Sigma SD15 Monochrome and/or IR, RAW?

danski0224 wrote:

xpatUSA wrote:

For SD15, I would invest in an application (e.g. RawDigger) that can separate the layers into three raw monochrome TIFF images and then load all three as layers into your favorite editor (e.g. PS, the GIMP, etc). After that, the world is your oyster!

I would recommend that you ignore advice on the web as to processing a Bayer IR image (channel swapping, etc) because it is mostly inapplicable to processing a Foveon IR capture.

Thanks for the feedback.

Any hints on where to start with this process?

There's probably not enough space here to cover all possible hints but here's one or two:

Shooting with the dustcover removed messes up the metering and what you see in the LCD and in the camera histogram represents only the roughest guide to the final product. So be prepared to do a lot of experimenting - main problem being blown bottom layer captures in the raw data. Often, -2, -3 or sometimes lower will produce good results.

I would start with 'full spectrum' shooting (no filter on the lens) and get accustomed to effects of the additional radiation reaching both the sensor and the metering/AF sensor. You'll be disappointed at first because the IR content acts like 'veiling flare' and causes a bit of back-focusing if you use AF. Persevere and you'll start getting better results.

f/8 or even f/11 would be good to start with even though that may be counter-intuitive.

ISO 100 should be OK so that the SD15's AFE does not introduce difficulties - ISO 50 might be worth a shot too (my guess - none of my cameras have an AFE).

When you move on to full IR, hold off buying the recommended Hoya 720nm. Buy a cheap 680nm which will just let you see the framing though the viewfinder and will let the AF work usually (for sunlit shots). Only when comfortable with the cheapie buy a higher nm, more expensive filter. I use a Marumi 700nm because it still AF's if needed. On the other hand, higher nm filters, e.g. 850, 950nm, 1050nm) can give blacker skies and more contrast but with much more difficulty in getting the focus and exposure right.

I strongly recommend getting an app that can show raw three-channel histograms.

I bought RawDigger - worth it's weight in gold and useful in many other ways too. After all, in IR, you're concerned with what the sensor saw, not the purple mess SPP makes of it!

Possible relevant online tutorials?

There are kajillions of them, so I've put you a couple up on my site plus the list of lenses that can give "hotspots".

http://kronometric.org/phot/ir/article/

There are some folks here that are better versed in the practicalities of IR shooting, hopefully they will butt in with more hints and tips.