Any idea whats causing this defect ???

[Skipper Billy]

Finally managed to get first light with my new setup for this season - Tak 106 - Atik 460EX - EFW2 - Baader LRGB filters and although the seeing was truly appalling I was quite pleased with the image.

BUT

On close inspection the bright stars in the bottom right corner show defects in the final image.

All the Lum subs have the defect - none of the RGB subs have the defect which initially made me think it was a filter issue - I pulled the filters and my old eyes cannot see any defect on the Lum filter.

Maybe my eyes just cant see it. I had expected to see a scratch or smear etc.

The other variables are that the Lum subs were taken binned 1x1 and the RGB subs were binned 2x2. (Would that mask the defect?) The seeing was truly appalling - I could only see the very brightest stars visually.

I have attached the full image marked to show the area of concern, and crops of that area - processed - Lum and Red. (All converted to Jpeg)

Has anyone seen anything like this before ??

Any ideas on where and how to start tracking it down ??

Any advice most welcomed - I am just hoping its not a defect in the scope - I really dont want to send it away just as the season kicks off !!

I am very happy to post any further images to help diagnose the issue such as XISF files etc.

Thanks in advance.

 

 

 

[Adam J]

Is it in all your lum subs or just some of them? 

Never owned a refractor even but to my mind a bite out of the halo like that normally means something is poking into the light path irrespective of the type of scope. 

I also note that your smaller stars are not fully round, at F3.6 it will not take much tilt to cause issues. 

Adam

 

[Skipper Billy]

Thanks Adam

It is in all the Lum subs but none of the RGB subs - but the Lum subs were binned 2x2 whereas the Lum subs were binned 1x1.

I am imaging at f5 so I would have expected a little tolerance if there is any tilt in the system and its an all 'screw together' system.

Its a mystery so far !!

[carastro]

I got something similar a few years ago and it turned out to be a dirty filter.

See image attached and look at the bright stars at about 5pm under the galaxy.

 

[Skipper Billy]

Thanks Carole

I am just hoping its something that simple !!

It does look remarkably similar.

Thanks for the suggestion.

David.

[ollypenrice]

It would be great if it were the filter.

However, there's a well known Tak anomaly which I've nicknamed the 'inverse light house beam' effect. Here's an example from one of our FSQs resized upwards several times so it's easier to see.

Sometimes folks message me to ask if I've noticed it in my images and, yes, I have. It doesn't bother me because it only appears on brighter stars and it's symmetrical. In your case it looks similar but isn't symmetrical. Given the large number of miscollimated FSQs being discussed recently I wonder if yours might need a tweak. 

It might be something else entirely, of course.

Olly

[Skipper Billy]

Thanks Olly

I am leaning towards a dirty filter as its only present on the Lum subs - not at all on the RGB subs but they were binned 2x2 - do you think that would mask the problem ??

Cheers

David.

[tomato]

I guess some full resolution colour subs will rule out if it’s a filter or scope issue.

Thats a very nice M31, especially when taken under the conditions you describe.

 

[Skipper Billy]

32 minutes ago, tomato said:

I guess some full resolution colour subs will rule out if it’s a filter or scope issue.

 

Yep - if only there was a clear or even semi clear night in the offing - at least 10 days of wind and rain forecast !!

I am thinking of upgrading to 2" filters and an EFW3 ready for a big camera upgrade - that would also tell me whether its filters or something else.

[ollypenrice]

3 hours ago, Skipper Billy said:

Thanks Olly

I am leaning towards a dirty filter as its only present on the Lum subs - not at all on the RGB subs but they were binned 2x2 - do you think that would mask the problem ??

Cheers

David.

I think binning might mask it but I really don't know since I don't understand the cause of the problem. I suppose that higher resolution might well capture the unwanted effect more easily. Greg Parker told me it was a pinching effect. I always think of pinching as creating triangular stars but he was adamant that it was pinching. He's far more likely to be right than I am given his professional expertise in Photonics.

Olly

[RayD]

I'm away at the moment, David, but back next week and have a spare Baader Lum filter that I can send you to try to see if it resolves the issue. 

[Skipper Billy]

@RayD    That's exceptionally kind of you but I am going to press the button an the EFW3 and 2" filters but that is a really kind offer - thanks a million.  David.

[carastro]

In my case I opened up the filter wheel and examined the filter and it was quite obvious it needed a clean.   Cleaned it and problem went away. 

Carole 

[RayD]

Not a problem at all, David, happy to send if you want to try.  I think Carole has a very good point with cleaning also as it does seem to be worse in that one area.

The EFW3 does sit very well on the FSQ106 and, when coupled with the 2" filters and larger sensor, such as the 16200, it is an absolute pleasure to use 

[Skipper Billy]

Thanks Ray

I took the Lum filter to a pal of mine who is an optometrist and he has all sorts of machines for looking at lenses and he confirmed it was absolutely filthy and cleaned it for me - to my eyes it was clean - to his there was a large grease mark across one side! Gone now. His comparison was that if the filter was the size of a dustbin lid then it looked as though a Mars Bar had been wiped across it from 4 o'clock to 6 o'clock

Yours setup is making me drool - I will still be getting the EFW3 and the 2" filters - soon to be followed by the Atik 16200.

Do you mind me asking if you find the Feather Touch a big improvement over the standard Tak focuser?? Please PM me if you prefer.

 

[carastro]

?

[RayD]

3 hours ago, Skipper Billy said:

Do you mind me asking if you find the Feather Touch a big improvement over the standard Tak focuser??

I was never happy with my Tak focuser, David, and the operation seemed somewhat rough and harsh.  Well made, but not as refined as I expected. The FT on the other hand is absolutely superb, and about as smooth as you could imagine.

I would say if your Tak one works well, then it isn't worth the high price of the FT as the Tak one is well made.  For me, on the other hand, it was worth every penny.

[Skipper Billy]

Thanks RayD