Infrared with modified K110D

*LeoTaylor* · 06-07-2007, 05:38 PM

This new section is suggested for for Infrared, so I'll post here.

I'm totally new to IR photography. I purchased a Hoya R72 filter from B&H and put it on my K110D which has been modified by removal of the internal filter for astrophotography. My first surprise - The viewfinder was totally black. I expected a deep red to allow me to frame the image. So I framed and focused with the filter off. My second surprise - I had to expose at 1/2000 or faster with a Sigma manual zoom lens at 70mm f4. I could not see light, but the camera sure could. Even setting the lens to f8 I needed 1/750 or faster. A quick sanity check by putting the filter on my unmodified K100D and an equal image required around 1/4 second. It is hard to compare them since they look very different. The K100D's internal filter suppresses mid IR, and reduces near IR and some visible Red.

Now I need to learn more about what to use my new filter for. My wife bought a book on IR photography, which we will read. A quick scan of the photos show a lot of trees.

I need to get out in the country where I can find trees without wires crisscrossing the view.

The first image below is a regular PEF to JPEG conversion where the IR shows as false red. As the viewfinder shows, there is little visible red in the image. The second image is the same RAW PEF, the red channel only was extracted from the Bayer encoding, and displayed as Black and White. Of course, it was only 1500*1000 pixels since these cameras have only 1.5 million Red Pixels.

I have a new filter for $40 that could provide me some interesting fun. My wife has an istD and I ordered a step up adaptor so she can use the filter on her favorite lens (Pentax Macro). The istD is known for good IR response compared to the newer models (and other brands).

jeddy · 06-07-2007, 06:34 PM

I don't know a lot about ir except that it can not be seen by our eyes so that is why you can't see anything through the viewfinder, the filter is only alowing light throught that can not be seen with the human eye. A point and shoot might let you see it on it's lcd...

egarrard · 06-15-2007, 10:26 AM

Use the digital preview to help you frame the shot. You might not be able to see through the viewfinder, but you should be able to see the image on the rear LCD.

**Adam** · 06-15-2007, 11:59 AM

All I can say is that IR is so much more fun with film, since film actually picks up more IR light than red light that the filter allows through. The percentage of IR light is further increased if you use a R90 filter instead of a R72 filter.

Here's a sample shot that I took a few years back of a hot lamp that was turned off:
(Pentax SuperProgram, SMC-A 50mm F1.4)

*LeoTaylor* · 06-21-2007, 08:12 PM

Originally Posted by egarrard

Use the digital preview to help you frame the shot. You might not be able to see through the viewfinder, but you should be able to see the image on the rear LCD.

Your suggestion prompted me to re-read that section of the manual. Now I can see a use for Digital Preview! I tried it quickly indoors, it is sort of like hitting the "playback button" except it does not store the image and is more convenient.

Thank you for the suggestion. Once I get the IR filter back from my wife I will use that mode next time out. She has an istD which does fairly well with IR without being modified. Many recommend the istD as one of the best IR cameras in stock form. But, I checked and she doesn't have Digital Preview.

*LeoTaylor* · 06-21-2007, 08:18 PM

[quote=Mo;67069]... The percentage of IR light is further increased if you use a R90 filter instead of a R72 filter. ...
QUOTE]

The price of Hoya filters goes way up from R72 to R90 and this is, "just a hobby" for my wife and I. At $40 from B&H for the filter we figured if we don't like the results we have not invested too much. I think we will have a lot of fun for a month or two.

pixelpruner · 06-23-2007, 04:01 AM

I've been thinking about getting an IR filter. Do I need to make any modifications to a K10d to do it?

carpents · 06-23-2007, 05:53 AM

Originally Posted by pixelpruner

I've been thinking about getting an IR filter. Do I need to make any modifications to a K10d to do it?

JensR has a great site about IR photography (he is a Pentaxian, too):
JensR's IR Basics Page

He links to another page describing a modification for a DS, and why you would want to do it. Essentially, you have to take apart the camera and remove the IR-blocking filter to allow reasonable shutter times - not for the light-hearted. However, you can certainly use the cameras without taking them apart, only their IR sensitivity is much lower.
xDeltax page on IR modifications

*LeoTaylor* · 06-23-2007, 10:39 PM

From what I've read and my limited experience the best Pentax Digital for Infrared is the istD. My K100D needs a LONG exposure with a Hoya R72 IR filter. I think the K10D will be similar. As "carpents" wrote, it works but the sensitivity is low. With a tripod you could use it. My wife's istD has a reasonable exposure time, she can do some outdoor IR photos handheld. My modified K110D takes outdoor IR shots at 1/1000 of a second and faster. I still use a tripod though, so I can frome the shot with filter off, put the filter on, and take the image.

If you read my thread on removing the internal filter from a K110D you will see I killed the camera and had to pay Pentax to replace the main board. No regrets, I took a risk and lost.

If you try IR you might read up on extracting only the red from the raw PEF file. 3/4 of the Bayer Array cells are wasted when you only need red, the effective picture size is 1.5 megapixels.

Leo Taylor