alcol620

Thanks William. I had an exchange of information with ZWO tech and they initially suggested the usual "moisture in the works" and dry it out. Later it was suggested get in touch with the retailer and get it sent back for repair. i bought the camera in a used condition so my optiona are limited. It worked fine over a period of months so I had no come backs on the seller, just my bad luck. I saw mention on another site to use dew heater on the camera to prevent moiture, but I ssume that this would only stop the camera outside glass from dewing up.

Hi William, I used the "Optical Wonder Fineoptical cleaning fluid" from Baader Planetarium.

Thanks again for your inputs. I have on 3 occasions cleaned the sensor as per the link that LandyJohn posted. Once when i took the old tablets out and dried them in the microwave, second when I dried them in a conventional oven and thirdly when I put new tablets in (after heating them in a conventional oven). If there had been moisture on the sensor I would have thought that my 3 attempts with dry tablets would have cured it. As symmetal suggests, maybe the camera is not sealed properly and allows dampness into the sensor area?

Thanks for the feedback you 2 guys. For clarification when I talked about cleaning the sensor, I now realise that I was only cleaning the sensor window. I am not sure that I have a job description that includes removing the sensor window to get to the sensor itself!!

With symmetal's info on noise, I think I will stick with simply taking subs with the camera temperature set above 0deg C.

Thanks again

A belated update. Since my last post I dried the existing tablets in a conventional oven, again cleaning the sensor. Replaced the tablets. Result no change. I bought new tablets from FLO, put them in the oven for an hour and put them in the camera. The new tablets were left in the camera for 10 days before the camera was next used. The result was no change, I still had the same noisy pattern in the same area of the subs with the camera cooled below 0deg C. Above this figure no noisy pattern appears. I have wasted so much time and mental effort trying to resolve the problem and have decided that the only option is to take subs a couple of degrees above freezing. I assume this will make subs a bit noisier but at least the noisy area does not appear? Sending the camera back to ZWO and losing it for 2/3 months and having to pay for whatever is found is not an option. Any further comments are very welcome

A quick update. Calibrated with new flats and stacked the new lights taken at +5degC and no suggestion of any noisy pattern on the master light. Awaitingthe arrival of the wider swabs and will then re-clean the sensor and bake the tablets as suggested.

Thanks HTH much appreciated. I took some flats earlier this evening at 5degC to remove the ise of ice forming and an initial look suggested no noisy pattern. Now taking lights at the same temperature to check out the result. I have "cleaned" the sensor a couple of times although not with a wide swab. Not of that cleaning has changed the pattern significantly, but I will get some wider swabs and give it another go. I will also give the tablets a bake in a conventional oven.

Hi  folks.  Followed the process of drying the inside of the camera. Took the 4 tablets out 2 minutes in the microwave, cleaned the sensor and put the camera cover back on, waited 48 hours for tablets to do their thing.  Just took some new flats. First ones at +1degC 10 minute cool down time. Took the second set of flats at -13deg C 10 further minutes to cool down. Result, I still have this noisy area on the flats, both at 1deg and -13deg. I have attaached images to illustrate the noisy area on the flats, including the "rejection high" images produced by Pixinsight and the resultant master flat.

Any further ideas folks? Help gratefully received

Thanks everyone, especially the fulsome answer from oddsocks. So many helpful and knowledgeable people on here. I am awaiting the next sunny and hot day to take the camera apart in my extremely hot and dry conservatory to deal with the tablets. Reassuring to know that you are still watching over us Steve.

Hi Folks       first test completed. set target temperature at 1 deg and took 10 minutes to cool down, left to run for 10 minutes. Took 30 flats usual settings and stacked them. Result: no indication of the usual noisy area.
Then cooled the camera down to -13deg left for 10 minutes and took another 30 flats. Result: the usual noisy area appeared.
Job for tomorrow: dry the tablets and see what the result is.
One thing that puzzles me it that if it is dampness inside the camera, why does the noisy area always appear in the same area of the image? I would have thought that the moisture would move around and the crystals, whatever they are, would form on different parts of the sensor?

Next on my list to try, but first I am checking if the problem goes away if I slowly cool to just above freezing. If the fails the the tablets will get dried. Thanks for you  help.

Thanks Anthony   Argon purge?

Many thanks Andrew, it didn't occur to me that could be the problem, although on a couple of occasions the issue didn't arise. I am cooling to -13deg in about 5 minutes for flats, dark-flats and lights. I assume that only cooling to 0deg will give more image noise. Next time out, if we ever get a clear night, I will cool down much more slowly like you suggest. You have raised my hopes of a solution to the problem that has caused the loss of lots of subs. Thanks again Ale

Hoping someone can give me feedback on the cause of spotty pattern on flats. This seems to have appeared a few weeks ago. Using Pixinsight, I have stacked around 30 flats callibrated with dark flats. The Pixinsight rejection-high image resulting from calibrating and stacking the flats is attached illustrates the area of distortion on the image. This also appears on the master flat image, to a lesser degree. Using the flat to calibrate the lights leaves slightly darkened area on the stacked light frame over the samea area as appears in the flats.
I also shot the flats with the same settings but with the camera rotated. The distortion appeared in the same place on the image. Suggesting that the problem is inside the camera. I opened the camera and cleaned it. It made little difference, apart from adding a few dust motes. Is there some sort of problem with the sensor? the flats are 9s duration and ADu around 35000. I have attached an image showing the area rejection-high  and a stacked flat frame. Feedback very welcome.

