Jump to content


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Criterion Dynamax 8

  • Please log in to reply
194 replies to this topic

#176 DAVIDG

DAVIDG

    Fly Me to the Moon

  • *****
  • Posts: 5197
  • Joined: 02 Dec 2004
  • Loc: Hockessin, De

Posted 20 April 2015 - 06:29 PM

The objective in the finder and new cross hairs installed.

 

                       - Dave 

Attached File  REPAIREDFINDER.JPG   55.97KB   18 downloads

 

 



#177 DAVIDG

DAVIDG

    Fly Me to the Moon

  • *****
  • Posts: 5197
  • Joined: 02 Dec 2004
  • Loc: Hockessin, De

Posted 20 April 2015 - 06:35 PM

Finally the back of the scope. I loosen the four screws on the back flange of the eyepiece mount to adjust the tip and tilt of the primary mirror and baffle tube assembly to place the laser on the center of the paper mask.

 

                    - Dave 

Attached File  BACKOFSCOPE.JPG   59.48KB   21 downloads


Edited by DAVIDG, 20 April 2015 - 07:57 PM.

  • Geo31 and Bomber Bob like this

#178 torq460

torq460

    Lift Off

  • -----
  • Posts: 2
  • Joined: 29 May 2008

Posted 20 April 2015 - 09:24 PM

George, Gil, Dave, Chuck, Duane - 

 

Thanks to each of you!  The explanations and photo's are super helpful.

 

Dave:  mine too seems to have that film on the inside of the corrector.  Any idea where it comes from?  When cleaning, are there coatings I need to be concerned with?

 

Mine did have the rubber o-ring properly installed, and it kept the main mirror from sliding off the baffle tube (for which I am enormously grateful).  

 

When reinstalling the baffle tube and mirror, should I assemble the baffle tube, with the mirror and cell together then somehow get  them into the main tube? That's how I got them out, but if that is the sequence, how does one connect the focusing mechanism, with the mirror in place?    

 

I'm thinking I will need to install them one at a time, starting with the baffle tube, then the cell and focuser, then installing the mirror onto the cell, and lastly the rubber o ring.  This is the only way I can think of to properly connect the focusing mechanism.  Does this sound right to you?

 

What do you recommend as lubricant between the mirror cell and baffle tube?

 

Thanks again!

 

Marty (aka torq460)



#179 DAVIDG

DAVIDG

    Fly Me to the Moon

  • *****
  • Posts: 5197
  • Joined: 02 Dec 2004
  • Loc: Hockessin, De

Posted 20 April 2015 - 10:39 PM

 The film on the inside surface of corrector is from out gassing from the paint and the tube.  Give the corrector a bath in warm water with dish soap and dry it with clean cotton towel and it will be perfect. As a chemist and someone who has been making optics for 30 years now, you don't have use all kinds of cleaning solutions and alcohols to clean the surface. That is how people wreck optical surfaces.  A little soap and warm water  work very well and are safe for optical coatings. 

 

                           - Dave 



#180 Gil V

Gil V

    Viking 1

  • -----
  • Posts: 729
  • Joined: 09 Sep 2012

Posted 21 April 2015 - 11:18 AM

Build the whole primary mirror and slide assembly. Once you slide that back onto the baffle, it is a simple task to rotate the assembly until you find the focus screw receptacle.

#181 mikey cee

mikey cee

    Cosmos

  • *****
  • Posts: 8611
  • Joined: 18 Jan 2007
  • Loc: bellevue ne.

Posted 21 April 2015 - 11:58 PM

 "George pointed out, it was worth what I paid, for the eyepieces, accessories, and tripod alone. If I had a tile countertop I could part it out and double my money." I just found this thread and all I can say is Chuck you are just plain mean! :lol:  :lol:  :lol:   Mike


  • Bomber Bob likes this

#182 orion61

orion61

    Fly Me to the Moon

  • *****
  • Posts: 5201
  • Joined: 20 Oct 2007
  • Loc: Birthplace James T Kirk

Posted 22 April 2015 - 01:44 PM

That was a great job, Many people do not realize how good some of the optics can be in many of those old Dynas. I found out over 20 years ago. I cant tell you how many times I have been ridiculed in support of these "mis-understood" scopes. They are still my favorite Mechanical fork mount. The version of DX-8 you have there (Light/Dark grey) are the ones with better optics in my experience. Gil V is my Brother in arms in support for these,  So beautiful in their simplicity.

