I had the idea to convert a dSLR to IR, preferrably of course a Pentax one, as I was and am using the Pentax system for visible light. But all the usual suspects would not provide Pentax conversions. (This has changed now, with various companies and people doing Pentax modifications.)
So I simply asked Pentax Europe (Hamburg, Germany) if they would assist in such a modification. The reply was quick and positive: I would just need to provide the matching filter and Pentax EU could modify all of the *ist models. Yay! Pentax Europe is currently (November 2008) still offering this service on a case-by-case basis. After some thinking whether I'd prefer an *ist D or *ist DS, I opted for the DS.
To determine the filter size, Pentax Europe was so kind to provide a stock filter for measurement. The filter is of dimensions 22.00mm x 28.00mm x 1.61mm.
I knew David Burren in Australia converted Nikons, which use the same size CCD sensor as the Pentax *ist DS I was going to have converted. Indeed, he could provide a matching filter of 2mm thickness and after his supplier supplied, it was only one week until I was the owner of an 715nm IR pass filter.
I sent the filter and my trusty DS to Pentax EU and received the modded camera only two weeks later. Wow, that was quick. And they even fixed the broken USB/AV/remote door!
Now, the real questions would need to be answered: Exposure? Focus? With a modded dSLR, the AF and exposure meter sensors see visible light, eventhough the capture sensor sees IR light. Professional modders won't reveal their secrets, so I was about to find out...
White Balance
The DSIR is not able to do a complete white balance on either foliage or grey/white surfaces. This means that there is a residual red/magenta cast to the images. Interestingly, the preview directly after shooting the WB shot indicates a perfect WB, but somehow this does not translate to the WB applied to the real shots. Due to the remaining colour cast and the difficulty in judging exposure that this causes and the general heavier processing IR needs, I strongly recommend shooting RAW with the DSIR.Interestingly, the difference in colour of different lenses is more pronounced in IR than in visible light. My DA 12-24 and DA 18-250 are very similar, whereas the FA 50/1.4 and other FA primes I used show a less magenta, more purple, almost blue tone with the same WB settings. Dealing with WB is also a topic in the "Processing" section.
Exposure
The difference in IR brightness and visible brightness can be very small or very large. My DS tends to need around +3 stops of exposure compensation for an average scene containing a bit of sky (darker than visible) and plants (brighter than visible). Only in M mode, I can verify EC above +/-2.oEV, so I use M mode mainly. Furthermore, the prevalent reddish cast makes judging exposure difficult: My eye and brain cannot really adapt to the red review image on the LCD screen and the luminance histogram is misleading in this situation, too. With experience and bracketing, this can be solved. Depending on whether you want colour IR or B&W IR, your exposure philosophy might differ. I usually try to not blow out the red channel, even if this means more noise in the blue channel. Please note: Different cameras have a wider custom WB range and RGB histograms - both are beneficial for evaluating IR exposures, maybe evenmoreso than for "normal" shots.Sharpness
As the AA filter is removed together with the IR-Cut filter, the modded camera has the potential to be extremely sharp. If the focus is right (see next point).
Dortmund from the "Langen Florian"
I have not yet seen Moiré (spatial aliasing). While I mainly shoot nature when I shoot IR, I have shot a good deal of buildings, too and have not found it to be an issue so far.
Focus
Well. #ahem# Weak. I expected some kind of problem and hoped that using the focus adjust menu to calibrate for front-/back-focus would work. But no luck. If it worked for close subjects, it didn't work for far subjects. Plus it was dependent on focal length, too. I was about ready to give up. Then the AF broke and I was really ready to give up. Shots were great and promising, but not focused...Then a trip to NYC draw close and I thought whether to bring my D7IR with the glacial speed and hotspot problem or the DSIR with the non-focus. I went out to test the DSIR with manual focus and took this shot:
Field Day!
So. It worked. Kind of...
I have now found out that for wide angles, focus is usually not an issue. But for long glass, especially for distant subjects, it is very hard and I rely on focus bracketing to get a shot.
Charleston Bridge IR
For cameras with live view, this is less of an issue of course. The convergence of technology of compact cameras and dSLRs will be really beneficial for IR, both for modded dSLRs and for normal dSLRs with lens-mounted filters.
Processing
After doing the WB, processing IR shots is not that different from visible light, but I find that IR shots often require (or can take) a good extra dose of contrast.
Kokerei Zollverein
If the shot shows some hotspot, I either give up and convert to B&W (it shows less there, because a huge part of the hotspot is a hue shift) or try to tweak the selective colour controls in my RAW converter to lessen the strength. Stopping down seems to worsen the hot spot and so far all my lenses show it sometimes to some degree.
In processing, I find there are three options when converting IR shots: Keep a reddish warm tone,
It was a sunny day in IRland
or swap the red and blue channels (Irfanview does this for free, others, too)
Blue Hour, courtesy of IR
or convert to B&W.
Forestal Upwardness
It depends on what mood you want to create and also on the original colour content. I write a bit more about processing on a dedicated section of my site. For my taste, use of levels and curves is essential.
Flare
Terrible. If you ever thought that all this "(digital) coating" stuff is marketing: You are wrong. The replacement filter is not specifically coated and flares like mad. Sometimes it is beautiful,
Show me Polygons and I show you the Sun.
but mainly it means you need to be very careful when the sun gets anywhere near the frame! If you have a chance to buy a multi-coated internal IR filter, I would recommend that it is worth a considerable premium. David Burren wrote me and said that at least part of the flare is due to the lens coatings not being as effective in IR.
Usage
While IR can be used for basically everything, I find that it excels in creating contrast where usually is only little (dark skies, dark water), cutting through haze
The IR Effect
and generally setting a unique mood. You can see more info in my introductory page. It can be used for landscapes, shapes and even for people. The IR effect can be quite flattering on skin, but as IR light can see through the upper skin layers, it shows veins much more than visible light.
IR palm (smooth palm, veins on fingers)
Depending on the light, your taste and the model, it may look like marble or like horror.
Summary
While I do not shoot very much IR, the DSIR usually accompanies me on my trips, mostly with the DA 12-24 mounted. It can't do everything and is certainly not a plug-and-play camera, with manual focus, manual exposure, and various restrictions to keep in mind when shooting and more involved processing. But yet, or maybe because of that, if I get something worthwhile out, I am very happy with it.
In. And Out.
copyright 2008 by jensroesner.de