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Equipment Discussions >> Classic Telescopes

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Gil V
professor emeritus


Reged: 09/09/12

Aligning my Dynamax
      #5841753 - 05/05/13 02:10 PM

As many of you know, I was recently able to fulfill a nearly lifelong dream and purchase a Dynamax 8 in very good condition. It was because of this website and the kindness of Mark Swanson that this happened.

Since I built so many of these in the year or so I was an optical assembler at Criterion, I always have this nagging feeling that "I could make this thing work better". My past experiences with the product have been such that I feel that I have to dial the scope in, or I'm going to spend too much time judging optics, and not enough time enjoying using the scope.

I had wanted to crack open the scope since I got it, because the scope had an assembly problem. On the main baffle tube, there are two grooves for the snap ring baffle stop. If the snap ring is incorrectly put in the front most groove, it doesn't work - the focus screw will disengage before the stop engages! (Family run company, what more can I say?)

The corrector was stuck pretty solidly to the rubber gasket, so my previous attempts to crack the scope had been unsuccessful. Since I couldn't free the corrector, there was no way I could align the scope or fix the baffle stop.

Using a plastic dental tool and some courage, I freed up the corrector today.

Fixed the stop, and set up an optical test bench to work on the alignment.

I set up my Meade 10" reflector horizontally, put a star diagonal and 10mm eyepiece in it, and set up a lamp with a pinhole in front of it. Aimed the Dynamax into the Meade, and got a perfect artificial star.

The scope had some astigmatism, so I rotated the corrector/secondary to get the best possible image. It took a good hour, because I had to collimate after every turn. Eventually, I got what I feel is the best image I could get from the scope. The airy disk has a slight triangular shape, but it's not bad overall. I expect much better results with the scope next time I take it out - probably tonight, because we've had a remarkable stretch of good viewing weather lately.

If you have the confidence to do some surgery on your scope - AND you think your scope has an astigmatism problem, I recommend you give this a try. Classic scopes only, if it were a newer scope, I'd ship it back and let the manufacturer deal with it.

Also, please note that this won't take care of over/under corrected optics. You could rotate the individual optics all day long, but it won't change the optical figure.

I'll post my thoughts once I've had a chance to use the scope outside.

A final note - even if you don't have astigmatism, this would be an excellent way to achieve perfect collimation. It's much easier to do it when you don't have thermal stabilization or poor seeing, plus you can see what the hell you're doing in the daytime!!

I considered removing the primary and reseating it on the baffle slide to get rid of that last touch of astigmatism, but I have no way of knowing if it's from the primary or the secondary. Plus, I don't have a cabinet of spare optics to swap around. Law of diminishing returns, I guess...

If the scope performs outside like it did on the DIY optical bench, the view through the eyepiece should be quite good.

Especially for a Dynamax! LOL


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greedyshark
professor emeritus
*****

Reged: 10/31/05

Loc: 3rd Rock
Re: Aligning my Dynamax new [Re: Gil V]
      #5841905 - 05/05/13 03:45 PM

Good luck this eve!

Charles


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tim53
Postmaster
*****

Reged: 12/17/04

Loc: Highland Park, CA
Re: Aligning my Dynamax new [Re: greedyshark]
      #5841942 - 05/05/13 04:07 PM

I look forward to a viewing report! Every now and then I see one of these for sale. Someday, I'm going to pick one up to try out.

-Tim.


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Gil V
professor emeritus


Reged: 09/09/12

Re: Aligning my Dynamax new [Re: tim53]
      #5841964 - 05/05/13 04:17 PM

The scope has pretty good glass to start with. I'm not expecting dramatic improvement, but the astigmatism bugged me a bit. Along with my own astigmatic vision (hello 50th birthday), it took me a while to troubleshoot.

I am expecting perfect collimation, though.

Edited by Gil V (05/05/13 04:18 PM)


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Andy Taylor
Twisted, but in a Good Way
*****

Reged: 09/24/08

Loc: Epsom - UK
Re: Aligning my Dynamax new [Re: Gil V]
      #5842952 - 05/06/13 05:46 AM

Good luck! I managed to get mine pretty good and got some fine shots of Jupiter.

Until it fell off of the mount and smashed the finder through the tube...!!!

I repaired the tube but have never managed to get the alignment right since.

I'll keep on trying.


