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(Further) Criterion Dynascope 4 Adventures!

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#1 ktran

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Posted 29 October 2018 - 05:31 PM

As I wrote in my earlier post, I picked up a vintage Criterion 4-inch Dynascope reflector this summer in Quebec City. I got it from a gentleman whose late father was an educator, and rescued it from a school when it was marked for disposal.

 

44600277_10156570984200569_1439644111014

 

There is no model or serial number information, but as near as I can tell, it's a 4" deluxe Dynascope, with the 1.25" focuser, and made from some sort of resin-impregnated cardboard. I have it on a quite usable GEM, with some nice clamping tube rings, but the fixed bolt on the tube tells me this was originally mounted on the older-style EQ mount without the tube rings. I have read all of the threads on CN I can, and have had a look through various era catalogue ads, and I still can't tell when this might have been made. I'll call it "1960s" and leave it at that smile.gif

 

Since then, I've:

 

  • disassembled, cleaned, and regreased the focuser mechanism and finderscope focusing threads. The brass focuser is a bit tired with age.
  • removed the primary mirror cell with a rubber strap wrench. Unfortunately, a previous owner has already attempted a cleaning, and as a result some fairly deep scratches are present, which I don't think can be addressed by a simple recoating. I carefully cleaned away the dirt and haze, and will just live with the scratches.
  • added teflon washers to both axes of the mount, which are an improvement over the half-century-old nylon ones, and added a small c-clamp to firm up the latitude adjustment a bit. Things are pretty smooth and sturdy now, though we're still upset a bit by the odd strong gust of wind. I also need to find properly-sized teflon washers.

45622833321_95a16d58cf_n.jpg 43805148900_a3d769ea33_n.jpg  44709306635_96039bdf9f_n.jpg

  • added a red-dot finder (temporarily zip-tied to the tube, as I don't want to make any permanent modifications yet. I find the combination of a magnifying finderscope and an RDF to be useful a useful one, especially in city skies when I don't have as many guide stars to use for hopping.

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  • shimmed the focuser with some black craft foam to centre things as well as I can using an Orion collimation cap. Initially, it was WELL off. I realise this isn't ideal with the much-maligned secondary mirror, but it's where things are going to be until I can get a hold of a spare focuser/secondary mirror assembly to modify. Just looking at the back collimation screws, I can see there's probably a slight tilt in the primary.

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Performance, I think, is as good as it's going to get for the moment. My only other scope is a 100mm Orion Skyscanner, which is dead-simple to use, is super-portable, and gets me good wide-field views. At f/11.5 vs f/4, I think the Dynascope can give a crisper image in most circumstances, and is certainly easier to get up into the 100x + magnification range comfortably. The 10mm and 20mm plossls that came with my Orion Skyscanner do pretty well on the Dynascope: better than the supplied Criterion H18, AR9, and AR7. Between those two eyepieces, a 2x barlow, and a 40mm MA, I've been able to bag the Messier objects I've hunted for so far, and gotten some lucky glimpses of planetary detail in the late summer when Jupiter, Saturn, and Mars were "doing their thing" higher up in the night sky.

 

Star-testing collimation is a bit weird with the square focuser, and also occasionally puzzlingly "off." I was stumped for a good while, until I realised that 1) the lack of any mechanism to tighten around the eyepieces meant that at certain angles and elevations, the wiggle-room in the focuser led to a misaligned eyepiece, and 2) the long, long tube takes more time to acclimatize than I'd expected!

 

41871751_10156478712075569_7972699829665

 

41703341_10156478712445569_5097714374592


Edited by ktran, 29 October 2018 - 05:58 PM.

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#2 Starsareus

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Posted 29 October 2018 - 07:18 PM

Nice. I recall seeing these in their showroom (a SMALL showroom)! Had the finder once, not a lot of fun using it though. Glad you saved a piece of History.  Now have two 6" and two 8" deluxe scopes to restore.


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#3 starman876

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Posted 29 October 2018 - 07:34 PM

Nice scope


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#4 Jim Curry

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Posted 31 October 2018 - 06:08 PM

My parents bought me this scope in 1969. Took two years to bag the messier list and a few Ngc’s. Wonderful times.
Jim
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#5 terraclarke

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Posted 01 November 2018 - 10:31 AM

That is a beautiful long classic Newtonian!


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#6 pstarr

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Posted 01 November 2018 - 03:45 PM

I had one of those. Many fond memories as a teenager.


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#7 apfever

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Posted 01 November 2018 - 04:20 PM

From looking at the rub marks on the lattitude lock tangs (C clamp is on them),  it looks like the tang on the RA housing might have been on the other side of the tripod hub tang. It's hard to get picture detail on that part. The tang on the RA housing has a slot for extra holding as well as the center lock nut?  That I recall but something still not seeming completely correct. I remember holding that position shouldn't need a C clamp,  it was a pretty solid factory clamping non concern. I'll go look at one. I don't think I've ever posted one on here, maybe. 


