A bit of diagnosis needed on the poor Leo Triplet effort

[Grant93]

Hello everyone,

A bit disapointed on my 3 hour Leo triplet. Although don't know what else I expected to be fair haha, probably a bit to small a target for a ZS61, heavily cropped due to a dust bunny that didnt get caliberated out from flats, must of moved before I did the flats. But yeah on all my photos from the ZS61, whether using the 800d or 600d, I notice I have some oblong shaped stars, regardless of exposure or guiding accuracy from that day. Is this some sort of tilt? Where abouts could the issue lie if it occurs on both cameras?

Let me know your thoughts.

But the image is 3 hours at 150 second exposures.

30 flats and bias.

ZS61 & HEQ5, guided and dithered.

Cheers

Grant

 

[Clarkey]

I must confess it does not look too bad to me. However, I am using a laptop with a rubbish screen. From what I can see, all the stars seem to elongated the same way (top left to bottom right). If they are all the same this certainly suggests tilt. If you are seeing it on more than one camera it may be the focuser is slightly misaligned? Always worth checking. Alternately, if you are using the same T-ring for both camera's it could be this?

[Grant93]

12 hours ago, Clarkey said:

I must confess it does not look too bad to me. However, I am using a laptop with a rubbish screen. From what I can see, all the stars seem to elongated the same way (top left to bottom right). If they are all the same this certainly suggests tilt. If you are seeing it on more than one camera it may be the focuser is slightly misaligned? Always worth checking. Alternately, if you are using the same T-ring for both camera's it could be this?

Sounds like it could be the T ring, Has only been happening continuously when swapping out cameras but leaving T ring on there, rather than keeping the T ring together with the camera, if you know what I mean. So that will be the first one to test. If it isnt the issue, how would you test / fix the focuser?

Cheers

[Clarkey]

7 hours ago, Grant93 said:

If it isnt the issue, how would you test / fix the focuser?

I guess one way would be to use a laser collimator to make sure the focuser lines up perfectly with the  centre of the objective lens. You could probably do something similar with a Cheshire and a centre marked piece of paper over the dew shield. I'm not sure with the ZS61 whether the focuser is adjustable though,

[Grant93]

2 minutes ago, Clarkey said:

I'm not sure with the ZS61 whether the focuser is adjustable though,

Not sure either, Just gotta hope its coming from the T ring.. if not then I'll have to look at the focuser 😆

[rickwayne]

Easiest way to diagnose it is to rotate the camera a bit and look at the results. The image inspector in the free program ASTAP is the go-to tool for this. 

[ONIKKINEN]

To me it looks like atmospheric dispersion is playing a not insignificant role in the elongation of your stars. Blues and reds are on the opposite side, as they refract through the atmosphere at different rates and so can land a few pixels apart on your sensor.

How high was Leo when shooting? I find this issue just about perceptible at somewhere around 50 degrees and increasingly distracting at lower altitudes. Anything lower than 40 and i find colour channel alignment after stacking a necessity rather than a bonus.

Im not a refractor owner myself so couldnt tell if chromatic aberration from the optics could separate colours like this but the atmosphere definitely will.

[Grant93]

5 hours ago, rickwayne said:

Easiest way to diagnose it is to rotate the camera a bit and look at the results. The image inspector in the free program ASTAP is the go-to tool for this. 

Cheers! Ill try this

3 hours ago, ONIKKINEN said:

To me it looks like atmospheric dispersion is playing a not insignificant role in the elongation of your stars. Blues and reds are on the opposite side, as they refract through the atmosphere at different rates and so can land a few pixels apart on your sensor.

How high was Leo when shooting? I find this issue just about perceptible at somewhere around 50 degrees and increasingly distracting at lower altitudes. Anything lower than 40 and i find colour channel alignment after stacking a necessity rather than a bonus.

Im not a refractor owner myself so couldnt tell if chromatic aberration from the optics could separate colours like this but the atmosphere definitely will.

Uhm it was around its meridian, about 40/50 degrees. But this has been happening a while on many of my captures on many different targets using the ZS61, I've been aware of it, just blissfully ignoring it 😅 Now wanting to perfect things I wanted to figure out the issue..

[Shibby]

Really not bad at all if you ask me - the galaxies are coming though nicely with some decent detail and very good colour. I guess you just need to keep going if you want to reduce the noise further.

To me, the star shapes look like (small) guiding errors, though perhaps not if you really do get the same with short exposures. I would test with a very short exposure just to be sure.

[ONIKKINEN]

14 hours ago, Grant93 said:

Cheers! Ill try this

Uhm it was around its meridian, about 40/50 degrees. But this has been happening a while on many of my captures on many different targets using the ZS61, I've been aware of it, just blissfully ignoring it 😅 Now wanting to perfect things I wanted to figure out the issue..

Right, that altitude will have an effect but its probably not the thing you're after.

I have 2 different T-rings for my 550D and both are loose fitting and i can rattle the camera in them a bit. I fitted some aluminium tape around the "groove" which the camera flange attaches to and they were snug afterwards. If you have the same kind of T-rings its an easy fix. Not sure how much that helps if there is tilt but it wont hurt and will make subsequent troubleshooting easier with that out of the way