39 replies to this topic

[jragsdale]

Anyone know on these older focusers that fit the 7" OD aluminum tube? Looks like it will unthread but I think it's all one cast piece. If I need to replace the whole flange, does anyone know a good source? I've heard there's some Burgess and D&G equivalents out there. I'd like to upgrade to a modern dual speed focuser if possible.

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[ccwemyss]

Yes, it'a all one casting. To replace mine, I bought a modern AP 2.7" feather touch focuser on AM from someone who was upgrading to a 3.5". Then I took it to a local machinist to make an adapter. It helps if you can give them a CAD file they can run on their CNC machines.

 

For a while, Starlight Instruments had a CAD model to adapt one of their focusers, but I don't know if they still support it, and the waiting time is quite long. Although, to be fair, my machinist bungled the first attempt and it ended up taking 6 months. I did contact Precise Parts, and they wouldn't do it. 

 

I wasn't able to find any other existing focusers with flanges of the right size. It's really trying to bridge two eras, going from the ATM use of Hastings irrigation tubing (which outfits like Jaegers catered to with their focusers) to the modern era of precision machined focusers designed for metric sized tubes. 

 

Regards,

Chip

[jragsdale]

Thanks for the info Chip! I'm wondering if I can have a machinist cut off the cast drawtube holder on this one and bore out to a larger female thread size that will work well with another focuser? 

[rachnoman]

If my memory serves me right, this focuser came in 2 pieces. The focuser housing and the back plate. The split is at the red arrow as indicated.

The back plate was heated, then dropped right over the focuser flange for a tight fit.

 

DG

[ccwemyss]

Never found a seam on mine. AP describes it simply as 2.7" focuser with aluminum casting. For a while they also used a 2" Japanese focuser that was inserted into a separate casting to fit the tube. 

 

https://www.astro-ph...oldfocusers.htm

 

I don't know if the cast metal is fine enough to take a good thread. It might be, because for a while they used them with an outer ring that the casting threaded into, to fit it to larger tubes. You'd need to have a machinist take a look at it.

 

I'm not sure it's worth the effort to try to reuse the casting, versus starting from a new piece of plate. Turning the diameters to match the inside and outside of the tube isn't hard, and then you can use whatever kind of opening is needed for the focuser of your choice. Rather than going into a thread, some focusers use a V groove and need screws to be driven in from outside. With plate, it's not hard to also turn out a second flange that supports doing that. 

 

Chip W. 

[jragsdale]

If my memory serves me right, this focuser came in 2 pieces. The focuser housing and the back plate. The split is at the red arrow as indicated.

The back plate was heated, then dropped right over the focuser flange for a tight fit.

 

DG

You're right! I did some exploratory pounding with a rubber mallet with some carefully placed wooden blocks and found that it does indeed come out. The hole is 4⅞". This should work for my needs to add a new adapter plate with some push/pull adjustments and threaded with new strong aluminum for a adapter to a new focuser.

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[rachnoman]

Great! Now this is where the fun begins!

 

By the way, the 4-7/8" hole fits a 5" aluminum which AP used for their 4" refractors. Larger units employed a Novak backplate as shown.

Also, the blue coating on the drawtube is Teflon based.

 

For openers, one option would be is to acquire a 1/4" thick plate x 7" round. This plate can be bolted to the original Novak back plate with 3 screws. Then mount them together on a lathe holding the Novak back plate. Ones you found a focuser with a specific flange diameter or thread; you can now bore a hole for a press fit or match the threads. 

 

Hope this helps....

Edited by rachnoman, 27 December 2024 - 08:13 PM.

[CHASLX200]

Mine was the same thing on my blue tube AP 6" f/9. But never took it apart.

[deSitter]

You're right! I did some exploratory pounding with a rubber mallet with some carefully placed wooden blocks and found that it does indeed come out. The hole is 4⅞". This should work for my needs to add a new adapter plate with some push/pull adjustments and threaded with new strong aluminum for a adapter to a new focuser.

Somehow it is hard to process the idea "I pounded on my Astro-Physics focuser with a rubber mallet until it came apart"

 

-drl

[CHASLX200]

Somehow it is hard to process the idea "I pounded on my Astro-Physics focuser with a rubber mallet until it came apart"

 

-drl

Had to do about the same thing on this 1960 U to get it apart.

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[jragsdale]

Somehow it is hard to process the idea "I pounded on my Astro-Physics focuser with a rubber mallet until it came apart"

When you know what you're doing and have nothing to lose anyways.

[ccwemyss]

You're right! I did some exploratory pounding with a rubber mallet with some carefully placed wooden blocks and found that it does indeed come out. The hole is 4⅞". This should work for my needs to add a new adapter plate with some push/pull adjustments and threaded with new strong aluminum for a adapter to a new focuser.

