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12-08-2009, 03:03 PM   #16
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QuoteOriginally posted by Andi Lo Quote
I need this clarified by someone... does IR sensitivity matter if you've removed the IR filter? I'm under the impression that the difference between the 6mp and 10mp sensor only matters when you use a screw-on filter on the lens.

@Frank: amazing images... are they all the same wvalength? did you do any exposure manipulation on the skies? It looks almost as if you got a DR boost by converting it to IR.
Thanks Andi

Those photos were taken by two different converted K100D, the last two were taken w/ a converted K100D w/ a 680nm IR filter installed (replaced the IR block in front of the CCD sensor), the others were taken w/ a K100D w/ a 720nm IR filter installed. Different wavelength IR filter will have different results/effect. If you wanna see some colors (instead of totally black and white) in the photo, you can choose a filter like 680nm or even 630nm. Personally I like 680nm filter the best.

And no, I didn't do any exposure manipulation on the skies. Just normal routines for IR processing: adjust level a bit, switch red and blue channels, add abit curve on the final, that's all.

12-08-2009, 03:58 PM   #17
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I have a K110D with the internal filter removed. I did that mainly for Astrophotography. Many red nebulas are 656 nm visible red but the simple filters inside cameras cut into the visible spectrum. The side effect of my modification is the camera is great for IR. Sunlight images with a Hoya 72 went from 1/10 second to well under 1/1000 second.

A few things to consider:

Removing the filter and not installing a clear or IR pass filter often upsets the Autofocus. Doesn't matter to me, astro requires manual focus anyway. I also discovered some lenses won't focus to infinity on a filterless camera.

Doing the job yourself incurs risk. I spent $212 having Pentax repair my new K110D! Still, having a filterless DSLR for $349 + $212 was worthwhile. Spencers was not an option back then.

I used a K110D since it doesn't have Shake Reduction (and was cheap). I was concerned the sensor motion system would not like my removing the filter.

Since a modified camera with external IR filter has virtually no Green or Blue data you will be displaying monochrome or near mono as seen in the above examples. There are many photographers who like the effect of pseudo color IR which you no longer will be able to do.

A 6 MP camera like mine becomes a 1.5 MP camera since a Bayer array has only 25% of the red pixels of a true RGB camera. I extract only the red and get 1500*1000 pixel monochrome photos.

You can take a shot with an external IR pass filter (eg Hoya 72) followed by an external IR block filter that simulates the original. Align and combine them to get IR luminous with true color. I've read of people doing this but never tried it.

There are many discussions of IR on this forum but you can't search for only two letters. I always insert Infrared in my messages to help those searching for information.

Last edited by LeoTaylor; 12-08-2009 at 04:05 PM. Reason: clarified
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