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80MM Brandon can't focus all eyepieces

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#1 kur3tking

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Posted 24 July 2020 - 09:08 PM

Attached is a photo of my 80MM Brandon refactor. This may be the " birding" scope. Under the night sky this scope only seems able to come to  focus with low power eyepieces. I successfully observed the comet with a 40mm and 32mm Plossl. When trying  higher power eyepieces such as a 15MM and 12MM, there was not enough focuser in travel. Is this a problem that some have overcome? What would be a solution to allow a wide range of eyepieces to be used?

Thank you for your assistance!

 

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  • 80mm brandon.JPG


#2 Augustus

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Posted 24 July 2020 - 09:36 PM

That's not an original focuser, and it is probably longer than the stock one. You're also using a 2" diagonal which reduces the amount of back focus you have.


Edited by Augustus, 24 July 2020 - 09:36 PM.


#3 Thomas Marshall

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Posted 24 July 2020 - 09:41 PM

I own the "Master Birder" version. I bought it without Vernonscope Amici, and it has single speed focuser. Using regular 1 1/4" or 2" diagonal, I have no trouble using wide variety of eyepieces. With your set up, you probably need to introduce a 'Barlow' to allow higher power eyepieces. I have used combo's up to 180X with this scope. I've observed 'Moon Shadow Transit's" on Jupiter, and seen the Polar cap on Mars, and Cassini's division in Saturns Rings, with this scope, and I love the "Triplet" views of Open Cluster's and M31 and other goodies like 'Alberio'. Rarely do I use it for Birding, - but it's a great little "Grab and Go" scope. Just minutes before seeing your post, I had been searching for the kind of quick release you have mounted on yours, - to go with my newly acquired Bogen 3063 Fluid Head. 



#4 RichA

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Posted 25 July 2020 - 01:03 AM

Attached is a photo of my 80MM Brandon refactor. This may be the " birding" scope. Under the night sky this scope only seems able to come to  focus with low power eyepieces. I successfully observed the comet with a 40mm and 32mm Plossl. When trying  higher power eyepieces such as a 15MM and 12MM, there was not enough focuser in travel. Is this a problem that some have overcome? What would be a solution to allow a wide range of eyepieces to be used?

Thank you for your assistance!

Isn't the light-path through those erecting diagonals longer than a regular 2" diagonal?


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#5 Rich V.

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Posted 25 July 2020 - 10:58 AM

Isn't the light-path through those erecting diagonals longer than a regular 2" diagonal?

Yes, those Schmidt roof 45° correct image prisms have four internal reflections so the light crosses through the prism multiple times.  A 1-1/4" version vs a 2" would help a lot, I suspect.  Image quality at higher mags is always suspect because of spiking off of the roof line that bisects the light path, just like a 90° Amici prism.

 

Giving up the correct image and using a standard 90° diagonal would be the best option for all eyepieces to come to focus.

 

Rich


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#6 kur3tking

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Posted 25 July 2020 - 04:46 PM

Thanks all for that informative discussion! Can you please recommend a quality brand 90 degree diagonal to use? Looking to acquire one quickly. Thanks!



#7 Thomas Marshall

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Posted 25 July 2020 - 05:27 PM

There are many, - but I would buy a 2" for sure. They almost always come with a 1 1/4" insert, for dual purpose. My new AT2" Dialectric @ $120.00 provides excellent resolution in all my scopes. 



#8 kur3tking

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Posted 25 July 2020 - 07:36 PM

Thanks for the suggestion on the 2” AT. I like the price and dialectic coating. The choice of BK7 for the mirror substrate is a little odd since BK7 has the same coefficient of expansion as plate glass. I ordered the carbon fiber version.


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#9 Thomas Marshall

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Posted 30 July 2020 - 06:06 PM

I took my Master Birder out last night for grab and go looks at Jupiter/Saturn/ and moon, and to test out how it does with my new sturdy Monopod and Bogen Manfrotto head. A 4mm Stellarvue 82* was pushing it at approx. 115X, at least on Jupiter. On Saturn and the moon it held up good. Put in my Stellarview binoviewer also, with 3xBarlow and 26mm eyepieces, and it held good, - but with 2x barlow there was not enough "In" focus room. Best views were with MK IV 8-24 zoom coupled with 2x barlow. Low altitude of planets was a definite factor, but of course the BIG problem was simply that a 'Monopod' is just not the right component for any Higher Power use. For nights of no moon and dark sky, when I want quick easy access to star fields/open clusters/large galaxies(M31) etc. at powers up to maybe 60x, - this should be an excellent set-up. Of course for best looks at planet etc. I go with my 4" ED refractor, or C8. Your set up reminded me of my focus issue with this birder scope, - 'fine focus' is not easy. So today I rigged up a 2 1/2" long "L" allen wrench, painted the end white for visibility, and used a 'coupler' to attach it to the focuser rod, replacing 1 of the knobs. This is going to make 'fine focus' adjustments easy. Can't wait to try it out in the dark. For a little birder scope, this thing amazes me, - but then again, I got the stripped down version back in the 90's, and even that was $650.00 I believe, so it should be a good scope. I also now have a 2" AT diagonal, and a couple of 2" 70* eyepieces that are fun with this scope.   Another great feature on this scope is the "close focus", it's got to be less than 10ft, so close ups on bushes/insects etc. is easy also.


Edited by Thomas Marshall, 30 July 2020 - 07:24 PM.



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