REDUCER-CORRECTOR
Kevin Parker
Hi all,
I am considering getting a focal reducer-corrector. I have read that it
offers wider views at lower powers, but is that it. I really need some
opinions, as the description I have read is not all that clear.
BTW, I have a Celestron Celestar-8.
Thanks for the input.
Sincerely,
Kevin
Forget the edge, live on the Event Horizon!!
>>Birds, fishing, crafts and astronomy!
>>www.geocities.com/Heartland/Meadows/6830. Tks. KP
Todd Gross
In article <6l50fg$8kh$1...@newsd-154.iap.bryant.webtv.net> ma...@webtv.net (Kevin Parker) writes:
>From: ma...@webtv.net (Kevin Parker)
>Subject: REDUCER-CORRECTOR
>Date: Wed, 3 Jun 1998 22:23:44 -0400
>Hi all,
>I am considering getting a focal reducer-corrector. I have read that it
>offers wider views at lower powers, but is that it. I really need some
>opinions, as the description I have read is not all that clear.
>BTW, I have a Celestron Celestar-8.
>Thanks for the input.
works with eps up to around 35mm (1.25" eps) and eps up to 27mm wide field.
Not particularly sharp views (but low power is not particularly sharp period
in the SCT, not sure why) but when used with let's say a 22mm Panoptic, it
effectively works like a 35mm Panoptic, so you don't ahve to go the 2" route.
The best use for it.. is for photography, as it shortens exposure time and
widens the field
William E Byrd
Todd,
A question for you and the group-
Todd Gross wrote:
<snip of Kevin Parker's question about reducers for SCTs)
> works with eps up to around 35mm (1.25" eps) and eps up to 27mm wide field.
> Not particularly sharp views (but low power is not particularly sharp period
> in the SCT, not sure why) but when used with let's say a 22mm Panoptic, it
> effectively works like a 35mm Panoptic, so you don't ahve to go the 2" route.
>
> The best use for it.. is for photography, as it shortens exposure time and
> widens the field
Thought I'd jump in here with another question about reducers: Is there
a reducer for *visual* use (I don't have a mount anywhere near good
enough for photography through the scope) on a 5" f/8 Brandon (2"
drawtube)? I had an early 5" f/6 AP and I miss the wider views of the
summer MW that it gave. Could I approximate those views with a reducer
and what would be the image quality when using a reducer on this type of
refractor? Anybody done this or am I on the wrong track here?
TIA,
Bill Byrd we...@flash.net San Antonio, Texas
Todd Gross
>Thought I'd jump in here with another question about reducers: Is there
>a reducer for *visual* use (I don't have a mount anywhere near good
>enough for photography through the scope) on a 5" f/8 Brandon (2"
>drawtube)? I had an early 5" f/6 AP and I miss the wider views of the
>summer MW that it gave. Could I approximate those views with a reducer
>and what would be the image quality when using a reducer on this type of
>refractor? Anybody done this or am I on the wrong track here?
not sure.. you probably could adapt one, but you would most likely run out of
in-focus in the diagonal position
Phil Harrington
William E Byrd wrote:
> Thought I'd jump in here with another question about reducers: Is there
> a reducer for *visual* use (I don't have a mount anywhere near good
> enough for photography through the scope) on a 5" f/8 Brandon (2"
> drawtube)? I had an early 5" f/6 AP and I miss the wider views of the
> summer MW that it gave. Could I approximate those views with a reducer
> and what would be the image quality when using a reducer on this type of
> refractor? Anybody done this or am I on the wrong track here?
Bill,
PMFJI, but to my knowledge, there are no focal reducers made
specifically for refractors. I've not heard of anyone trying an SCT
reducer-corrector in a refractor, but it might be an interesting
experiment.
Personally, I'd recommend that you size your eyepiece choice based on
the desired end result, rather than rely on a focal reducer.
FWIW,
Phil
--
***********************
Phil Harrington
Go ahead...make my day! Visit the Star Ware Home Page
http://ourworld.compuserve.com/homepages/pharrington
RMOLLISE
>works with eps up to around 35mm (1.25" eps) and eps up to 27mm wide field.
>Not particularly sharp views (but low power is not particularly sharp period
>in the SCT, not sure why) but when used with let's say a 22mm Panoptic, it
>effectively works like a 35mm Panoptic, so you don't ahve to go the 2" route.
