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Prinz 660 Refractor

Carbon Brush

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Carbon Brush

Carbon Brush

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Way back in 1986 my father bought a used scope. Prinz refractor 3" with FL1250mm.

It came with an EQ mount, wooden tripod, eyepieces, diagonal, sun(!!) and moon filters, etc. All in a big wooden box.

At the time I knew even less about scopes than I do now and decided the package was not much good.

Quite simply the eyepieces gave far too high magnification with all but zero eye relief and narrow fov.

The mount was not up to holding steady at the high magnification and it was a fuss to set up everything.

The scope was left untouched for many years.

Recently I pulled it out with a view to seeing if there was anything in the box worth using.

To my surprise the scope appears to give sharp views with decent contrast. Though this has not been properly tested.

Colour correction looks good. But so it should be for an F16 doublet.

The big weakness is the 965 eyepieces. Followed by the overloaded EQ mount.

Having made the criticisms, the mount build quality compares well against the modern chinese stuff.

For a smaller scope, it should perform well.

The scope focus assembly is good, for the price bracket. The only issue I have is trying to fit 1.25 eyepieces.

The focus tube has a female thread to take the 965 adapter.

Thread size is around the 35mm mark that doesn't fit anything in my 'bits box'.

Does anyone know of an adapter?

So instead of clearing out a large box of scope kit, it is looking as if I will be keeping it!

Should we get a break in the weather and I can fit a half decent eyepiece, I hope to be able to comment further on this aged scope.

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Tiki

Tiki

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Lucky you.

It seems like you need a vixen/takahashi 36.4mm threaded adaptor. There are plenty of different types to choose from.

.965" eyepieces aren't necessarily bad, but the 'kit' eq mount supplied with the scope is usually rubbish. I bet that the objective is pretty decent though.

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Carbon Brush

Carbon Brush

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Thanks everyone for your comments.

I'm going to get an adapter so I can use my 1.25 eyepieces, though this will take a few days to arrive.

But then I can try my standard daylight test.

Out of the conservatory doors, I can see a brick chimney, electricity pylon and trees at 2KM. By setting up indoors and looking through the open doors, there is no worry about the possibility of rain.

Given half decent visibility, these horizon objects are very good for taking a scope to high magnification, showing contrast problems and chromatic aberration.

I will put something else alongside for comparison to get a feel for how the objective compares with other scopes.

No prizes for predicting it will be either foggy or raining from next week for a month!

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Carbon Brush

Carbon Brush

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Here's one I made earlier.

Apologies for the rather strange EQ mount assembly.

It just came out of the box that way and I was interesting in checking for completeness, rather than functionality!

The R&P focusser is really well made. Much more solid and rigid than some I have seen on modern SW refractors.post-6286-0-75777700-1357052010_thumb.jp

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Carbon Brush

Carbon Brush

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Just encopuntered the first problem.

As far as I can tell, the focus/eyepiece thread is M36x1mm.

The (male threaded) eyepiece holder and prism erector both show about 35.7mm OD with 1mm pitch.

Despite a bit of wear and tear on the threads, these easily screw into a fitting I have which is M36x1.

Unfortunately the female thread inside the focus tube has been damaged slightly.

The threads are still there and recoverable.

The original eyepiece holder & prism still screw in OK, but these have obviously worn threads.

My unused undamaged M36 adapter becomes sticky about about a turn.

The obvious fix is to run a tap down the focus tube.

But I don't have an M36x1 tap and as far as I can see, it will cost over £100 to buy one!

So my first move will be to see if some kind person will lend me a tap, or perhaps I can send them the focusser.

If that fails, then I will probably take a file and wire brush to my M36 fitting to wear out the thread.

Messrs Heath and Robinson would be proud!

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NGC 1502

NGC 1502

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Maybe a local engineering firm has a M36 tap they will loan for a fee ? Worth a try perhaps ?

As you will only fit the adapter once, the thread doesn't need to be perfect, just ok to allow it to fit.

