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Edmund Palomar Jr

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#1 xnasageek

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Posted 07 January 2019 - 11:05 PM

Hi Cloudy Nighters! I've been lurking for a few weeks and just signed up for an account.

 

My dad recently gave me the 4 1/4" Edmund Newtonian (white tube) that he bought as a teenager. My goal is to bring it to a "useable" state while staying as true as possible to it's original form.

 

This is the first telescope I've owned so I'm sort of a newbie at this, but I used to run collage observatory open houses with a Celestron 16" SCM back in the early 90's so it is all a bit familiar at the same time. I'm also getting involved in our local astronomy club and may eventually bring the Edmund to star parties for the sheer "look at what you can do with this antque" value.

 

From what I can tell the primary is in pretty decent shape (especially given that it has spent about 50 years in attic!) the but the "secondary" (aka mirrored prism) has a thick yellow cast to it. Do you guys have any advice on how to clean the secondary, and especially how to get it back in exactly the right place once it has been cleaned?

 

Another related question is what do you find is the best way to collimating these scopes? I'm very reluctant to mark the center of the primary because if it's small size and the coating's age. At f10.5 it shouldn't be too challenging but I would like to get the best performance I can out of the little old scope...

 

Thank you, Andrew


Edited by xnasageek, 07 January 2019 - 11:06 PM.

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#2 JamesMStephens

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Posted 07 January 2019 - 11:18 PM

Seems I've been referring this to a lot of people lately!

 

https://www.skyandte...or-your-optics/

 

Jim



#3 wrnchhead

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Posted 07 January 2019 - 11:25 PM

I have this same scope, that I have repurposed.

 

I have the mirrored stalk secondary (just got up and verified), It's in perfectly servicable shape for what it is. No yellowing of the coating. The original owner took really good care of it and I rescued it off of an estate sale hawk lady from craigslist.

 

The secondary is serving no purpose sitting in my storage cabinet (replaced it with a spider style).

 

 I would be glad to send it to  you for the price of postage, just to see it do more than take up space! 



#4 petert913

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Posted 07 January 2019 - 11:51 PM

I have a special affection for the Palomar 4.25".  Never owned one, but sure loved that old scope.



#5 xnasageek

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Posted 08 January 2019 - 12:02 AM

Thank you Eric & Jim! Now I'll have a backup in case the coating is going (I sent you PM by the way) and the knowledge to clean it if it's just super dirty.bow.gif



#6 DAVIDG

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Posted 08 January 2019 - 01:10 PM

 With the coatings be original even if they look good, having them redone will brighten the image and reduce scatter. I would send them to Majestic Optical coatings. Jeff is very fast, typical turn around is few days and he'll coat the secondary for free when sent with the primary. 

   The prism with the coating on the hypotenuses is actually better optically then the rectangular diagonals they used after that. These were surplus binocular prisms and the hypotenuses needs to be very optically flat  while the rectangular sheet glass ones were not very good. I must have 20 of them and only three tested at 1/4 wave or better.  

  If the mirror is a clean sphere, then at best focus it is true 1/8 system. That is far better then many scopes and one of the optical designs were the Law of Optics is going with you vs against. So with fresh coatings and a good diagonal it will give a very nice image. By the way I have one as well.

 

                       - Dave 

 

https://www.majestic...pe-coating.html


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#7 wfj

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Posted 08 January 2019 - 01:16 PM

I got two in an Edmund Scientific Scheleiren system that was in the big box of ATM junk from a CL post. Only wanted a 5" parabolic mirror from it, turned out to be a rough sphere.



#8 DAVIDG

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Posted 08 January 2019 - 02:21 PM

   I have a couple of Edmund 4.25"  f/10 mirrors from these Palomar Jr and all of  them have some amount of zones. It is  on my list to clean the one up in my scope and parabolize it. 

   Are the ones I have going to give a fuzzy mess of an image ? No but at the same time they won't give the image quality of what a clean sphere would which as I said at best focus is true 1/8 wave.

   I also found the original rectangular diagonal  far from optically flat. It was about a wave. Replacing it will a good 1/8 wave one made a large differs in the  image quality.  As I said the odds are much better that the prism using the back surface is  most likely optically flat. 

      

 

                         - Dave 


Edited by DAVIDG, 08 January 2019 - 10:04 PM.

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#9 clamchip

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Posted 08 January 2019 - 06:16 PM

Mine was proudly at zenith in a customer's front yard!

The mirror was being used as a bug bath!

Just enough coating there to blow my socks off though!

Great scope!

Robert!

 

post-50896-0-52239900-1481217273_thumb.jpg


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#10 grif 678

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Posted 08 January 2019 - 07:14 PM

I never owned one, but when I was very young, around 8 years old, I use to order the Edmund Catalog every year. I remember the Palomar Jr telescope very well. They also had the 3 inch, and the 6 inch space conquerer. Those were the good old days, it would be nice to re-visit for a while. I always wanted one of those scopes, but being raised of a farm, you could not get the things you wanted. But that scope is a good one to hang on to.


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#11 terraclarke

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Posted 08 January 2019 - 07:50 PM

Congratulations on your first Classic. You’ve come to the right place. Welcome.



#12 bremms

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Posted 11 January 2019 - 02:52 PM

   I have a couple of Edmund 4.25"  f/10 mirrors from these Palomar Jr and all of  them have some amount of zones. It is  on my list to clean the one up in my scope and parabolize it. 

   Are the ones I have going to give a fuzzy mess of an image ? No but at the same time they won't give the image quality of what a clean sphere would which as I said at best focus is true 1/8 wave.

   I also found the original rectangular diagonal  far from optically flat. It was about a wave. Replacing it will a good 1/8 wave one made a large differs in the  image quality.  As I said the odds are much better that the prism using the back surface is  most likely optically flat. 

      

 

                         - Dave 

The diagonals on these were really bad. A number of years ago I fixed a Palomar Jr up buy putting in a good 1" elliptical diagonal mounted on a real adjustable spider. Images were greatly improved. The primary mirror star test showed it was decent but not great. Images were much better than with the astigmatic diagonal.  Funny thing is, I fixed up a 4.5" Japanese reflector a gift to my flight instructor and put a better diagonal on that scope too. I think that primary mirror was better than most.  It's star test was better than it should have been. The diagonal was rubbish.


Edited by bremms, 11 January 2019 - 02:55 PM.

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