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07-09-2008, 09:35 AM   #1
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Updated info on removing the Pentax IR filter for Astro and IR imaging

It has been over a year since I modified my Pentax K110D camera by removing the internal IR blocking filter. Some new information has surfaced so it is time for an update on the project. I am not an expert, just someone who has enjoyed using a filterless camera which may be of interest to other people. This message is rather long if you are not interested in the subject.

Warning: I am not advising that anyone remove the internal filter in their camera. It is not a project for the faint at heart, and will void any warrantee. The filterless camera will not be good for normal daytime photography.

I’ve been very happy with my K100D purchased in November 2006. In the Spring of 2007 I purchased a K110D with the intent of making a dedicated Astrophotography camera by removing the internal filter. Why a K110D? At $349 it was the lowest priced DSLR at the time. My wife and I have several manual lenses. The sensor and filter are mounted solidly on the circuit board, I did not want to deal with a floating Share Reduction system.

Why remove the internal filter?

Two reasons: Astrophotography and Infrared Photography

Most all digital cameras have an Infrared blocking filter mounted internally. The filter severely blocks IR from the sensor to prevent it from distorting the visible light image the camera is intended for. Many people don’t realize the low cost filter manufactures use also attenuates deep red visible light. The manufactures boost the red response (white balance) but the camera still has weak response to deep red. Astrophotographers know the there are many red nebulas that emit light at the visible wavelength of 656 nm, called Hydrogen Alpha band. My K100D was near dead at that wavelength, from my light polluted location most nebulas were not imageable.

The poor response of DSLRs to IR is well known, requiring long exposures in bright daylight.

How did I removed the filter?

After trying out the new camera a few days I opened it up. It was not easy, but eventually I reached the filter which comes out with four screws. Unfortunately the camera was near dead when re-assembled. The symptoms were exactly like the memory door was open. It took many hours for me to realize the door open switch had been mounted on the main board. I had broken it off so clean I could not see how the door open was detected..

Knowing I was licked I sent the camera to Pentax Colorado with a note as to what I had done and why. It took 5 weeks and $212 but I received the camera back without the filter. I had feared Pentax would, “Do me a favor” and fix the camera to work like new.

I was a happy camper, the total of the camera plus repair was still less than the cost of a professionally modified “Big Two” camera.

My results for Astro?

I’d estimate sensitivity to deep red visible light went up by a factor of four. After years of unsuccessful attempts with a $3000 astro camera my DSLR produced a usable color image of the Rosette Nebula when combined with an external Ha filter. Several other nebulas were now possible in color for the first time.

My results with IR?

Though not my original intention, I realized filter removal will improve IR response. I bought a Hoya R72 filter and found the modified camera to be a delight. Awhile back I posted my results of comparing daylight IR images between my filterless K110D, my normal K100D, and my wife’s istD. The reduction in shutter time is about 100:1. IR photography went from tripod images of 1/10 second to handheld at 1/1000 second or less.

Are there any problems with filterless camera?

Yes. When you have a professional modify a “Big Two” camera for astrophotography, they replace the poor cutoff internal filter with a fast cutoff filter that blocks IR but passes all red. This makes it possible to use the camera normally with some color balance. This was not a concern to me since I had my K100D for daytime shots. At least one company makes an external filter that simulates the response of the original filter, this may be an option to get normal daytime use from a filterless camera. I think it is better just to have two cameras.


If a professional modifies a camera for IR they replace the internal filter with a clear filter. This is because having NO filter affects the focus slightly, usually at the infinity end. I had no problems with focusing on the Moon and stars with either a telescope or my manual Sigma 70-210 mm zoom from K1000 days. I thought perhaps the Pentax was immune to this problem the “Big Two” have. Recently I read the “Digital lenses” are less forgiving than the older film lenses. I slipped on my Tamron 75-300 mm AF lens and found it will not quite focus on stars. It will focus on objects a half mile away, but hits the stop before reaching infinity. This does not bother me, there is no need for autofocus in Astrophotography, but something one should be aware of.


The bottom line?

If I had to do it over I’d do everything again, except perhaps break the camera.

