Canon G15 focus feature for infrared work

shearline

2

« on: 31 / October / 2013, 06:41:08 »

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The Canon G15 is a GREAT camera to modify for infrared work because it has view finder and an available lens adapter for filters. It would be a SUPER GREAT IR camera if an allowance could be made for the chromatic aberration that occurs with the IR spectrum. Many manual focus lenses lenses have some sign on the barrel to help re-focus for IR photography. This may be a red dot or line on the focus ring that slightly shortens the focus. Can such a correction feature be added to the CHDK firmware.

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waterwingz

12139

Re: Canon G15 focus feature for infrared work

« Reply #1 on: 31 / October / 2013, 10:03:39 »

Does the camera still focus properly in the visible once the filters are changed ? If so and you can define either a conversion equation or a set of conversion points (normal SD vs IR SD) then a small script that will first focus in the visible and then offset for IR before taking a picture would be simple to write.

It would also be easy to let you dial in the real focus distance via a script UI user parameter and then offset via the table or formula to calibrate for the chromatic aberations prior to shooting.

« Last Edit: 31 / October / 2013, 10:16:43 by waterwingz »

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Ported : A1200 SD940 G10 Powershot N G16

Microfunguy

4037

Re: Canon G15 focus feature for infrared work

« Reply #2 on: 31 / October / 2013, 10:59:13 »

Quote from: shearline on 31 / October / 2013, 06:41:08

It would be a SUPER GREAT IR camera if an allowance could be made for the chromatic aberration that occurs with the IR spectrum.

How can you get chromatic aberration with the IR spectrum ?
That is a contradiction.

Quote

The Canon G15 is a GREAT camera to modify for infrared work
Many manual focus lenses lenses have some sign on the barrel to help re-focus for IR photography. This may be a red dot or line on the focus ring that slightly shortens the focus. Can such a correction feature be added to the CHDK firmware.

If it has been modified you do not need any correction.
The IR-blocking filter is replaced by a clear piece of optical glass of such a thickness that focus is maintained.

David

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shearline

2

Re: Canon G15 focus feature for infrared work

« Reply #3 on: 01 / November / 2013, 03:03:19 »

Thanks all!

I think I missed diagnosed my problem. When I take two photos of the same subject, one in IR and the other in the visual range, and then try to layer them up they do not align properly. Even with transform tools it is difficult to match them up. A tripod was used when taking the two shots, the only thing that changed was swapping out the external 720nm and hot mirror filters.

I mistakenly thought this was a focus issue, but both images have crisp details. Any other thoughts on how to correct this?

Shearline

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Microfunguy

4037

Re: Canon G15 focus feature for infrared work

« Reply #4 on: 01 / November / 2013, 06:55:13 »

Can you post a pair of images ?

In theory, they should just be slightly different size.

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