Esprit 100 Star Trailing in corners - why?

[PeterCPC]

I am getting trailing stars in the corners of my images - any ideas why?

I am using an Esprit 100 with IDAS D2 filter and ASI294 Pro camera. Second image is bottom left corner enlarged.

Any help appreciated.

Edited January 21, 2023 by PeterCPC

[rnobleeddy]

Are you using a field flattener or reducer?

The full image appears to be low quality when I download it, so hard to see the corners, but worth checking how the pattern varies across each corner. Are they symmetric around the centre of the image, or all pointing in the same direction?

[PeterCPC]

12 minutes ago, rnobleeddy said:

Are you using a field flattener or reducer?

The full image appears to be low quality when I download it, so hard to see the corners, but worth checking how the pattern varies across each corner. Are they symmetric around the centre of the image, or all pointing in the same direction?

I loaded them as png taken from single RAW image. I use a field corrector bought from FLO at the time of purchasing the scope. All the trailing stars seem to be elongated from the corner towards the middle. Do I need a flattener? If so any suggestions.

Edited January 21, 2023 by PeterCPC

[rnobleeddy]

11 minutes ago, PeterCPC said:

I loaded them as png taken from single RAW image. I don't use a flattener or reducer. All the trailing stars seem to be elongated from the corner towards the middle. Do I need a flattener? If so any suggestions.

It's a common OTA so I imagine others will know the answer for sure - but the Esprit series don't claim to offer a flat field, so yes, I'd imagine this will need the dedicated field flattener to get a flat frame across a 4/3" sensor.

 

Edited January 21, 2023 by rnobleeddy

[rnobleeddy]

16 minutes ago, PeterCPC said:

I loaded them as png taken from single RAW image. I use a field corrector bought from FLO at the time of purchasing the scope. All the trailing stars seem to be elongated from the corner towards the middle. Do I need a flattener? If so any suggestions.

To add a suggestion - it's almost certainly worth using the dedicated flattener https://www.firstlightoptics.com/esprit-professional-refractors/skywatcher_flattener_esprit_100_20188.html

I guess for astrophotography, I'd consider the matching flattener a must buy for the Esprit series, unless you just want to image very small objects, or are happy to fix the curvature in processing.

[PeterCPC]

1 minute ago, rnobleeddy said:

To add a suggestion - it's almost certainly worth using the dedicated flattener https://www.firstlightoptics.com/esprit-professional-refractors/skywatcher_flattener_esprit_100_20188.html

I guess for astrophotography, I'd consider the matching flattener a must buy for the Esprit series, unless you just want to image very small objects, or are happy to fix the curvature in processing.

Sorry but I misposted before. That's exactly what I do use. You say fix the curvature in processing. How would you do that - I just crop normally.

[rnobleeddy]

4 minutes ago, PeterCPC said:

Sorry but I misposted before. That's exactly what I do use. You say fix the curvature in processing. How would you do that - I just crop normally.

Ah, in that case it looks like a classic case of the spacing being a little out. 

Take a look at this thread - it's usually easiest to get some kind of variable spacer, and on the next imaging session, spend some time at the start systematically finding the best spacing for the flattener.

In terms of processing, I use startools, which has a star repair function that rounds mis-shaped stars. Different tools will have different options, and probably won't please purists, but if it's just stars out there, I'm happy!

 

 - 

Edited January 21, 2023 by rnobleeddy

[david_taurus83]

11 minutes ago, rnobleeddy said:

Ah, in that case it looks like a classic case of the spacing being a little out. 

Take a look at this thread - it's usually easiest to get some kind of variable spacer, and on the next imaging session, spend some time at the start systematically finding the best spacing for the flattener.

In terms of processing, I use startools, which has a star repair function that rounds mis-shaped stars. Different tools will have different options, and probably won't please purists, but if it's just stars out there, I'm happy!

 

 - 

When I look back at that thread I remember the many nights i used to stress out about not having perfectly round stars in the corners. Now I'm like, meh! 

I have the Esprit 100 and the matched flattener gives me nice round stars all the way to the corners of my 533MM. Even without the flattener on Peter's scope the corners don't actually look that bad. The flettener would give a huge improvement though.

[michael8554]

Hi Peter

There is trailing in the same direction everywhere in the image.

But worse bottom left.

Which means Tilt.