07-09-2008, 09:44 AM   #2
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so you still need a special filter for your lens to shoot IR

or does your camera magicaly become IR ready after removing the filter?
07-09-2008, 10:32 AM   #3
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QuoteOriginally posted by Gooshin Quote
so you still need a special filter for your lens to shoot IR

or does your camera magicaly become IR ready after removing the filter?
After removing the IR blocking filter that is in front of the sensor, the camera will pick up both IR and visible light. But if you want to shoot only IR you need something to block the visible light, that's where the Hoya R72 filter helps - it blocks almost all visible light, but not IR.
07-09-2008, 10:42 AM   #4
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what would a picture look like with both visible light and ir?!

07-09-2008, 12:45 PM   #5
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QuoteOriginally posted by Gooshin Quote
what would a picture look like with both visible light and ir?!
Well, since only red photosites of the sensor can detect it - it will look more red. Not much though, since most of the light detected will still be visible light.
07-09-2008, 12:56 PM   #6
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QuoteOriginally posted by Gooshin Quote
what would a picture look like with both visible light and ir?!
Like these:



Lots of nice IR-info here and here...
07-09-2008, 01:25 PM   #7
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Leo,

Interesting information and nice write up. Thanks for sharing!
07-09-2008, 07:35 PM   #8
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Sounds pretty similar to what my friend has been doing. But he also add an IR filter in front of the CCD sensor where internal filter (to block IR) locates, so you don't need to put an IR filter in front of a lens to take IR phots But then the camera can only take IR photos. Good thing about this conversion is that you can take IR photos as easy as you take normal photos.

07-10-2008, 05:11 AM   #9
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Gooshin:

Procyon answered your question. With no filter my filterless K110D records both IR and visible light. It looks "IR like", very red, but some color appears. With a Hoya R72 it sees very little visible light, in fact I use "Images Plus" to extract only the red pixels then convert to B&W. BTW: there are only 1.5 million red pixels so the photos are 1500x1000.

Moo:

Great links! I learned some things from the Filter article. I thought my Hoya R72 was a band pass filter, learned it is a low pass (longer wavelengths) starting at 720 nm. The article mentions the "X-NiteCC1 sold by www.maxmax.com" that I had heard was the best external filter to make a filterless camera work like a normal camera. I thought of buying one, but decided to just carry my K100D instead. The author also repeats what I had read elsewhere, that a filterless conventional DSLR can't do heat images. I stood outside in 15F degrees taking pictures of my house with and without the Hoya R72 to see if I could detect an open window and other heat leaks, but had no luck. I still wonder if without street lights I could have taken a long enough exposure to show some heat.

Tom S:

Thank you.


Frank:

An internal filter replacement would be nice, but I have not found any aftermarket filters for a Pentax. There are a variety of filters for the "Big Two" including the IR pass you mention and the sharp cutoff IR block astronomers need. At an astronomy show I once asked Pentax about providing a service to remove or replace internal filters. I wonder if the sales people passed the idea on.

Last edited by LeoTaylor; 07-10-2008 at 05:15 AM. Reason: Punctuation
07-10-2008, 03:01 PM   #10
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Hi Leo, when you removed the AA (anti aliasing) filter (one of the layer fused into the original filter) did the picture get little sharper as stated in maxmax.com? Their sample photos are sharper w/o AA filter. They estimate that the manufecturer blurs certain percentage (30% ?) in order to diminish moir. I am just curious to see how much sharper Pentax DSLR will be w/o AA filter since maxmax did not have any Pentax mod pics.

Can you measure in mm the dimention of the filter taken out from camera and post it? I am searching several glass mfg. to find a proper filter.

Wave length of heat/IR radiation is longer than 1200nm which is outside the sensor sensitivity.
07-10-2008, 08:01 PM   #11
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QuoteOriginally posted by LeoTaylor Quote
Frank:

An internal filter replacement would be nice, but I have not found any aftermarket filters for a Pentax. There are a variety of filters for the "Big Two" including the IR pass you mention and the sharp cutoff IR block astronomers need. At an astronomy show I once asked Pentax about providing a service to remove or replace internal filters. I wonder if the sales people passed the idea on.
Actually my friend buys the aftermarket IR filters and cut them into the size for our Pentax cameras himself But nowadays since he's been converting too many cameras, he's asked the filter manufacturer to cut the filter directly for him. Now he'd got filters from 720nm all the way to 860nm Personally I like the 720nm IR filter the best, it's similar to the one sold by Hoya for using in front of a lens.

