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Collimating a jones bird reflector?

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#1 Orion64

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Posted 01 August 2010 - 06:22 AM

I recently put a new focusser onto my 8inch jones bird reflector. The problem is it is severely out of collimation and cannot get it back. I have spent many a hour on reading collimation for normal newtonian reflectors. I also have a collimating eyepiece, chessire eyepiece and orion laser mate as well as a center spotted primary.
Please I am losing hope of ever using this scope again. Any tips will do.

#2 Howie Glatter

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Posted 01 August 2010 - 10:03 AM

Collimate with the lens removed. Then install the lens as centered and square as you can get it.

#3 Orion64

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Posted 01 August 2010 - 10:17 AM

Okay I did this: Removed the lenses and collimated with 3 steps using chessire.
Then put back the lenses.
Still my collimation was out a bit, but better than before.
The tricky part is here: With the lense system you can actually see another reflection of the spider veins (from reflection of spider in primary on jones lenses). The trick is to get this second reflection over the first reflection. This should be done by iterating between first moving the secondary so that the two reflections overlap. Then by adjusting the primary so it is centered under the secondary. By now the two reflections have moved again. Now repeat.
Important is step one in collimation: Centering the 2ndary under the focusser!
This is much more difficult than to collimate normal newtonians but it can be done it seems...
In the end I got everything lined up and will see tonight how well my scope performs.

Any comments on my explanation??

#4 Howie Glatter

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Posted 01 August 2010 - 11:59 AM

>Any comments on my explanation??

Sounds good.
Just one thing - It's vanes, as in weather vanes, not as in varicose veins.

#5 cavefrog

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Posted 01 August 2010 - 07:11 PM

with a friends bird-jones, I not only had to remove the lens, but the lens holder as well. with just the lens removed, I could not see the edge of the secondary. so I removed everything from the end of the focuser tube, untill all that was left was the focuser tube itself. yeah had to reiterate between parts in and parts out, but finally got it.
good luck.

Theo

#6 Orion64

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Posted 01 August 2010 - 07:18 PM

Thanks Howie Glatter! English is only my second language but will remember...
So okay, I tested my collimation and it was perfect under 140X. This was the best my scope performed in years!
However, if you are thinking of buying a bird jones... DON'T!
Otherwise if you already own one...Good luck.
I am thinking about playing more with this and write an article about collimating a bird jones, as there arent many places the collimation of these telescoppes are discussed...

#7 avarakin

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Posted 02 August 2010 - 08:22 PM

Never heard of 8" Bird Jones scopes. Normally they are some junk scopes in 114-130mm range.

#8 dpwoos

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Posted 02 August 2010 - 09:38 PM

Makes me laugh when I think about folks complaining about collimating a plain old Newtonian! My dog used to do it for me before he recently died, and it never took him more than a couple of minutes with my Glatter laser collimator.

#9 deSitter

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Posted 03 August 2010 - 12:33 AM

Just like collimating a Newtonian, but must remove the corrector element. The resulting scope is extremely fast, so extremely sensitive to miscollimation. It may be f/6 but collimates like f/4. An additional difficulty is the small secondary, so that the drop/offset is a large fraction of the actual size of the secondary.

A "real" Jones-Bird can be a phenomenal scope. They are very good with certain kinds of eyepieces and have very little coma. I would imagine the larger Chinese JBs are at least realistic attempt at the design, as opposed to the "short tube" 4.5" reflectors one sees.

-drl

#10 Jon Isaacs

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Posted 03 August 2010 - 07:12 AM

Just like collimating a Newtonian, but must remove the corrector element. The resulting scope is extremely fast, so extremely sensitive to miscollimation. It may be f/6 but collimates like f/4. An additional difficulty is the small secondary, so that the drop/offset is a large fraction of the actual size of the secondary.

A "real" Jones-Bird can be a phenomenal scope. They are very good with certain kinds of eyepieces and have very little coma. I would imagine the larger Chinese JBs are at least realistic attempt at the design, as opposed to the "short tube" 4.5" reflectors one sees.

-drl


The one I had was not...

Baytronix 150/1400

I gave the mirror to someone who wanted a blank. He tested it and told me it was worse than 1 wave...

I did find a webpage that I have since lost discussing the development of the Jones-Bird with many examples, it's conclusion was that the design never was able to achieve it's promise. I am curious what Jones-Bird scopes you have viewed with that gave those phenomenal views.

Jon

#11 deSitter

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Posted 03 August 2010 - 08:50 AM

John, my knowledge of this design is completely theoretical. Rutten and Van Venrooij discuss it in their "Telescope and Eyepiece Combinations" section. Spot diagrams are given, which are very convincing.

A 1 wave mirror - that's pretty bad.

-drl

#12 Orion64

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Posted 06 August 2010 - 07:57 AM

I must say that after collimating my jones bird, I had a very good view through the scope. And NO coma over the entire fov.






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