ZWO EFW filter wheel and tilt ? - Forums

Topic starter

Jul 24, 2021 · Edited: Jul 24, 2021

I am using the ASI EFW and ASIs relatively heavy (700g) 6200MM pro camera on my TAK 130D. Since I always had problems with elongated stars in some corners of the images, I also installed Gerd Neumanns (Astronomik) camera tilting unit (CTU).

The CTU is working quite well. However I found that the correction is gone and the elongated stars move to other corners as soon as the mount does a meridian flip. This points to a gravitational component of the tilt, i.e. that gravitation pulls on the optical train causing the tilt.

Since collimation is rock-solid, the tilt must occur somewhere between the TAK optical corrector and the camera. It appears that manually pulling and pushing on the optical train makes the ZWO EFW bend slightly, even though the bend is small and hard to perceive, so I am not 100% sure the EFW is the culprit.

Has anyone had similar tilt problems with a filter wheel - and ideas how to solve this ?

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Douwe79

Jul 24, 2021

Can I ask what de eccentricity/roundness of your stars is in numbers? (in other words, how bad is the tilt? Is it only in one corner?

Götz Golla

Topic starter

Jul 24, 2021

yes, sure.

Yesterday, before tilt adjustment, the star sizes in the 4 corners of the image where (in arcsec):

6.0 x 4.1, 19.9 x 8.1, 5.3 x 4.1, 12.7 x 5.0

When tilt was adjusted, stars had the following sizes in the 4 corners:

3.4 x 2.2, 3.3 x 2.5, 3.0 x 2.5, 2.8 x 1.8

After meridian flip, they were similar to the unadjusted image, but in different corners. I did not measure them because I gave it up for the night.

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John

Jul 24, 2021

sometimes the screw tread will be bad,mine has it too,the ewf is from alliminium,to soft i think.

Douwe79

Jul 24, 2021

Thank you.

I’m not familiar with your telescope but have (had) elongation problems myself due to tilt. My refractor doesn’t have a threaded connection. I use the ZWO EF too. I’ve had some details adjusted to counter tilt, such as better compression rings, connecting 2 ‘loose’ parts with epoxy etc.

I’m a surprised that your star size has reduced with such margin after your adjustment. The elongation is still significant though as far as I can see.

If it’s tilt all the stars should be elongated in the same direction.

Have you already tried to image without the filter wheel to test if if gets better?

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Mariusz Golebiewski

Jul 25, 2021

Hi,
maybe not similar but I had some problems with ZWO EAF 7x36. There was a wheel wobble that caused flats and lights misalignement.
Fortunatelly the solution was quite simple in my case - there is a big screw in the midle of the wheel, covered with a sticker, it was enough to tighten it up a bit.

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Götz Golla

Topic starter

Jul 26, 2021

Thank you.

I’m not familiar with your telescope but have (had) elongation problems myself due to tilt. My refractor doesn’t have a threaded connection. I use the ZWO EF too. I’ve had some details adjusted to counter tilt, such as better compression rings, connecting 2 ‘loose’ parts with epoxy etc.

I’m a surprised that your star size has reduced with such margin after your adjustment. The elongation is still significant though as far as I can see.

If it’s tilt all the stars should be elongated in the same direction.

Have you already tried to image without the filter wheel to test if if gets better?

Hi, as far as I know a tilt in the optical train of a reflector with a build-in field flattener is different from the situation for reflector without a field flattener. A tilt "behind" the flattener is something like a variable backfocus across the field. Stars are not alongated in the same direction because typically in one corner you have to much backfocus and in the other corner not enough.
I cannot easily build the optical train without the EFW because the backfocus wouldnt fit anymore. Yet it may be the only way to locate the origin of the tilt.

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Götz Golla

Topic starter

Sep 11, 2021

Now thats interesting. Since my ASI 6200 is in repair right now I build a totally different optical train with my Canon EOS R as camera. All the parts of the train are different. I just used a manual filter drawer and some adapters. Yet I see exactly the same "tilt", i.e. stars in the same one corner of the image are distorted.

Could it be that the thread of the Takahashi field flattener is introducing the tilt ??? I will have to think about a way to measure this.

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Michael McGowan

Sep 11, 2021

I have a setup similar to yours and I am also trying to fix what appears to be tilt issues. I have the TSA-120 along with the ZWO filter wheel and 6200mm. I have ordered the CTU, but who knows when I'll receive it. I recently downloaded the trial version of CCD Inspector and had it analyze my images from a night of shooting, It can measure "Tilt X" and "Tilt Y". If I plot these 2 measurements versus the time the image was taken, I can see that the tilt is changing through out the night. This makes me believe that there must be some flex in my optical train. You might want to try out CCD Inspector to see if it can shed some additional light on your situation.

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MrSpaceman

Dec 9, 2022

Sorry to dredge up an old topic, but I’m having similar tilt issues when using a ZWO 7x2” EFW on a SW80ED (with 2600MM). It’s not collimation, tube/focuser flex, gravitational etc - I’ve done quite thorough testing over the last few months. I believe mine is caused by the actual EFW not being perfectly flat/perpendicular. The ‘flat’ edges of the EFW have slight convex curve on both sides, making the camera sensor not sit exactly perpendicular to the scope. I’ve used the tilt plate that comes with the 2600MM to get tilt from about 30% down to about 4%, but geewhizz it’s a bugger to adjust that plate - having to remove it from the EFW each time.

I was wondering if anyone else has noticed this with the 7x2” EFW? And maybe that’s the cause of OPs issues?

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Olly Barrett

Dec 11, 2022

Sorry to dredge up an old topic, but I’m having similar tilt issues when using a ZWO 7x2” EFW on a SW80ED (with 2600MM). It’s not collimation, tube/focuser flex, gravitational etc - I’ve done quite thorough testing over the last few months. I believe mine is caused by the actual EFW not being perfectly flat/perpendicular. The ‘flat’ edges of the EFW have slight convex curve on both sides, making the camera sensor not sit exactly perpendicular to the scope. I’ve used the tilt plate that comes with the 2600MM to get tilt from about 30% down to about 4%, but geewhizz it’s a bugger to adjust that plate - having to remove it from the EFW each time.

I was wondering if anyone else has noticed this with the 7x2” EFW? And maybe that’s the cause of OPs issues?

Hi…
I have 2 x 2600mm Pro/ZWO 7x2” EFW that I use on 3 different scopes, I have no tilt issues on my Esprit 100ed and EDGE HD 8” and the same elongated star issue on my Redcat regardless of which EFW is connected to it (tube optics misaligned probably and under investigation) …
so, to answer your question none of my EFWs are causing tilt …
Good luck in solving your tilt issue 👍🏻

Clear Skies‼️
Olly

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