Re: [APML] 2 inch camera adapter question

["Brian Larmay" <astrobri@ameritech.net>]

Thanks Frank,

Does the length of focus, such as the focusing barrel/tube have impact on
vignette or how long to expose for also?

or....

Should I make the main barrel of the refractor tube as close as possibe to
prime focus, so I dont have to have a long focusing barrel?

This is hard to explain because Im making this refractor from scratch and
Ive never built one before.
I should really be going to ATM, but being that this scope is photographic
in nature, I will ask here.

Thanks,
Brian



----- Original Message -----
From: "Frank Parrotta (Navy Yard)" <FParrotta@TSC.COM>
To: "Discussion of Film Astrophotography" <astro-photo@seds.org>
Sent: Tuesday, March 04, 2003 10:09 AM
Subject: RE: [APML] 2 inch camera adapter question


> Brian,
>
> As John has said, you really can't use the 1.25" if you want to illuminate
> as much of the 35mm frame as you can.  However, you're still not home
free.
> The camera T-ring will also vignette the frame as well - the amount
> depending on the focal ratio.  I find that the corners get pretty dark but
> the central core of the frame is usable with some vignetting removal
> processing.  If you want to get an idea of just how much light falloff
> you'll have to content with, set up your scope with the camera attached
and
> aim it at an evenly illuminated source (e.g., blue sky, white painted
wall,
> etc.).  Set the shutter to "B" and open the camera back.  Fire the shutter
> and look through the camera back opening (where the film would be) and
> notice the illuminated circle produced by the objective.  Move your eye
> around to the frame's edges and corners - the amount of the illuminated
> circle that is obscured at each location will be proportional to the
amount
> of vignetting you will get at those locations.  Hope this helps.
>
> Frank
>
> -----Original Message-----
> From: Brian Larmay [mailto:astrobri@ameritech.net]
> Sent: Sunday, March 02, 2003 3:40 PM
> To: astro-photo@seds.org
> Subject: [APML] 2 inch camera adapter question
>
>
> Hi!
>
> What are the advantages photographically of a 2 inch camera adapter over a
> 1.25.
>
> Thanks,
> Brian
>
>
> My Photography
> Nature: http://www.astrobri.com/nature_photography.htm
> Astrophotography: http://www.astrobri.com/astrophotography_ind.htm
> Storm chasing photography:
> http://www.astrobri.com/weather_pictures_2002_season.htm
> Northern Lights: http://www.astrobri.com/northern_lights.htm
> Miscellaneous: http://www.astrobri.com/miscellaneous.htm
>
>
> ---
> Outgoing mail is certified Virus Free.
> Checked by AVG anti-virus system (http://www.grisoft.com).
> Version: 6.0.456 / Virus Database: 256 - Release Date: 2/18/03
>
> _______________________________________________
> 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


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.456 / Virus Database: 256 - Release Date: 2/18/03

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