Do I need to change my ZWO RGB filters too?

[symmetal]

I recently changed my ZWO 31mm unmounted Ha filter for a Baader 31mm unmounted for my ZS-61 and ASI1600 setup due to halos and edge light leakage in Ha. I recently imaged the Pelican when there was no Moon (rare) in LRGB and the blue shows bad flares from the two central bright stars in the top right of the image. The LRG images show no flaring there and the blue flats are fine. I'd expect flares from very bright stars near the edge of frame but these are modest 4.8 and 5.0 magnitude stars near the centre. Is this just a filter problem?

Baader LRGB filters don't seem to be available in 31mm unmounted so I'd have to get the 1.25" mounted which should be OK as it's the mini filter wheel mounted on the camera and vignetting shouldn't be an issue. If I have to change then to 1.25" I could have got the Ha 1.25" too in the first place. Now I'll have an odd one out again.

Here's a quick process of the RGB image with the blue corner at full size. Excuse the star shapes. I was still having some problems with tilt/spacing at the time.  The blue lines appear to point towards the two stars to pretty much confirm it as flare. Do you think I need to change the LRGB filters to cure this?

I recently had to resort to using a tilt adjuster to correct the star shape problems. The coke can strips jammed in the threads was too much hassle. 

 

Blue top right.

Alan

[iapa]

I have a vague memory that ZWO provide filters specifically mathews to the ASI1600mm and their filter wheels.

In which case, you may need to change filters.

But, don't take my word for it

[symmetal]

Hi iapa. The ZWO RGB filters are meant to be matched to the ASI1600 response curve but how much that's an advantage over any other manufacturer's filters is debatable, but if they aren't working very well I'll have to get some from another manufacturer. 

Alan

[iapa]

I just went for the ZWO wheel and filters when i get the 1600mm - didn't really dig really deeply into the focal length or transmission characteristics; I had the money and went for it  or

 

[ollypenrice]

In the top right corner of the colour image we may be seeing part of a large circular reflection in blue, I suspect. I'd certainly try a different filter if possible.

Olly

[symmetal]

5 hours ago, ollypenrice said:

In the top right corner of the colour image we may be seeing part of a large circular reflection in blue, I suspect. I'd certainly try a different filter if possible.

Olly

You could be right Olly as the extreme top right (outside the flare) is more yellow than the rest of the image. I'd have thought if is was something other than the filter, the L image would also show a hint of a flare too, bit it doesn't. I could try turning the filter over first to see if it makes a difference. Some filters it's easy to see which is the more reflective side which faces the scope but when I checked during my Ha checks a couple of the LRGB filters were not obvious, ( I can't remember if blue was one of those.) I could swap the filter with the Baader one in my Atik as a final check too but didn't want to upset that imaging train if I didn't have to. 

Alan

[Adam J]

On 18/10/2018 at 17:56, symmetal said:

I recently changed my ZWO 31mm unmounted Ha filter for a Baader 31mm unmounted for my ZS-61 and ASI1600 setup due to halos and edge light leakage in Ha. I recently imaged the Pelican when there was no Moon (rare) in LRGB and the blue shows bad flares from the two central bright stars in the top right of the image. The LRG images show no flaring there and the blue flats are fine. I'd expect flares from very bright stars near the edge of frame but these are modest 4.8 and 5.0 magnitude stars near the centre. Is this just a filter problem?

Baader LRGB filters don't seem to be available in 31mm unmounted so I'd have to get the 1.25" mounted which should be OK as it's the mini filter wheel mounted on the camera and vignetting shouldn't be an issue. If I have to change then to 1.25" I could have got the Ha 1.25" too in the first place. Now I'll have an odd one out again.

Here's a quick process of the RGB image with the blue corner at full size. Excuse the star shapes. I was still having some problems with tilt/spacing at the time.  The blue lines appear to point towards the two stars to pretty much confirm it as flare. Do you think I need to change the LRGB filters to cure this?

I recently had to resort to using a tilt adjuster to correct the star shape problems. The coke can strips jammed in the threads was too much hassle. 

 

On 19/10/2018 at 09:15, ollypenrice said:

In the top right corner of the colour image we may be seeing part of a large circular reflection in blue, I suspect. I'd certainly try a different filter if possible.

Olly

Could this be an issue with the blue filter flats rather than a reflection?

If using a ASI1600 and ZWO wheel they are mounted very very close together, a reflection of that diameter would have to be from two surfaces a long way appart probably from the back of the primary, it could be light leakage from the edge as opposed to a reflection but then why only in that corner. Also this does not look like other examples of ZWO filter reflections that I have seen posted. 

