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Have i purchased a bad field flattener? Optical Vision Ltd (OVL) Field Flattener · Maltasar_ · ... · 9 · 411 · 0

Maltasar_ 0.00
Maltasar_
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Hi, I hope this is the right forum/category

A couple of days ago i made a post on Reddit about my field flattener not flattening the field properly.

I have since then tried pretty much everything, yet the corners and sides all have elongated stars. I can put as much as 60mm (the flattener requires 55mm +-2mm) of distance between the field flattener and my camera without the stars changing shape. I have tried with a bahtinov mask aswell, where all 4 of the corners have stars that have the vertical light streak to the left of the "X". No matter at what distance the camera is from the field flattener.

I found a post of another person having the same problem, and it ended up being the field flattener. It was bought used and apparently not working. They bought a new one, and the corners were then immediately sharp. 


Imgur link with some photos with my setup: https://imgur.com/a/cNEkpKB

Optical train: TS-Optics 70/420mm doublet -> OVL field flattener -> Astroessentials t-ring -> Canon 600D. 


If you guys have any input, i'd be really happy. Thanks in advance.
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RafaDeOz 6.32
Rafael Amarins
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I had a field flattener that was specified to 55mm of spacing and it it was only optimized when I set it to 68mm
It was a 72/432mm 
The stars shape on your image suggest the sensor is too close to the field flattener. Try adding a 5mm spacer and see what happens
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drpafowler 2.41
Philip F.
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Looks like you are too close. Start adding spacers until the stars get better.  

TS optics makes specific flatteners for your scope. They might be better than the OVL. I didn’t see a lot of praise for the OVL flattener.
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WhooptieDo 10.40
Brian Puhl
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55mm is always just a suggestion.     Since your flattener is not made specifically for your scope, you could be wayyy off.
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andreatax 9.89
andrea tasselli
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As others have mentioned the OVL isn't a great flattener (I had it, tested it and returned it). So, if you can, get a TS-specific flattener.
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Maltasar_ 0.00
Maltasar_
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Rafael Amarins:
I had a field flattener that was specified to 55mm of spacing and it it was only optimized when I set it to 68mm
It was a 72/432mm 
The stars shape on your image suggest the sensor is too close to the field flattener. Try adding a 5mm spacer and see what happens

Wow… 68mm… Problem is, i have run out of threads, so i can’t screw it off any more. I may have to buy an extender or something. 

But when you finally did space it out correctly, was it fine to look at or was the quality bad?

Thank you for the answer.
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Maltasar_ 0.00
Maltasar_
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Philip F.:
Looks like you are too close. Start adding spacers until the stars get better.  

TS optics makes specific flatteners for your scope. They might be better than the OVL. I didn’t see a lot of praise for the OVL flattener.

I did try to add spacers, but ran out of thread so i couldn’t screw it off any more.

Yeah, i might just buy the ts optics one, even though its a bit more expensive.

Thank you!
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Maltasar_ 0.00
Maltasar_
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andrea tasselli:
As others have mentioned the OVL isn't a great flattener (I had it, tested it and returned it). So, if you can, get a TS-specific flattener.

I might just get the ts optics field flattener. It a bit more expensive, but at least i know it’ll work.

Thanks for the comment.
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Tom914 0.00
Tom914
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I had this flattener for years and there is nothing wrong with it.
Backfocus distance is usually dependent on telescope's focal length, it's almost never 55mm. Mine needed also 68mm to have acceptable stars in corners (480mm FL scope).
this one should work better for you.
By the way TS also sells flattener which looks exactly like this OVL, with their brand name on it. They are most likely the same and from the same chinese factory anyway.
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valterreis 0.00
Valter Reis | Observatório Astronómico dos Reis-OAR
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I´ve got one of those and it´s what i use on my setup.
Also used it in the past with a 600D and a Evostar 72ED. If you check my images, no elongated stars in the corners.
Try replace it for a new one and if it doesn´t work either, try the TS flatenner.
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