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Andy Taylor
Twisted, but in a Good Way
*****

Reged: 09/24/08

Loc: Epsom - UK
Re: Aligning my Dynamax new [Re: Andy Taylor]
      #5842955 - 05/06/13 05:57 AM

By the way - make sure the screws around the corrector retaining ring are not tight...

I used some 2.5mm hollow silicon tube around the corrector to hold it gently in the centeral position.

Over tightening the collimation scrrews is not a good idea either.


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Andy Taylor
Twisted, but in a Good Way
*****

Reged: 09/24/08

Loc: Epsom - UK
Re: Aligning my Dynamax new [Re: Andy Taylor]
      #5842964 - 05/06/13 06:11 AM

>>>>I considered removing the primary and reseating it on the baffle slide to get rid of that last touch of astigmatism, but I have no way of knowing if it's from the primary or the secondary. Plus, I don't have a cabinet of spare optics to swap around. Law of diminishing returns, I guess...<<<<<

Remove the primary and the sliding tube. Remove main baffle tube.

Slide primary back on and place upright on a flat surface.

Check centering from edge of primary to baffle tube. (mine was "centered" using insulating tape from the factory!).

If good, mount a laser pointer to project a beam onto the primary with the reflection on the ceiling. Revolve primary on the tube and watch the laser spot. If it revolves in a circle then the mirror alignment is off.

Have fun shimming it!


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Gil V
professor emeritus


Reged: 09/09/12

Re: Aligning my Dynamax new [Re: Andy Taylor]
      #5843056 - 05/06/13 08:01 AM

I'm leaning towards doing that, Andy. The views through the scope were nice, but the astigmatism bugged me while at the eyepiece. A bright star shows more contrast than my artificial star did, making the optical error more prominent. Not going to do anything just yet, I'll think about it for a bit.

The artificial star did work very well, though. The scope looked identical outdoors - it was perfectly collimated, and looked identical just inside and outside of focus.

Edited by Gil V (05/06/13 08:03 AM)


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Starsareus
member
*****

Reged: 07/27/08

Re: Aligning my Dynamax new [Re: Gil V]
      #5843193 - 05/06/13 10:07 AM

A little off topic-I have a B&L 8001 bought from an employee & LOVE this scope!! Images good(so far-have not pushed it).Concern is focusing knob seems hard to turn and does not seem "smooth" to touch. Any ideas?/I lived near original factory/Hartford & with blessing of Krewalk brothers, was allowed to search floor for parts! Good old days. Never forget that place. Nor them!!

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GeneT
Ely Kid
*****

Reged: 11/07/08

Loc: South Texas
Re: Aligning my Dynamax new [Re: Gil V]
      #5843904 - 05/06/13 04:17 PM

Quote:

Since I built so many of these in the year or so I was an optical assembler at Criterion




I count myself as one of those who was very disappointed with the optics of my Dynamax 8. All objects were poorly resolved and not sharp. By comparison, my C8 performed extremely well.

Could you shed any light on why so many Dynamax 8's were released with such poor optics?


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Gil V
professor emeritus


Reged: 09/09/12

Re: Aligning my Dynamax new [Re: GeneT]
      #5844169 - 05/06/13 06:33 PM

My thoughts on this - I would refer you to the article I wrote here.

I do think that there were variations in the quality of the glass we purchased. Plus, each master block was different, I am sure that some were better than others.

I was an enthusiast as well as an employee - so I had a pretty good idea what the customer would think when they got their scope. I was not the only assembler in the plant, though. I was certainly the most avid amateur astronomer doing optical assembly in the plant when I was there - before me and after me, I cannot comment on. Some of the assemblers I worked with probably looked through a scope for the first time when they were training to assemble them.

Edited by Gil V (05/06/13 06:35 PM)


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Gil V
professor emeritus


Reged: 09/09/12

Re: Aligning my Dynamax new [Re: Starsareus]
      #5844182 - 05/06/13 06:41 PM

The only time I encountered stiff focusing was when the focus screw did not line up perfectly with the hole in the mirror cell. We would file the hole with a rat-tail file to correct that.

If the focus is stiff, but the scope works well with little-to-no image shift, I would leave it alone.

The plant could have changed the focusing mechanism for the 8001 line, although I don't think it's likely. If they did, then the stiff focusing could be for a reason I'm not familiar with.