My shed is full of Heath & Robinson projects, half finished, abandoned, given up, just the occasional success :smiley:

Regards, Ed.

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Carbon Brush

Carbon Brush

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Hi Ed. Thanks for the suggestions.

At M36, there are several thread pitches in use. I have seen between 1 and 4mm. For general engineering, I think they will be using a coarse pitch.

Really it is probably someone doing optical engineering who is more likely to have a tap. Even so, they may choose to cut threads on a lathe.

I have a set of thread pitch gauges made from steel. Maybe scraping the 1mm gauge on the brass threads in the focusser will be good enough?

I have considered the 'fit once' idea. The extra length unfortunately stops me from using the nice wooden storage box. Already the original EP holder has to be unscrewed.

At least I don't need clear skies for all of this!

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Carbon Brush

Carbon Brush

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Today I sorted out fitting the 1.25" eyepiece connector.

Closer inspection of the scope threads showed they are a square profile and in reasonable condition.

They are perhaps not exactly 36mm. Maybe an imerial size a fraction smaller diameter? The pitch is though as near as I can gauge 1mm.

This would explain the fitting problem. They are quite hard brass.

I decided to take a gentle file to the aluminium M36 adapter.

With some careful work I took the tops off the threads with a smooth file, finishing off with a fine nail emery board.

Using the screw thread gauge and a wire brush, I took the anodizing from the bottom of the threads.

After a few minutes the slight diameter reduction, combined with the tiny undercut (more of a clean out really) meant that it fitted into the focus tube.

So the next part will be a proper assessment of image quality against other scopes, swapping eyepieces between.

If I can fix the tube to a standard Vixen or Losmandy plate, that will make things much easier for me.

A wanted ad for 76mm rings has been placed here.

Looking out of the window, I can see that the 'test' chimney and electricity pylon are vanshing into the mist.....

post-6286-0-75593900-1357402134_thumb.jp

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Ludd

Ludd

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I owned one of these beauties some years back. I was very fortunate to find a Vixen-branded adapter on the Orion Optics stand at Astrofest that was a perfect fit. I used the scope on an EQ3 for a while to look at the moon and planets but eventually sold it when I bought a TAL2.

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Brian Nordstrom

Brian Nordstrom

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Lovely old scope , I just did a quick google on 76mm telescope tube rings and there is pages of these , cheep as well .

On the mount yes an eq5 with at least a 12 inch extention pier will do nicely , you will need the extention as the physical length of the tube is way longer than most scopes avaliable today and the tripods aint designed for something this long so without one you will be close to sitting on the ground to view the zenith .

I bet it will give awsome views of the moon and planets using new plossles or similar .

I like old scopes .

Brian.

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Carbon Brush

Carbon Brush

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I can buy rings from TS in Germany, and via their Amazon shop. But they are £30+.

I'm not sure about hanging on to the scope and have heard some bad press recently about TS not coming up with goods.

So waiting a day or two to see if a 'wanted' yields a response seems a good idea.

If I lose patience, then I might lash the tube to a long dovetail bar using gaffer tape!

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Tiki

Tiki

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I faced similar problems with my Swift. I have tube rings now, but initially I was able to attach the original clamshell to my SP mount via a scrap aluminium plate. I only bought tube rings because it was a bit of a fiddle changing set-ups.

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Seafury

Seafury

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Hi you probably will not be able to get rings small enough I tried a while for my old Prinz 550 and ended up getting the smallest guide scope rimgs from FLO that I could , I then found the holding screws they came with were too short to reach the tube but found the supplier of the rings in the USA http://admaccessories.com/default.htm and they can supply three different lengths of screws and I ordered the middle sixe ones and they did the job a treat, I now have it mounted piggy back style on my other scope but you could probably mount it directly onto a dove tail bar, I have replaced the original lens with a 60 mm Carton lens and had to use an extension tube to get the fl right but the views are so much better than the original which to be fair wasn't that bad

Gordon

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