HI Todd:
I'm a little surprised. In my (Ulima) C8, low power views are razor shart
without--and with--the Celestron R/C. In fact, in my scope and most of the
other SCTs I've used one with, it's been my impression that the RC _improved_
edge of field sharpness at least! Very good on photography use, though. I
wouldn't dream of taking a deep sky photo through an f10 SCT without one!
Peace,
Rod Mollise
Mobile Astronomical Society
http://members.aol.com/RMOLLISE/index.html
The Home of _From City Lights to Deep Space_:
The Urban Observer's Guide to the Deep Sky
*********************************************************
Todd Gross
>PMFJI, but to my knowledge, there are no focal reducers made
>specifically for refractors. I've not heard of anyone trying an SCT
>reducer-corrector in a refractor, but it might be an interesting
>experiment.
it's done all the time , was done on my vixen 90mm by Scotte Cooke
(of Stabilite fame.. and Phil,if you dont' know what Stabilite is, find out
fast)
re Home Page
>http://ourworld.compuserve.com/homepages/pharrington
Todd Gross
>I'm a little surprised. In my (Ulima) C8, low power views are razor shart
>without--and with--the Celestron R/C. In fact, in my scope and most of the
>other SCTs I've used one with, it's been my impression that the RC _improved_
>edge of field sharpness at least! Very good on photography use, though. I
>wouldn't dream of taking a deep sky photo through an f10 SCT without one!
if you compare on-axis a 32mm Televue plossl with reducer-corrector, to a
similar size field in a 5" refractor let's say.. you might very well sell the
SCT first chance you have. You can't really tell until you compare it to what
the wide field *should* look like. Try it on the moon at a star party, and
report back!
Erwin van der Velden
A focal reducer is certainly usable visually for a Celestar 8, only you have
to keep in mind that the distance of the eyepiece shouldn't be too far from
the reducer, because otherwise the exit pupil will only contain a part of
the front aperature, resulting in lower brightness (you use only a smaller
aperature) and lower contrast (obstruction is relativily bigger in the exit
pupil). You can check this by projecting the exit pupil on a transparent
plane (I use a ocular dust cap) and measuring the size of the obstruction in
the exit pupil relativily against the size of the exit pupil. When the value
is equal to the relative diameter obstruction of the Celestar 8 (34%), the
ocular is not too far away from the reducer. The further away the ocular is
away from the reducer, the lower the resulting power will be. This can be a
problem when using a prisma or mirror. I use a 40mm Celestron Plössl in
combination with an intes prisma with a screw connection onto a Celestron
6.3/10 reducer, which gives a 35% obstruction in the exit pupil, a power of
31x and an true field of 1,35 degrees.
George Normandin
RMOLLISE <rmol...@aol.com> wrote
> >works with eps up to around 35mm (1.25" eps) and eps up to 27mm wide
field.
> >Not particularly sharp views (but low power is not particularly sharp
period
> >in the SCT, not sure why) but when used with let's say a 22mm Panoptic,
it
> >effectively works like a 35mm Panoptic, so you don't ahve to go the 2"
route.
>
> I'm a little surprised. In my (Ulima) C8, low power views are razor shart
> without--and with--the Celestron R/C. In fact, in my scope and most of
the
> other SCTs I've used one with, it's been my impression that the RC
_improved_
> edge of field sharpness at least! Very good on photography use, though. I
> wouldn't dream of taking a deep sky photo through an f10 SCT without one!
>
Rod,
None of what you say is too surprising considering that the lens is
designed to reduce the curvature of the image plane that you get with an
SCT. However, with a refractor, I would bet that the Celestron C-R lens
would take a flat image plane and curve it!! The best bet would be to just
make your own focal reducer from something like a 50mm binocular objective.
As you point out, these lenses are needed for SCT photography. One reason:
a SCT focuses by moving the primary, and this also changes the effective
focal length and focal ratio. After you crank the focus to bring the image
out to a 35mm camera a "F/10" SCT is more like a F/12.
However, for visual use, on lower F-ratio scopes, I don't understand why
someone would want to add more chromatic aberration from another lens, and
to cut the light by 4 to 7 percent.
George Normandin