photography by mike finley : A little experiment with Sony Alpha cameras and infrared :

Infrared photography with the Sony Alpha 100 and 700 DSLRs

I've had an interest in infrared photography for some years, but with the demise of the infrared film I liked (Konica 750) I more or less gave up on it. I've now done a couple of quick tests with my DSLR cameras to see how they behave ... with mixed results. The image below was taken with the Alpha 100 and shows the scene and lighting used for the tests (click on thumbnails for a larger image):

Lens Minolta 24-85mm, ISO 400, 1/1000 sec F8, 24mm.

Alpha 100

I have two IR filters, one roughly equivalent to a Wratten 89B filter, the other to a Wratten 87 filter. With these on the Alpha 100 and with the same lens I got the two images below (after processing):


A100, 89B, ISO 400, 1 second at F8		A100, 87, ISO 400, 4seconds at f8

Alpha 700

I also tried the Alpha 700 with the same filters and a Minolta 50/1.7 lens, with the following results:


A700, 89B, ISO 400, 4 seconds at F8		A700, 87, ISO 400, 16 seconds at f8

Processing

All images were processed from RAW (cRAW for the A700) using the Sony Raw convertor. For each image the conversions were adjusted as follows:

adjust white balance on a patch of grass patch of grass for IR shots
adjust exposure and contrast as necessary to get good histogram
save as jpeg

All the infrared images needed an exposure adjustment of one or two stops, giving a final required additional exposure over the normal scene of

A100: 12 stops with the 89B filter, and 14 stops with the 87
A700: 14 stops with the 89B filter, and 15 stops with the 87

A contrast boost was required as well with the 89B filter with both cameras, but not for the 87 filter.

Conclusion

Its clear from the images that the 24-85mm lens causes a noticeable hotspot at the 24mm end. Separate checks show it is the lens and not the camera, though the effect is more noticeable with the A700, and that the effect does not extend throughout the focal length range. It can also be seen that, for this image at least (bright sunshine, early Spring - I'm in the UK, not Australia!), the A700 camera gives noticeably more colour differentiation than the A100, and with both cameras that there is more colour differentiation with the 89B filter.