Posts Made By: Mark Peterman

I paid my $12 way back when.

In August this year, I SUPPORTED with $15 thinking this would make me good for another year.

Now my letter has come up in October, am I good to go or do I owe another $15?

Looking for some feedback on this...

I have a 12" dob (F/4.9) with a 2.75" secondary and a 2" focuser. The Newt program indicates there is vignetting at the focuser of the 75% ray. The diameter of the 75% illuminated area is 1.8304 inches.

If my lowest power eyepiece (Nagler 26mm) has a field stop of 35mm (1.3774 inches) which is half an inch smaller than the 75% zone. So is the vignetting really an issue? It seems like the field would be illuminated by the 100% and 75% rays and the vignetting is occuring outside the field.

Lastly, if I change the secondary to 2.6" the vignetting goes away but the 100% zone gets smaller. I'm not sure if the tradesoff are worth it. The central obstruction only changes from 23% to 22% and I am not sure I would see a difference.

Thoughts?

Thanks,

Mark

Paul,

Check out this article:

http://www.cloudynights.com/documents/naglers.pdf

Mark

I found the existing telfon pad positions, were approximately 110 degress apart. Since moving them in to the prescribed 90 degrees was fast (and cheap), I decided to try that part of the solution first.

The result was a BIG improvement. I will have to wait until I get the scope outside and tracking through the eyepiece to know for sure but I can tell right away that it requires a lot less force to get it moving and it does not jerk like it used to.

Going by the loading formula, I do need larger pads which is what I will change next if I determine this step did not completely solve my problem.

Thanks again to everyone who responded.

Mark

I think you are looking for Eyelights by The Right Stuff.

http://www.the-right-stuff.net

I would be curious to hear from others who have used both.....

Is this opinion "value" or "performance" based?

While moving the teflon pads to 90 degrees helped considerably, it was not enough. There was still that stickyness that had to be overcome which resulted in the scope 'jerking' before gliding.

The original pads were 3/4" square and according to the formula posted earlier in this thread, they should have been 1-3/8" x 3/4".

The difference is night and day after I installed the larger pads. Now when I go to nudge the scope, it just glides, no sticktation, and when I stop and let go, it stays where I put it.

Thanks again to everyone for their feedback.

Mark

I've owned one of his 8" f/6 mirrors, number 1298217 - EXCELLENT!

The 9mm is available. The 4mm is not yet available.

The first production run of the 6mm had some problems (mainly internal reflections and shorter than advertised eye relief) so that run is being sold at half-price ($49) and there are some still available. A fixed 6mm is in the works but no word on when it will be ready.

I purchased the first run 6mm just to give it a try - I'm pleased with it as a $49 eyepiece. It is built very well, the twist up eyecup is nice. It gave me some nice views of Mars the other evening but yes, there was some bad glare with Mars just outside the fov, it deminishes as you get closer to on axis. Pinpoint stars across the fov in my 10" f/4.5 dob. Eye relief may not have been 20mm but it was definately more than 10mm. YMMV.

When the final version of the 6mm comes out, I would love a direct comparison with a 6mm Radian.

Mark

I just spoke with a lady at Burgess Optical who said that the 4mm Planetary EP's are in the country, waiting to clear customs. They are expecting them any day.

Further, anyone who purchased a 6mm Planetary EP will be getting a new retaining ring which is supposedly the culprit in the glare problem. No word on when though.

Mark