OVL field flattener not working as expected with Skywatcher 72ED and DSLR

[StarlightHunter]

Hi there.

 

I am using an OVL field flattener with the Skywatcher 72ED and I am getting some weird distortions.

In the image https://starlighthunter.com/imagenes/galaxia-de-andromeda-m31/  the distortion is very evident at the bottom side.

In the images https://starlighthunter.com/imagenes/nebulosas-trifida-y-de-la-laguna/ and https://starlighthunter.com/imagenes/cumulo-globular-m4/ it is at the bottom-right  side and barely noticeable.

Today, watching some images at astrobin I found this one:

https://www.astrobin.com/full/379566/0/

Same configuration, same problem (this time left side). Any clues about this?

[vlaiv]

Distortions to one side of the image could mean sensor tilt.

It could be due to camera, but also because of way the camera is attached to the scope.

Best way to assert this is to take a test shot - note how much distortion there is (which corner / side) and rotate camera. If same side / corner is affected - it is sensor tilt. If aberration moves accordingly (you rotate camera by 90 degrees and aberration does the same - usually in opposite direction) - it can be because of attachment.

If it' due to attachment - you need to check if attachment is firm but tilted or if it is loose and camera sags under gravity. For this - take a test shot and then don't rotate camera but rotate scope - point to another part of the sky so that camera is oriented differently with respect to the ground (usually west and east is good direction to test this).

If you determine that you have connection problem and it is loose - for example because you are using standard clamping by either screws or compression rings - think about upgrading to threaded connection if your focuser supports that - or maybe upgrade of focuser itself - if you are using any sort of extension - check if it is causing sagging under gravity (too loose attachment).

If you have firm tilt - try to figure out what component is causing it - usually extension ring / tube and try replacing it.

if you have sensor tilt - you need tilt adjuster since you are using DSLR and it does not have integrated tilt adjustment.

Hope this helps.

[StarlightHunter]

In the images the distortion changes the position and they are taken with different camera rotations.

Thanks. I supposed the problem would be most probably due the attachment. I will order a threaded attachment because I'm using the most basic 2 thread rings that comes with the scope focuser.

 

[vlaiv]

3 minutes ago, StarlightHunter said:

In the images the distortion changes the position and they are taken with different camera rotations.

Thanks. I supposed the problem would be most probably due the attachment. I will order a threaded attachment because I'm using the most basic 2 thread rings that comes with the scope focuser.

 

Using threaded attachment certainly won't hurt, it can only improve stability. Do be careful about it - you will need rotator part as well, unless you feel comfortable rotating scope in the rings when you want to frame an object (some scopes have permanent attachment of dovetail bar so they require rotator to allow for camera orientation).

[StarlightHunter]

Yes, I was about to buy this one:

 

But I'm pending of FLO answer about compatibility with the FLO flattener

 

[StarlightHunter]

Ok. To finish this thread and to solve the problem I had, the real problem in my case was the ED72 not being well aligned.

The focuser body was misaligned with the rest of the telescope because of a failure in the body attachment building. I just got a colimation eyepiece like the one of the photos and I was able to align the body and retight the screws so now it is well aligned.

 

[newbie alert]

On 28/06/2019 at 00:52, StarlightHunter said:

Yes, I was about to buy this one:

 

But I'm pending of FLO answer about compatibility with the FLO flattener

 

A friend of mine bought the rotator and then couldn't achieve focus...

You need to be careful of the spacing too

[StarlightHunter]

At least for me, I get focus without any problem. I attach the rotator, then the OVL flattener then spacers to get 55mm backfocus and then the ASI294MC-P.

All works like a charm.

[boulderbelly]

To: Starlighthunter   is that rotator not custom made for the SW .85X reducer/flattener?

[Skyline]

That rotator is made to fit the 0.85x reducer. I think it has a M68 thread size.

[Skyline]

On the OVL flattener try using a 58mm back spacing.

[StarlightHunter]

 

Here you can see my setup.

In the top-down order:

72ED without the 2" eyepiece adapter

treaded to:

Field rotator from FLO

threaded to

OVL flattener

threaded to:

ASI 294MC-Pro camera and spacers (using the OAG).

The spacers I used with the camera are the ones in this image

 

 

And I achieve focus without any problem.

Edited October 8, 2021 by StarlightHunter

[StarlightHunter]

I edited the comment as the image was not being shown.