IR

[compilerbitch]

I just got an IR filter (square, Cokin P-series, 89B). To the naked eye,
it looks completely black -- if you look through it, you can /just/ see
bright objects as a dim red image. I wasn't stupid enough to look at the
sun through it, of course (it's pretty much transparent at IR frequencies).

Anyway, putting it in the filter slot in the compendium shade on the
Cambo worked a treat. I focussed the image with no filter in place on
the ground glass, locked everything down, then inserted the BetterLight,
stopped down to somewhere between f16 and f22 and put the filter in
place. Doing a prescan, I found I'd way underestimated the sensitivity
at IR, so I ended up upping the line time to about 1/250th and dropping
the ASA rating to the minimum (just under 400). The focus looked OK, so
I made an exposure and checked it in Photoshop. It wasn't bad, but the
focus was slightly off -- this is not too unexpected for IR. I then used
the BetterLight's focus meter to get it dead on -- the next scan was
fine. This is a crop from that scan, actually a fairly small area in the
top right of the original.



The shot was taken in reasonably bright sunlight, about an hour before
sunset. I took the image data from the red sensor only, but
(interestingly) I found that all three sensors (R, G and B) seemed to be
about equally sensitive to IR.

Comments

[randwolf.livejournal.com]

Wow. Just wow.

More, maybe, when I'm actually awake.

[mirabehn.livejournal.com]

Oh, that is absolutely stunning. :-)

[compilerbitch.livejournal.com]

Infrared photography has always fascinated me -- I've seen other people's images of trees with snow-white leaves, surreal skies and brilliant white clouds, and have always been attracted by their surreal quality. It's a bit like taking a magic lens and seeing a world that is right beside us, but not accessible to us.

This is the first time I've had access to equipment that can take IR photographs. In my film camera days, I never quite got around to trying infrared film -- it always had a reputation of being difficult to use. You had to keep it in the fridge, because heat could fog it. Focussing was difficult because lenses focus different frequencies of light at slightly different distances -- they tend to be corrected quite well for visible light, but IR can cause an appreciable focus shift. So I didn't ever quite do it. I now feel amazingly lucky to have a digital camera (albeit something of a monstrosity, in all senses of the word!) that can do it. All I have to do is to swap from using a filter that is designed to block IR (most digital cameras have them built in, but the BetterLight doesn't so you have to put one in front of the lens instead to take normal photographs) to one that blocks visible light and only allows IR through.

I can't wait to take it out into the countryside around here. There is some spectacular landscape in northern California that seriously needs to have a camera pointed at it sometime soon. :-)

[darcydodo]

*is an idiot* I don't know why I haven't pointed you to cuthalion before now. Oh wait, that's right, 'cause I'm an idiot.

Hope you're coming to Bab5 on Thursday -- it's in Redwood City!

[compilerbitch.livejournal.com]

Yes, I am planning to come to Bab5 this week. I wanted to go last week, actually, but I was feeling really dead tired and wanted to get some rest before my epic trip at the weekend (SFO to London Heathrow, arriving about 8am, pick up hire car, drive to Leytonstone in East London for breakfast and to pick up doseybat, then to Cambridge for lunch in College and my graduation in the afternoon (I'll post more about this later in a locked post), then to a hotel for the night. On Sunday, drove to Gatwick, got on a plane at 1pm to Dallas, Texas (10 hour flight), 2 hour wait at the airport, then a 3 hour flight to SFO. I got home at 1.30am Monday morning. Something like 13000 miles in 3 days).

I will friend cuthalion forthwith. :-)

[cuthalion.livejournal.com]

From the rainbowing on the moving objects in the big color jpeg, I'm guessing the back has a filter with three large strips of red, green, and blue instead of a mosaic or something? Anyway, CCD responses are similar to CMOS ones even in IR, the 89B is pretty similar to an R72, and it seems probable your R,G, and B filter response curves extend past visible similar to canon's, so you might be able to pull some neat false color out of the full color picture!

Here is something I wrote about about false color IR, although the response spectra graphs honestly aren't all that accurate.