But the overall trailing could be due to guiding/tracking errors, is that a short exposure ?

Michael

[PeterCPC]

50 minutes ago, michael8554 said:

Hi Peter

There is trailing in the same direction everywhere in the image.

But worse bottom left.

Which means Tilt.

But the overall trailing could be due to guiding/tracking errors, is that a short exposure ?

Michael

300 secs

Have a look at last nights effort. I added another shim to increase the backfocus. Again it's 300 secs and guiding was good throughout. I did do a slight crop.

Edited January 22, 2023 by PeterCPC

[PeterCPC]

On 21/01/2023 at 11:23, rnobleeddy said:

Ah, in that case it looks like a classic case of the spacing being a little out. 

Take a look at this thread - it's usually easiest to get some kind of variable spacer, and on the next imaging session, spend some time at the start systematically finding the best spacing for the flattener.

In terms of processing, I use startools, which has a star repair function that rounds mis-shaped stars. Different tools will have different options, and probably won't please purists, but if it's just stars out there, I'm happy!

 

 - 

I downloaded Startools and I can see that there is a repair tab. However, I can't for the life of me work out how to do it. Any chance that you could let me have a basic workflow in how to use it?

[david_taurus83]

Is it a recent problem or has it always been like this? I've just re-read the thread and seen that you are in fact using the flattener so you should have better results. Pinched optic because of the cold weather? @Adam J is this similar to the issue you had?

FYI my IDAS D2 also gives me bad halos on my Esprit but was fine on my other scopes.

[Adam J]

17 minutes ago, david_taurus83 said:

Is it a recent problem or has it always been like this? I've just re-read the thread and seen that you are in fact using the flattener so you should have better results. Pinched optic because of the cold weather? @Adam J is this similar to the issue you had?

FYI my IDAS D2 also gives me bad halos on my Esprit but was fine on my other scopes.

Its similar to the issue i had with the scope i returened a few years back yes, but I would actually say this is much worse, its certainly looks like badly pinched optics to me and I would be returning this scope if it was mine.

Adam

[Adam J]

On 21/01/2023 at 10:49, PeterCPC said:

I am getting trailing stars in the corners of my images - any ideas why?

I am using an Esprit 100 with IDAS D2 filter and ASI294 Pro camera. Second image is bottom left corner enlarged.

Any help appreciated.

 

 

As above you should return this its within warrenty looks badly pinched.

Adam

Edited January 22, 2023 by Adam J

[PeterCPC]

Thanks everyone. I have asked FLO (who sold it to me bench tested) what they can do to help.

 

[PeterCPC]

@FLO Please see above. I have sent you an e mail as well. I see older posts about pinched optics on the Esprit 100 so this looks to be a known problem.

[Adam J]

1 hour ago, PeterCPC said:

@FLO Please see above. I have sent you an e mail as well. I see older posts about pinched optics on the Esprit 100 so this looks to be a known problem.

Its less a know problem with the Esprit than it is a problem almost universally, you will see examples of pinched optics from all makes and models of refactor unfortunately. I have even seen clear cases from Takahashi. SW sell lots of these scopes and so it will pop up from time to time. Its certainly not a design issue. 

Adam  

Edited January 23, 2023 by Adam J

[PeterCPC]

FLO have come back and said that they do not see any optics pinching. They suggest that I concentrate on the back focus (spacing) issue. It's true that this occurred in sub zero temperatures so I hope to see an improvement as temperatures rise. We'll see.

[Adam J]

48 minutes ago, PeterCPC said:

FLO have come back and said that they do not see any optics pinching. They suggest that I concentrate on the back focus (spacing) issue. It's true that this occurred in sub zero temperatures so I hope to see an improvement as temperatures rise. We'll see.

Your back spacing is indeed wrong, that is the problem your seeing in the corners, what we are looking at are the hexagonal shaped stars and the dark wedges within the star halo that align with the points of the hexagon indicating that the optics may be pinched.

Normally the other possible cause is lens spacers, but that just cant be the case in a Esprit 100 as individual spacers are not used. The lens elements are separated by a thin plastic gasket ring that is complete around the perimeter of the lens element and these are not visible without taking the lens apart. 

Reference: http://interferometrie.blogspot.com/2014/08/esprit-tuning-how-we-finetune-esprit80.html

The early Esprit models could have a gap in these rings causing issues but this was addressed quite some time back by SW and you should not see this on a modern model. 

