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08-23-2011, 05:03 AM   #1
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Cokin P Infrared (round) Filter

I have a K7 and am keen to make a start in Infrared photography. To begin with (and due to expense of a dedicated infrared camera) I'm going to use a Cokin Infrared round filter.

A number of questions please.
1) As you can see I have a few lenses - is there any 'best' focal lengths/ranges to use?
2) Does ISO matter?
3) Is there a best F No to use?
4) I usually shoot in RAW (PEF). Are JPGs better?
5) For post processing I use Elements 7 and Camera Raw - any suggestions on how to get the best out of the image via Camera Raw and then into PE7?

Thanks in anticipation of your help

Cheers.....John

08-23-2011, 05:50 AM   #2
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This is a broad subject and I don't have simple answers for you. There is information out there on the web about this including this site, you just have to search for it. I can tell you that using an infrared filter while clearly a cheaper solution that getting a camera converted, is to me, a very unsatisfactory solution. I know, I went that way first and gave up on it. The reason is that images will typically require long exposure times, like 20-30+seconds and it's very difficult to get accurate focus through the lens. These issues will limit the kind of subjects you can capture. All that said, I've seen some excellent results from this setup by photographers on various forums. Last year I bit the bullet and got an older K100ds converted to IR. It's so much easier to do IR photography that way. I suggest you read the document on IR image adjustment at this link. Spencers Camera & Photo Digital Camera Infrared (IR) Conversions, Modifications and IR Photography :: Blog & Tips

Lens choice - I don't have any of those lenses but I can tell you that lenses behave differently in IR light. Some lenses flare like crazy in IR, some have a hot spot near the center of the lens, and some do just fine. This tends to be true with my wider angle lenses but it's related to the coatings too. I'd suggest that you start simple and experiment with your 50mm lens. Oh, you definitely want to shoot in RAW.
08-23-2011, 08:11 AM   #3
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Locate the plastic viewfinder cover that was in your camera box and you haven't seen since. Exposure times are long enough with the unmodified K-7 so that cover can make a big difference.

RAW is just about a requirement because of white balance. I could use leaves and grass sometimes for white balance with my *ist DS, but the K-7 is so much less sensitive to IR, that doesn't work. Without a good white balance starting point, images are mostly red and black.

On the K-7, you can set a color temperature of 2500K manually and that's closer to what I use in ACR. I set this when I'm shooting for better previews and color channel histograms. Be careful not to get clipping in the red channel.

Because post-processing may mean a lot of manipulation of the data, I really prefer the lowest possible ISO to start with. With clear skies and high altitudes, 100 works fine for me, but in the UK, maybe not.

My lens choice is driven by the filters I have (49mm and 58mm) and focusing. On my DS, I could use the FA 35mm f2 wide open and get shutter speeds that were almost hand-holdable. The K-7 requires a tripod and I end up using f8-f11 for typical landscape depth of field. Live view allows you to check the focus, so manual focus lenses don't mean guessing, but can be tedious.

For processing visible-light images, I stay close to reality. With IR, color is all false and reality is whatever you want. I like to start by setting the color temperature to 2000K and tint to -50, then try to use imagination. Look at examples on IR sites for ideas. I revisit my IR shots frequently to see if I can do something different. I keep thinking that some of the extreme HDR techniques could work for IR images but haven't gotten them to work for me yet.

I really want to take an IR photo with lightning in it but thunderstorms haven't cooperated.
08-23-2011, 08:48 AM   #4
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Great info from Dave. Here's my take:

QuoteOriginally posted by Kenty1 Quote
1) As you can see I have a few lenses - is there any 'best' focal lengths/ranges to use?
2) Does ISO matter?
3) Is there a best F No to use?
4) I usually shoot in RAW (PEF). Are JPGs better?
1) Wider lenses are better, aesthetically. Narrow-FOV IR shots look to me like surveillance. But your wide zooms take large filters -- will Cokin work with them? I use the kit 18-55 @18mm to hang 52mm filters on. Too bad I can't hang filters on my ultrawide nor fisheyes.