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#8 ktran

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Posted 01 November 2018 - 08:15 PM

From looking at the rub marks on the lattitude lock tangs (C clamp is on them),  it looks like the tang on the RA housing might have been on the other side of the tripod hub tang. It's hard to get picture detail on that part. The tang on the RA housing has a slot for extra holding as well as the center lock nut?  That I recall but something still not seeming completely correct. I remember holding that position shouldn't need a C clamp,  it was a pretty solid factory clamping non concern. I'll go look at one. I don't think I've ever posted one on here, maybe. 

If you have a photo of how it should look, that would be much appreciated. I received the mount as a mess of incorrectly sized washers, etc. No lock washer.



#9 apfever

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Posted 01 November 2018 - 09:24 PM

I'll get a photo tomorrow.  Don't use any kind of lock washer on the mount. NONE. All that will do is scar up the soft casting metal.


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#10 bremms

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Posted 01 November 2018 - 09:55 PM

Like this one a lot.


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#11 apfever

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Posted 02 November 2018 - 12:35 PM

Off to the barn and what I found was:

a motor drive.

 

The tang on the tripod hub is slightly offset such that one face of the tang is in the center of the hub. You want to mount the RA tang to that centered face on the hub. 

The tang on the RA housing looked symmetrical as best I could tell without pulling it. Facing the scope from behind (motor end), the RA is mounted on the left side of the hub. This should be noticeable in the pictures. Sometimes I'm not sure which way is up.

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Edited by apfever, 02 November 2018 - 12:40 PM.

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#12 apfever

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Posted 02 November 2018 - 01:06 PM

This is an early one with the word "CRITERION" deeply engraved in the motor cover.

 

I knew there was something solid about this mount. The RA housing tang has TWO slots for holding the altitude adjustment in addition to the center bolt. The center bolt here is likely not original since it is a flat top carriage bolt that rest on the end of the square part. The center bolt goes through slip fit holes in both RA and hub tangs, and has a clamp knob to tighten.  This pulls the square part of the carriage bolt awkwardly into the face of the RA tang - this could be better.

 

The lower slot system has a threaded hole in the hub tang, and the clamping bolt simply screws in to tighten on the RA tang. To help keep it easy, the hand clamping parts are on opposite faces on the system.

 

Here's a strange part. The upper slot in the RA tang has never been used. The hub tang was never drilled or tapped for a clamp bolt in the upper slot. Still, this locks in solid with just the center bolt and lower slot bolt.  I see no need to add the upper slot bolt. 

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#13 apfever

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Posted 02 November 2018 - 01:19 PM

The other side of things.

 

Clamping knob on the center bolt.

Lower slot bolt end threaded through hub tang.

No hole for upper slot on RA tang.

RA housing on left side of hub tang, facing from back of scope. 

 

I found split lock washers on each bolt, with a regular washer between them and the soft castings. I removed the lock washers since they weren't necessary.  It's still rock solid. There was a loose washer on the end of the lower slot bolt which explains the 'dust' ring on the hub tang. The tang is threaded there so nothing is needed on top and I removed the loose washer. The motor may help in balancing the scope but I don't see and issue with the two clamp bolts holding position with motor or not. As long as threads are good.

 

Questions?

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Edited by apfever, 02 November 2018 - 01:22 PM.

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#14 ktran

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Posted 02 November 2018 - 02:44 PM

Thanks for the pictures and info!

 

I had the RA tang mounted on the wrong side of the hub tang. I hadn't noticed the asymmetry on the tripod hub, so it's good that I have that sorted out now! The C-clamp isn't strictly necessary, but I put it on there to snug things up, especially as for me to get to a darker sky site, I have to walk with the mount and scope (one in each arm) a block or two to get to my local car-share rental spot smile.gif

 

I only have the one slot on my RA tang. I wonder what the upper one on yours is for?

 

Does the motor drive work? I wonder how much effort would be involved in adapting a modern drive motor to this mount.

 

If you happen across a spare focuser and secondary assembly somewhere in your barn and/or junk drawer, please let me know!


Edited by ktran, 02 November 2018 - 02:46 PM.


#15 ktran

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Posted 13 November 2018 - 01:40 PM

Off to a Gig With the Stars?

45815293082_45bf892ef7_z.jpg

 

It sort-of, kind-of, almost fits into my bass gig bag. At the very least, it makes it easier to carry to rental cars in one trip with accessories and eyepieces in a sling bag, leaving both hands free for the heavier mount!


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