Posted 15 April 2008 - 12:45 PM
Thanks in advance for the help.
Posted 15 April 2008 - 01:06 PM
Posted 15 April 2008 - 01:15 PM
Posted 15 April 2008 - 07:58 PM
Posted 15 April 2008 - 10:00 PM
Posted 15 April 2008 - 11:06 PM
Posted 16 April 2008 - 04:50 PM
Posted 16 April 2008 - 05:05 PM
Posted 18 April 2008 - 12:34 AM
Posted 18 April 2008 - 01:36 AM
Back in the day (before 1990) there were not any really good film emulsions off the shelf. They all suffered from very bad reciprocity failure, which meant that the film tended to be less sensitive to faint light the longer the exposure.
To solve that problem, there were two techniques that astrophotographers did:
1. Freeze the film. You turned your camera into a "Cold Camera". This required you to make the camera air-tight and then had to replace the back with a home-built MOD that allowed you place dry-ice up against the film plane. You then pumped all the air out of the camera to prevent fogging and dew. The camera became a one-shot system as you could not wind the frozen film!
2. The second method was easier, and was called Hypering. The goal was to remove all the oxygen molecules from the film emulsion - which in-turn made the film more sensitive to faint light over time. In effect, it reduced the reciprocity failure. This was done by baking the film (low heat) in a bath of hydrogen. The hydrogen attached to the free oxygen and the resulting water vapor was dried out in the heat. The film (even the whole film canister could be done) was placed in a small pressure tank and then all the air was removed. Next, hydrogen (or a mix of H and HE for safety) was pumped in under a little pressure. The whole chamber was then placed in an insulated box (or Ice-Chest) along with a heating element (light bulb) and allowed to make for hours or days. There was even a commercial product by Lumicon that made this easy. Do-it-yourselfers also made chambers that worked very well.
Once treated, you had to use the film within hours. You could pack the film back in its canister along with some desiccant to keep it dry. Then you could keep it in your freezer for a month! But once you open it, it had to all be used within hours and immediately developed for optimum results.
The above two techniques also pretty much meant that all astrophotographers needed their own darkroom or access to one.
With the arrival of Fujichrome 400F Provia (now discontinued) and Kodak E200 - that all changed. These two films were (are) perfect for Astrophotography straight off the shelf.
Posted 18 April 2008 - 04:14 PM
Posted 18 April 2008 - 04:28 PM
CF is talking about the old "Cold" cameras that used dry ice to chill the film while you exposed it.
Posted 20 April 2008 - 07:05 PM
Professional film is usually the same exact film as store bought film, but it has been kept refrigerated to keep it "fresh"
I could be wrong, but for long exposure astrophotography, the off the shelf consumer grade Kodak E200 is just as good as the professional grade. I think that after a certain time during exposure, that little bit of an extra edge for the "professional" film doesn't matter.
Again, I could be wrong.
Posted 20 April 2008 - 08:51 PM
Freezing film will allow you to use the film well past the original expiration date. When E200 is on its way out, I will be filling my freezer, and it will not just be me!
Posted 09 May 2008 - 02:36 AM
Posted 09 May 2008 - 08:07 AM
Will you be imaging at prime focus (without a lens)?
If so, what the scope's focal ratio?
Gobulars always do better with a stacked set of 2 or 3 shots. One quite short to show the center, and then longer exposures to capture the faint outer details. Then you stack them in photoshop. Otherwise you end up burning out the center.
DSO's need very long exposures, from 30 to 45 minutes at f/4. Much longer if you have a slower system.
Posted 02 June 2008 - 07:45 PM
Posted 03 June 2008 - 02:39 AM