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#51 wfj

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Posted 28 November 2013 - 01:14 AM

I hadn't thought of an enlarger lens, good point on that. I think they have click aperture stop sizes like camera lenses if I remember correctly.

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.

#52 fjs

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Posted 28 November 2013 - 02:24 PM

Anybody only stay on classics forum?

Comic Relief

#53 clamchip

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Posted 02 December 2013 - 12:58 AM

Cassegrain Telescopes for Amateurs
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 clamchip

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Posted 10 December 2013 - 09:27 PM

When the weather warms up I think a fun research project is going to be:

"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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#55 mikey cee

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Posted 10 December 2013 - 11:15 PM

My old Jaegers 38mm Erfle fits my 2" adapter perfectly also! :jump: Mike

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#56 terraclarke

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Posted 10 December 2013 - 11:27 PM

Robert, as I understand it, the chromatic aberration is a function of the curvature of the primary achromat which is also determining the focal ratio; however adding a negative secondary to produce the effect of a longer focal primary by narrowing the light cone does not change the original factor (the primary's curvature) and reduce the CA. The same is true for a telecentric which renders the light rays almost parallel. I am sure I am not explaining this as clearly as our resident optical expert Dave G could, but I'm pretty sure a Barlow or even a more expensive telecentric like a Powermate will not do what you are hoping for. Otherwise, everyone would be buying cheap, convenient short high CA achromats and turning them into semi-apos with an inexpensive barlows.

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.

#57 clamchip

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Posted 11 December 2013 - 12:21 AM

I'd sure like to be at those controls Mike!

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 terraclarke

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Posted 11 December 2013 - 08:23 AM

The good older coated Japanese prism diagonals are wonderful Robert. I think the images are sharpens, brighter, and more contrasty. I bet you'll detect a difference when you make your comparison too. :)

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 clamchip

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Posted 11 December 2013 - 10:55 AM

I have a minus V filter but didn't care much for the yellowing. But I was reading last night that you can add a light blue filter to the minus V to help with the yellow so I would like to try it.

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 fjs

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Posted 08 April 2014 - 03:24 PM

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. :scratchhead:

Average Annual Daytime Cloud Coverage :cloudy:

#61 clamchip

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Posted 08 April 2014 - 05:26 PM

I'm in the gray too.
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 fjs

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Posted 08 April 2014 - 06:12 PM

Robert, I knew what I was getting into when I moved out here 18yrs ago. I've only just resumed my interest in astronomy last year after a long layoff. So, my impression might be wrong. Until last year, I thought a typical year was six months of no sun followed by six months of no clouds. Was last year unusual, or did I just not notice all of the summertime cloud cover like we had?

#63 clamchip

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Posted 08 April 2014 - 06:31 PM

I don't remember last year being better or worse. I can usually remember if a summer is dramatically different than normal.
Fortunately for us classic telescopists we never run out of telescope restoration and rebuilds when its cloudy.

#64 clamchip

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Posted 08 April 2014 - 08:08 PM

I'm going to put this here:
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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#65 clamchip

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Posted 08 April 2014 - 08:09 PM

Esco Optics 6 inch cell:

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#66 Bomber Bob

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Posted 08 April 2014 - 08:27 PM

"The good older coated Japanese prism diagonals are wonderful Robert."

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 Bomber Bob

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Posted 08 April 2014 - 08:33 PM

"I picked up a Classic C5 at a pawn shop for $100"

An amazing find! (Guess I need to start browsing pawn shops.)

#68 DocFinance

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Posted 08 April 2014 - 08:45 PM

"I picked up a Classic C5 at a pawn shop for $100"

An amazing find! (Guess I need to start browsing pawn shops.)

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.

#69 RacerX69

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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. :scratchhead:

Average Annual Daytime Cloud Coverage :cloudy:


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 clamchip

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Posted 09 April 2014 - 11:36 AM

Celestron's C5 finder is on the left. I don't have very good vision in my right eye so I use my left eye at the finder.
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.

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#71 clamchip

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Posted 09 April 2014 - 11:37 AM

Side view

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#72 A6Q6

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Posted 09 April 2014 - 11:38 AM

"I picked up a Classic C5 at a pawn shop for $100"

An amazing find! (Guess I need to start browsing pawn shops.)

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. :lol:

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#73 A6Q6

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Posted 09 April 2014 - 11:39 AM

2

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#74 A6Q6

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Posted 09 April 2014 - 11:40 AM

3 a $26 toy :scratchhead:

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#75 Bob Myler

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Posted 09 April 2014 - 12:12 PM

Attach a miniature solar array to each side and you got yourself a working model of the Hubble!


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