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Re: [APML] 2 inch adapter and now focusers and such
Thanks George!
Speaking of abnormal glass, if I were to grab a lens from somewhere and
wanted it coated, where would I have to send it to to have that done?
Does Astrophysics deal in anything like that?
Is one able to buy an Objective just by itself from there?
What are the major differances in lets say an Vixen flourite over an
Astrophysics flourite?.... Glass? The workers? Testing?
Thanks,
Brian
----- Original Message -----
From: "George Anderson" <georgea@cam.org>
To: "Discussion of Film Astrophotography" <astro-photo@seds.org>
Sent: Wednesday, March 05, 2003 9:31 PM
Subject: Re: [APML] 2 inch adapter and now focusers and such
> Hi Brian
>
> What you have is an achromat, the number of elements does not determine
> APO vs Achro. An apochromatic lens uses abnormal glass (eg flourite) for
> one of the elements so that all colours fall into focus on the same
> plane.
> The 4 element copy lens is sort of like a very large Kellner eyepiece,
> two identical achromats placed back to back.
> To Roland and the others, please correct any misleading information
> above.
>
> George Anderson
> Montreal Canada
>
> Clear skies and good health
>
> Brian Larmay wrote:
> >
> > Hi Clay,
> >
> > Its just a 280mm f 1:4.5 tominon copy lens, which appears to be a four
> > element objective with a stop in the middle.
> > I read somewhere and found only one bit of literature that it is a six
> > element, but I doubt that from what I can see.
> > Being a four element, wouldnt that make this an apochromatic instead of
> > achromatic?
> >
> > I know its just a copy lens, but hey, why not<g>!
> >
> > As far as facilities are concerned, notta..Im at the mercy of a very
limited
> > budget right now, and I have access to nothing.
> >
> > So as far as the 2" focuser...
> >
> > I went to ace yesterday and brought my t ring with so I could find some
thin
> > metal tubing to thread to it but with no availe..
> > I even went as far as...Hey...I can try to weld or solder this thing to
a
> > makeshift drawtube over the whole T-ring itself so I get no
> > obstruction...again..lol.
> > By that time my wheels were turning too fast and I was getting ahead of
> > myself without draw plans...I need to make one of these....probably
going to
> > end up with a few of them.
> >
> > Well my brain is on overload due to no sleep last night so Im going to
give
> > it a rest for a few hours
> >
> > Thanks for your support Clay, Im sure I'll have more questions and Ill
> > contact you off list.
> >
> > Thanks again,
> > Brian
> >
> > > 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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