Posts Made By: Paul Preto

Hmmm? Why are you being ignored? Care to clarify your post?

I am trying to build a binocular "mirror box" to ease my aching neck. My binos are Oberwerk 20X80's. Does anyone know where you can get a affordable mirror for binos of this power?

One source states: Our PREMIUM mirrors have a wavelength error of ~/= 1 lambda.... While some purchasers have successfully used this mirror with binoculars up to 20 Power, 18x is the recommended limit.

So, what surface accuracy will I need for 20X binos, and where can I get one?

I am trying to build a binocular "mirror box" to ease my aching neck. My binos are Oberwerk 20X80's. Does anyone know where you can get a affordable mirror for binos of this power?

One source states: Our PREMIUM mirrors have a wavelength error of ~/= 1 lambda.... While some purchasers have successfully used this mirror with binoculars up to 20 Power, 18x is the recommended limit.

So, what surface accuracy will I need for 20X binos, and where can I get one? I've been searching the web and emailing vendors without much success.

After over a year of waiting, I'm finally going to receive my new 16" f/4.5 truss tube dob from Astro Sky at the end of this month. Actually most of that wait was for Steve Swayze to complete work on my primary, which he got out to Spectrum Coatings late in March. James Grigar at Astro Sky got it in April and quickly completed my scope. I'm posting a picture here.

James is a real gentleman and stayed in touch with me via email and phone throughout the entire ordeal. I changed my preferences more than a couple times, which did not upset him at all. It's got a Moonlite dual speed focuser, Antares 1/20 wave secondary, Sky Commander w/10K encoders. James even flocked the UTA at no extra cost. Now I just can't wait to get it in time to enjoy it this summer and fall. I'll post a review here, once I've had a chance to use it a few times.

Since I got my 16" Astro Sky dob, I've encountered what appears to be a new dimension in the collimation procedure - UTA position. I marked my poles to insure I put them on the same each time. But I still get what appears as a misalignment of focuser to secondary, even though these parts have not moved. My laser is pointed at center of primary and the primary is collimated with catseye cheshire. But I see that the reflection of my laser off the primary does not converge on the secondary surface with the spot where the laser hits the secondary on first pass. Any procedure or other suggestions for avoiding having to tweak the focuser each time?

Not that kind of smoke. I mean all the fires going on in the state right now. So where will all you California astronomers go to get away from smoky skies in the next couple weeks?

Wondering how the smoke from the CA fires is affecting Oregon? I searched the web for fires in OR, but was surprised to find none, considering that we have about 1,000 going here in CA.

I'm thinking of driving up there next week and would like recommendations on good astro locations that are not too crowded and have picturesque surroundings (since my wife is not a diehard like me). I notice the area northeast of crater lake is national forest and appears black on the CSC light pollution charts. But I'm wondering if that is more like high desert?

I'll try to check out Todd's report. I have done the procedure as described in Dan McShane's website instructions - move scope to place image at edge of field where it looks circular, then adjust primary to bring that circular image to center of the field. Doing this numerous times gives me the best image, but I can never eliminate totally the astigmatism, which is obvious when racking inside versus outside focus.

In reply to the most recent posts, I appreciate all ideas whether based on optical theory or just careful speculation.

To confirm some things I'm hearing and questions, the focuser is tilted to be at a 90 degree angle to the center of the mirror segment that forms my primary. I have used RTV silicon to mount both primary and secondary (no cell or holder pressure), so stress is probably not an issue. I don't have astigmatism (not in my good eye at least), and I've ruled out the eyepieces.

I thought the orientation of the primary might be critical, that is that it could not be rotated. But someone said that primary collimation would negate any slight rotation of the thin edge of the primary relative to the secondary's major axis orientation. Some others have thought it is critical. I'm still perplexed about this one, though I tend to feel a small rotation could be collimated away.

I suppose worst case I could get the primary tested and replaced by Dan McShane if necessary. Would he give me a free one after some four years??? (I'm not the first owner either).

I thought this thread was dead, but I can see it has struck a nerve for some, like you Bill. I also have a big dob and have used an aperture mask. That's what made me believe this design could work. Miscollimating the primary certainly does give you strange looking stars, but what most struck me about what you just said is that the thinnest edge of the primary (mirror segment) has to be aligned with the secondary (major axis). I think if it is off at all, you are not looking down the center of the light cone but rather intersecting it at an angle. I can see this in my mind, but don't have any tools to illustrate it. I don't believe tilting the primary can compensate for its rotation, since the outside and inside edges of the cone will now not be aligned with the major axis of the secondary.