Re: Field Flatterner w/out Focal Ratio changes

On Jan 31, 8:21 am, Bhogi <bh...@xxxxxxxx> wrote:
On 31 jan., 00:07, Paulie <jones.pau...@xxxxxxxxx> wrote:

Hi, This is my really last inquiry after hours net research... or
just
for confirmation especially as it pertains to your MTO 1000 and
optical physics.

When using a barlow/refractor.. increasing the distance to
the eyepiece increases the magnification. This needs
a corresponding decrease in the spacing between
the barlow and the objective lens.. so you move the
focuser inward. Now in an SCT where the secondary
acts like a barlow. If one moves the focus backward from
the rear. One has to make the mirrors (between primary
and secondary) move closer, right??

Yes.

Now when one is focusing an object just 2 meters away.
The mirrors have to be move closer too. Right? So all
catadioptrics mirrors are adjusted closer in most applications.

Wrong. You move the secondary out.

Now going tohttp://www.telescope-service.com/maksutovs/MTO/MTO.html

The MTO 1000 is supposed designed as f10 at a point maybe just 2"
from the rear. If one put a diagonal and move the focal point
backward,
one moves the mirrors closer (by removing the screw stop) and
the focal ratio changes to something like f/12, right?

In the above url. They said that using a 20mm plossl in the diagonal
(with screw stopper removed) would create magnification 1000/20=50X.
Since the f10 of the MTO 1000 is designed for one without diagonal.
The 20mm plossl plus star diagonal would produce something like
f12-13 and 60X magnification contrary to the web site data, right?

Yes.

Lastly. Is there another screw stopper to prevent one from moving the
corrector tube out of the main primary tube? I remembered someone
just removed the corrector tube out of the MTO 1000 10 years
ago to make me see the inside primary mirror. Does all MTO 1000
do this without any screw stopper? Have you tried removing
the corrector tube from the main primary tube at least once??

If I recall correctly, in rubinar there is only one focus stop, which
prevents the focus ring from turning full 360 degrees.
I removed the tube, cleaned the focus threads, put in a less sticky
lythium grease (which as I hear is a mistake but after a few years the
optics are still clean), and disassembled the secondary group with
both corrector plates. In short the lens was totaly disassembled,
greased and put together working impecably.
Without the focus stop you can focus to about 1m, before the tube is
unscrewed. The lens can then serve as a long distance microscope :)



Many thanks.

Paul- Hide quoted text -

- Show quoted text -

btw... knowing that you have completely disassembled the rubinar.
There is a description in the cloudynight review that mystify me.
It is described "The secondary mirror is affixed to the outermost
aperture lens. A set of two full aperture lenses is situated between
the secondary and primary".

I have never heard of a catadioptic with lens *between* the primary
and the secondary mirror. In SCT. There is no lens between them.
Do you know what is the function of each of the 2 lens in between the
primary and secondary mirrors of your rubinar? Note I know the
third lens is the corrector itself. I'm not talking of the corrector
but of the lens that lies between the mirrors which is described
above.

Also I need to know something. If the rubinar is designed for f/10
with 45.5.mm flange focus depth. I want to know how many times
is the diameter of the diffraction pattern of the airy disc compared
to the reference 1/4 wave at f/10 when the focus is moved further
back (becoming f/16) and the mirrors move closer (which can affect
the spherical aberrations). How do you calculate it. It's for purely
theoretical understand purpose because the eyes may not detect it
significant in practical usage. Thanks.

paul

.

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