Aligning my Dynamax
Posted 05 May 2013 - 01:10 PM
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
Posted 05 May 2013 - 03:07 PM
Posted 05 May 2013 - 03:17 PM
I am expecting perfect collimation, though.
Posted 06 May 2013 - 04:46 AM
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.
Posted 06 May 2013 - 04:57 AM
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.
Posted 06 May 2013 - 05:11 AM
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!
Posted 06 May 2013 - 07:01 AM
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.
Posted 06 May 2013 - 09:07 AM
Posted 06 May 2013 - 03:17 PM
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?
Posted 06 May 2013 - 05:33 PM
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.
Posted 06 May 2013 - 05:41 PM
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.
Posted 10 May 2013 - 06:38 AM
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!!
Posted 10 May 2013 - 07:07 AM
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.
Posted 10 May 2013 - 07:54 AM
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
Posted 10 May 2013 - 08:03 AM
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.
Posted 12 May 2013 - 11:48 PM
Posted 13 May 2013 - 07:25 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.
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...
Posted 13 May 2013 - 09:03 AM
In design, perhaps. At the eyepiece, not so much.