Testing Diffraction Effects of Lens Aperture on Digital Infrared Photography

We test the diffraction effects when using two lenses on an infrared converted Canon 350D digital camera.
When we got our recently converted for infrared photography Canon 350D back from www.MaxMax.com it came with a convenient set of comments. One of these waas that, because of diffraction effects, you could expect to get the sharpest images with the lens either wide open or at the first one or two f-stops down from wide open.

To test this, we took two of our single focal length Canon lenses, a 50mm F1.8 and a 100mm f2.8 macro out for some shooting in the sun. These are 100% crops from the center of the RAW image with no sharpening sone and the results presented as minimal compression JPEGs.

For those who wish to see some complete images taken with this camera, you can see them by following this link over to a different website.

Test 1: Canon 50mm f1.8 (the first two images are over exposed compared to the others because in the bright sun, even at 100ISO, the 350D could not set a fast enough shutter speed.

f1.8
Canon 50mm f1.8 Lens on Infrared Converted 350D

f2
Canon 50mm f1.8 Lens on Infrared Converted 350D

f2.8
Canon 50mm f1.8 Lens on Infrared Converted 350D

f4
Canon 50mm f1.8 Lens on Infrared Converted 350D

f5.6
Canon 50mm f1.8 Lens on Infrared Converted 350D

f8
Canon 50mm f1.8 Lens on Infrared Converted 350D

f11
Canon 50mm f1.8 Lens on Infrared Converted 350D

f16
Canon 50mm f1.8 Lens on Infrared Converted 350D

f22
Canon 50mm f1.8 Lens on Infrared Converted 350D

Here the sharpest image seems to be that taken at f5.6

Test 2: Canon 100mm f2.8 Macro

f2.8
Canon 100mm f2.8 Macro Lens on Infrared Converted 350D

f4
Canon 100mm f2.8 Macro Lens on Infrared Converted 350D

f5.6
Canon 100mm f2.8 Macro Lens on Infrared Converted 350D

f8
Canon 100mm f2.8 Macro Lens on Infrared Converted 350D

f11
Canon 100mm f2.8 Macro Lens on Infrared Converted 350D

f16
Canon 100mm f2.8 Macro Lens on Infrared Converted 350D

f22
Canon 100mm f2.8 Macro Lens on Infrared Converted 350D

f32
Canon 100mm f2.8 Macro Lens on Infrared Converted 350D

Here the sharpest image seems to occur at f8.

This seems to suggest, at least for these lenses, that 3-4 stops down from wide open is 
a better bet. As soon as I can I will shoot the same lenses at the same location on a conventional digital body to see which are the
sharpest apertures in visible light.

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No Responses to “Testing Diffraction Effects of Lens Aperture on Digital Infrared Photography”

  1. I Wayan MawaApril 18, 2011 at 5:57 am #

    This is excellence. I try to get one converted ir camera but here i do not know here in South East Asia bit difficult to find the stores. Any suggestion please!

    Regards
    Mw

    • Wayne CosshallApril 18, 2011 at 6:06 am #

      I don’t know for sure of anywhere is SE Asia to get the conversions done, though I think there is someone in Indonesia. Try google. I used maxmax.com in the US to do mine.

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