Re: Disassembling Rubinar 10/1000

On Mar 26, 4:22 pm, Bhogi <bh...@xxxxxxxx> wrote:
On 26 mar., 01:50, Winstone <winstonewar...@xxxxxxxxx> wrote:





On Mar 26, 8:28 am, Bhogi <bh...@xxxxxxxx> wrote:
On 26 mar., 00:35, Winstone <winstonewar...@xxxxxxxxx> wrote:

On Mar 26, 5:40 am, Bhogi <bh...@xxxxxxxx> wrote:
http://ejarm.com/m42to125diagonal.jpg
I made it from black delrin plastic. Your adapter is thinner I think,
I left 10mm of space to use the m6 screws. I use the inexpensive 1.25"
diagonal from surplusshed. I shortened the tube on the diagonal as
much as possible, because I wanted to use the lens with the field
flattener lens, otherwise I'm not sure I could focus to infinity. The
1000 rubinar is ok with all my eyepieces (surplusshed), but the 500 f/
5.6 can't focus to infinity with one eyepiece.

What 500 f/5.6 are you talking about?

http://www.rugift.com/photocameras/rubinar_500_lens.htm

I also ordered a lumicon 1" eyepiece extension (not yet received)
so that I can put any diagonal and it won't hit the rear field
flattener. Why did you cut your diagonal. You can just secure
the front 10mm of any diagonal without getting it all the way
inside that can hit the field flattener. Unless you want shorter
diagonal to avoid aberrations? Why have you compared
using normal diagonal and shortened diagonal? Is the
aberration of the normal diagonal significant? What other
issues or pro/con between using each of them?

You obviously haven't tested the lens with the diagonal yet. The lens
is designed for use with cameras that have 44mm flange distance.
That's not enough distance to mount any 1.25" diagonal. Without the
infinity stop you can focus past the infinity - increase the "flange
distance" - but not by very much. That's one reason to keep the
diagonal as close as possible.

For optimum quality. Why don't you use a diagonal that has the
same 44mm flange distance. Not possible? The reason I'm
using a 1" eyepiece extension is because I'm using a Televue
Everbright diagonal and i can't just cut the tube to focus it
closer.

A 1.25" diagonal needs some space + the eyepiece needs somespace, I'd
guess all in all a minimum of 60mm. Now if you have a long diagonal
tube this increases.
I think your diagonal tube is not very long so I think you won't have
any problems.

With your inexpensive surplusshed diagonal that
you can cut shorter. What is the estimated equivalent
flange distance closest you can get? If close to 44mm.
Then it means I don't even have to adjust the infinity stop
(except perhaps if I want closer focus)?

My guess about 60mm, maybe more. You definitely need to remove the
infinity stop.
Why don't you just try it with the unmodified lens? Just be careful
not to touch the field flattener.

Also to focus at closer like 1 meter and beyond infinity,
the adjustment of the screws of the aluminum ring is
the same, right. Or is there a separate adjustment if
one wants to focus closer and beyond infinity?

The adjustments you are talking about are just about the distance
scale, how the focusing collar is oriented. With the changed flange
distance I don't think the distance scale is acurate enough. I actualy
never use the distance scale.
All the lens does is move the front group of lenses relative to the
primary mirror. Other than that there is no optical adjustment
possible.

But there is a big difference. I mean normally one can't
adjust the front all the way to focus at 1 meter and less until
the front lens cell comes off. So is there something inside the
aluminum tube that stops it. So you mean by simply loosening
the 3 screws, the front cell itself can be unscrew all the way
from the second half or rear part? Also the two front lens are
contained in one cell?)?

This is last detail I need to know before I start disassembling
it and in the point of no return.

Win




Win

The other reason is, the lens is designed for 44mm distance. To focus
past this designed distance you move the secondary and full aprture
lenses towards the primary mirror which is not what the lens was
opticaly designed for.

Like I said my 500mm rubinar can't focus to infinity with all
eyepieces but 1000 fortunately can do it. But if the diagonal was 5mm
further, I'm not so sure...

I can't remove the rubber grip because it's stuck between
the body. See again picture at:

You must remove the grip to unscrew the tiny screws. It's thin and
comes off easily you just have to lift it a bit somehow. Putting it
back on is also easy.

