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07-14-2012, 06:34 PM   #1
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Why are my BW IR pix fuzzy?

Is IR usually fuzzy? Sharpness is crap. Maybe my IR cam conversion?

Not my lens. Tried 3 different WA's, all high grade glass, all results the same. I took the pix at 6.30 to 7 pm if that matters, when sun was going down.

07-14-2012, 07:21 PM   #2
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QuoteOriginally posted by slackercruster Quote
Is IR usually fuzzy? Sharpness is crap. Maybe my IR cam conversion?

Not my lens. Tried 3 different WA's, all high grade glass, all results the same. I took the pix at 6.30 to 7 pm if that matters, when sun was going down.
Yes! IR is usually fuzzy.
07-14-2012, 08:31 PM   #3
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While the lens likely will be less sharp, the bigger effect is generally that IR will not be in focus for most lenses if visible light is used to set the focus. Many lenses have a IR marking (red line often). Or (and better) focus using the image on your digital display. Did you account for this?
07-15-2012, 04:00 AM   #4
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Yea, I know about the focus shift. But I am shooting landscapes and the whole thing is fuzzy. So something should be in focus one way or another.

07-15-2012, 01:39 PM - 1 Like   #5
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Aside from equipment issues, IR is far less physically capable of reproducing fine details. As wavelength increases, the finest reproducible detail becomes larger. Search Rayleigh Criterion on the internet. The physical definition of the Rayleigh Criterion is wavelength dependent.

Related to resolution, with IR, you reach the diffraction limit of the optical system much sooner than with visible light.
07-15-2012, 01:59 PM - 1 Like   #6
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I suggest you do a test to see if you can take a sharp IR photo under any circumstances: Perhaps a large newspaper page shot at an angle so that a strip of it is in focus. That'll tell you where the true focus lies and how good it is. Use a tripod & delayed shutter to avoid motion blur.

Can you tell us more about the conversion? Was the hot-mirror replaced with an IR filter (what IR filter?) or is it broadband?

If it was a broadband conversion was a clear compensating plate substituted for the hot-mirror?

If you'll post a clip, we can look at the individual color channels.

What camera & conversion service?
07-15-2012, 03:18 PM   #7
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QuoteOriginally posted by newarts Quote
I suggest you do a test to see if you can take a sharp IR photo under any circumstances: Perhaps a large newspaper page shot at an angle so that a strip of it is in focus. That'll tell you where the true focus lies and how good it is. Use a tripod & delayed shutter to avoid motion blur.

Can you tell us more about the conversion? Was the hot-mirror replaced with an IR filter (what IR filter?) or is it broadband?

If it was a broadband conversion was a clear compensating plate substituted for the hot-mirror?

If you'll post a clip, we can look at the individual color channels.

What camera & conversion service?
Don't know the deatils. Bought it used from another person.

Seems possibly the pix may be sharper early morning as opposed to later in the day. But nothing concrete on that. Should sharpness be the same throughout the day equally?
07-15-2012, 03:34 PM   #8
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QuoteOriginally posted by slackercruster Quote
Don't know the deatils. Bought it used from another person.

Seems possibly the pix may be sharper early morning as opposed to later in the day. But nothing concrete on that. Should sharpness be the same throughout the day equally?
There is no time-of-day effect I can think of that'd cause a big sharpness effect.

At this point your time will be best spent seeing if a sharp picture is possible. That implies a rock-solid camera, delayed shutter (so no mirror slap), maybe f:11 to use center of lens. Maybe pointed at some tilted target with detail so you can see if there is sharp focus anywhere. Take multiple shots at different focus points. All you need see is one in sharp focus to know what's possible.

Are you manually focusing thru the viewfinder?

Dave in Iowa

07-15-2012, 03:51 PM   #9
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OK, will test it out.
07-15-2012, 04:49 PM   #10
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Here is the pix in question. Should it be sharper? 6mp Pentax
07-15-2012, 05:14 PM   #11
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Here is a sharper one. This is about as good as it gets with IQ.

07-15-2012, 05:33 PM   #12
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Looks pretty sharp to me but it is not big enough to evaluate.

Can you crop steeple & send it?
07-15-2012, 05:59 PM   #13
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QuoteOriginally posted by newarts Quote
There is no time-of-day effect I can think of that'd cause a big sharpness effect.
The color temperature of sun light changes throughout the day. When the spectrum is shifted more toward the blue end of the visible spectrum, detail will be better than when the spectrum is shifted more toward the red. See my post above with respect to the Reyleigh Criterion.
07-15-2012, 06:06 PM   #14
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OK, that explains it then. i took some about 8 - 9 am that were pretty nice with sharpness. Late PM they crap out.

What about flash? How will people show up if fill flash is used?

(BTW, would not let me like your last post. Said I had to spread it around.)
07-15-2012, 06:09 PM   #15
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Flash is usually around 5000 to 5500K, and simulates the most neutral sun light periods of the day (ie, mid day). So, the results with flash should be reasonably good if that is the only light source.

Edit to add: I don't actually know how far into the IR the Pentax sensor sensitivity is. I just want to add a caution that people emit heat, which is basically what IR is. So, the mixing of reflected visible light with the emitted IR light from people's bodies will definitely not look as sharp as a "normal" visible spectrum photo.

Last edited by Asha; 07-15-2012 at 06:14 PM.
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