Star Smearing on images?

[Droogie 2001]

Hi,

I am hoping that with the help from the Forum that I can resolve this frustrating issue.

When imaging with my Celestron 8SE I get what I would call 'Star Smearing' across the entire image.

I have tried to rule out various equipment with trial and error.

1. This issue occurs whether I take a 5 or 30 second exposure. The mount has been polar aligned twice so it is not a tracking issue. I used a Bahtinov mask to focus. I even tried with guiding and no guiding same results. I also have a separate scope which whilst is a refractor it does not have any such issue, with this I can easily track for 5+mins guided with no issues.

2. It is not the camera as I have recently upgraded the camera and I get the exact same issue.

3. I thought and it still think it could be a collimation issue. Having had this issue for a while I decided check my collimation  and it was a little out. So yesterday I worked through it and got to a stage where everything looked good.
Took the images again and exactly the same issue.
All I add is after collimation is that if I unfocused in a clockwise direction the donut shaped star looked perfectly centred. Yet if I un-focused it in an anti clockwise is was not central.
This alone makes me suspicious but I struggled badly with just trying to get it correct when it was un-focused clockwise. I do not understand why it would not be same when un-focusing anti clockwise? I guess it should be correct in both focusing directions?

4. The imaging train is F6.3 focal reducer then a Baader Click lock and then an extension tube attached to an M48 connector. This tube is then clamped inside the Click Lock. M48 is attached to the Canon 1100d

The length of total imaging train does not appear to be excessive and I get no vignetting.

The focal reducer looks ok and does not appear to have any damaged or dirt on it and the fact that it is the whole image suggested it something else.
I cannot recall if in the past I have left the FR off to see what results it yields so this is another option I guess but it seems unlikely to me..

It all seems to point to collimation but I am not sure, please can anyone help?

I have posted a 30 & 5 sec cropped images as well as a single RAW 30 second image of M13 to give you an idea of what the issue looks like.

Thanks

30 Sec Exposure Cropped - Bottom right

5 Sec Exposure Cropped - Bottom right

30 Sec Exposure Full image

[Freddie]

Looks like coma to me. Can be caused by not having the correct distance between the FR and cam chip.

[Alien 13]

I agree with coma and the FR Sensor distance but its worth checking for any tilt in the FR and camera assemblies.

Alan

[Droogie 2001]

Thanks for both of the rapid responses. Do you guys have any links suggestions on how to address the issue? Thanks.

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[Alien 13]

From memory the FR to Sensor distances are normally in the range of 55-80mm depending on manufacturer but I cannot advise on your example.

Alan

[Owmuchonomy]

I concur with the coma comments. My 0.63 reducer causes this on my 9.25 SCT. It is particularly bad on bright objects.

[Droogie 2001]

Thanks. How do you address this? Do you use spacers? I use a Baader click lock and a reasonably small tube to attach to the M48. I don't see how I can reduce this much more. Unless i have to extend it further. I know some is trial and error but the setup are reasonably generic.

I'll get the tape measure out later and make some notes of distances.

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[Davey-T]

From memory the distance from the rear of the 6.3 f/r to the sensor is around 110mm, I use one on my 10" SCT and the distance is not too critical.

Dave

Have a quick try without the f/r

[Owmuchonomy]

I have to live with it. Spacing doesn't change matters for me. I heavily crop any images taken with the reducer that contain brighter stars. I also use the click lock. Celestron don't even know how to fix it.

[PeterCPC]

As an experiment I suggest trying it without the click lock. Try attaching the visual back to the reducer then use a standard T adapter on the camera.

Peter

[Droogie 2001]

That's odd. Also my stars are smeared in the Center so cropping is not going to be enough. Maybe I can at least reduce by getting the distances correct?

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[Droogie 2001]

Thanks Peter. Annoyingly I got rid of my T Adapter but I had also considered this option. but as I was not sure if it was related to the issue I didn't want to waste the money. That said as it seems to be related I may have to have rethink (they are pretty cheap so not a big issue)

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[Owmuchonomy]

That's odd. Also my stars are smeared in the Center so cropping is not going to be enough. Maybe I can at least reduce by getting the distances correct?

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No, I don't suffer that, just the edges are affected. There was a report on here of someone that had received the Cel 0.63 reducer from new and the glass was in the wrong way round!

[msh1]

i had exactly the same problem with my c6 in that when collimating it was fine on one side of focus but out on the other, it drove me nuts so i used metaguide and a webcam and recollimated it was miles out now got really good stars across the field HTH

mark

[Droogie 2001]

Ok thanks for the heads up. I have Metaguide but have never used it, will give it a go. Also have T Adapter on order so hopefully can get this resolved.

[Droogie 2001]

Sorry to drag this thread back up but rather than creating a brand new one I thought I would add my woes to the existing thread.
I went last out night. Not ideal as it was windy however by the time it was dark the skies was very clear. My tracking was not great but it did not matter a huge amount as I was only interested in taking very short 5-30 sec exposures.

So I ordered a Celestron T Adapter and T Ring to see if the Baader Click lock was causing the star smearing. After some basic tests it does not appear to have made any discernable difference.

If I use either the Celstron FR 6.3 or not the issue is there so there is nothing wrong with the FR.

Not to mention I had gained a significant new problem.
 

To help counter light pollution I recently purchased a Astronomik CLS clip filter for my modded Canon 1100d which I have used on my WO Star 71 with pleasing results.
However this was the first time I had used it on the Celestron 8Se, partly because it is attached to the camera and felt no need to remove it.

When I took a 45 sec image of Vega I was slightly horrified to see what looks like a huge secondary mirror donut and some over horrible light artefact. (see image attached) (Ignore the star trailing!)

If I remove the CLS filter it disappears entirely.

Has anyone experience this with the CLS filters? I appreciate Vega is very bright but this just seems odd to say the least.

All in all I have reached breaking point with trying to achieve any kind of DSO photography with my SCT. I realise it is mainly designed for Lunar, Planetary but I have seen stunning DSO images from C8 / 8SE's so see no reason why I cannot at least get somewhere with this.

I had read up that the light path distances are important but in reality I am using pretty much standard adapters and when I measure the distance it seems to match the recommended distances (Around 106mm?). However I do need to spend more time with the tape measure out.

My main setup from last night is the rear of the SCT, Celestron F6.3 FR, Celestron T-Adapter, Canon T-Ring, Canon 1100D. That's it I cannot make the path any shorter. It I use the Baader Clicklock it replaces the T-Adapter and there is a slight difference in distances but the results seem to be the same.,

Its crazy that I am using pretty Celestron kit all of the way along and I get very poor results. I must be missing something, do I need to increase the light path if so what with?

Can anyone help me please?

Thanks.