Back spacing will not effect the shape and halo of stars in the centre of the field. As a note its hexagonal as opposed to a Maltese cross or triangle because SW use 6 adjustment screws not 4 or 3.

Some have 3 which would give a trefoil aberration, reference: https://www.cloudynights.com/topic/697015-what-is-a-pinched-optic/

https://www.cloudynights.com/topic/691489-poor-stars-with-esprit-80ed/

But I don't want it to just be my assessment, so it would be good to get another opinion from other members with the required optical knowledge. 

What I would do is get an artificial star and do a star test (De-focus either side of focus by 3-5 diffraction rings) if you see indentations in the outermost ring then that indicates pinched optics.

It is 100% possible that ambient temperature is playing a big part but personally i tend to think that temperatures above freezing should never result in this issue as this is not primarily a summer hobby. So i would re-test on a milder night and see if you still see this and if you continue to see issues at temperatures above freezing then that is really not right in my book.

My Esprit will not show that effect at any temperature I have used it at (touch wood) and I have imaged down to -5c at least. 

Adam 

 

 

 

 

Edited January 23, 2023 by Adam J

[PeterCPC]

@Adam J Hi Adam

I used my artificial star and came up with these. I cannot see a problem as you describe but image 4 looked a bit odd so I carried on moving out of focus and got image 5. Try and ignore the dust specks.😟 These were done indoors so not low temperature.

What do you think? Thanks for all your help by the way. FLO have suggested that maybe the focus draw tube needs tightening up slightly to stop tilt. I'm not sure which of the 8 screws on top does that so I e mailed Slywatcher.

[Adam J]

16 minutes ago, PeterCPC said:

@Adam J Hi Adam

I used my artificial star and came up with these. I cannot see a problem as you describe but image 4 looked a bit odd so I carried on moving out of focus and got image 5. Try and ignore the dust specks.😟 These were done indoors so not low temperature.

What do you think? Thanks for all your help by the way. FLO have suggested that maybe the focus draw tube needs tightening up slightly to stop tilt. I'm not sure which of the 8 screws on top does that so I e mailed Slywatcher.

Its none of the screws on top don't touch those as they hold the linear bearing in place and if that falls out its a world of hurt. 

The adjustments for the friction pads are on the bottom sides, diagonally into the body of the focuser. You will find 4 of them two either side of the focus nobs, whatever you do don't loosen them too much or again the linear bearing will fall out. They are little grub screws that are basically pushing up against the tube via a Teflon pad and hence ultimately up against the linear bearing holding it in place. 

Its difficult to say as you are too far out of focus, the further out of focus the less sensitive the test as the errors blur together. But having said that I dont see anything obvious, noting that room temperature is a long way from any temperature you are likely to be imaging at.  

I would say you need to be at least half the size of this one. But you need to be at more like 5c than room temperature. 

However, a comparison between this and any current outdoor temperature will be informative. 

Adam

Edited January 23, 2023 by Adam J

[PeterCPC]

@Adam J

I set up my artificial star outside - temp around 5C or so.

Air currents were a nightmare but these were about the best I got either side of focus. I will have a go at a real star when I get the chance.

 

[Adam J]

2 minutes ago, PeterCPC said:

@Adam J

I set up my artificial star outside - temp around 5C or so.

Air currents were a nightmare but these were about the best I got either side of focus. I will have a go at a real star when I get the chance.

 

I have not really experianced turbulance like that from an airtificial star normally its too close to see anything, did you let the scope cool to ambient once you got it outside.

I would also say that its still too big though better, but I am starting to see some potential notches in the outer ring.

Adam

 

[Adam J]

5 minutes ago, Adam J said:

I have not really experianced turbulance like that from an airtificial star normally its too close to see anything, did you let the scope cool to ambient once you got it outside.

I would also say that its still too big though better, but I am starting to see some potential notches in the outer ring.

Adam

 

When  you get a chance try a range of differnt focus positions from in focus to a size like your original images and ill take a look.

[PeterCPC]

10 hours ago, Adam J said:

I have not really experianced turbulance like that from an airtificial star normally its too close to see anything, did you let the scope cool to ambient once you got it outside.

I would also say that its still too big though better, but I am starting to see some potential notches in the outer ring.

Adam

 

Yes I let the scope cool for about an hour first. I'll try again soon.