Posts Made By: Doug Scobel

I started out in my early teens with a 6-inch f/8 homemade reflector. My dream at the time was to someday bypass the 8 inch size and go ALL THE WAY to a 10-inch f/6. Thanks to John Dobson and others I've been using my homemade 13" for over 20 years now. So, yeah, I realized my dream and then some!

Doug

I finally got a chance last night to try the 19mm Panoptic in both my scopes last night. Again, lots of coma in the 13" f/4.5, but sharp right to the edge in the 8" f/8. As I suspected, I think I'm simply seeing the coma inherent in the fast dob - it's not the eyepiece's fault. I also was borrowing a friend's 27mm Panoptic, and in the 13" that was showing a lot of coma too. I think I'm just spoiled by my trusty old 28mm Pretoria, which is designed to remove coma, which it does very well. It only has a 50 degree apparent field and a lot of distortion, though, which is why I was considering the 27mm Panoptic. I may have to reconsider that.

Doug

Ron Bee said:

...and I just came in shivering from the 55d F cold night after spending a frost biting ;-) 2.75 hours with the zomm...

Ron B[ee]

55d F cold? Frost biting? Are you kidding??? Some folks in these parts would kill for a warm night like that!!!

Doug

Sorry, Linton, I don't have time to read ALL the replies, so I'll apologize in advance if I'm repeating what someone else has already said.

I don't think you'll see that much of a difference between a 12.5 and a 14.5. I would say go with the 18 or none at all.

I've often considered moving up from my 13.1", and I've decided the smallest I'd want to go up to would be an 18". But that's me.

Good luck,
Doug

Hi, Floyd, I installed a Protostar single arch secondary support in my 8-inch f/8 Newt last year, replacing a Novak four-vane spider. Definitely gets rid of the diffraction spikes, but do I see more planetary detail? Difficult to prove one way or the other, since I am limited by the atmosphere virtually all the time. Images were very good before, they’re very good now. I like the aesthetics of not having diffraction spikes, though.

Compared against a good four vane spider with thin vanes (like a Novak), a four curved vane spider will probably add total diffraction, three vanes will probably be a wash, and a single arch will probably reduce total diffraction. A curved vane spider is useful in eliminating the diffraction spikes, but IMHO its effect on planetary detail is marginal at best.

Good luck deciding!
Doug

Well, the clouds parted temporarily tonight and I had about 15 minutes to do a critical evaluation on the 19mm Panoptic in my 13-inch f/4.5. I was comparing it against another 19mm Panoptic that I borrowed from a fellow observer. And as we expected, the views were identical in each eyepiece. So my original statement that "There’s definitely something wrong with this eyepiece" was premature. The chances of both of them being defective are almost nil. And this should also put to rest any thoughts that somehow the seller was trying to pull a fast one.

Stars were good and sharp near the center of the field, but about one third of the way from the center of the field to the edge I could just start to see some coma. About half way to the edge coma was becoming more obvious, about two thirds to the edge it was obvious, and near the edge it was ridiculous. This eyepiece definitely needs a Paracorr in a fast scope. But in an f/8 or slower scope, it's a gem all by itself.

I also tried a borrowed 24mm Panoptic, and just like in my original evaluation, coma is much less pronounced across the entire field, despite it's larger true FOV. Not perfect, but pretty clean to within I'd say four fifths of the way from the center to the edge. Near the edge the coma is visible but not terribly objectionable. Being a newer design I guess it's just better corrected than the 19.

So, it's going up on AM. Keep in mind that it will work great in an f/8 Newt or an f/10 SCT. But in a fast scope expect to see some coma.

I'd be interested in hearing from anyone else who has done a critical evaluation in fast scopes to see if you get similar results.

Best regards,
Doug

You gunky!

Gatorboard is a high density foam board, laminated on both sides with a heavy posterboard-like covering. Here's a link to just one of many places that sell it (no sales plug, just the top of the list when I googled "gatorboard"):

http://www.backgroundstobasics.com/pages/gatorboard.html

I was recently at a graphics art place and the guy had this stuff all over his shop. It is very light and appears to be very rigid. Seems like an ideal telescope making material, especially where you want to save weight.

Doug

Find a used 17.5" Coulter mirror on Astromart. They were all f/4.5 I believe. Only a little less than 18", probably under 2" thick also. But close to what you want.

Doug

I think all the 17.5" Coulters were under two inches thick.

Doug