Posts Made By: Keith Lawson

What type of astrographic telescope? SCT, Newt, Refractor, Houghton? Try looking here: http://www.telescope-optics.net/ You might be able to get some design specs here. I hope this is helpful.

Keith

Here is an 8" F/12 I built back in 06. The OTA splits into three parts for easy portability and setup.

Keith

My observing experience has shown that the "conditions of use" are a big factor in what you see at the eyepiece. What I mean is that "aperture rules" only when allowed to rule under the right conditions. Number one is that the big aperture must be good aperture (well corrected). I have also found that the larger the central obstruction is in a telescope, the more sensitive a telescope is to the seeing conditions. Despite all the number crunching concerning an obstructed telescope's contrast factor etc. etc., I have noticed an obstructed telescope's seeing sensitivity more than that of the contrast factor through many obstructed instruments.

Temperature plays a big part in telescopes as well. If you don't control the "weather" in the telescope it will not perform as good as the aperture should allow. Collimation is another factor in performance. Many SCT's are severely crippled in planetary performance by many who don't know how to properly keep one collimated.

I could mention more factors but I hope you get the idea. A well corrected 8" SCT should beat a 6" with a minimum obstruction on planetary work but this is not always the case :S There are a lot of things that have to be right with the SCT.

I'm currently using a 10" F/8 Newt with a 15% obstruction.

Question: the telescope you compared your well designed instrument to, did it have good overall correction, was it well collimated, cooled off?

Keith

I don't claim to know everything but I do have a lot of experience in designing, building and using telescopes. Almost 40 years. There are some of us that have had a lot of hours behind the eyepiece and are not trying to be know-it-all's when we share our real life telescope experiences. At one time I was quite content with my Sears 60mm refractor when I was stationed in Alaska. That was a long time ago.

By your response it seems as though you have never seen Jupiter or Saturn through a good 8" to 12" telescope on a night of good seeing. A crisp view Saturn or Jupiter at 400x is not to be forgotten. Though a 4" will give a good "view" it can never match the details seen through a large high resolution telescope.

I'm not aganist smaller telescopes. I have a 90mm refractor that I use quite often. I use it on those so-so nights of average seeing. Very rarely is the seeing bad enough that I have to put the scope away. I can't say the same for my 10" reflector.

Despite how good it is, the 90mm refractor can never approach the level of definition that my 10" can provide on those rare nights of good seeing. Some of us are willing to pay the "price" (either in dollars, comfort or patience) for such views.

Keith

Try here: http://bobmay.astronomy.net/CassNotes/index.htm

And here: http://www.alpo-astronomy.org/jbeish/Cass_Equ.pdf

Any idea who made the optic set? Are there any markings on the back or edge of the primary/secondary?

Keith

I have built an award winning open tube 8" F/9 refractor. I found the two main advantages of an open tube refractor to be ease of construction and cooling. Even a 6" lens needs to be at ambient temperature to give its best performance.

Please weigh the opinions expressed that have no experience with open refractors. Just because something is different does not make it bad. Some refractor users can be "purists" and come against anything that departs from the "perceived" norm. Properly baffled open tubed refrctors can perform very well and I have evidence to back this claim up. My scope easily out performed a 130mm apo on Saturn.

Keith

Added wheels and removable handles. Set up couldn't be easier. Saves my back from loading the OTA

Scopejunkie

Added a manual altitude drive. 12 degrees of tracking 8)

Update:

Since I don't have an observatory I figured I would set up an observing "area." This old guy is getting lazier by the year. The scope now stays outside. Wish me luck, rain is coming

Scopejunkie

Cooling system installed. Testing tonight. Just had a front pass through yesterday. Hopefully I can get in some views in before the dew wipes me out.



Scopejunkie