Yes, it would not have occurred to me to start beating on it, just to see if it would come apart. Not that it would have helped in my case. I wanted a neat, clean, anodized adapter to match the new focuser, and the old one was going into the Jaegers 6"f5, which it fit perfectly.

 

Chip W. 

[jragsdale]

Yes, it would not have occurred to me to start beating on it, just to see if it would come apart. Not that it would have helped in my case. I wanted a neat, clean, anodized adapter to match the new focuser, and the old one was going into the Jaegers 6"f5, which it fit perfectly.

 

Chip W. 

I'll probably strip the flange of paint before proceeding, then when it is all done I'll sand any bumps smooth and have it anodized or powder coated depending on the metal condition. No dents/dings added by any rubber-malleting today.

[starman876]

You're right! I did some exploratory pounding with a rubber mallet with some carefully placed wooden blocks and found that it does indeed come out. The hole is 4⅞". This should work for my needs to add a new adapter plate with some push/pull adjustments and threaded with new strong aluminum for a adapter to a new focuser.

Has to be a strange feeling to take a hammer to a AP focuser.   Now maybe something like a cave sounds reasonable 

[John Rogers]

The Jaegers Super Eyepiece Mount is the same.  The base looks like a single casting, but is in fact two pieces that were assembled before application of the wrinkle paint.

 

[jragsdale]

Has to be a strange feeling to take a hammer to a AP focuser.   Now maybe something like a cave sounds reasonable 

It's not like it's a high end focuser like a feathertouch, and I had a clue that it separated, I noticed a tiny gap on one side that was causing a slight wedge, so I knew it wasn't all one piece. I used wooden blocks while hammering it, so no damage done.

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[deSitter]

The Jaegers Super Eyepiece Mount is the same.  The base looks like a single casting, but is in fact two pieces that were assembled before application of the wrinkle paint.

 

Jaegers_Super_Eyepiece_Mount_wM17.JPEG

I always wondered about this - how they dealt with fitting a generic focuser to a specific tube.

 

-drl

[ccwemyss]

Maybe this qualifies it for the BEATERS thread? 

 

Chip W. 

[jragsdale]

Maybe this qualifies it for the BEATERS thread? 

 

Chip W. 

Maybe we need a BANGERS thread?

[Don W]

As my dear old dad used to say, “If it don’t work, use a bigger hammer!”

 

DonW

[jragsdale]

Here's the plan for an upgraded focuser:

 

TS-Optics 2.5" R&P Dual Speed Focuser

 

 

https://www.teleskop...-rotation-12539

 

It is about the same height from flange to eyepiece as the original so no tube cutting required. Original flange can be used so all the original holes in the tube can be used too.

 

I ran this by my "lathe master" friend and he suggested an adapter that will use the existing flange with 4 sets of push/pull screws drilled into the existing flange as the connection which also provides tip/tilt collimation of the focuser. The adapter will also have male M117 threads for this TS optics focuser to attach to. I've had several of these TS optics R&P focusers and they've all been very good, much better than the typical Synta/GSO dual speed stuff, almost on par with a Feathertouch in some incarnations. 

[The Ardent]

Please allow me to suggest an older used modern AP focuser , one with the same threads as the current ones. Single speed and often in the classifieds as owners upgrade to the current version. Has “Astro Physics “ engraved. That’s the best part.

Examples below.

https://www.astromar...-focuser-605929

https://www.astromar...-focuser-582264

https://www.astromar...ser-and-adapter

[The Ardent]

Years ago I bought the AP 5” f/12 from a nice CN member. It had the same 80’s focuser as yours. I had Joe Castoro of the Binoscope Company shorten the tube and replace the backplate for a new AP focuser with the fine focus. He did excellent and unique work. 
 

The original scope fit the case. The modified scope has room to spare. 

I kept the focuser . A couple of years later it came in handy for the Jaegers 6” f/5 build by Parallax. 
 

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[jragsdale]

Please allow me to suggest an older used modern AP focuser , one with the same threads as the current ones. Single speed and often in the classifieds as owners upgrade to the current version. Has “Astro Physics “ engraved. That’s the best part.

 

My current one is not threaded so these will not be any easier to upgrade to than the one I'm looking at. And they're relatively simple and basic, similar to the one I have now. I'd really like to have a nicer high end focuser with dual speed and rotation that can work with modern reducers and is fairly "future proof".

[The Ardent]

Machining is unavoidable in your case, unfortunately.

The AP Star 12 is from 1991.
In 2011 I was able to upgrade it to the current AP 2-speed focuser easily by simply threading on. It’s a good system for easily changing focusers, a system still in place. Although in 2011 the focuser was half the price of current ones.