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f/5 5 inch FLAT Refractors?

Takahashi TOA-130 Equipment Refractors Buying Advice
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Ashraf AbuSara avatar
Ashraf AbuSara avatar
I am looking at 5 inch refractors that are f/5 with flat field on a full frame sensor with minimal to no aberrations. 

The only option I am aware of is the Televue NP127is. But I am not able to aquire any real life raw images to substantiate its ability on a full frame sensor, nor do I easily find spot diagrams for this refractor. 

I was considering a TOA-130 with a TOA-35 reducer but it seems that it is not adequate for a full frame sensor. Any other good options out there?
Fabio Acquarone avatar
Fabio Acquarone avatar
i am testing a TS-Optics 140mm F6.5 …. i am not using a full frame but they claim that with rducer the field is correct for full frame.
Ashraf AbuSara avatar
Ashraf AbuSara avatar
Fabio Acquarone:
i am testing a TS-Optics 140mm F6.5 .... i am not using a full frame but they claim that with rducer the field is correct for full frame.

I was hoping for a focal ratio of f/5. I had someone claim that their TV NP 127is is "flat" on a full frame sensor with the 0.8x reducer, and this is what it looked like:

andrea tasselli avatar
andrea tasselli avatar
Don't know about refractors but I know of lenses that would meet the criteria and be faster, sometimes MUCH faster, in the bargain. It is just a matter of dosh.
Arun H avatar
Arun H avatar
The Astrophysics 110GTX. Not quite 5”, but handles full frame no problem and is f/5 with reducer.  Get on the waiting list or pay a premium to buy used if/when some scope flipper puts it up for sale.
Ashraf AbuSara avatar
Ashraf AbuSara avatar
Knowing Astro-physics the waiting list could be decades, and the second market is extremely unpredictable plus for something that expensive not willing to try.

Any viable other options that are more readily available?
Ashraf AbuSara avatar
Ashraf AbuSara avatar
andrea tasselli:
Don't know about refractors but I know of lenses that would meet the criteria and be faster, sometimes MUCH faster, in the bargain. It is just a matter of dosh.

Which lenses?
andrea tasselli avatar
andrea tasselli avatar
Ashraf AbuSara:
Which lenses?


I can think of a 400mm f/2.8 or 600mm f/4 or, and the best for last, 800mm f/5.6 (ok, a bit slower this one). Latest generation of Nikkor lenses, e.g., Nikon AF-S Nikkor 400mm f/2.8E FL ED VR or Nikon AF-S Nikkor 600mm f/4E FL ED VR. Or Nikon AF-S Nikkor 800mm f/5.6E FL ED VR. The Nikon AF-S Nikkor 500mm f/4E FL ED VR should also meet your criteria and then some.
MaksPower avatar
MaksPower avatar
What you're asking for is basically the intersection where the refractors + reducers/flatteners overlap the top end of camera lenses, as well as other alternatives:

1. Celestron C6, C8, C9.25 or C11, with Hyperstar. F/2 and a smaller camera (forget the DSLR).
2. Celestron RASA - F/3, several sizes, can put a DSLR on a C8 RASA or C11 RASA.
3. Newtonian astrographs with coma correctors. Anything from a 6" f/4 upwards; and with a large diagonal can cover full frame, though more fiddly to use than refractor
4. Maksutov-newtonians, which are much underestimated IMHO.
5. If you have deep pockets, this is probably nirvana https://www.baader-planetarium.com/en/instruments/telescopes/tec/tec-300vt-houghthon-terebizh-telescope.html

Or for mere ordinary folk...

https://www.apm-telescopes.net/en/skywatcher-esprit-150ed-apo-triplet-refraktor-150mm-apm-riccardi-apo-reducer-s-f525
https://www.apm-telescopes.net/en/skywatcher-esprit-150ed-triplet-apo-refractor-150-mm-f525-with-corrector-and-apm-riccardi-apo-reducer-set
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