Some problem with flattener - Forums

Topic starter

Dec 4, 2022 · Edited: Dec 4, 2022

Today i've tested, for the first time, my new APO130F7 FPL73 (TS Photoline) with the Tecnosky FF 1x Flattener using, how declared, 55 mm of backfocus.

And there is some problem.

Once focus done, the focal solved is 1050 mm (!!!) and not about 910 mm.

And the stars are really bad.

Tomorrow i'll call the seller, but i thing that there is a big problem in my flattener.

Without flattener the focal solved is 907 mm.

I also tested 60, 65 and 75 mm of backfocus but stars do not change and remains "comet" style.

Second image is my optic train.

Thank u.

IMG_20221204_192917.jpg

andrea tasselli

Frequent contributor

Dec 4, 2022 · Edited: Dec 4, 2022

The issue is with the flattener, which should not have any optical power on its own but this is belied by the ~15% increase in focal length. My hunch is that internal spacing is wrong or something has worked loose. Returning it is the first port of call.

Il problema e' chiaramente lo spianatore di campo che dovrebbe avere zero diottrie (zero magnificazione) ma invece produce un'incremento di focale del 15%. A naso direi che o la spaziatura interna degli elementi e' sbagliata o qualcosa si e' mosso nel trasporto. Rimandaglielo indietro senza esitare. Dato il rapporto focale del tuo APO uno spianatore "generico" andra' senza dubbio bene.

Insightful Concise

Jim Matzger

Dec 4, 2022

There is either a problem with the flattener, or alternatively you are speeding rapidly to the center of the Universe! :-)

Well Written Respectful Engaging

Jeff Reitzel

Dec 4, 2022 · Edited: Dec 4, 2022

"Tails out" means you need to move in on backfocus most likely. It certainly has not worked moving out if I am understanding what you have already tried correctly. I had a 130mm refractor that produced images just like that at the advertised 55mm of backfocus. Solution was moving in to 52mm for me. It most likely will be a small adjustment. Spacing will also change the reduction factor you get. I have never had plate solve solutions match the advertised number on focal length for any of my scopes.
Good luck and CS,
Jeff

Helpful Concise Supportive

Michele Campini

Topic starter

Dec 5, 2022

andrea tasselli:
The issue is with the flattener, which should not have any optical power on its own but this is belied by the ~15% increase in focal length. My hunch is that internal spacing is wrong or something has worked loose. Returning it is the first port of call.

Il problema e' chiaramente lo spianatore di campo che dovrebbe avere zero diottrie (zero magnificazione) ma invece produce un'incremento di focale del 15%. A naso direi che o la spaziatura interna degli elementi e' sbagliata o qualcosa si e' mosso nel trasporto. Rimandaglielo indietro senza esitare. Dato il rapporto focale del tuo APO uno spianatore "generico" andra' senza dubbio bene.

Thank u for reply.
In the flattener i can see, inside, one only element that is convex (curved) in the camera direction. For me this is very strange, normally all my flattener are the opposite.

Thank u all guys for the reply, i'll send it back of course.

Michele Campini

Topic starter

Dec 5, 2022

The seller will be shipping me a new flattener tonight.
He told me that on that model he had similar problems to mine and in practice the lens group was mounted upside down.