How many mm distance from the nearest boundary are the screws
located? If I can't lift all of them up. I'd just cut a portion of it.

I'm not sure about that, but once you can remove the focusing collar
there's enough space to unscrew and remove the stop which is just a
small piece of a aluminium. The main obstacle you're facing is the
large bearing with the tripod thread. It has to go off, because you
can't slide the collar to the front of the lens, it's just a bit too
wide.

What I mean to say is. If I can't lift up the rubber grip (or
risk damaging the entire rubber grip). I'd just cut a hole
in the middle of it to access the 3 screws. What you
were saying was that once I lift up or cut the rubber
grip I can see 3 screws?

I don't see why you coouldn't do it. Just wedge a small screwdriver
under the grip, lift it gently all around and pull/slide it off. It's
not glued, it's not stiff and it's not very tight. No problem at all.
Just don't cut it.
Under the grip you'll see the screws yes. After you unscrew them slide
the loosened collar to the mount side and below you'll see the
infinity stop.

Beware, when you remove the infinity stop you can focus to about 1m,
nearer than that the front might come off and you'll have difficulty
putting it back correctly.

Why do you say I'd have difficulty putting it back "correctly"?
What's correctly and incorrectly? You mean it can change
the collimination?

because the lens' helicoid has 4, maybe 6 threads. If you don't mate
the correct threads the whole front will be turned differently. I'm
not sure this presents any problems, I'm just telling you.

Separate issue. Do you know how to adjust the mirror
holder in case there was astigmatism? And it is possible
to test for astigmatism at daytime by defocusing it?

The mirror holder can't be adjusted it has the mirror glued on it with
some silicone and it's simply screwed on. From the testing the lens
seems to be diffraction limited as is. My observations of diffraction
patterns confirm it's very good and doesn't need adjustments.
At daytime I just focused realy close on some specular highlights to
get pinpoints of light.

One thing you can do is to unscrew the mirror holder a bit to release
any tension from the mirror. To do this you have to remove a tiny
locking screw from the side of behind part and unscrew it completely
off together with the baffle. You'll need a spanner wrench to unscrew
the mirror holder if it's screwed on too tightly.

Oh. It was because I remembed something in cloudynights review
of the Rubinar which mentioned about astigmatism. It said
specifically:

"It is relatively easy to loosen the retaining ring which holds
the outermost full aperture lens to the scope (without
dissassembling the entire scope). By doing this, one can
then rotate the outermost full aperture lens relative to
the inner most full aperture lens. In the case of my scope
this has allowed me to "worsen" or "improve" the amount
of astigmatism in the system."

Do you know what he meant by "outermost full aperture
lens related to the inner most full aperture lens"? What
outermost and what innermost?

Here's how the rubinar looks:http://ejarm.com/rubinar.jpg
It has 2 full aperture lenses in the front. These are the correctors
for the primary mirror. The secondary mirror is a mangin mirror and is
screwed to the meniscus "outer most" lens.
You can also loosen the front retaining ring just to get rid of any
unwanted tension in these large lenses.

Thanks.

Win- Hide quoted text -

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Relevant Pages

  • Re: Disassembling Rubinar 10/1000
    ... flattener lens, otherwise I'm not sure I could focus to infinity. ... That's not enough distance to mount any 1.25" diagonal. ... the front cell itself can be unscrew all the way ...
    (sci.astro.amateur)
  • Re: Disassembling Rubinar 10/1000
    ... I left 10mm of space to use the m6 screws. ... flattener lens, otherwise I'm not sure I could focus to infinity. ... any tension from the mirror. ...
    (sci.astro.amateur)
  • Re: Disassembling Rubinar 10/1000
    ... I left 10mm of space to use the m6 screws. ... flattener lens, otherwise I'm not sure I could focus to infinity. ... That's not enough distance to mount any 1.25" diagonal. ...
    (sci.astro.amateur)
  • Re: Disassembling Rubinar 10/1000
    ... I left 10mm of space to use the m6 screws. ... flattener lens, otherwise I'm not sure I could focus to infinity. ... That's not enough distance to mount any 1.25" diagonal. ...
    (sci.astro.amateur)
  • Re: The length of the focal length?
    ... a lens system's physical length may be short than its focal length. ... that F effective equals F when u is at infinity. ... Object distance has no bearing. ...
    (rec.photo.digital.slr-systems)