Refractor Flattener performance or finger trouble

[paul]

Apart from the Moon being up and full it has been clear for three nights so it was a good time to first light my new 70mm with the 0.8 Reducer Flattener. I spent 2 nights adjusting the spacing to the flattener not knowing enough I assumed I got my spacings horribly wrong....

ASI533MC-Pro shot of M3 with the flattener fitted and camera at manufacturers recommended spacing:

 

On the 3rd night I decided to try without the flattener and surprise surprise...

 

So the reducer didn't reduce, and it certainly didn't flatten.

 

I don't have a lot of experience with refractors but this doesn't seem like something that can be adjusted out to me.

Do we think its faulty or did I do something wrong?

 

[TerryMcK]

No that is not faulty Paul. Look at the edges of the non flattened image. The stars are egg shaped. There are also more of them. Compared to the top image which shows perfectly round stars at the edges and a more 'zoomed in' view which it will do. The flattener/reducer is working fine but you may need to get the shimming better. I suppose it came with a number of thin packers. All mine are adjustable flatteners which you simply alter a threaded collar but a lot of flatteners come with a kit of shims.

Shimming is then a case of trial and error.

Edited March 2, 2021 by TerryMcK

[AstronomyUkraine]

6 hours ago, paul said:

ASI533MC-Pro shot of M3 with the flattener fitted and camera at manufacturers recommended spacing:

Have a look at the telescope manufacturers recommended backfocus. ZWO recommend 55mm for the ASI533MC-Pro, but the telescope could require 56mm, or 54mm. My Esprit requires 75mm backfocus, although ZWO say my 1600mm needs 55mm.

[paul]

(I should never post late at night when I cant sleep😉). I should have said this is supposed to be a 0.8 reducer flattener so I excepted the fov of the first image should be considerably different to the second. When I uploaded it to astronomy.net the pixel size it reported was for F6 which is native F for the scope!   This is why I suspect the flattener but don't have enough experience with flatteners  and fast scopes (not since I sold my Megrez 72 +flattener many years ago  which was almost perfect at the edges with crop DLSR and I never adjusted it).

 

On the first night I was pretty methodical in adjusting spacing from around 54 to 57.5 mm at no time did these flares disappear. Its possible I missed the sweet spot, if people tell me this is normal I'll happily go round the loop again at higher precision in the 55mm area. But I cant get ove the fov issue.

 

Its the first image where I think its focused one colour but the rest of the spectrum is out of focus and as the spheres are offset if you are saying this is normal in your experience because of wrong spacing I'll give it another go. The flattener recommends 55mm (it came with the scope) and the top image is with the default:

I agree the second image has distortion at the edges - but I expected it.

Reading up it seems people make very small changes to tweak the star shapes, which I can  appreciate. I've not read anywhere that the distortion is so dramatic unless spot on. 😵.

Edited March 2, 2021 by paul

[AstronomyUkraine]

1 hour ago, paul said:

I should have said this is supposed to be a 0.8 reducer flattener so I excepted the fov of the first image should be considerably different to the second. When I uploaded it to astronomy.net the pixel size it reported was for F6 which is native F for the scope!   This is why I suspect the flattener but don't have enough experience with flatteners  and fast scopes (not since I sold my Megrez 72 +flattener many years ago  which was almost perfect at the edges with crop DLSR and I never adjusted it).

The two images align perfectly, which shouldn't be the case. The scope with the reducer is transformed from an F6 to an F4.8 scope, so the FOV should be increased, resulting in a smaller target. It looks like you have a reducer problem, I can't think of any other explanation. Might be a good idea to contact the supplier.

[Astroarg]

I have this issue and its driving me nuts!!

 

I had it on every 0.8x Lightwave reducer/flattener image I took, more prominent on one side, which led me down the tilt path.

 

I then managed to get a 2nd hand 1x Lightwave flattener, and first night of imaging... exactly the same problem.

 

 

Mine is meant to be 55mm, I tried 52 - 56mm and had the same issues, I started getting out toward 60mm and it appears to be better.

 

I also tried to set NINA to not focus on the centre and instead between 0.9 and 0.7 of the image frame, in case it was an issue on the focal plane.

 

 

This has given me grief for most of the year since getting my 72EDF. I wasn't sure where the issue lie, but next chance of a clear sky I'm aiming for 60mm+ spacing with the L Extreme to see if it finall resides

 

EDIT: I don't think it is colour spectrum, as with the L Extreme i'm seeing it with both HA and OIII

 

 

This was as far as I got last week before the clouds kicked in - this was 57.5mm as I was maxed out with what I had.

 

 

 

Previous to this, at 53-56mm - same top left

 

and my stars at the centre - round, nice, no eggs and no "comet tail" (where it's lighter than the rest of the star)

Edited March 3, 2021 by Astroarg

[paul]

22 hours ago, Astroarg said:

I have this issue and its driving me nuts!!

I share your pain. After a conversation with the another supplier I ordered and received within 36hrs, from Brighton, a TSRED297 which is the TS x0.79 flattener.  It was an expensive way to investigate my spacing issue but if I got bad results twice I would at least know it was me and I could resell which ever flattener I decided not to keep.

 

The TS device recommends a back focus of 65mm for 420mm. I pointed the 70EDT-F at a land target and shot with a DLSR, with and without the flattener ...  and bingo I got the 0.8 f reduction I was expecting🤩. The disadvantage of using the TS flattener is that even though it has the right thread to mate with the draw tube, the draw tube baffling stops it from going in far enough. So I must use the scopes 2" focuser ring which is not ideal. Also it has an M42 thread rather than the M48 of the Altair one so I am a little concerned about extra vignetting with the short f and an APS-C DSLR (I haven't looked in to that yet).

 

I repeated the test with the Altair x0.8 flattener with spacing of 55, 65,75 and got what looked like 1.0 to 1.1!🤢 So its conclusively faulty. While I wait to hear from the original supplier I will carry on with the TSRED297 and 🤞 I might get a clear sky to evaluate the field distortion. I suspect that with the ASI533 I might not need to do any tweaking. 

 

One thing that I find very frustrating is the poor accuracy of the descriptions on all the supplier websites I visit ( I sometimes drop a note to be helpful but I find it doesn't lead to any revisions). The TSRED297 is variously described as a quad or triplet reducer on the same webpage. The one I received is a triplet based on the reflections I counted , I only hope it actually has the ED glass it claims!  As it happens the Altair 0.8 for this scope is also a triplet but the spacing is very different (again based on reflections ... there is no description which seems like a missed opportunity).

 

<TLDR rant>

One day my supplier may notice the email, web-mail and messenger traffic and who knows even the odd forum post.😄

 

In my previous carrier I was a Product Manager, and took a (marketing buzzword incoming) holistic approach to all the dozens of products I designed and launched on the market. The product is more than the gear you are selling, its the whole package. So the after sales, information, how the customer feels about your brand are very important. In particular when things go wrong is the time to shine. And stuff often does go wrong. Its how you handle the unfortunate things that leave a lasting impression.

</TLDR end rant>