Here are a couple shots I took recently w/ the converted camera (w/ 720nm IR filter installed):







You can see the 720nm filter still allows some visible light (colors) to pass through, which makes the results look more colorful than those pure black and white like IR photos.
07-10-2008, 09:39 PM   #12
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Pentax IR Conversion...

Jim Chen will convert Pentax dSLR cameras to IR only. I know he did mine, the first one he did. I told him he could try to convert it and if it didn't work he would owe me nothing. It worked great. Now I have more use for the old *ist. I don't know what he charges as since he was experimenting he didn't charge me.

Digital Infrared at Jim Chen photography

In my opinion you want the IR filter on the sensor and not on the lens. First the filters are cheap and you would need one for each lens you want to use at least for the ones that have different thread sizes. Not all lenses have threads (Pentax 10-17 fisheye being one and it is awesome for IR).

Also, the filter on the lens can cause exposure and focusing issues. Finally whatever you use you want to set a custom white balance aiming the camera at something green (like grass, or green paper or fabric) and this will compensate for the red cast.

If you don't want to do a custom white balance the auto color feature in Photoshop gives a very nice color rendition. Also, before you convert to black and white play around with swapping the R, G and B channels around, you can get some very nice coloration's that way as well.

Finally, in case anything is thinking it. You can't fake an IR image using software or plug-ins. It is strictly a photographic thing that must be done when taking the photo. Some plug-ins try, none of them pull it off.

One more thing. Digital Infrared is the most fun you can have with a camera. It can turn the most mundane thing in to something really incredible. It also makes the best black and whites. Keep in mind that man made things don't change much when shot in infrared. But, when you include lots of natural things like trees, bushes, grass, etc you get awesome. It also brings out the skies.

Robert
07-10-2008, 11:54 PM   #13
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Frank, those are the sharpest IR photos I have seen so far. Which camera and lens are you using? Exposure data available? How can I reach your friend?

Filter replacement is the easy part. Real challenge is to find a proper thichness filter/window(clear glass) to bring camera to focus just like before the modification. People get around the focus problem by using small aperture. Ultimat goal is to be able to shoot at all aperture and obtain sharp photos like yours w/o post processing.

Last edited by Nico; 07-11-2008 at 01:13 AM.
07-11-2008, 02:47 AM   #14
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QuoteOriginally posted by Nico Quote
Frank, those are the sharpest IR photos I have seen so far. Which camera and lens are you using? Exposure data available? How can I reach your friend?

Filter replacement is the easy part. Real challenge is to find a proper thichness filter/window(clear glass) to bring camera to focus just like before the modification. People get around the focus problem by using small aperture. Ultimat goal is to be able to shoot at all aperture and obtain sharp photos like yours w/o post processing.
Focus for the IR modified camera that frank has is adjusted in debug mode to focus at the IR wavelength. That assures sharpness at any aperture or exposure setting. More importantly, normal handheld shutter speeds are possible, which is a tremendous advantage.

Of course when composed in the viewfinder the viewfinder appear to be a little unsharp as the camera's focusing is deliberately adjusted for the IR wavelength and not the visible light spectrum but the images captured by the sensor will turn out sharp.
07-12-2008, 03:12 PM   #15
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Nico:

I did not notice a change in sharpness but I was not looking for one either. I usually assume blur is my fault, not the camera.

I'm not sure I can measure the filter accurately enough for you, but with my metric metal rule I see is 21.5 x 26 mm. If you email me via the forum with your postal address I could send you the complete filter with mounting frame. Free, I have no intention of opening my K100D as long as it is working.
-----------

Frank:

Wow, there IS someone modifying Pentax cameras! I had looked for anyone doing IR block or clear glass for astro cameras, I may have missed those doing IR mods.

Your shots are great! I'm beginning to find pure IR (displayed as B&W) is not as interesting as keeping some color. I took some IR only photos on Thursday but not are worthy of posting.
-----------

Robert:

Another person modifying Pentax cameras!

Though having an IR filter internally has advantages my original intention was Astro. I have a few adaptor rings to mount the Hoya on a few lenses, mostly my old manuals. If my wife wants to try IR we can share the Hoya. The focus issues are not a problem for the manual lenses I use, though I did notice a Tamron AF won't reach infinity.

I've seen others swap color channels around to advantage. I need lots more time to play with IR, as you wrote it is great fun.
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