[orbital-decay]

You can do this even without any motion and possibly even with no focusing optics, just with a single sensor, diffraction grating and a lot of math. This is called single-pixel imaging and is an ongoing research topic in computational imaging.

[anfractuosity]

Could you explain in laymans terms how that would work? If you're only obtaining a single value for a single pixel and there's no movement, how does the pixel value change even if there's a grating in front? Or do you mean the grating can still move?

[orbital-decay]

The pattern still needs to be different at each sampling, yes. Moving the grating is one way to do it, or it can be done with a micromirror array, for example.

[anfractuosity]

Gotcha cheers! A while ago I saw a single mirror MEMS device, could be useful for something like this, I believe you could control the horizontal/vertical angle.

[keithpeter]

And noise? I used to do long exposure photos of interiors of buildings on film (~2h) but digital cameras seem challenged to me.

[anfractuosity]

That's very interesting re. film. I'd be curious why that is. I've only ever done exposures less up to around a couple of minutes with film & digital. Do you have any examples that you shot for 2hr out of curiosity. Was that with ISO 50 or less, or did you use a darkening filter too?

Edit: I wonder if it is due to reciprocity failure with film - https://en.wikipedia.org/wiki/Reciprocity_(photography) ?

[keithpeter]

125 asa FP4 roll film (all monochrome and hand developed needless to say, I used a Rollieflex camera on a tripod when I was playing with this stuff decades ago).

I found the correction chart below on t'web [1] just now.

I recollect using 2.5x per stop over 1 second which gives slightly longer exposures than [1], but then I did tend to 'pull' the development a bit (contrast goes up), so a 2 minute metered exposure would be 2.5^7 seconds (10 minutes) instead of 2^7 seconds roughly. A 10 minute exposure on the meter corresponds to two hours and a very significant contrast hike - I recollect printing on grade 1 and grade half filter settings (multigrade paper). I only used extreme exposure times in old dark interiors e.g. churches in the UK in November or something. Inside so no need for any filters - not astro.

I'll dig a few prints out and scan them over the weekend. Nowt astounding. See if you can find a book about Edwin Smith if you are near a library with a very good photography collection.

I have a fantasy of using 10x8 film with a pinhole camera and just doing contact prints... but then I remember the darkroom days and the amount of water that got used up...

[1] http://home.earthlink.net/~kitathome/LunarLight/moonlight_ga...

[anfractuosity]

That chart looks very interesting, thanks!

Cheers, I'd be very curious to see your prints.

I've just had a little look on google images at some of Edwin Smith's photos, they look stunning! The light in the photos look amazing.

I still have an old Pentax K1000 film camera I think it is, I'll have to dig it out again some time :) I'd really like to get a medium format camera, but they're still not super cheap, I was looking at the Mamiya RZ67 (I'd actually like to try shooting landscape with it, which could be impractical due to the weight, but would be fun nonetheless ;).

10x8 film would be awesome to play with!

[keithpeter]

Well I did say fantasy - a sheet of 10 x 8 film is the same cost as a roll of 35mm (similar area if you think of a contact sheet).

A 35mm camera on a tripod with shutter release would allow experimentation and allow you to decide about weight and carrying for hiking. I used the long exposures mainly in buildings in a city.

My images are not on Edwin Smith's level by any means, but the movement of the Sun direction over an hour does make a sort of smoothing of the light.

[madaxe_again]

That's why most actual astrophotography is done with peltier cooled CCDs - firstly a lower temperature means less noise, but more importantly more consistent noise. You can then shoot dark, bias and flat frames, respectively average those, then subtract them from your stacked (averaged using any number of algorithms) light frames.

No reason it couldn't be applied to regular long exposure photography using a DSLR, either.

[Frenchgeek]

http://www.gperco.com/2014/10/single-pixel-camera.html

[orbital-decay]

This is incredibly cool! I wonder what the simplest possible non-mechanical modulator is. (LCD?)