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09-12-2011, 06:09 AM   #1
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K-r: Which IR filter to buy?

Hello,

I'd like to capture IR images with my K-r camera. I am comletely newbie in IR / Kr's zone. I've read some posts in the forum, but I can't answer to myself:

1/ Does K-r support to capture IR images?

2/ Which IR filter to buy to have IR images with K-r?

Please help me. Thank you very much.

09-12-2011, 06:42 AM - 1 Like   #2
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The best way to get into IR, if you're sure you'll have a long lasting interest in it, is to pick up a second DSLR body (it can be an old one) and convert it for IR specifically. This involves carefully removing or replacing the high pass filter on the camera sensor, which blocks most IR light.

There is some information here about converting a K10D: Pentax dSLR conversion to Infrared - The Home Shop Machinist & Machinist's Workshop Magazine's BBS

And here's a thread about using a non-converted camera: https://www.pentaxforums.com/forums/pentax-dslr-discussion/34035-infrared-pho...rted-k10d.html
09-12-2011, 06:52 AM - 1 Like   #3
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I personally use a Hoya R72 filter which blocks a large portion of the visible spectrum but passes 100% of light a 720Nm and longer wavelengths - which makes the exposure times rather long. Additionally if you are using a non-IR converted camera the built in Hot mirror is also going to have a substantial impact on exposure times, you will need a good tripod - exposure times can run into several minutes - though this depends heavily on weather conditions.

Pentax K-7 (not IR converted) SMCP-DA 15mm f/4 ED AL limited + Hoya R72 filter
09-12-2011, 07:58 AM   #4
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That is an expensive filter. Anyone have any luck with the Opteka brand R72? It's 1/4 the price. Maybe it would be worthwhile to gauge interest.

EDIT: I wonder if I can get away with a shorter exposure on the K100D.

09-12-2011, 08:04 AM   #5
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Original Poster
Thank you guys very much.

I'd really like IR - as IR provides completely new views of the reality Buying an old camera may be expensive at the moment. I would buy a filter first, and try with my non-IR converted pentax K-r.

Thank you again.

Last edited by icy; 09-12-2011 at 08:05 AM. Reason: fix after kenafein's post
09-12-2011, 08:29 AM - 1 Like   #6
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An IR-pass VL-block filter can be used on a non-converted camera but you must expect long exposures -- the deeper the filter, the longer the shot. IR filters are made with various cutoff wavelengths. You can start to approximate IR with just a #25 Red filter -- IIRC its cutoff is around 680nm. 720nm filters (as mentioned above) are popular because they pass enough VL (visible light) to be usable on unmodified cams. I use 780-900-930-1000nm filters on a camera with no IR-blocking hot.filter. The 780nm is barely usable on an unmodified cam in bright light, where the others involve guesswork on focus and exposure.

Some cheap IR-pass filters may have hot-spots with uneven light transmission. Some costly filters, too! Of my not-real-cheap filters, one has a hot-spot and the others don't. Ya pays yer money and ya takes yer chances, eh? With any fairly expensive item, make sure you can return it for a refund if not satisfied.
09-12-2011, 08:35 AM - 1 Like   #7
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QuoteOriginally posted by kenafein Quote
That is an expensive filter. Anyone have any luck with the Opteka brand R72? It's 1/4 the price. Maybe it would be worthwhile to gauge interest.

EDIT: I wonder if I can get away with a shorter exposure on the K100D.
Digitalis saved a bit by using a lens that takes a 49mm filter. I have the 49mm and a 58mm Hoya R72 that I got on eBay from "slphotogear", but it was 1/3 the price they have today. I guess I should treat it better.

My *ist DS is about 5 stops more sensitive to IR than my K-7. On a sunny day at noon, I can sometimes get handheld photos at ISO 200 with the DS and a fast, normal lens wide open. I use the Pentax-F 28mm f2.8, the FA 35mm f2 and the F 50mm f1.7 because they are AF. On the newer cameras, a manual-focus lens could be focused with Live View.
09-12-2011, 08:55 AM   #8
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QuoteOriginally posted by kenafein Quote
Anyone have any luck with the Opteka brand R72
I have - used it on the KX and it works quite well. Here is the exposure times I use to get a proper exposure with that filter attached:

Clear Sunny Day: f/8 = 30 Seconds / 100 ISO
Clear Sunny Day: f/16 = 60 Seconds / 100 ISO

This is with a 35mm 2.8 attached, keep in mind these may (well, more than likely will) vary depending on the lens you are using.




