Posts Made By: Gary Weber

A thread starting with message 273493 had a bit of discussion on this topic.
https://www.astromart.com/forums/viewpost.asp?forum_post_id=273493&poll_id=&news_id=&page=

This was also discussed in a thread beginning with message 157453.
https://www.astromart.com/forums/viewpost.asp?forum_post_id=273493&poll_id=&news_id=&page=

Gary Weber

A couple years ago there was a discussion on Astronomik OIII filters on the BigDob Yahoo group. based on initial reports of improvements with the Astronomik, I purchased one to compare to my Lumicon.

Using a filter slide in my 12.5" f/6, I did a few nights of comparison between the Astronomik and Lumicon OIII filters, primarily on the Veil Nebula. During evenings where the limiting visual magnitude was not great (5.8 - 5.9) for this site, I could not discern any significant difference in the detail of the nebula. The Astronomik seemed to pass more light and stars were brighter and not coloured so much as through the Lumicon.

During another test with the limiting magnitude at ~6.4, I noted that the Lumicon provided better contrast and showed significantly more detail in the twists and curls of the nebula.

The discussion on the BigDob group seemed to have people preferring the Lumicon and people preferring Astronomic with no consistency among the opinions.

I also had an oportunity to test each filter with a spectrometer and the passband of the Astronomik is considerably wider than the Lumicon. This is confirmed by the results from testing a number of different filters at this web site.
http://home.freeuk.com/m.gavin/grism2.htm
This also shows the Astronomik to have a wider passband.

This wider passband is also shared by Tele Vue's OIII filter. I eventually sold my Astronomik to a fellow with a 4 inch refractor. Because it passes more light, it works well in smaller scopes and I always thought this was consistant with the design of the Tele Vue OIII filters. Tele Vue only makes small scopes and perhaps they chose a wider passband to be more successfull in small scopes. I believe older advertisements for the Lumicon filters suggested use on scopes larger than 6" to benefit best from the filters.

Anyway, I liked the Lumicon better, but others find the Astronomik to be great.

Gary Weber

I did something similar for a Discovery 8" f/8. I simply used a 12" square piece of cheap floor tile (<$2) and placed the fan on the outside. I use the elastics to hook around the outside screws that hold the mirror mount in the tube.

I run the wires to a small switch box with a rheostat for speed control. The power also plugs into the switch box which mounts to the upper portion of one of the dob base uprights with velcro.

Gary Weber

Here is a shot of the inside of the fan mounting board. I lined it with flocked paper and used a strip of sorbothane along the perimeter as a gasket for vibration reduction.

I have the fan drawing air down the tube and exhausting out the bottom.

This system has worked very well and is cheap and easy.

Gary Weber

Here is another shot. Same hike, different scene.

Gary Weber

Having ordered a Tom O platform, I can tell you one reason that was important to me...

The platform easily works on more than one telescope.

Gary Weber

I had some eyepieces that were similar. All I did was cut some flocking paper and rolled it up and inserted it into the EP barrel. I never had to glue it as the pressure kept it in place. You could do something similar with the diagonal and see if the problem is still there. This would be a little easier than a full paint job, although you may find the paint job is necessary.

Gary Weber

The best advice is simply to start moving air through the tube as Floyd suggests (choose your direction) and experiment. I have found that using more fans, or a bigger fan than one would think, is a good thing. This way you can drop the voltage to reduce the fan speed and still get enough air movement to provide the necessary cooling. This helps to reduce the vibratin potential from operating the fans while viewing at high power. It's at high power where the most noticable improvments are noticed.

Gary Weber

A few years ago I changed the secondary in my 12.5 f/6 from a 2.6 to a 2.14. I recall doing considerable research on what was "appropriate" for a fully illuminated field. As I recall, the target to shoot for with a fully illuminated field was something between 0.3° and 0.5°. Your choices are quite widely separated with the fully illuminated field being either 1.0° or 0.2°.

Without having any real experience seeing a dropoff in illumination on any scope, I would still be hesitant to reduce the fully illuminated field to 0.2°. So if I was choosing, I would probably stay with the 2.6 inch secondary size. If this was a scope on a driven mount, then I might be willing to try the smaller secondary.

Gary Weber

http://www.fpi-protostar.com/diagmnt.htm

I have replaced the spiders in three reflectors. One, four vaned (12.5") and two, three vaned (8"). In a 10", I would opt for the three vaned spider. IMHO you can't go wrong with Protostar products.

Gary Weber