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Refractor


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1 hour ago, johninderby said:

Was looking at the 127S version but the 127L is a lot cheaper. 🤔

That due to at least one of two things.  One, the ground, figured and polished surfaces of a short focal-ratio, crown-and-flint doublet, the curvatures, are steeper(convex), deeper(concave), a bit more exotic if you will.  That requires more attention, and labour, in getting it just right.  It's the same with a 150mm f/4 parabola vs a 150mm f/8, among Newtonians.

Then, imagine yourself at a shop at the end of a dark alleyway.  You know absolutely nothing about telescopes, yet one is earnestly desired nonetheless.  The sign above the shop is faded and soiled.  You can barely make out the name: Soso Telescopes & Pet Shop.  The door creaks as you enter, and a bell tinkles, alerting the proprietor...

"Good Day.  I'd like a telescope, please.  Ooooh, that one's nice and long.  How much?"

"220."

"Hmm, what's that short one over there, by the dead parrot?"

"It's the same as the long one, but shorter."

"I can fit that one in my car!  How much?"   

"420."

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  • 5 months later...
On 13/09/2020 at 20:25, johninderby said:

Slight thread resurrection however this scope has piqued my interest.  I am potentially in the market for a long focal length frac and this is local to me.  Can anyone tell me anything about it.  Price is perhaps a shade on the high side  but looks a nice thing... 

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22 minutes ago, dannybgoode said:

Slight thread resurrection however this scope has piqued my interest.  I am potentially in the market for a long focal length frac and this is local to me.  Can anyone tell me anything about it.  Price is perhaps a shade on the high side  but looks a nice thing... 

A Belgian company that, for that model, use an Istar R30 objective lens:

http://www.frtelescopes.com/

Here is a review of the objective in an Istar tube:

http://www.istar-optical.com/istar-127-mm-(5”)-r30-f12-doublet-refractor-review.html

Neil English on his Istar 127mm R30:

https://neilenglish.net/5-inch-shootout-5-f-12-refractor-vs-a-5-1-f-5-reflector/

Hope that helps !

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16 minutes ago, John said:

A Belgian company that, for that model, use an Istar R30 objective lens:

http://www.frtelescopes.com/

Here is a review of the objective in an Istar tube:

http://www.istar-optical.com/istar-127-mm-(5”)-r30-f12-doublet-refractor-review.html

Neil English on his Istar 127mm R30:

https://neilenglish.net/5-inch-shootout-5-f-12-refractor-vs-a-5-1-f-5-reflector/

Hope that helps !

Thanks John.  Interesting piece by Neil and food for thought.  Trouble is once you have frac fever, even though much of what he says on the subject of a good reflector being more useable, just doesn't matter!!  Rather than hijack this thread any more I'll start a new one in the Whole Scope section - thanks again :)

 

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