Category: "Pentax *ist-D"
I’m a big fan of infrared photography, and increasingly that means shooting digital IR. My personal setup has been based around a Pentax *ist-D 6 megapixel DSLR and a Hoya RM 90 filter. This has produced some pretty nice results, but it has some drawbacks. The RM90 blocks all visible light, and even infrared light up to 900 nanometers. As a result, exposure times on the *ist-D are fairly long. I also find a fair amount of “sensor flare” – light reflections within the digital sensor itself – when using the RM90.
Since just about everyone else who shoots digital IR uses a Hoya R72 filter, today I decided to pick one up and try it out. The R72 blocks visible light, but allows light transmission from about 700nm on. So I made a quick stop to the local camera store, which actually had them in stock, and then headed out to the Allegan Forest to run some tests.
Mother Nature did not entirely cooperate. Although the forecast was for clear skies and sunshine, by mid morning the sun was shining through high overcast clouds, and the only blue sky to be seen was in the southern half of the sky, which meant shooting into the sun to some degree.
Although I took several shots, I picked the one I liked the best and tried to make the best images I could from both the RM90 version and the R72 version. The photo of the Walnut Tree is the one I picked to work on. At the start of this post is the best shot I could make using the RM90 exposure. At the end is the best shot I could make using the R72 exposure. Granted – this test is a bit skewed. I’ve been shooting with the RM90 for a few years now, and have a lot more experience with it than with the R72 (used for the first time today.)
I’ve also enclosed the two RAW files, straight off the camera with no adjustment. These pretty clearly show the difference in color, white balance, and contrast between the two filters. If you look closely at the shot taken with the RM90, you can see some sensor flare in the form of a brighter cyan band running horizontal about 20% above the bottom of the frame. (Minor flare like this can be handled by using the sponge tool in Photoshop to de-saturate the flared area and blend it back into the rest of the image.)
Nonetheless, I shot several dozen images with the two filters, attempting side by side comparisons. Here’s a rundown of what I found out:
1. Speed – the R72 was consistently about 3 stops faster than the RM90. Throughout the morning I was shooting at f11. With the RM90 in place exposures were 2 to 3 seconds at ISO 1600. With the R72 exposures were 1/4th to 1/3rd of a second at the same ISO. In either case – a tripod was a necessity.
2. White Balance – When shooting RAW files, white balance can always be adjusted later. But it’s great to get it close to the mark during the actual shooting process. For a long time I just shot with the RM90 using either daylight or auto white balance settings. This resulted in a low contrast magenta image that could easily be adjusted in Adobe Camera RAW or in Photoshop itself.
These days, with the RM90 I just take a custom white balance reading, with the filter on the camera, off a white card. This results in blue skies that are deep burgundy to black, white clouds, and somewhat cyan colored foliage.
The R72 proved to be more of a challenge on this front. When the white balance was set to auto or to daylight, the camera produced a blood red image, with almost no discernable detail in it. (The detail could of course be teased out in the RAW conversion process, but with these white balance settings it was virtually impossible to access the composition on the preview screen.) I had heard that setting the white balance off foliage was one approach that worked with the R72, so I tried that out and set a custom white balance off green foliage with the filter in place. That resulted in a much better image – although it was still tinted orange
3. Sensor flare – sensor flare seems to be tied to the length of the exposure, and with the much shorted exposures from the R72, it was greatly reduced when using this filter.
At the end of the day, I can only say that the two filters simply represent two different sets of tradeoffs. The long exposures resulting from the RM90 can result in too much motion blur. The shorter exposures of the R72 help to address that – but I can’t see hand holding the *ist-D with either filter in place. Color balance is probably just a matter of taste - I can see liking the RM90 in some situations, and the R72 in others. It looks like the R72 will result in a lot fewer shots lost to sensor flare.
At any rate – I’m pretty sure that an IR converted camera is in my future, probably the near future to boot.
The drought has been continuing in southwest Michigan – though last night’s half inch of rain was a small relief. This past week temperatures in the mid 90’s F have only served to make the drought more acute.
On Friday I visited the Allegan Forest, looking for mid season dragonflies and opportunities for some landscape photographs. It must have been the oppressive heat, or perhaps the dusty dry soil, but there was nary a dragonfly or other insect to be found. For the first time in months I didn’t both with insect repellant, and not even a mosquito was to be found.
I decided to concentrate on shooting some digital infrared work. I’m seriously considering getting a dedicated digital IR camera – which unfortunately would mean moving away from using a Pentax since no one seems to do digital conversions of Pentax gear. But for now, I’ve been happy to work with the *ist-D and Hoya RM 90 filter.
Only one acceptable image came of the day’s IR shooting. This was shot at the edge of a restored section of Oak Savanna, right about where the deer can be seen in this shot from last summer. The image has been manipulated a bit more in Photoshop than I usually do, but the effect of increasing detail in some areas, while losing it in others, is interesting. Of course – the hot dry wind that made some branches wave during the 8 second exposure also had something to do the blurred areas of the shot.
This image was taken north of the Kalamazoo River. While there I took a few shots of one of the only large tree standing oak trees I’ve ever found in this so-called forest. Those shots were a disappointment – a plain tree, so what?
