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open OTA for refractors???

Started by thx1138, 03/29/2014 02:19PM
Posted 03/29/2014 02:19PM Opening Post
I have been an ATM most of my life and have been building and re-building scopes a long while. I am just asking the question, to all out there, [COLOR="Maroon"]what you think of an open OTA design for a refractor.[/COLOR] I am thinking of a 180mm f/8 objective.

Any thoughts - positive, negative, suggestions, etc.

Thanks, JohnD
Posted 03/29/2014 08:35PM | Edited 03/29/2014 08:46PM #1
Hi John,
With all your experience, I think you know the answer very well...Aside form being minimalist is there some compelling reason for an open tube, so many disadvantages strength and associated flexure, even a truss structure with long throw and small base has flexure issues, air currents dirt and dust.. 180 is not that big I'd go with a carbon tube if you are concerned with weight, an aluminum tube will be a lot simpler and less expensive. These are all things you know well from your years building and rebuilding... No irreverence intended just an affirmation of what you already know...
OH and building a refractor of that size and speed is one #$%% of an accomplishment, hats off to you...
Best regards,
Posted 03/31/2014 11:50AM | Edited 03/31/2014 11:56AM #2
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.


Attached Image:

klawson's attachment for post 148273


40 year old restored C14 with recirculating cooling w/Skywatcher DOB GOTO Conversion (CPC14)

10" F/15 thermally managed ATM Coulter Cassegrain mounted on a Celestron C14 wedge to GEM conversion

"Electro-DOB" mounted Sky-Watcher Evostar 150mm/1200mm ED Refractor

"Rescued" Craig's List Orion 120mm/1000mm Refractor