2) Lower ISO is better. Higher may be necessary depending on subject. Remember that you're essentially throwing away 3/4 of your pixels, only getting data on the R channel. IR turns a 12mpx camera into a 3mpx image system.

3) Tighter f-stops are better. You'll get enough softness anyway, which doesn't look great in IR. Maximize DOF and detail. There are dramatic exceptions of course, but IR 'scapes demand detail.

4) RAW is just about mandatory. Much PP intervention is needed. And because of the effectively reduced resolution, you'll probably want to downsize the images you produce.

What you didn't ask, and what is very very important, is: Which IR-pass filter should I use? These are labeled by their cutoff wavelengths. A #25 Red filter is essentially 680nm and gives a pseudo-IR effect with lots of visible light. 720nm is common and admits a bit of visible light. I often use 780-900-930-1000nm filters which pass almost no visible light (780nm) to total blockage (the others). These deeper IR-pass filters are effective for deep ND effects, forcing LONG exposures on unmodified cameras. My 1000nm filter is something like ND50.

So the filter used determines just which part of the EMF spectrum you're slicing. Near-IR (680-720nm) looks much like visible light, just very contrasty. Deep-IR (900-1000nm) looks totally different than what we normally see. In PP you get to decide how to render those spectral slices as impossible colors.
_________________________________________________

I also like to play at the other end of the visible spectrum. Early photo emulsions could only see ACTINIC (UV-violet-blue) light. A few decades of chemistry slowly produced the dyes that made plates and film sensitive to green-yellow-orange-red-IR spectra. If you'd like to replicate US Civil War-era photography, use a Blue or violet-CC filter to block longer wavelengths. You can use the Blue digital filter in your camera but that's rather harsh; I prefer a #47B blue-violet or a #80C light-blue filter for handheld shooting. Like an IR-pass filter only feeds the R channel, so a deep-blue filter only feeds the B channel. You'll want the same low-ISO thick-DOF settings as with IR work.


Last edited by RioRico; 08-23-2011 at 09:00 AM.
08-23-2011, 10:53 AM   #5
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Some real solid advice already given by the previous posters.
I can only add what seems important in my experience.
Establishing proper WB is essential for good results and less frustration. After all the process is time consuming.(Setting up tripod, focusing, adding filter, then exposing 15-30 seconds). And yeah, covering the viewfinder is important to fight light leakage.
From IR info on the internet and from experience, I have found the older D series to be more sensitive to IR than later bodies. I have never used the K-7 though.
Any lens should work as long as hotspots do not develop. The kit lens (18-55mm) works real nice. I prefer wide angles like your Sigma 10-20mm as the results are more pleasing to the eye. But a 50 or 55 can work as well.
Don't know what diameter of Cokin you are looking at or what their widest is. But I decided to go with 67 to 77mm IR filters and then use step up rings to fit small diameter lenses.
In the end, it is trial and error. The results will come and with IR anything is possible.
08-24-2011, 09:22 AM   #6
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Many thanks Jools, RioRico, Just1MoreDave and blackcloudbrew for all your useful help - seems I have a lot to learn and to experiment. I do still have the viewfinder cover (somewhere) and will dig it out to keep in my camera bag.

I use Cokin P and the round filter slots into the slot nearest the lens so that should help to keep out extraneous light too.

The Cokin Filter is the P007(89B). The P series is good for up to 82mm threads and the Sigma 10-20mm has a filter thread of 77mm so this should be OK although I suspect there could be some vignetting at the wider end of this lens.

Now up to me to find the right weather and scenery and try it out - to sum up: -

Tripod, low ISO, wide(ish) angla, F8-F11, viewfinder cover, White balence about 2500K. Plenty to consider!!

Thanks again.

Cheers...John
08-24-2011, 09:31 AM   #7
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Good luck. Post some of your results (success or failures). My personal feeling is that color IR is fun to play with but I really love B&W images in IR light. Although it's with my converted K100ds, my IR work is here on my flickr site.

Flickr: blackcloudbrew's stuff tagged with ir
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