My first guess would be a flats problem and if not that then I would be making a set of masks for the 31mm filters, I think that ZWO actually made a set to combat the issue.

It might be easier to see whats going on if you posted the individual channels without a crop and their corresponding flats. 

I am a little shocked you needed a tilt adjuster to get round stars with a F6 refractor. I might be sending the camera back if my sensor was that badly tilted. 

Adam  

[Laurin Dave]

I use the same zwo filters and recently moved them into a 7 position ZWO wheel which came with the masks ... my flats are much improved ad a result.. no edge refractions.  I’d try and get hold of some direct from ZWO

Dave

 

[symmetal]

11 hours ago, Adam J said:

Could this be an issue with the blue filter flats rather than a reflection?

If using a ASI1600 and ZWO wheel they are mounted very very close together, a reflection of that diameter would have to be from two surfaces a long way appart probably from the back of the primary, it could be light leakage from the edge as opposed to a reflection but then why only in that corner. Also this does not look like other examples of ZWO filter reflections that I have seen posted. 

My first guess would be a flats problem and if not that then I would be making a set of masks for the 31mm filters, I think that ZWO actually made a set to combat the issue.

It might be easier to see whats going on if you posted the individual channels without a crop and their corresponding flats. 

I am a little shocked you needed a tilt adjuster to get round stars with a F6 refractor. I might be sending the camera back if my sensor was that badly tilted. 

Adam  

Hi Adam. Here's the individual calibrated colours given a rough similar stretch and their flats, all resized to be more manageable. None of the LRGB flats show any real edge leakage so didn't think that the ZWO rings would make much difference.

I needed the tilt adjuster mainly due to the ZS-61 field flattener which was 0.3mm shorter on one side compared to the other. You could measure the difference from the back of the lens mounting ring to the rear of the flattener so thought a tilt adjuster needs to be mounted after the flattener, and it has greatly improved the star shapes. I can't blame ZWO for that.  I suppose I could have returned the flattener but as it was quite a while after purchase before I found the problem I was in two minds. The tilt adjuster is handy as you can make adjustments without having to disturb anything else in the train so is quick to set up. I was spending hours trying to sort it beforehand with varying success wasting valuable imaging time which is scarce as it is. 

Luminance

Red

Green

Blue

Luminance Flat

Red Flat

Green Flat

Blue Flat

Alan

Edit: flats replaced with stretched flats.

[symmetal]

3 hours ago, Laurin Dave said:

I use the same zwo filters and recently moved them into a 7 position ZWO wheel which came with the masks ... my flats are much improved ad a result.. no edge refractions.  I’d try and get hold of some direct from ZWO

Dave

Hi Dave. My LRGB didn't seem affected by edge leakage according to the flats though bright stars near the edge could cause problems I suppose. Only my Ha filter showed awful edge brightness variations which I've now swapped for a Baader one, though haven't done a flat for this one yet to compare. 

Alan

[Adam J]

5 hours ago, symmetal said:

Hi Adam. Here's the individual calibrated colours given a rough similar stretch and their flats, all resized to be more manageable. None of the LRGB flats show any real edge leakage so didn't think that the ZWO rings would make much difference.

I suppose I could have returned the flattener

Blue

You might want to stretch those prior to posting the flats.

I dont think that is a reflection. Try masking and new blue flats.

I would 100% have sent that flattener back.

Adam

[symmetal]

47 minutes ago, Adam J said:

You might want to stretch those prior to posting the flats.

I dont think that is a reflection. Try masking and new blue flats.

I would 100% have sent that flattener back.

Adam

Yes, it was a bit dumb posting unstretched 8-bit jpgs.  I've replaced the flats in my post above with stretched ones and the blue one looks pretty normal (to me). As the top right blue 'flare' is composed of lines pointing towards the two bright stars I assumed it's a diffraction effect caused by them, but quite why is what confuses me.

I'll see if I have any other blue subs on different subjects taken with that filter. Most clear nights recently have been moonlit so I concentrated on Ha. 

Alan

[Adam J]

19 minutes ago, symmetal said:

Yes, it was a bit dumb posting unstretched 8-bit jpgs.  I've replaced the flats in my post above with stretched ones and the blue one looks pretty normal (to me). As the top right blue 'flare' is composed of lines pointing towards the two bright stars I assumed it's a diffraction effect caused by them, but quite why is what confuses me.

I'll see if I have any other blue subs on different subjects taken with that filter. Most clear nights recently have been moonlit so I concentrated on Ha. 

Alan

I think you need to try the masks. Direct reflections from the filter would be much smaller, it is looking like the edge of the filter.

[symmetal]

OK. I'll try some masks as you and Dave suggested. Thanks for the help 

Alan