Re: [APML] Medium format cameras (was:Tak. FSQ-106 for mediumformatfilm?)

["Steve Walters" <s-walters@comcast.net>]

Alan,

I've used a few different systems but now have the Mitsuboshi 6x9 format. I
use an off axis guider with this because I got tired of chasing down flexure
in guidescopes.

I started with a Pentax 6x7. Some points on these is that the old cameras
can have some problems with film advance. There is a trick to advancing the
film that you have to know about, it is to never allow slack at the lever
when advancing. If you do, it will stop mid frame. But if you steadily
advance in a single move, it does fine. Also, most older 6x7 do not have
mirror lock up.

The Mitsuboshi system is expensive but very well built. It has a vacuum film
plate to keep the film flat. This can be a problem with other systems,
especially if you shoot 120 format film. 220 format usually stays flatter
since there is no paper backing to bunch up under the film. The Mitsuboshi
also has a purge fitting. It took me some time to get everything right on my
BRC250 due to the fixed spacing needed between the field lens and the film
plane. But once that was set, it works very well. Hutech sells this system
including a knife edge focuser.

For any medium format system, I strongly recommend a knife edge focuser.
After several years of trying other arrangments and finally switching to KE,
I've learned that it is the only way to accurately focus in a repeatable
fashion. You can also get KE from Stilletto for some medium format cameras.

Another thing to remember is that you will need to do a better polar
alignment to avoid seeing field rotation with medium format due to the
larger frame size. This means spending more time drift aligning, not a big
deal, but until you learn to get it right you'll have trails.

One last point, temperature and humidity variations can cause substantial
changes in the film's size. This is because these effects operate as a
percentage of the film size. With larger film, you see a larger change in
length. In my case, I use a nitrogen purge to keep the film dry and I have a
temperature controller that tries to keep the camera at a constant
temperature during exposures. Not everyone seems to need this but on my 6x9
format, I can see some trailing without these controls. This is one reason
why observatories used glass plates for photography.

Also, don't forget about scanners and printing for these larger formats. A
good med format scanner will be about $2K. Prints need to be larger in order
to show the same detail you're used to seeing. I regularly print 8"x12"
prints of my images and make 20"x30" of the ones I really like. All your
costs will go up for scanning/printing because of the larger format.

Anyway, it is not as simple as just sticking a bigger camera on your OTA.
There are a few challenges and substantially higher costs.

Take the plunge, but take a deep breath......

Steve...

----- Original Message ----- 
From: "Alan Voetsch" <critter12952@yahoo.com>
To: "Discussion of Film Astrophotography" <astro-photo@seds.org>
Sent: Saturday, November 08, 2003 3:25 PM
Subject: [APML] Medium format cameras (was:Tak. FSQ-106 for medium
formatfilm?)


> Hey all,
>
> The discussion between Dean and Kirk has gotten me thinking about
> moving up to a medium format camera. Actually I've thought about it
> many times, but I only now have an instrument that can utilize MF. The
> Tak FS-102 will be able to handle that format and once I'm comfortable
> with it and the new G-11 with Gemini, I would consider trying a bigger
> format camera.
>
> What I would like to know is if anyone has a tutorial, or such on their
> website regarding this. Or barring that, can anyone give any pointers
> on what to look for in such a camera. The reason I ask is that I saw
> one advertised on astromart last week that had a purge system already
> installed. This camera had been used on a 102 and I assume that the
> user knew what he was doing. My assumption has always been that a
> camera body is basically just a film holder. I'll qualify that by
> saying that I would probably also use it for piggyback shots.
>
> All things being equal, is the camera manufacturer important here? Are
> there certain things to look for? To avoid? Is a Pentax 67 the wise
> choice in the long run?
>
> What I really want is to be pushed in the right direction so when I do
> have the cash for such a purchase, I hace done my homework and can jump
> on it then without screwing up. At that point, I would like to know of
> any adapters, etc... that would be necessary. Any guidance would be
> much appreciated.
>
> Thanks,
> Alan
>
>
> __________________________________
> Do you Yahoo!?
> Protect your identity with Yahoo! Mail AddressGuard
> http://antispam.yahoo.com/whatsnewfree
> _______________________________________________
> Astro-Photo mailing list
> Astro-Photo@seds.org
> http://seds.org/mailman/listinfo/astro-photo

_______________________________________________
Astro-Photo mailing list
Astro-Photo@seds.org
http://seds.org/mailman/listinfo/astro-photo