Thanks for adding to this post on these ubiquitous closet dwellers ..

Duane


Edited by orion61, 22 April 2015 - 01:45 PM.


#183 apfever

apfever

    Mercury-Atlas

  • *****
  • Posts: 2996
  • Joined: 13 May 2008
  • Loc: Colorado

Posted 17 May 2015 - 12:40 PM

I'm going to give two of these a shot.

I'll reset the correctors and secondary before further optics testing since the secondary measures between 1/8" and 1/4" difference from edge to each side of the cell. I'll also laser the focusers with a mask while the correctors are out.

 

How does the primary cell come off. I haven't found any information on removing the primary, focusing mechanism, or cell in general. Both cells (primary and corrector) seem to be integral to the tube. If so, then the primary assembly would have to come out the front.

 

I have an interested party in one of them so I want to get the existing glass as close as I can. Final results will fall were they may. One has some fiddling to be done with flop.  Also, I need to take one base apart and check the RA gearing. It works but is 'wumpy' and some positions have way too much wump.

 

Thanks.



#184 DAVIDG

DAVIDG

    Fly Me to the Moon

  • *****
  • Posts: 5197
  • Joined: 02 Dec 2004
  • Loc: Hockessin, De

Posted 17 May 2015 - 02:06 PM

 You need to determine if the offset in the secondary is from the corrector/secondary assembly not being centered in the corrector cell and/or the secondary cell is not centered in the corrector  and/or the secondary is not glued to it's mounting plate so it is centered on it. My corrector was also resting on rubber gasket that went around the full diameter. It was stuck down hard and that type of force could easily warp it. I placed three taps of Kapton tape over the rubber gasket  and also on the retainer ring at 120 centers so the corrector was held at only these positions

  There are two baffle tubes for the primary. A slightly smaller diameter one that is attached to the back of the scope and a larger diameter one that goes over the smaller on and the primary mirror is attached to. There is either an O-ring or a C-clip near the top of the baffle tube that stops the baffle tube that the mirror is mounted too from going too far forward when you focus. You need to remove that clip and also the focuser knob. The mirror will now pull forward with it's  baffle tube attached. There are two cut out at 180 degrees on the corrector cell that will allow you to tip the mirror and remove it from the tube through those two cut outs. 

  The primary and corrector cells look to be glued to the tube so that are not removable. 

 

                          - Dave 



#185 apfever

apfever

    Mercury-Atlas

  • *****
  • Posts: 2996
  • Joined: 13 May 2008
  • Loc: Colorado

Posted 17 May 2015 - 02:51 PM

It sounds easy enuff for an idiot like me so I'll just womp all on it and rip it up.

Focuser must be mechanically simple enough and I've read the rebuild strings on CN. Seems some focuser shaft tends to be sloppy and shaft build up in the paper thin category is mentioned. I was thinking of thin shrink wrap but it depends on the thousandths by then.

 

Yeah, I just measured the distance form inside (threaded) cell to edge of outer secondary mount, in opposing sets, at several positions. I then bypassed the literal pile of lateral slop positions (simplicity) and went straight to the mind position of the secondary. Just going by the push of 1/4" difference in the outer mount, I saw a secondary more likely to be in Timbuktu than closer to right. Performance showed this as well. 

 

I loved the breakdown pictures of the corrector rebuild. Might as well get it all. For all practical VISUAL, what is a reasonable throw for secondary off axis error. I take it the secondary is not spherical.

 

Foolish me, pictures of course. Here's the project to move one out if I can get it to perform OK.

Dang, those things are sure pretty. Even better with the hopper legs.

Attached Files


  • Chuck Hards, terraclarke, mitsos68 and 1 other like this

#186 Rich (RLTYS)

Rich (RLTYS)

    Fly Me to the Moon

  • *****
  • Moderators
  • Posts: 5671
  • Joined: 18 Dec 2004
  • Loc: New York (Long Island)

Posted 18 May 2015 - 05:03 AM

Nice looking scopes.  :waytogo:

 

Rich (RLTYS)



#187 Gil V

Gil V

    Viking 1

  • -----
  • Posts: 729
  • Joined: 09 Sep 2012

Posted 18 May 2015 - 09:26 PM

Where are you at? With two full models, it would be an afternoon's work to isolate the best glass and build one very good scope, and one who-knows-what scope.

If you're near Connecticut, I'd very much enjoy assisting you. PM me with any and all questions.

