suggestion that was made to me was that I use the exposure that the camera, with IR filter in place, recommended and then go +2 and -2 stops on that. Generally one of the images ended up being good to work with. I suspect that this would still be a good place to start.

With the display on the back of the camera, you can get a decent idea of what the image looks like and the histogram will always be a good guide. Far less expensive than with film where it took 3 exposures to get one shot.

[Manfred M]

I remember experimenting at different times of the year.

In the winter, I might have just as well shot regular B&W film as there was very little that reflected IR, in the summer with all the plants, grasses and foliage, everything with a high chlorophyll content was quite bright.

I remember shooting IR Ektachrome film in early spring. Unlike the B&W IR I shot, no filter was used so the colours looked "normal" with some red highlights, rather than some of the greens I would have expected. I expect that the red layer in the emulsion was sensitive into the near IR. Kodak's recommendation was to focus normally instead of using the IR marking on the lens barrel.

I don't think I've ever seen a digital equivalent of that process. Are you aware of anything like that Ted? I assume that by removing the IR blocking filter on the sensor stack, one also removes the Bayer sensor (except for Foveon, of course).

[xpatUSA]

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I remember shooting IR Ektachrome film in early spring. Unlike the B&W IR I shot, no filter was used so the colours looked "normal" with some red highlights, rather than some of the greens I would have expected. I expect that the red layer in the emulsion was sensitive into the near IR. Kodak's recommendation was to focus normally instead of using the IR marking on the lens barrel.

I don't think I've ever seen a digital equivalent of that process. Are you aware of anything like that Ted?

A big long thread on an almost identical subject (The Aerochrome look) here, Manfred:

https://www.dpreview.com/forums/post/64714988

Warning: High xpat content ...

Lots of links to references about simulating that look in digital, plus a link to another thread on the same subject.

I assume that by removing the IR blocking filter on the sensor stack, one also removes the Bayer sensor (except for Foveon, of course).

Correct, but most outfits offer to add various types of filter internally including one (Kolari) that claims to get the Aerochrome look SOOC!

Let me know if I can help further ...

[Manfred M]

Thanks Ted - I had a quick look through some of the postings. Aerochrome seems to be a bit more red than I remember Ektrachrome IR, which tended to be more magenta than red, if I recall correctly.

I'm going to spend some time going through the thread, some interesting information there. One thing I read was the Hoya 25A filter. I remember using that with B&W IR film.

I also remember shooting IR with a Pentax Spotmatic, which had a cloth shutter that turned out to be less than 100% opaque to IR wavelengths and caused some film fogging. Switching to a Praktica LLC fixed that. It had a metal shutter that blocked the IR.

[rpcrowe]

I remember Aero Ektachrome film that the Navy used in five-inch and 70mm rolls on the RA5C (Photo Vigilante) and F8U1P (Photo Crusader) reconnaissance aircraft for camouflage detection. Live foliage would show as a reddish color while dead or artificial foliage would appear black....

Regarding the IR filter exposure, I read somewhere that a "factor of eight" might be a starting point - that is 80 seconds at f/8 at 800 ISO. I will try tomorrow with that as a basis and work up or down from there.

[billyb1191]

I've had the same answer. Thanks for the recommendations.