I'm going to open a tab here on CN to catalog my experience with this new astrograph by Askar (a Sharpstar subsidiary).
The homepage for this refractor can be found here:
And the optional 0.7x reducer here:
The specs and accessories are listed as:
- Aperture: 72mm
- Focal Length: 400mm
- Focus Ratio: f/5.6
- Objective Type: Quintuplet Dual ED Air-Spaced APO
- Overall length: 317mm
- Weight: 2.56kg
- Options Weight: 2.88kg
- Back-end Adapter: M68x1 Male Thread, 2" Adapter/1.25" Adapter
- Back focus: 140mm
- Pair of Tube Rings
- Dovetail Plate
- M68-M48 adapter, 2” adapter, 1.25”-2” adapter
- Inspection List
Michael Fong of Sharpstar listed this new astrograph in the Vendor's forum here:
The timing was perfect, because I was interested in a new refractor that could handle full frame sensors, and which had a wider field of view than my Esprit 100 reduced to 412mm focal length. With the optional Askar 0.7x reducer, the focal length of the FRA 400 reduces from 400mm to only 280mm. The price point of $1,100 plus $250 for the reducer seemed more than reasonable for an f/3.9 Petzval astrograph, but just how good are the optics, especially spot size and CA at the edges of the field of a full frame sensor? The docs suggest typical spot sizes @ native f/5.6 of 4.5um RMS at centre, increasing to 6.2um @ 22mm radius. With the reducer added the spot sizes are reported to increase to 5.7um and 13.2 respectively. I'm not sure how that compares to something like a Tak or other high-end refractor, but for this price point the numbers do seem quite good.
After a short debate in my mind (to buy or not to buy) I contacted Michael via email, and after receiving example images taken with the scope at both f/5.6 and f/3.9, I purchased the FRA 400 and reducer, with payment via PayPal. I received the tracking link the following day, with the shipment's arrival estimated to be in seven days time.
(more to follow)
Disclaimer: I know very little about scope optics, so I will not be able to offer much technical discussion in this thread.