RE: [APML]: astrophoto questions

[Mike Thenhaus <MikeT@7thlevel.com>]

Jim,

Here are some tips:

(1) Faster film will reduce the exposure times but increase the grain.
I'm
not sure what you would like to produce, but if you want really good
astrophotos you need to invest some money in a good telescope and
accessories.

(2) The exposure times for a tripod mounted camera rely upon the
film speed and the focal length of the lenses used. The wider the
field, i.e. the shorter the focal length (24-70mm), the longer you
can expose the film without any trailing. The narrower the field,
i.e. the longer the focal length (70-500mm) the exposure times
are reduced drastically.

(3) The Meade telescope may be great for observing, but since it
is a reflector, you fail to mention the focal length of the scope, I 
assume it is f/4.5 to f/6, you probably require more back focus
than the scope can give you. If you want to use a telescope to
take prime focus photos you need substantial back focus. I
would recommend either a Schimdt-Cassegrain or a ED or
Flourite Refractor for prime focus photos.

(4) You can use zoom lenses that have good color correction for
"close-up" astro-photos. The problem with most commercial lenses
made for daylight photos is that they are not color corrected for
chromatic aberrations. You can reduce the aberration by using
a Wratten type filter for your lenses, either a 3 or 4 Wratten yellow
filter will reduce the chromatic aberrations but they will also reduce
the light gathering capability of the lenses. This will cause you to
have to "guide" the exposures over time to get a good exposure.

I recommend that you invest in a book on beginning astro-
photography like Terrence Dickinson and Jack Newton's
new book Splendors of the Universe, a practical guide to
photographing the night sky. This can be found at local
book stores or ordered from any book dealer.

Michael "The Edge" Thenhaus
miket@7thlevel.com
(972) 498-8114


> ----------
> From:         Jim Fedina[SMTP:jfedina@sbsusa.com]
> Sent:         Thursday, February 19, 1998 10:01 AM
> To:   astro-photo@nightsky.com
> Subject:      [APML]: astrophoto questions
> 
> 
> I have an older SLR that has the bulb setting on it and two weeks ago
> I
> figured I'd try astrophotography. I had a roll of 1000 speed Kodak
> film
> in it and went outside on a clear night. The moon was almost full so
> there was a lot of light pollution. I took a couple of shots with it
> on
> a
> 
> tripod and got some good shots of Orion. The moon made the picture a
> little light but there was definately more stars on the picture than
> what I could see with my eyes. There was also some color. The Orion
> Nebulae had it's reddish tinge to it and Betelguese had it's
> yellow/orange. I will send the photo to anyone interested in giving
> comments about it.
> The questions that I want to ask are:
> 1. Would a faster film (1600 or greater) produce a better picture?
> 2. If faster film, how long to make the exposure without star trails?
> (the picture taken was 20 seconds).
> 3. I have a Meade 4.5" model 114EQ-D reflector and would like to hook
> a
> camera up to
> it. Orion Telescope Center sells a camera adapter and T-ring for my
> camera, but I'm not sure if my scope can handle the added weight.
> Would
> love to have closer shots of the Orion Nebulae and Betelguese and
> various other objects.
> 4. If the telescope can't handle the weight, can zoom lenses be used?
> I
> have an 80-200mm adjustable lens and also a 500mm bug lens (my
> nickname
> for it). If they can be used, would the same exposure time be used?
> 
> Any help on these matters would be great.
> 
> Thanks,
> Jim Fedina
>