
Miscellany
#51
Posted 28 November 2013 - 01:14 AM
But I did take out the element, cleaned it, and was able to confirm that its a plano convex lens. The only one I have ever seen that is coated on both sides, possibly multicoated.
Also, the cell it is in could only accept a thin lens, and from the shoulders of the threaded side you can't get a multi element lens that close to it on a threaded insert.
I wondered if it could be a microscope condenser stage, but you usually have a long handle on the iris for adjustment, and this only has a nub, no thread or means to attach. I've only seen uncoated, thick, condenser lenses in thermally conductive, "loose" cells.
So, yeah, I can't place it either.
#53
Posted 02 December 2013 - 12:58 AM
by Jeff Beish:
http://www.alpo-astr...sh/Cass_Equ.pdf
Classical Cassegrain design and optimizing existing telescopes.
And making sure its setup properly.
Robert
#54
Posted 10 December 2013 - 09:27 PM
"The effect a barlow has on the chromatic aberration of a achromatic lens".
I know our classic/vintage refractors do not produce much in the way of CA due mostly to the high focal ratio.
I do have a few in the f10-f12 range that do seem to have high amounts of CA. Even my Edmund 4"f15 can be forced to the point of color fringing.
I would like to see if a modern doublet or triplet barlow can possibly cancel out some of the CA. It probably depends a lot on the particular telescope, and not all will behave the same.
I've heard a prism star diagonal can also improve some scopes.
Robert
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#56
Posted 10 December 2013 - 11:27 PM
As far as prism star diagonals, they are my choice over mirror diagonals on all of my long focal length refractors. With regard to solar h-alpha with rear etalons, prism diagonals and telecentrics are a clear choice over mirror diagonals and barlows for the best image.
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#57
Posted 11 December 2013 - 12:21 AM
That makes perfect sense Terra. Probably no point experimenting with barlows.
I do remember something about star diagonals though. I might try various diagonal and eyepiece combinations.
I have a very nice Meade 310 80mmf10 made by Mizar and Hino Optical. I would sure like to reduce the CA in this otherwise super nice scope.
And if I could tame the CA in my Celestron 6"f8 I would have a superb big refractor. It already is a great scope as long as you stay away from the moon and planets, its fine for everything else.
Robert
#58
Posted 11 December 2013 - 08:23 AM

I don't have any 2 inch prisms so I can't say that with 2 inch eyepieces but it sure seems to hold true otherwise. My favorite is a Lumicon Japanese 1.25 inch from around 10 years ago. I also have a nice Zeiss 1.25 that is superb. But even the vintage 0.965" prisms I think are really quite good. You get great throughput with a prism. I've heard its even higher than with a dielectric.
Have you tried any of the color reduction filters to reduce CA? I have a Sirius minus Violet filter that does a decent job.
Terra :flower:
#59
Posted 11 December 2013 - 10:55 AM
I wish I could find the star diagonal articles discussing prism vs mirror and the prisms ability to improve some telescopes. It was quite lengthly and mainly about faster scopes prefer mirror diagonal and slower scopes are best with a prism.
This may be one. I'll put it here and we can read it later:
http://www.cloudynig...6224960/page...
Robert
#60
Posted 08 April 2014 - 03:24 PM

Average Annual Daytime Cloud Coverage

#61
Posted 08 April 2014 - 05:26 PM
We should think about radio astronomy, with modern technology maybe we could listen to the big bang.
Only problem is the dish needs to be rather large to have a reasonable resolution.
Oh well when it is clear the atmosphere is very clean.
Robert
#62
Posted 08 April 2014 - 06:12 PM
#63
Posted 08 April 2014 - 06:31 PM
Fortunately for us classic telescopists we never run out of telescope restoration and rebuilds when its cloudy.
#64
Posted 08 April 2014 - 08:08 PM
http://www.escooptics.com/
Some of our oldie stuff has ESCO cast into it or scribed on it and I thought it may have been Edmund Scientific Co. but in fact it is Esco Optics.
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#66
Posted 08 April 2014 - 08:27 PM
I've found that to be true, even though we have better grinding technology, and superior coatings today. I suppose someday Machines will be programmed with equivalent craftsmanship, discipline, and attention to detail...
While I'm thinking about it: My junk box of optical odds & ends apparently did not survive our last move. So, the Jaegers 60mm, a 4" Maksutov set, and at least a dozen small achromats and/or eyepiece components are in the landfill.
(And I call myself a pack rat!)
#67
Posted 08 April 2014 - 08:33 PM
An amazing find! (Guess I need to start browsing pawn shops.)
#68
Posted 08 April 2014 - 08:45 PM
I used to have a circuit when I was in grad school. Pawn shops were pretty good, as were thrift stores. There are too many thrift and resale places these days to do that."I picked up a Classic C5 at a pawn shop for $100"
An amazing find! (Guess I need to start browsing pawn shops.)
#69
Posted 09 April 2014 - 08:35 AM
Just found this while poking around. I might have been better off to have looked for it before moving under that grey patch in the upper left.
Average Annual Daytime Cloud Coverage
Well if you move to Sequim you would enjoy the lowest rainfall in the state, even if there are lots of cloudy days.
And hey, Robby Knievel lives there!
#70
Posted 09 April 2014 - 11:36 AM
But because the finder is on the left and I use my left eye, I can't use the finder without my face running into the scopes star diagonal and eyepiece.
Here is my solution.
Make a wood platform for the factory photo tripod fitting for a Telrad reflex finder. Flip the optical tube over and use my left hand for focusing.
If some of you have the same problem as me you may want to consider this option.
#72
Posted 09 April 2014 - 11:38 AM
They are relatively new in this area (the Pocono's) lots of fun. Also picked up a Celestron firstscope for $26. at a different pawn shop. Stand 1000ft away and that's what Saturn looks like."I picked up a Classic C5 at a pawn shop for $100"
An amazing find! (Guess I need to start browsing pawn shops.)

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#75
Posted 09 April 2014 - 12:12 PM