---

09-12-2011, 09:50 AM   #9
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Looks like Hoya is the only one to make one for 49mm. I wanted to use it on my FA35 and the smallest Opteka makes is a 52mm. I guess it would still be cheaper to get a step up ring, but the cost benefit is shrinking. Might just go for the higher quality filter. I can use it on my FA50mm, A28mm, FA35mm and some Taks, all my fastest glass.
09-12-2011, 10:50 AM   #10
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QuoteOriginally posted by kenafein Quote
Looks like Hoya is the only one to make one for 49mm. I wanted to use it on my FA35 and the smallest Opteka makes is a 52mm. I guess it would still be cheaper to get a step up ring, but the cost benefit is shrinking. Might just go for the higher quality filter. I can use it on my FA50mm, A28mm, FA35mm and some Taks, all my fastest glass.
I find that with IR, wider is better, in both filters and lenses. IMHO wide shots are the most appealing -- narrow-FOV IR looks too much like surveillance to me. None of the lenses you mention are very wide. A 52mm filter will fit the DA18-55 and some 24mm lenses. A 55mm filter will fit many 24's. I don't know if shorter lenses have narrower threads; mine don't. IR with a longer lens (~50mm) is interesting for unflattering portraits and forensics. But most IR still-lifes look better when wider.

EDIT: I forgot to mention that fast lenses aren't necessarily your friends when shooting IR. Remember that you're already losing a lot of resolution, since EMF is only hitting the R pixels, not the G and B. The Bayer filter is RGBG so you've lost 75% of the pixels -- that 12mpx camera now outputs an image with 3mpx real resolution. That means that the image looks a bit fuzzy. Using a fast lens wide-open softens the image even more -- and for IR still-lifes, that doesn't look great. If your subject demands softness, fine. But for anything resembling sharpness, you want as much DOF as possible. To maintain resolution, you'll need to downsize the output image by 50%. C'est la vie.

Last edited by RioRico; 09-12-2011 at 03:01 PM.
09-12-2011, 06:25 PM   #11
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QuoteOriginally posted by RioRico Quote
Some cheap IR-pass filters may have hot-spots with uneven light transmission
And certain lenses are know to contribute to this effect - the DA15 has a hot spot with the R72 it isn't as bright as the hotspots caused by other lenses - but it is there.

QuoteOriginally posted by Just1MoreDave Quote
Digitalis saved a bit by using a lens that takes a 49mm filter.
Indeed I did, however I currently have a Lee R730 square filter on order to be used with other lenses and camera systems

QuoteOriginally posted by RioRico Quote
I forgot to mention that fast lenses aren't necessarily your friends when shooting IR. Remember that you're already losing a lot of resolution, since EMF is only hitting the R pixels, not the G and B. The Bayer filter is RGBG so you've lost 75% of the pixels -- that 12mpx camera now outputs an image with 3mpx real resolution. That means that the image looks a bit fuzzy.
Ever heard of forbidden transmissions? the G and B pixels are still receiving light - because the molecular structure of the organic dyes used in the CFA in our cameras are much smaller than the wavelength of IR. Infared wavelengths can pass right through/around them

Honl Flash filters photographed under visible light:


the same flash filters as seen through a Hoya R72 IR filter:



just a word of warning with IR photography - lenses like the DA 15mm f/4 ED AL have superb handling of flare under visible light - but this is the kind of flare you get with the Hoya R72 on the DA 15mm f/4:

Last edited by Digitalis; 09-12-2011 at 07:46 PM.
09-15-2011, 06:45 AM   #12
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Heat loss?

Would IR pictures of your house show where you needed more insulation?
09-15-2011, 07:24 AM   #13
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QuoteOriginally posted by Chicken George Quote
Would IR pictures of your house show where you needed more insulation?
No, to do that you need specialised equipment that is designed to see even further into the infared than consumer Digital cameras can.
09-15-2011, 08:02 AM - 1 Like   #14
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I had my old *istDL2 modded for IR shooting and it enables me to get around the long exposure limitation of using screw mounted IR filters.

09-15-2011, 08:50 AM   #15
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QuoteOriginally posted by Chicken George Quote
Would IR pictures of your house show where you needed more insulation?
Only if your house was afire.
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