What type of film for astro? & how to use?

[Paulius]

From reading a number of article on astrophotography, the norm now is using digital and then stacking numerous 10 - 30 sec exposures to give a final picture of greater detail (after a lot of tweaking with various photo editing programs).

I have a perfectly good Praktica BCI 35mm camera that I can attach directly to my scope. I understand from a question posted in the equipment forum that there is yet to be produced a ccd to fit in a film camera and transparency film was suggested as an option.

Is this because it would enable scanning of the slides and then stacking these as in digital process? or is it that a very long exposure can be taken (assuming the tracking is spot on!) to give a slide that has the detail of a stacked digital image?

If the latter is true how dose one work out the length of exposure, etc? is there a formula?

If these questions are stupid and there are places to get this information please tell me, so not to waste your collective time!

Regards,
Paul

[Malcolm_Stewart]

From reading a number of article on astrophotography, ...

I have a perfectly good Praktica BCI 35mm camera that I can attach directly to my scope. ...

If the latter is true how does one work out the length of exposure, etc? is there a formula?

If you're really keen on using film for astro photography, you need a copy of "Night Sky Photography" by H J P Arnold, published 1988, ISBN 0-540-01180-0. It might be in your local library, or available from a s/h bookseller (Google for it); and has masses of practical information. (Home made guiders etc.)

There's a whole chapter devoted to films and whether push processing is beneficial.
It suggests some exposures for the moon: e.g.
Moon quarter phase 1/250s f8 on ISO 400 film.
and
Jupiter 1/250s using a 500 f8 lens and ISO 400 film.

There's also guidance on the max length of exposure time for different telescope magnifications etc.

[Malcolm_Stewart]

Googling for "astro photography film" returned pages of what looks like useful sites - I assumed that you did this before asking here?

[beejaybee]

Is this because it would enable scanning of the slides and then stacking these as in digital process? or is it that a very long exposure can be taken (assuming the tracking is spot on!) to give a slide that has the detail of a stacked digital image?

The former.

The real problem with film is reciprocity failure, a serious secondary problem is that fogging from light pollution & natural skyglow restricts the exposure length. The background can be eliminated digitally. Taking lots of exposures, scanning & stacking can be effective but takes a lot longer total exposure than working with a digital camera to get an acceptable signal to noise ratio (because of lower sensitivity & reciprocity failure).

If you can find Kodak Technical Pan 2415, try baking it in a reducing atmosphere (hydrogen rich, natural gas is good) at medium high temeperature (60C) for 24 hours then using immediately, this increases the sensitivity and reduces reciprocity failure, even so digital sensors will beat it by a factor of 10.

[AJUK]

I'm surprised film isn't still more popular than it is in photography needing that length of exposure time, I have struggled with long exposures with a DSLR it tends to eat batteries, and then the camera freezes for a while if you have anti noise on, although with traffic trails the time is deliberately extended and because I'm capturing moving objects reciprocity isn't as much of an issue. If you have to stack multiple exposures in PS is that actually making things easier?

[beejaybee]

I have struggled with long exposures with a DSLR it tends to eat batteries, and then the camera freezes for a while if you have anti noise on

Oh yeah, battery draw is a real problem especially in low temperatures (which are otherwise helpful .... readout noise halves with every 7C drop in temperature), those of us who do astro work with DSLRs have found ways round this by using very high capacity external power packs (which we tend to have around to run tracking mounts, autoguiders etc.)

Anti noise can be switched off, take a few dark frames (same settings but with the lens cap on), average these & subtract from the "light" frames to remove the noise. You really don't need one "dark" frame for every "light" which is what you get when the camera's long exposure noise reduction function is switched on.

[FujiSigmaNolta]

I think you can still buy hypersensitization kits to "hyper" your film, making it more sensitive to the fainter light of galaxies, nebulas, etc. I was at some point very interested in astrophotography, but could not afford it and came across this. It did seem to me though from the mags I used to read a few years ago("Astronomy Now" and "Astronomy Today") that the majority of amateur astronomers tended to favour Sensia 400 and some hypersensitized it. Hypersensitizing film involves putting the film in what some called "baking process" using a mixture of nitrogen and hydrogen gas if I recall well, resulting in the above mentioned effect of making it more sensitive to faint light.