After working the areas north of the river for a while, I headed over to some familiar fields south of the river. I took the Allegan Dam Road, driving over the dam that backs up the river to make Lake Allegan. This turned out to be a scouting trip – it had been some time since I last drove along the dam – and I looked without luck for some promising areas in which to shoot.
After several visits to familiar haunts, coming up empty with regards to insect shots, I wandered down to the Ottawa Marsh. After all, if dry weather was the problem, than what better place than a marsh to find some moisture.
I saw quite a few bluet damselflies as I hiked down the dirt drive towards the board launch and the entry way to the marsh. Back in the marsh itself the effects of the drought were not as profound as in other areas. Of course – I was walking through areas that are probably knee deep muck during normal years - so that fact that the soil was still moist and vegetation as flourishing should be taken with some measure.
A ways in the marsh, following the river bank, I encountered an area of several acres thick with iron weed and joe-pye weed, all ranging from 4 to 6 feet in height. I wasn’t travelling light – I brought both the insect setup and the digital IR setup (complete with tripod) but I ditched the camera and tripod in a dense thicket, and wandered off into the iron weed.
Red spotted purples, spicebush butterflies, and more than a few giant swallowtails (lovely insects) were attached to the ironweed. It was difficult to get shots with a clean background - literally standing in flowering weeds as tall as me – but I managed a few good captures of giant swallowtails – to be included in a future insect photography update.
Wandering into a patch of vegetation that is pretty much growing over your head is usually not a great idea. Once you are ten feet into the patch, only your own trail leads you back out. But between the handy GPS system and noting a few large trees along the river, it was pretty simple to bee-line right out of the weeds once I was done shooting.
And from there it was a quick hop home.
Where do the dragons go when they don’t want to be seen?
Beats me, or else I would have seen some recently…
West Michigan’s unusual dry spell finally broke this last week. I visited the Allegan Forest on Sunday and again on Tuesday, both days after heavy local rains. It’s amazing how quickly the plants in the sandy soil of the pine barrens quickly turn from brown to green. The marsh I’ve been visiting off 48th street has progressed from dried, cracked mud, to muddy mud, to gooey muddy mud. Good sign for all the moisture loving creatures there.
But on both days, no dragonflies were to be found. A few spicebush and red spotted purple butterflies flitted about. So far this year, I’ve seen no Karner Blues, and it’s it’s likely I won’t see any this summer at all.
So I set my sights on landscape photography. In particular, I did some more digital infrared work using the *ist-d and Hoya RM90 filter. It seems that some of the best results are to be had on high overcast days. The few cool and dry, crystal clear days when I shot digital IR seemed to result in an undue amount of sensor flare and other problems.
The first image shown here was shot laast week, using the Pentax *ist-D and an IR filter. It is from the old farmstead off 48th street.
The second image was shot last August from a similar vantage point as this shot, which was taken using Maco 120 format IR film in the trusty Pentax 6x7. Perosnally, I like the digital IR effect better – and while the digital shot required a fairly long exposure, it was not much longer than that required by the rather slow B&W film.
I also experimented with more ‘time and motion studies.’ These are 25 – 100 multiple exposure shots, building up a composite of light on the negative that bears no resemblance to the actual subjects shot. I realized that the Pentax Mz-S, with its capacity for unlimited multiple exposures, was the perfect tool for this technique. No results to show, but the studies continue.
My next opportunity to visit the forest is three weeks out. That’s disappointing, since a lot can happen in three weeks. But I’ve managed to carve out a few hours this Friday to visit the McLInden Trails, so with luck, a dragon or two might appear here in the near future.
I’ve been shooting a lot of infrared these days, and feel that some of my best recent work has been accomplished through the use of digital infrared techniques. This is a fairly new technique for photography – up till recently infrared work was done on film. So here’s a tutorial that covers the technique that I use to create infrared images with my Pentax *ist-D.
I should start out with the caveat that there are many different ways to take digital infrared photographs. The technique I use is one that I more or less stumbled upon by happen chance – I happened to acquire an infrared filter, and chanced to use it on the *ist-D in a way that worked. But different digital cameras have different sensitivity to infrared light, and there are many different types of infrared filters out there that, for all I know, might work better than the Hoya RM90 filter that I use. So, as the saying goes, your mileage may vary.
So just what is infrared light anyhow? The technical definition is that it is electromagnetic radiation close to but outside of the visible light spectrum. Infrared light is just beyond the red end of the spectrum of visible light – meaning that IR light has a longer wavelength than visible light. To get even more technical, the human eye can see light in the (approximately) 400 – 700 nanometer range. Infrared light lies beyond that, consisting of frequencies of 700 to 1000 nanometers.
The characteristics of infrared light contribute to the look and feel of IR photos. For example, due to the long wavelength of IR light, it is less prone to be dispersed by airborne dust particles. As a result, a clear blue sky will appear deep black in IR shots. IR light also reflects off foliage, resulting in what Ansel Adams described a “plaster white trees” in infrared photos.
