(Second of an indeterminate number of parts)
This week's column by Ctein
Last week I told you how I got my Olympus Pen E-P1 camera converted to 830 nm (a.k.a. "deep") infrared by Life Pixel. I didn't opt for the full-spectrum conversion, although I considered it. I have some theoretical interest in exploring ultraviolet photography, and I have done false-color infrared work (figure 1). Converting for full-spectrum, though, would've required me to buy a whole bunch of auxiliary filters. Just about every lens I own uses a different filter size. Even with step-down rings, I'd be more than doubling the cost of the endeavor, and the equipment would be a lot less convenient to work with. Life Pixel assured me that if I wanted to opt for that (re-)conversion later, they could do it (for additional money, of course).
As soon as I started working with the IR-converted Pen several characteristics jumped out at me. First, a Micro 4/3 type design is really ideal for IR work. There are no problems with focus shifts or corrections, because the camera is focusing based on what the sensor sees. There are many fewer issues visualizing how a photograph is going to look in the infrared, because what you see on the back screen of the camera is a black-and-white infrared photograph. It's a very natural way to work.
The photographs that come out of my camera are very flat (figure 2). There are no true blacks and the only time there are pure whites is if there is a direct light source or specular reflection in the photograph or the contrast range of the original scene is really extreme. I can't say whether this is inherent in the scenes themselves, in the behavior of the sensor/filter stack in the deep IR, or purely a consequence of the fact that anti-reflection coatings on lens elements don't work especially well in the IR.
Whatever the reason, photographs are typically low in contrast with extremely poor micro-contrast and tonal separation in fine detail. My standard conversion in ACR for the IR Pen pushes the contrast slider up around +65 and has the clarity slider pegged at +100. Even that's often not enough; I may pull in the black and white clipping points in ACR or do additional local contrast enhancement in Photoshop using wide radius unsharp masking or ContrastMaster. The photographs look great after I make those adjustments (figure 3).
High-ISO noise was less of a problem with my converted camera. That's because the first noise to kick in offensively with the Olympus Pen is chroma noise. No chroma in these photographs! I've previously written that I considered the Pen usable up to ISO 800 for professional-quality work. After the IR conversion, it's ISO 1600.
(Important side-note: in all discussions of noise in this camera, I'm going to be talking about what it looks like after I've made the contrast adjustments needed to make the overall photograph look good. The appearance of noise is awfully sensitive to global and local contrast, so what you really care about is how it looks in a photograph with good contrast characteristics, not what comes out of the camera.)
Noise is an important consideration, aesthetically, because in the IR the sky is almost always very dark and there's more noise at the dark end of the exposure scale than the light end. Furthermore, because Raleigh scattering goes as the fourth power of wavelength (that's why the sky is blue, in case you didn't know), shadows are even darker in the infrared than they are invisible light.
Most conventional cameras show little difference in noise at the lower ISO settings, but noise steadily grows with increasing ISO in my IR Pen. The camera exhibits extremely low noise at an ISO 100 setting, but every stop above that shows a clear increase in noise (figure 4). It's very uniform and smooth; really, it looks like film grain rather than annoying digital noise, but it does increase with each increment. In subjective language, I'd describe ISO 100 as being essentially grainless, ISO 200–400 as being very fine-grained (relative to 35mm conventional black-and-white film), ISO 800 still fine-grained and ISO 1600 medium/coarse-grained. Above 1600, I don't consider the camera usable because large-scale stripe patterns appear, and the "grain" loses the totally random, uniform quality.
Between that and wanting/needing to use lens apertures in the ƒ/3.5–ƒ/5.6 range (I'll get to that in the next installment), one can wind up a bit light-starved even on a sunny day. A sunlight exposure at ISO 100 would be something like 1/300th sec at ƒ/4, after the two-stop deep-IR-conversion loss. But, with far less light in the shadows you can readily drop 3–4 stops. If you want to stop down for more depth of field or better sharpness or use a longer lens, well... ISO 100 doesn't cut it. I'm willing to accept the two stop speed loss to get purer IR characteristics, but I can understand why many folks might prefer the conventional IR conversion.
Putting this in perspective, though, the IR Pen still produces photographs at ISO 800 that are less grainy than the brute-force IR photography I talked about last time.
The next time I come back to this subject, in two (?) weeks, I'll tell you how a whole bunch of different lenses performed in the IR. Stay tuned to this station.
©2013 by Ctein, all rights reserved
Weekly columnist Ctein's work usually appears on Wednesdays, but Mike the Ed. was traveling this week.
Original contents copyright 2013 by Michael C. Johnston and/or the bylined author. All Rights Reserved. Links in this post may be to our affiliates; sales through affiliate links may benefit this site.
(To see all the comments, click on the "Comments" link below.)
Featured Comments from:
Oskar Ojala: "Out of curiosity, is the false color IR picture taken on Kodak EIR or something else? I tend agree with your conclusions though; in my experience false color IR usually turns into a gimmick rather than something that stands on it own and thus I've concentrated on BW IR this year. There are good examples of false color IR—I've even managed to take some shots myself that I liked—but it's a very challenging medium.
"For a while I've used converted Sony NEXes for IR, before that a Nikon and have also converted a prosumer Canon as an experiment. All except the Canon were multispectral versions. The Canon, with a deep enough filter to render an entirely monochromatic image, worked very well actually. While my IR pictures tend to have flatness, it hasn't been as extreme as your example, although the settings might differ. Specifically, blacks aren't nearly black enough for me. There could be many reasons for that.
"One thing I have found is that there are huge differences in lenses for IR and especially most wide angle lenses tend to work lousy, with too many aberrations ruining everything but the center. Contrast also varies a lot. My lens selection has been a long process."
Tim: "Perfect timing with these posts, I recently (last Thursday) acquired a second hand full spectrum E-PL1. I've only used it for a weekend, but I think I'm going to have a lot of fun with it. The full spectrum images converted to black and white at first glance are really appealing to me. I wanted to let you know that I'm really enjoying these posts."