#188 Gil V

Gil V

    Viking 1

  • -----
  • Posts: 729
  • Joined: 09 Sep 2012

Posted 18 May 2015 - 09:30 PM

BTW, the optical config of the Dynamax is spherical F/2 primary, spherical secondary, aspheric corrector. Those corrector retaining rings are a major PITA, though, to do it right, I'd drill and tap the corrector cell and reconfigure it to hold the corrector with eight socket cap screws.

#189 apfever

apfever

    Mercury-Atlas

  • *****
  • Posts: 2996
  • Joined: 13 May 2008
  • Loc: Colorado

Posted Yesterday, 11:54 AM

Hi Gil,

 

Forget the PM, people here may want to know. First thing is getting the drive apart to fix the 'whomp whomp' in the RA. It is not a bent control knob, is stiff in erratic positions, sometimes it's very springy on each side of movement and has to be popped through the tight spot to continue on, then be smooth.

 

At any rate, it's coming apart.

 

I removed the top label, bolt, and washer from the center shaft.

 

From inside the base, I removed the two large set screws shown by red arrows. This allows the entire base, motors, and all electrical items to come off in one convenient package.

Attached Files



#190 apfever

apfever

    Mercury-Atlas

  • *****
  • Posts: 2996
  • Joined: 13 May 2008
  • Loc: Colorado

Posted Yesterday, 12:04 PM

Base assembly removed from the shaft. This leaves only mechanical gearing on the fork assembly.

 

Close up from other side of base for better detail. On of the threaded set screw holes can be seen inside the center shaft bore. This is a nice slip fit on the shaft and needs to be wiggled off carefully. The burs in the shaft from the set screws can be a little hindrance, but I managed by hand without any prying on the delicate upper plates or setting circle.

Attached Files



#191 apfever

apfever

    Mercury-Atlas

  • *****
  • Posts: 2996
  • Joined: 13 May 2008
  • Loc: Colorado

Posted Yesterday, 12:17 PM

The red arrow points to a threaded set screw hole. There are two set screws on this collar. I removed them both.

 

The green arrow points to a smooth hole that looks to be for a spanner wrench. Hopefully it is not a stamped machine assembly hole.

 

I'm not sure how to disassemble the rest of the gearing from the fork assembly. I'd like to get this after work today. Also will consider removing both OTA from the forks for an oil flat test. I have one of those Ronchi grating 1.25" eyepieces. I believe it is 100 lpi, I'll have to check.  The OTA to Fork assembly looks straightforward but any tips are welcome. The OTA may have to come off anyway if I have to press the gearing out of the fork base.  

Attached Files



#192 apfever

apfever

    Mercury-Atlas

  • *****
  • Posts: 2996
  • Joined: 13 May 2008
  • Loc: Colorado

Posted Yesterday, 12:21 PM

Forgot the bench pictures.  These are the temp work bench stand. Just the right height with the top on.

Both in great shape all around, working locks, great interior with hinge and foam, and they come with keys.

Attached Files



#193 Gil V

Gil V

    Viking 1

  • -----
  • Posts: 729
  • Joined: 09 Sep 2012

Posted Yesterday, 03:21 PM

The upper thrust bearing is a press-fit on the polar shaft. That is the scope's weakest link, so to speak.

You'll have to find a way to press the bearing back on in order to reassemble the mount correctly. That will be your biggest difficulty.

The entire base and gear assembly is then secured to the grey circular base with the two set screws.

When the base/gear assembly is properly assembled, the blue base and the black "hat" section of the RA gear assembly act as a single piece (because of the press fit), and the RA gear spins independently - engaged by the RA slow motion knob.

I am sorry about your desire to not E-mail me, but I generally do not respond to specific repair instructions in the forums.

#194 Gil V

Gil V

    Viking 1

  • -----
  • Posts: 729
  • Joined: 09 Sep 2012

Posted Yesterday, 03:24 PM

Also, by loosening the set screws in the Sealmaster bearing at the south end of the RA shaft, you have added to your difficulties.

#195 Joe Eiers

Joe Eiers

    Messenger

  • *****
  • Posts: 449
  • Joined: 08 Sep 2011
  • Loc: Sacramento, Ca.

Posted Yesterday, 04:12 PM

Nicely done Neil!  This is going to be very helpful for people.   Thanks for doing it here.

  Joe




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.



Recent Reviews


Imaging/Sketching Contest






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics