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Re: [APML] 2 inch adapter and now focusers and such
Brian,
I know the feeling. What objective are you using for this scope? And, if
you don't mind my asking, what facilities do you have access to to make the
various "parts and pieces". I went through a lot of the same decision
processes that you are doing now when I built my first refractor. It was
well worth it. It has become my most used astrograph to date and can take
much better astrophotos that I can - even if it is a "lowly achromat".
I second Don's recommendation for a larger than 2" focuser if possible.
Don't forget - you may want to try medium format sometime in the future. I
did not find a large format commercial focuser at a reasonable price when I
was building my scope but there are more choices out there now.
I don,t know where you are located. If I can be of help drop me a line
"off-list".
Clay
----- Original Message -----
From: "Brian Larmay" <astrobri@ameritech.net>
To: "Discussion of Film Astrophotography" <astro-photo@seds.org>
Sent: Tuesday, March 04, 2003 9:50 PM
Subject: Re: [APML] 2 inch adapter and now focusers and such
> Hi Clay,
>
> Im starting to get picky on how Im building this thing now..
> Im getting the itch to make this scope into superscope, but I need to
start
> from scratch starting with the tubeing first so that I can adapt a decent
> focuser...maybe a megrez.
> I hear those are nice little focusers.
> I opened the B shutter with the film door open to see how much the frame
> gets cut between 1.25-2" and theres a huge differance.
>
> This is turning into a little bit of fun here:)
>
> I have 2 more main objectives to work with so the last two Ill be thinking
> of a bigger game plan.
> Hopefully Ill have this project done in time for summer.
>
> Thanks again,
> Bian
>
>
>
> > Brian,
> >
> > The length of the focus tube can hav an effect on vignetting and
exposure
> IF
> > it blocks part of the objective (forming an effective apature mask).
When
> I
> > built my 4" f6 refractor I wanted it to focus both a camera and my range
> of
> > eyepieces. This dictated a rather long draw tube. I used a 2" focuser
> for
> > a while but I eventually built a 3" crayford focuser. In this I have a
> > drawtube with a large inside diameter. I bring this to 2" at the end
> only.
> > This has worked out well. I have some pictures of the focuser parts and
a
> > description of the build process here:
> > http://www.gatecom.com/~ckessler/ATM%20Focuser.htm
> >
> > The refractor kit is described here:
> > http://www.gatecom.com/~ckessler/bw_optik_4.htm
> >
> > I hope this helps
> >
> > Clay Kessler
> >
> > ----- Original Message -----
> > From: "Brian Larmay" <astrobri@ameritech.net>
> > To: "Discussion of Film Astrophotography" <astro-photo@seds.org>
> > Sent: Tuesday, March 04, 2003 3:39 PM
> > Subject: Re: [APML] 2 inch camera adapter question
> >
> >
> > > 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
> > > >
> > > >
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