12" SDM upgrade complete!

[pgc hunter]

Just got word from SDM Telescopes that my 12 incher is very soon due for pickup! Some of you might remember that I already had this scope, but I decided to get a few upgrades done.

The old primary has been replaced with a thinner Zambuto 12", and it'll also have an Antares 1/30 wave secondary. The primary will have Catseye's radioactive collimation spot and a few minor touchups have been done.

Getting real excited and anticipation for first light is growing! All that's left to do now is find a suitable day for pickup.

[Shark Bait]

Interesting. This is the first time I have heard of this method being used for telescope collimation.

Is there going to be a tritium vial glued to the primary, or are you going to use a dot of tritium paint?

The tritium vials in my Silva compass are quite bright, while the tritium paint under the mirror is less intense. They will last approx 7 to 10 years before they start to fade.

Will this permanent glowing point of light mess with your view at the eyepiece?

My 12" Dob wishes it was an SDM, and so do I. Bet you are keen to get it back!

[DavidU]

It is the shape of the spot used (it looks like a radioactive sticker/sign)

[JethroB76]

I thought this scope already had nice locally made 12.5" mirror in it?

[erick]

Congrats Sab! I'm sure it will be superb!

[pgc hunter]

it did, but after a year and a half of use under all manner of seeing conditions, I've found that there was some mild astigmatism somewhere in the optical train. Compared to my 8", contrast appeared to be a little less and stellar images were noticably "less clean" at high power. The primary was tested, and IIRC it had a couple of zones, which threw some of the light out of the airy disk. I can't remember if the primary was causing the stig though... could've been the secondary. So with that, I decided to go ahead and replace both mirrors, which will eliminate all doubt.


THanks Eric! Peter's evaluation of the mirror - sensibly perfect :P

[Satchmo]

Just to clarify there the on the Adcock 12" mirror I tested for Seb . The main problem was the thermal inertia of a 2 1/8" thick mirror , and a minor zone out near the edge and there was no astigmatism. A thinner mirror will perform much better in real world conditions and as the seeing will effect high power viewing with a 30cm on more nights than a 20cm allowance must be made for the increase in aperture.

[Astroman]

Congrats on the upgrades Sab... sounds like a nice scope your getting out of it....

[JethroB76]

Ah, yeah given it was an Adcock mirror, I thought maybe a move to a thinner mirror was behind the change. Was also making sure I hadn't missed it coming to grief in some way :sadeyes:

[pgc hunter]

Thanks for clearing that up and for doing the test Mark. Looks like the secondary would've been the culprit behind the astigmatism. The zones you've found in the primary and its struggle to cool would've contributed aswell.




cheers Astroman, this'll be pretty much my dream scope... until I can afford a 30 incher with an observatory :D



Taking Mark's test results into consideration, and subsequently the likelyhood of the secondary introducing some astigmatism, I had to think long and hard.... could I live with some minor zones on the primary and just replace the secondary? I decided to replace both, as it was a good opportunity to go for a thinner primary while I'm at it, and for piece of mind that whenever the view is bad, it is for sure the seeing, not the optics.

While the scope is in Peter's shop, he not only did a few other minor jobs on it at my request, he also took it upon himself to replace the temp gauge with a new probe for the mirror and the SDM logo on the focuser board, as it became a little stained. Now that is service! :thumbsup:

[pgc hunter]

pick up is today :party:

[Shark Bait]

:thumbsup: New Moon, dark skies. Hope the skies are clear.

[pgc hunter]

It is appropriately cloudy :sadeyes: