ES127 Refractor

[Simon Pepper]

Hi all

I need expertise again I am consistently struggling with this scope and I am considering just selling it! Probably had it a year now and not managed one respectable image! Its so annoying as when it comes to widefield I have no issues. I get that this would be harder but really a year....

I assume my elongated stars are a guiding issue they do all appear to be the same was but these are only 60s subs surely that should be obtainable? I see others with similar setups on the same mount not having this issue. I am thinking about getting the rowan upgrade for the HEQ5 and going down the OAG route but before this costs me another £500 I want to be sure this is the issue?

Flats as well with this OTA are doing my head in I cant remove the black mark and I also have no idea where this is coming from. Its not the filters as its on more than one, its not the camera sensor as I shoot on my widefield scope and don't see it, so that leaves the scope, but I don't see any issues on the OTA and I cleaned the lens yesterday so its not that! Why wont the calibration remove it ahhhhhhh!!!

 

I have screen shot lower right corner of the image you can see the corresponding dark spot from the master flat. I have attached the masters as well. Also the trailing is more evident on the fainter stars I think my total RMS was 1.2-1.6 I guess this is just not good enough?!?!?

 

masterFlat_BIN-1_FILTER-R_Mono.xisfmasterLight_BIN-1_EXPOSURE-60.00s_FILTER-R_Mono.xisf

 

 

Vlaiv tried to assist here: https://stargazerslounge.com/topic/396743-flats-issue-with-larger-scope/#comment-4260660 but turns out the compression ring was not causing any of these issues.

 

 

Thanks

Edited July 8, 2022 by Simon Pepper

[Elp]

Does the guidescope pixel image scale match the main scope? I don't read too much into the technical side of things but I found when I changed from a 30/120mm guidescope to a 50/202mm my guiding improved by approx 0.2rms at least when the seeing was similar. The improvement was better when using an OAG but I went back to the guidescope. For a long refractor are you positive the balance is spot on.

[Clarkey]

With regards to the star shapes this does look like a guiding issue. The RMS you are getting is not very good for an HEQ5 - it should be well under 1. The Rowan upgrade will help, specifically if there is significant backlash, but I do find my HEQ5 does require regular 'tweeking' of the worm drive to keep the guiding to its optimal. The end float on the bearings is also critical. I think you need to get this better before going to OAG as you may end up with the same problem.

As for the black mark - this definitely looks like dust/dirt close to the sensor - probably on the sensor glass.

[AstroMuni]

2 hours ago, Simon Pepper said:

I assume my elongated stars are a guiding issue they do all appear to be the same was but these are only 60s subs surely that should be obtainable? I see others with similar setups on the same mount not having this issue.

Have you tried to see the longest duration you can get without guiding? I can easily get 30s with no elongation and mine has no Rowan modification. HTH

Edited July 8, 2022 by AstroMuni

[Simon Pepper]

3 hours ago, Elp said:

Does the guidescope pixel image scale match the main scope? I don't read too much into the technical side of things but I found when I changed from a 30/120mm guidescope to a 50/202mm my guiding improved by approx 0.2rms at least when the seeing was similar. The improvement was better when using an OAG but I went back to the guidescope. For a long refractor are you positive the balance is spot on.

You could be into something here I wonder if the difference in FL mm could be causing it. Guide scope is 120mm and main scope is 952mm it maybe too much of a gap! 

[Simon Pepper]

1 hour ago, AstroMuni said:

Have you tried to see the longest duration you can get without guiding? I can easily get 30s with no elongation and mine has no Rowan modification. HTH

I can get 15 minutes subs on my other scope but as soon as a put this scope on it goes toilet on me. I tried 30 seconds and there was. I difference between that and 60s. It’s almost instant… 

[Simon Pepper]

2 hours ago, Clarkey said:

With regards to the star shapes this does look like a guiding issue. The RMS you are getting is not very good for an HEQ5 - it should be well under 1. The Rowan upgrade will help, specifically if there is significant backlash, but I do find my HEQ5 does require regular 'tweeking' of the worm drive to keep the guiding to its optimal. The end float on the bearings is also critical. I think you need to get this better before going to OAG as you may end up with the same problem.

As for the black mark - this definitely looks like dust/dirt close to the sensor - probably on the sensor glass.

Thanks this is really helpful I guess it’s time to try the belt and maybe a full strip down and re grease! 

[AstroMuni]

35 minutes ago, Simon Pepper said:

I can get 15 minutes subs on my other scope but as soon as a put this scope on it goes toilet on me. I tried 30 seconds and there was. I difference between that and 60s. It’s almost instant… 

Could this be due to balance? Otherwise cant see why a different scope can change the behavior of the mount.

[alacant]

Hi

How is the guide telescope mounted? Could you post a photo? It looks as though it is moving relative to the main telescope as the tube angle changes. I think the English term is 'differential flex' OWTTE.

Before you begin any software analysis and after you have secured the guide telescope, it is essential to make certain the mount mechanics are as perfect as possible. This means dismantling, cleaning, re-greasing and adjusting, even -especially some would say- new new mounts as described here.

Guiding a ~1000mm refractor with a small guide telescope on a low end mount, everything must be perfect. 

Cheers and HTH.

Edited July 8, 2022 by alacant

[Elp]

If you've still got the widefield scope you could try mounting that as your guidescope as a test.

Proper Dec and RA balance is the easiest thing to check first.

[Simon Pepper]

3 minutes ago, Elp said:

If you've still got the widefield scope you could try mounting that as your guidescope as a test.

Proper Dec and RA balance is the easiest thing to check first.

Ooo another awesome shout here is a pic of the setup. Balance and PA are good at least I thought they were lol. 

[Simon Pepper]

[Simon Pepper]

24 minutes ago, AstroMuni said:

Could this be due to balance? Otherwise cant see why a different scope can change the behavior of the mount.

I can get slightly better with my wife filed scope as it’s lighter not so demanding I think. Also at 250mm I can expose for longer without any trails. 

[Clarkey]

7 minutes ago, Simon Pepper said:

wife filed scope

Keep her away from your scope🤣

Looking at the image I would say there are two things that will improve your guiding.

Firstly a bigger and better mounted guidescope to ensure no flex. Secondly adjust the mount to get the RMS down.

[Elp]

It might mount better onto the handle if it can be done, you'll likely have more fixing points or a guide rail to minimise any flexure. The dec balance will also be better if it's centrally mounted.

Think of the FL difference like this, it's like trying to centre to shoot a target a few KM away using only your human given eye FL. To the eye the target may seem to be stationary, whereas in reality it could move a few meters.

Edited July 8, 2022 by Elp

[Simon Pepper]

8 minutes ago, Clarkey said:

Keep her away from your scope🤣

Looking at the image I would say there are two things that will improve your guiding.

Firstly a bigger and better mounted guidescope to ensure no flex. Secondly adjust the mount to get the RMS down.

Haha amazing! 

[AstroMuni]

24 minutes ago, Simon Pepper said:

I can get slightly better with my wife filed scope as it’s lighter not so demanding I think. Also at 250mm I can expose for longer without any trails. 

I looked up the ES127 here https://www.rothervalleyoptics.co.uk/explore-scientific-ed-apo-127mm-f75-aluminium-essential-triplet-refractor-ota.html
And if we are talking about same scope, I think you could be stretching the weight limits of the HEQ5 Pro.

[Simon Pepper]

18 minutes ago, AstroMuni said:

I looked up the ES127 here https://www.rothervalleyoptics.co.uk/explore-scientific-ed-apo-127mm-f75-aluminium-essential-triplet-refractor-ota.html
And if we are talking about same scope, I think you could be stretching the weight limits of the HEQ5 Pro.

I think there weight is wrong there or its the shipping weight I got mine here https://www.bresseruk.com/EXPLORE-SCIENTIFIC-ED-APO-127mm-f-7-5-FCD-100-Alu-HEX.html?mtm_campaign=Doofinder&mtm_kwd=0112134&mtm_source=English&mtm_medium=OnSite&mtm_cid=UK&mtm_group=SiteSearch which states its 7.7kg with accessories. Mine probably a little more with updated dove tail, filter wheel camera etc but pretty sure I am only about 8.5kg so well under the max weight. 

[Pompey Monkey]

I know you probably have been told this, but a 1000 mm telescope at very close to the manufacturers (optimistic) payload capacity of an heq5 is always going to give you headaches.

The pain of paying once for a better mount (eq6 minimum), while intense, will fade into the past and soon forgotten about when it works every time.

The chronic discomfort of having to constantly fettle your current mount to perform to your satisfsction will, however, slowly sap at your soul for as long as you continue using it with that scope.

Edited July 8, 2022 by Pompey Monkey

[Simon Pepper]

I feel I am going to have to dig deep into the wallet again then and speak to FLO who have four in stock! 
 

Thanks all for your help with this one really appreciated. 

[newbie alert]

Before you have to dig deep, or drive yourself into a state of frustration , your  big stars look roundish and the small stars much more oblong... I've had this with a William optics and it was focuser sag... So worth checking that everything is tightened down 

[Simon Pepper]

On 08/07/2022 at 16:42, newbie alert said:

Before you have to dig deep, or drive yourself into a state of frustration , your  big stars look roundish and the small stars much more oblong... I've had this with a William optics and it was focuser sag... So worth checking that everything is tightened down 

Well funny you should mention this because I wondered how the bigger stars were unaffected but I heard somewhere that could have something to do with pixel scale... I assume I can test this by pointing up to the 
Zenith and taking a long sub? Also did you just tighten them up? Mine is tight but it’s the standard hex focuser. I feel this could now be three or four potential issues and no idea how to narrow that down 😭

Edited July 11, 2022 by Simon Pepper

[newbie alert]

3 hours ago, Simon Pepper said:

Well funny you should mention this because I wondered how the bigger stars were unaffected but I heard somewhere that could have something to do with pixel scale... I assume I can test this by pointing up to the 
Zenith and taking a long sub? Also did you just tighten them up? Mine is tight but it’s the standard hex focuser. I feel this could now be three or four potential issues and no idea how to narrow that down 😭

Mine ended up as one of the bearings had seized and disintegrated in the end... A friend had a look, changed the bearing and it worked fine... Not saying it is that but it's a possibility as it shows the same symptoms 

[Simon Pepper]

Hi all 

Firstly apologies for bringing this up again but I decided to run some tests last night with the clear hour I had. I also stripped down the OTA, replaced extension tubes and changed the compression rings on the flattener closer to the compression ring on the ES to ensure good connection. I am 99% confident there is no sag in the focuser or anywhere along the OTA. Guiding was awful between 1.1-2.2.

• There is not much change in the way of elongated smaller stars between 20s and 180s (60s vs 180s below). As my guiding was bad I would have expected to see even worse stars at 3 minutes but they are not too bad even at 5 minutes. Yes they do get worse but I expected more.
• Pretty sure even after 1s/2s they were trailing but hard to see due to lack of exposure. Its like the issue happens as soon as the exposure starts. Correct me if I am wrong but if PA is aced at 950mm should I be able to get 5/10 s before trailing? 
• I turned off guiding and things got worse after 30s (expected really).
• I tested on M13 and M51 both quite near the zenith. 
• I do have backlash I can wobble both axis so could be this also.

I believe this has to be either flexure (which I don't really know what that is) or the fact my guiding scope is only 120mm. Unfortunately I don't have the correct attachments to try the Redcat as the guide scope, however I have an OAG on the way to try that out. This option was a lot cheaper than the EQR6! I will report back my findings once it arrives.

 

 

Thanks

Edited July 12, 2022 by Simon Pepper

[AstroMuni]

15 minutes ago, Simon Pepper said:

I will report back my findings once it arrives.

Good luck!