In general, infrared photography is best accomplished on bright, clear days. Due to it long wavelength, infrared light can penetrate some barriers – like haze – but also can be blocked completely by others. After doing a lot of IR shooting, both with film and digitally, I still find it very difficult to predict how certain scenes – especially when shooting under foliage – will come out.
The CCD or CMOS sensors in digital cameras are generally sensitive to infrared light, but they also have infrared blocking filters incorporated into their design, apparently so the IR light will not interfere with normal photography. While you can have the IR filters removed from you digital camera, this will render the camera pretty much a dedicated IR device. Some day, when my *ist-D is obsolete for regular shooting, I plan to take that approach. But in the meantime I prefer to work around – or perhaps through – the build in anti-infrared filter.
To do this, I use a Hoya RM90 infrared filter. This filter allows transmission of light from the (roughly) 750 – 3000 nanometer range. (There is actually diminished transmission of frequencies out to ~4700 nm.) This is the heart of infrared, and completely outside of the visible light spectrum. In fact, as shown by the image of the filter, the glass in the filter is jet black. So once it is attached to the lens, you are truly working with ‘invisible light.’
While the *ist-D has a built in infrared blocking filter, it is not 100% effective. For my infrared work I frame up the shot, attach the RM90 filter, and set the camera to manual mode. The camera actually reads and responds to the IR light passing through the filter, and the meter shows an exposure setting and the autofocus works quite well.
The ability to have autofocus through the IR filter is a real boon. Infrared light focuses to a different point behind the lens than does visible light. Good lenses (and most older lenses) have an IR focus guide on them. The idea is that you focus the camera using the visible light, and then adjust the focal point back to the point indicated by the IR focus guide. Since the *ist-D’s autofocus is working off only IR light, it focuses accurately right from the start.
The camera’s autoexposure meter, however, is not as accurate with IR light. In my experience, the camera will suggest and exposure setting that is at least 3 to 4 stops under exposed. You are also facing very long exposure times at high ISO settings when shooting digital infrared. My starting point, with the RM90 in place, it to set the camera to manual mode, and start exposures at ISO 1600, f16, 2 seconds shutter speed.
Depending on the actual lighting, the shutter speed at ISO 1600, f 16, can vary from 0.3 seconds to 15 seconds. While that may sound like an amazingly long exposure, it’s not that much longer than the exposures demanded by some IR films. The old Konica IR 750, for example, with a #25 red filter had an effective ISO of 6 (taking into account the filter-factor.) That’s about 1 stop from the starting point for the digital IR setup I’m using, and as Konica and all other film producers like to say when it comes to infrared – “bracket widely.”
The nice thing about shooting digitally is that you can look at the histogram and see how the exposure worked out. So, like I said I start out at 2 seconds, f16, ISO 1600, and see what the histogram shows. On a bight clear day that starting point will probably be over exposed, and on an over cast day that starting point might be a stop or two under exposed.
In any a case, forget about getting a histogram that shows a full tonal range from black to white. It just doesn’t happen – at least with my setup. Instead I get a compressed histogram, and a monochrome image. Once the photo is taken, a fair degree of post exposure processing remains to be done.
Here is a shot of “Thunderheads Over Mount Pisgah” – the first image (the magenta one) is the off the camera, unadjusted digital IR shot. The second image has been processed in PhotoShop.
The post exposure processing is really pretty simple. The image first mush be desaturated (turned to B&W). The white and black points must be set to punch up the contrast in the image. After that, its just the normal routine of dodging and burning to get the look you want
There are still some pitfalls to the whole digital IR process. First off, noise can be an issue. A 2 or 4 second exposure at ISO 1600 is bound to be fairly noisy. I rely on the camera’s build in noise reduction to deal with most of this, and apply dust and scratches or other noise reducing filters as a last resort.
Second is the issue of sensor flare. This is where light bounces around or flares within the digital sensor assembly itself. Just like with lens flare, the result is a bright spot in the image. Here are two examples:
In the first one you can see a huge arch of flare cutting through the right side of the image. In the second you can a smaller line of flare running parallel to the bottom edge of the image, and just a short distance above the bottom.
I loose about 20% of my digital IR images to this phenomenon, and I’m not sure what exactly causes it. I do know that it seems to be related to the angle of the camera to the sun, and to either the length of the exposure or f stop setting. By opening up the aperture and using a shorter exposure, the flare usually diminishes or disappears altogether.
So to sum up the steps I use when shooting digital infrared with the *ist-D and RM90 filter –
1. Compose the shot with the IR filter off the camera (since you won’t be able to see through it once it’s mounted.) 2. Mount the IR filter, let the AF handle focusing (since it will need to adjust the focal point to compensate for the IR light.) 3. Start as ISO 1600, f16, 2 seconds. Look that the histogram and adjust as needed. 4. Process the RAW file by desaturating, and then setting the white and black points to compensate for the compressed tonal range. 5. Apply anti-noise filter if needed, and make normal image adjustments.
The really nice thing about digital IR is that, with the digital filter in the pack, you always have the infrared option open to you as a creative choice. That is something harder to achieve when dealing with finicky, perishable, and difficult to handle IR films!