Orion Clear aperture telescope

I came across this on telescope-service.
www.telescope-service.com/OrionUSA/refle...eflectors.html#Clant

I remember reading about this a long time ago, and never saw a working model. Like was already mentioned, it might be one for the future.

Seanie.

I thought this might be a discontinued product, but I did find it on the Orion website. Regarding obstructions - they can be negligible on large Newtonians, it's a question of construction and design - but they are never so on smaller aperture instruments. Not using a spider would certainly give this instrument an advantage over traditional Newtonians of similar aperture and the f/13.6 design also minimises the effects of coma and potential abberations that could be caused by the assymetric design.

Another type of telescope that can deliver near-APO quality is a Mak, if in the f/14 to f/15 range of focal ratios where the central obstruction size is minimised; however they do suffer from mirror shift like an SCT. On the positive side they tend to offer slightly better contrast than an SCT.

Your obstructed 12" SCT will show about the same CONTRAST in Jupiter's clouds as an 8" refractor.

The 12" will,of course, show a much BRIGHTER image.

Peter.

It about alot more then just contrast and brightness, for planetary viewing its about sharpness and I just cant see any SCT been as sharp as a good 8 inch refractor, anyway, we're deviating from the topic so I'm not going to go on about this...

Another type of telescope that can deliver near-APO quality is a Mak, if in the f/14 to f/15 range of focal ratios where the central obstruction size is minimised; however they do suffer from mirror shift like an SCT. On the positive side they tend to offer slightly better contrast than an SCT.

Not always, the Intes MK67 has a fixed primary mirror and you can collimate both mirrors, it uses a crayford focuser and is fantastic for planetary viewing, on night of poor seeing I can see more through it then the 12" and on nights of average seeing you dont see a whole lot more through the 12".
This Intes Mak is of course not a typical Mak with this focusing system.

Just one last point deviating from the topic.

When Gary Seronik wrote the following lines on page 98 of the September 2006 edition of Sky & Telescope he was talking about your telescope Dave:

"When it comes to resolving low contrast detail on the planets,simply subtract the obstruction diameter from the aperture.This means that if your 12-inch scope has a 4-inch obstruction,it has the low contrast resolution of an unobstructed 8-inch,while retaining the light gathering power of a 12-inch."

Peter.

So contrast is a function of aperture less the diameter of the obstruction (A-O), while the light gathering area is a function of area (πA^2-πO^2)?

("^" denotes "to the power of" in the absence of superscript)

If that's the case then using an instrument with an obstruction means losing a huge amount of contrast vs using an unobstructed aperture of the same size. My Scopos 66 ED for instance. though not gathering as much light, would have similar contrast to a typical 90mm Mak.