Folded Refractors

[Visionary (David)]

The concept-function of a Folded Refactor is intriguing. Has any Icer, either used or owned a Folded Refractor?
Even better, has any Icer's built a Folded Refractor?

[anj026]

There are lots of examples on the internet and I have thought of making one myself a few times. It seems you trade the inconvenience of a long tube/large mount for the added complexity/slight loss of light transmission. Depends on your priorities. I guess the introduction of lower cost ED refractors has reduced the appeal of folded refractors somewhat.

Here is a link to a nice big one;
http://www.iceinspace.com.au/41-465-0-0-1-0.html

There is some good information here;
http://davetrott.com/telescope-proje...ded-refractor/

[Visionary (David)]

Originally Posted by anj026

There are lots of examples on the internet and I have thought of making one myself a few times. It seems you trade the inconvenience of a long tube/large mount for the added complexity/slight loss of light transmission. Depends on your priorities. I guess the introduction of lower cost ED refractors has reduced the appeal of folded refractors somewhat.

Here is a link to a nice big one;
http://www.iceinspace.com.au/41-465-0-0-1-0.html

There is some good information here;
http://davetrott.com/telescope-proje...ded-refractor/

Andy,

The second source you have cited makes Folding Refractors sound even more interesting! One of the obvious issues raised is re: Achromatic scopes. Within the articles describing Folded Refractors is the continuing reference to the excellent characteristics of a precision Achromatic.
I have a 5" Achromatic, I have fitted a GSO Crayford style Focuser and discovered to my complete delight that it's a wonderful optical instrument. The underlying prejudice against Achro's seems to be limiting experimentation.
With all this said, folded Achro's are very interesting if I had the ability it's something I would love to play around with.

[ZeroID (Brent)]

Your 5", what is it's focal length ?
Longer focal length Achromats show less effect of chroma. My 80mm/f11 is excellent visually but put put a camera on it and you will see the fringing effects. My 80mm/f5 is a good wee scope but chroma is very easily seen visually.

[glend (Glen)]

I have a 127mm iStar R30 Anti-astigmatic objective (f12) in my long refractor that I built two years ago. It is a wonderful scope with almost no detectable CA (cleaned out the last bit with a Fringe Killer). I did consider making it into a folded design but the necessary mirrors would increase the weight. Collimation is harder but that wasn't the stopper, in the end I decided the additional weight and plain butt ugly nature of most folded designs convinced me to stay with my light-weight truss open tube design (ala the iStar TCR). I have looked at folded designs now and then since but no one has produced one I'd want to own. If I was building it again, I would go with a carbon fibre truss tube design like my imaging newt, it would weigh even less and be great to look at.

[dannat (Daniel)]

forget folder refractor , schiefspiegler telescope is what you're after

[Visionary (David)]

Originally Posted by ZeroID

Your 5", what is it's focal length ?
Longer focal length Achromats show less effect of chroma. My 80mm/f11 is excellent visually but put put a camera on it and you will see the fringing effects. My 80mm/f5 is a good wee scope but chroma is very easily seen visually.

Brent, the scope has a focal length of 1000m and i believe it is an f12. I really like the scope. It's been placed upon a Japanese made Mizar mount. The crazy thing about this scope is I paid only $50!
I have a feeling my Achro maybe a good example of type.

[Visionary (David)]

Originally Posted by dannat

forget folder refractor , schiefspiegler telescope is what you're after

I had a look at Schiefspiegler scopes, they look as though the produce a "coherent light stream" via their complex baffling construction. An intriguing scope. Have you used one?

[Visionary (David)]

Originally Posted by glend

I have a 127mm iStar R30 Anti-astigmatic objective (f12) in my long refractor that I built two years ago. It is a wonderful scope with almost no detectable CA (cleaned out the last bit with a Fringe Killer). I did consider making it into a folded design but the necessary mirrors would increase the weight. Collimation is harder but that wasn't the stopper, in the end I decided the additional weight and plain butt ugly nature of most folded designs convinced me to stay with my light-weight truss open tube design (ala the iStar TCR). I have looked at folded designs now and then since but no one has produced one I'd want to own. If I was building it again, I would go with a carbon fibre truss tube design like my imaging newt, it would weigh even less and be great to look at.

Do you have a pic of your scope, I would love to see how it developed

[dannat (Daniel)]

Barry adcock has constructed his own schiefspiegler, looked thru at a lunar eclipse & maybe a solar event -refractor like views with mirrors -only thing they don't do is Wide fields

[anj026]

David if your scope has a focal length of around 1000 mm and an aperture of 5" (127 mm) then the focal ratio is 1000/127 or around f8. A 5" f12 would have a focal length of around 1500 mm (5" x 12 = 60").

I've thought about a folded refractor myself. For a long scope like a 5" or 6" f15 it can make the telescope a lot more convenient and easier to transport.

[ZeroID (Brent)]

One of the issues with folded scopes, refractor or reflector is the induced distortion caused by the angle of the required mirror to the axis of the light path. Theoretically you could introduce another mirror working at right angles to the first which would compensate in the other direction and thus also gain a small modicum of magnification but the build and collimation issues could be fun.

And it would still look ugly ...

[glend (Glen)]

Originally Posted by Visionary

Do you have a pic of your scope, I would love to see how it developed

Here you go, pics are all through this truss refractor build thread:

http://www.iceinspace.com.au/forum/s...Star+refractor

http://www.iceinspace.com.au/forum/a...1&d=1399811184