Photography

Biggest, in terms of money involved, piece of equipment is a nice piece of glass to put in front of our camera.

Since my wife had been using a Canon SLR since forever (and we stayed with that when moving from the EOS 300 to the current EOS 40D), the choices to upgrade from the kit EF-S 17-85mm f/4-5.6 basically have been:

• EF-S 15-85mm f/3.5-5.6 IS USM: since it's been announced with the 18Mp 7D it should be quite good on the 10Mp 40D. Newest design, certainly one of the best IS on Canon, true wide angle.
• EF 24-70mm f/2.8 L USM: The old trusted one. No IS, but a constant f/2.8. Narrowest zoom range of the lot. A real tank, at almost 1kg.
• EF 24-105mm f/4 L IS USM: The other full frame L lens. Not quite as big, longer, but only f/4.
• EF 24-70mm f/2.8 L IS USM: including waiting for it to be announced and available, of course.

In the end I got the EF 24-70mm f/2.8 L USM, because the EOS 40D is no high ISO monster (we don't plan to upgrade immediately.) Also: I bought the Tokina AT-X 116 PRO DX (11-16mm, f/2.8) a while back and we're quite happy with that so wide-angle is covered. And since we're often shooting indoors (family and other events), f/2.8 is a big plus. On the tele end, there's quite a gap from the 24-70 to the old EF 100-300mm f/4.5-5.6 USM [age of the page to reflect the age of the lens ;-) ] but then the latter is probably the next lens to be replaced anyway.

Since I only got 24-70 I can not directly compare these lenses. But after a few early tests I think I'm happy with the 24-70: while it seems to be a bit soft wide open at 24mm and at 70mm, it seems to be very sharp center to edge even at f/2.8 when used in the 35-50mm range. (Note that the 40D is a crop sensor camera, so I'm nicely using the sharp “center” area of a lens designed for full frame!) Yes, it's huge, so for casual walking around the 17-85mm will probably still get some use. Time will tell. And since it can, potentially at least, be used on a a EOS 5D Mk II, I now have another gadget to covet. Although this would mean giving up the Tokina 11-16mm. Anyway, not for quite some time yet...

(The test also included the venerable EF 50mm f/1.8, Mk I, and I must say I'm quite surprised how sharp that one is in the f/4 to f/11 range.)

I am eager to get feedback on some of my pictures. Some people already liked them, so the ego is quite well right now... :-)

A topic I've been trying to understand more about for some time is color calibration. I've used lprof to get a very rough starting point for my old CRT (sorely in need of replacement by now...)

Since hardware colorimeters are not cheap and probably not many can be used with Linux (I've not really looked, to be honest) I've wondered if I couldn't use the one device that is (should be) calibrated that I already have: my camera. With some kind of feedback loop like “shoot screen, analyze img file, adjust settings, shoot again” (and the same process for the printer, and, possibly a bit more error prone since the freshly calibrated printer would be used to produce the template, the scanner), shouldn't it be possible to arrive at sane settings? The camera explicitly allows using sRGB or Adobe RGB color model, so I'd think the colors should be more or less narrowly defined, at least when shooting raw or using manual white balance.

(Another thought: I have a dual screen system. Can X even do this? And if X can do it, is it possible to tell Gimp to set this up? But this is just idle speculatio. I've not really looked at Google's results yet, either.)

Update: Haven't really thought about ambient light. But the display emits light, so I'd shoot the screen in a darkened room, with white balance of the camera set manually. OTOH — thanks Joël — if I can get a colorimeter for not much above 100$, it's not worth investing too much time. I had always thought these devices were much more expensive. divide_by_zero Yes, I know CRT are usually much better than LCD, but OTOH my screen apparently starts to show its age: it will suddenly, and visibly, change brightness and color every few hours. I suspect the high voltage circuitry is not too stable anymore... And I won't buy another CRT, those things are just huge...

Just stumbled on the Optical RayTracer by Paul Lutus, a fun program to play around with optical lenses. After an initial look around, the next obvious step was, of course, to re-build an existing lens; I guess it worked somewhat. Compare the screenshot below with the block diagram of Canon's EF 50mm 1.8 lens. (No, I'm not paid by Canon, it's just the brand of the camera we own, and it's probably one of the simplest lenses around, too. Which, no surprise, we happen to own as well.)

Optical RayTracer is not in Debian yet. I've asked Paul if he'd mind if I did a package. Not within the next two, three weeks, though, sorry.

The Canon EF 50mm 1.8 re-built in Optical Raytracer

(Note to self: also look at OpenRayTrace)