Recommended 1.0 x flattener for 90mm f6 CF APO

[900SL]

I have a 0.8x WO 6Aiii that I use with the TS CF APO 90mm

I'd like to get a 1 x flattener but the TS optics recommended flattener TS Flat 25 DEL is rather expensive and sized for full frame, which is overkill for my intended use (533MC pro or an APS C on rare occasions)

TS optics do a generic 2" flattener available through FLO, with about 100mm backspace

FLO also do a cheap as chips Stellamira 2" flattener with M48 adapter. Anybody using this? Appears too cheap to be any good but you never know

Then there is the Hotech SCA FF and the ridiculously priced WO Flat 68iii

Recommendations?

 

 

[iantaylor2uk]

I use the Hotech flattener on my WO 81 mm refractor and on my Tak TSA 102 mm refractor. It says on the flattener it works on telescopes from f/5 to f/8. Backspacing to sensor is approx 55mm. I have found it to be quite good. It also has a self centering action - you screw it in and that forces 3 rubber bands against the inside of the tube so this helps avoid tilt.

[900SL]

Hi Ian, yes the Hotech could be an option. My only concern is the length required to accommodate the expansion disks. A quick look at my scope and the 2' adaptor doesn't appear long enough.

Thinking about it I'd also prefer a screw on flattener, with an M48 connection, does the Hotech rely on the expansion and 2' lock?  

[Clarkey]

On 07/01/2023 at 16:04, 900SL said:

FLO also do a cheap as chips Stellamira 2" flattener with M48 adapter

I actually purchased one of these with the 0.8 reducer when I got my StellaMira 90mm Triplet (same as the TS). Unfortunately, I cannot tell you what it is like as I have never used it. I stuck with the 0.8 and never bothered to change.... Unfortunately, I have so few clear nights I tend to work on the 'if it ain't broke don't fix it' theory.

[Peds]

I'd go with the recommended TS Flat 2,5 or the identical Sharpstar 2.5" version. You may be able to find one of these used.

The thing to keep in mind with those two is that the threads on the camera side are actually M69, while threads on the telescope side are M68.

[iantaylor2uk]

21 hours ago, 900SL said:

Hi Ian, yes the Hotech could be an option. My only concern is the length required to accommodate the expansion disks. A quick look at my scope and the 2' adaptor doesn't appear long enough.

Thinking about it I'd also prefer a screw on flattener, with an M48 connection, does the Hotech rely on the expansion and 2' lock?  

Yes - it just relies on the self centring action and locking - there is no way to screw it into something on the telescope

[Clarkey]

On 07/01/2023 at 16:04, 900SL said:

FLO also do a cheap as chips Stellamira 2" flattener with M48 adapte

I might be a little late, but since my last post I have now added a 115mm triplet to my collection. I thought I would try the SM flattener with it to use its native FL (and to save a few hundred quid on a new one). I actually works pretty well. Certainly as well as some of the more expensive flatteners I have tried. I have not tried it on the F6 90mm, but I see no reason it would not give decent results. After all, F6 is right in the middle of its design range.

[900SL]

Forgot to update this.. went with the TS Flat2 in the end. Works well with the 533 sensor, not tried APSC yet. Flat field, nice stars.

There's significant backfocus with this, around 120mm or thereabouts, so I needed an extension tube and a spacer between flattener and camera. Getting the right backspacing is a case of trial and error with APSC, from what I have read