Are Reducer/flattener "universal" for any refractor with the same focale length?

What do you think, AB community? Can a reducer/flattener be designed specifically for one refractor, making other "universal" flattener worse?
Or is it pure commercial statement?

Both statements can be true. Yes, you can design a reducer/flattener to match a certain design which may (or might not) make some universal reducer/flattener perform worse and also be a commercial statement as it is well possible that "a" specific universal reducer/flattener might just perform as well if not better.

andrea tasselli:
Both statements can be true. Yes, you can design a reducer/flattener to match a certain design which may (or might not) make some universal reducer/flattener perform worse and also be a commercial statement as it is well possible that "a" specific universal reducer/flattener might just perform as well if not better.

Hi Andrea,

You're absolutely right!
My question should then be reformulated to:
Does anybody have comments on the 0.77x reducer designed for the skywatcher Esprit 120ED? Is it really better than other premium quality reducer/flattener (such as Riccardi suggested by Roger)?

Stéphane

Monty Chandler:
The skywatcher 120ed has a specific flattener that comes with it.  You can also buy a reducer specifically for that scope.  I love mine, but wouldn't think of putting an off brand flattener or reducer on it.  The performance of this scope at 840mm is phenomenal.   Not cheap by any stretch, but what a telescope!

Thank you for your answer!
i agree, super happy with the telescope. It’´s just that I try to get the max possible items on the second hand market. If I have to buy a brand new reducer, I will most probably go for the .77x from skywatcher.

I owned a 120 Esprit for many years and used it exclusively with the Riccardi 0.77x flatener/reducer.  I used the 63mm (small) model and it has male 63mm threads pointing towards scope and female 63mm threads pointing to camera so you would need adaptors (Precise Parts makes great ones) for both sides. You will need 73.7mm spacing from output to chip. Please check that on the APM website documentation.  I had the reducer attaching directly to the focuser output rather than trying to put inside and focus was close in at I think 16mm out reading the scale on the draw-tube.   I took 100's of images (many here) all trouble free and tended to guide off-axis because the Esprit focuser is good but will indeed sag with weight a wee bit so guide scope was hit or miss.

The included corrector was of course excellent but slow at F/7.2.  I had F/5.2 with the Riccardi. It was tack sharp corner to corner but the biggest chip I used was the QHY294m. It is ~19.3x13mm so a bit smaller than APS-C. I sold "Stella" to a gentleman who is using with a zwo2600. I know he had to go through adaptor heck to get spacing right.

An advantage I would see with the SW reducer is it would be a turn-key solution and going with the excellent Riccardi means you will likely spend an additional ~$300 in adaptors and have that worry.

Thank you Ron, Thank you José,
Your comments are very valuable!

NO.  The Esprit 120ed has a flattener built specifically for that telescope.  Works extremely well.  Flat to the edges and beyond - OAG stars are perfectly round too.  Wouldn't think of putting anything else with it.