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Gil V
professor emeritus


Reged: 09/09/12

Re: Aligning my Dynamax new [Re: Gil V]
      #5851475 - 05/10/13 07:38 AM

Second attempt. Pulled primary out this time. Primary was shimmed improperly - I fixed that. Did not test alignment of primary on baffle slide - don't think that is the root cause. Locking ring was not very secure. Cork washers were normally used, but not in this particular scope - fiber washers only on primary. I removed the fiber washer from the coated side, so the primary has a rubber washer on the optical side, and a fiber washer on the back.

Reassembled and realigned. Still a little bit of astigmatism, but it seems better. Just inside and outside of focus with 4mm eyepiece nice and round.

I think the astigmatism is from the secondary. Anyone out there have a DX-8 secondary mirror that they are willing to part with?

Not clear, hasn't been for a few days. Can't test the scope outside yet!!

Edited by Gil V (05/10/13 07:41 AM)


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Andy Taylor
Twisted, but in a Good Way
*****

Reged: 09/24/08

Loc: Epsom - UK
Re: Aligning my Dynamax new [Re: Gil V]
      #5851505 - 05/10/13 08:07 AM

I think you should have done the laser/rotation check as well.

If the primary is pointing off axis then you are just compensating by adjusting the secondary.

What I think of as "dog leg" collimation...

Someone mentioned that the secondaries were made by Carton. If so, they should be pretty decent quality.


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orion61

*****

Reged: 10/20/07

Loc: Birthplace James T Kirk
Re: Aligning my Dynamax new [Re: Andy Taylor]
      #5851580 - 05/10/13 08:54 AM

I have a DX6 with Outstanding optics!
What % of Dynamax were 6" like mine?
I was surprised how good the optics are in it. I got it with the trunk and the Dyna Tracker. It had never been used. It fried the 1st time I used it. seems it wasn't put together right from the Factory. Dave was kind and fixed it free. That was so kind of him.
I have had 3 Dynamax. One had exceedingly good optics,
Grey/Dark Grey color, one had fairly bad optics Blue/grey, and the 3rd was good,also Grey/Datk Grey color. I'D 1/6TH WAVE by compairing with my known 1/8th wave Newtonian.
I have always loved the mechanics of the Dynamax! Thay seemed "Tighter" and smoother than my C8.
I also had a B&L 6" and serviced another B&L 6" EX optics.
It seems the 6" had MUCH better optics on average than the 8" Why is that?
Thanks for the post


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Gil V
professor emeritus


Reged: 09/09/12

Re: Aligning my Dynamax new [Re: orion61]
      #5851587 - 05/10/13 09:03 AM

I hear you about aligning the primary to the slide. It will depend upon the view when I get the scope outside.

Please note that I might enjoy this kind of project. It doesn't bother me at all that I might have to do it again.

If I have to take that next step, I'll probably make a target and align the main baffle as well.

We never (and I mean never) checked the optical alignment of the primary on the baffle slide. We just shimmed the slide with electrical tape and assembled. The kind of astigmatism I'm seeing was typically fixed by rotating or replacing the secondary - that triangular shape at focus is familiar to me.

That being said, with the scope working like it does now (assuming it works the same outside), we would have shipped it without a second thought. The airy disk is round-ish, it's not a sharp triangle. If it were, I'd be thinking about pinched glass somewhere.

Oh, the secondaries were Japanese, and we had very few problems with them.

Edited by Gil V (05/10/13 09:04 AM)


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Gil V
professor emeritus


Reged: 09/09/12

Re: Aligning my Dynamax new [Re: Gil V]
      #5856688 - 05/13/13 12:48 AM

Scope performed well tonight. I did have to touch up the alignment, but after that it was all good. Think I'll be using the scope for a while without further surgery.

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Andy Taylor
Twisted, but in a Good Way
*****

Reged: 09/24/08

Loc: Epsom - UK
Re: Aligning my Dynamax new [Re: Gil V]
      #5856955 - 05/13/13 08:25 AM

Quote:

Scope performed well tonight. I did have to touch up the alignment, but after that it was all good. Think I'll be using the scope for a while without further surgery.




Hey! Think how much better it would be if you knew the primary was aligned...

I had another look at mine over the weekend and found that after my last careful setup I had missed the fact that I had installed the corrector back to front...

Onwards & upwards...


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Gil V
professor emeritus


Reged: 09/09/12

Re: Aligning my Dynamax new [Re: Andy Taylor]
      #5857114 - 05/13/13 10:03 AM

Hold off. Although I've seen writing about that, my personal experience is that the front-to-back orientation is irrelevant. And my personal experience is assembling a couple hundred of them.

In design, perhaps. At the eyepiece, not so much.


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