On 03/08/2022 at 20:00, Adam J said:

Happy for you that you are now happy with it. It would be really hard to get that perfect without star testing but its great you got it close enough. I would now get some tape / mark the position of the red ring incase it shifts in future. 

For the record tilt is actually much less common in imaging than collimation issues. What most think is tilt will actually be collimation 90% of the time.  Thinking about it one reason for this is likely that telescope makers and stores have a vested interest in convincing users that their issues are between the scope and the camera (tilt) and not the scope itself. 

As for what caused it, a slight knock is all it can take. 

Adam 

Thanks Adam, your help is much appreciated. Take care, Alec

On 25/06/2022 at 13:42, Adam J said:

This is the foil spacer I use. To be exact I used aluminium tape from B&Q, rapped around the ring one and a half times. 

It wedges the primary cell just enough to bring it into perfect alignment. 

Hi Adam, I didn't get to try the artificial star test, but continued to adjust the ZWO tilter without moving to any improvement. I reset the scope so it had no tilt adjustment to it and tried your suggesttion of the foil spacer to adjust the primary cell. To my great relief it had an immediate effect and once I found the best position of the red spacer, the tilt reading on the software ASTAP was significantly reduced, see attachments, and the image visually showed the improvement. Although not perfect, I am happy to accept this degree of improvement. Many thanks for your patience and help. I assume the cause was the Primary cell being slightly out of line, caused by what I do not know. Thanks again

37 minutes ago, PadrePeace said:

I’m with AdamJ on this one. An artificial star test is the best way. It can be done  indoors any evening and repeated at will to confirm any mods. Waiting for stars in the Uk is going to take a lot of your time.  Really is worth breaking up your rig and letting AdamJ cast his eye. 

Thanks Adam and PP for further encouragement and feedback

On 19/07/2022 at 23:21, Adam J said:

Hi you are too far out of focus, you should have only about 5 rings visible. If you get too far outside focus the test becomes less sensitive as the errors blend into each other.

Not sure what your using but you dont want to auto stretch the image as it will ruin the detail. You want to set exposure so that you can see the rings correctly with autostretch turned off in something like NINA.

I tend to do this with a mono camera so not sure how well it works with OSC, the problem being that the different wavelengths may blure the result, I tended to use a green filter for best results.

This is an example star test from a friends scope, I did not have any of my own saved.

Green filter on a mono camera three rings seen. What you are looking for is that little dot in the middle to be dead in the centre of the outermost ring.

As you have less rings the effects of seeing on the star test will be increased and in these temperatures I really doubt you will get good seeing, so defo use an artificial star, 5 meters of atmosphere is much more stable than 10km.

Hi Adam, thanks for getting back. I am using a ZWO294MC camera so I have no option but to use a colour camera for testing. At present I am reluctant to break down my rig to use the artificial star. With my set up I can't position the star to point at the scope.

On the issue of: is it tilt or some other factor in producing the misshapen stars, I have stumbled on some free software that stacks subs and measures tilt and off-axix aberration. (ASTAP) and subject to clear skies I am going to retrace my steps and use ASTAP to produce tilt values for various adjustments, rather than currently visually assess images for improvements.

One other thing I noticed with my set up is a small amount of play when holding the objective lens tube and the flattener tube. A small amount of play can be felt. Is this normal? Thanks again for your help in this ongoing saga.

Alec

On 17/07/2022 at 22:49, alcol620 said:

Thanks Adam, appreciated. Much to my surprise I found an artificial star amongst my bits and pieces that I must have bought a few years ago (and didn't know I had). I currently have a fixed set up and I may need to break this down to enable the artificial star to be aimed at the ASKAR set up. As soon as I have an image I will take up your offer of further help.

Regards Alec

Hi Adam it is the old duffer again. Last night I tried to check out collimation with the set up I have without an artificial star. Method: I ran my normal set up with the ASKAr riding piggyback on the ED120 scope and the AZEQ6 mount. I found Polaris and put this in the centre of the image. With accurate guiding running, I defocused Polaris  in and out. The 2 images obtained (attached) were debayered and stretched in Pixinsight. I am not sure what the results indicate, apart from the fack that the stars are round!! Your input is appreciated.

Alec

23 hours ago, Adam J said:

No not quite, its not how circular the stars are that you are looking for. You want to defocus the star so that you get a ring with a bright centre just on the outside of focus, this is undercorrection in a bright APO. It best to do this with a mono sensor but you can do it with a OSC its just harder. Once you have that then you need to make sure that the brighter central dot is in the centre of the outer rings. This must be done with the star dead centre in the FOV.

With such a short focal length you can have it very close (relatively speaking) 20 x focal length is the minimum. So I would think 5 metres is a safe bet.

If you find the defocused star is concentric in the centre of the FOV then you can be reasonably sure that it is tilt and not colimation. In this case you can move the star to each corner and focus on it. If you have an auto focuser you can read off the movement relative to the centre focus position, that way you know which direction you are out in.

Post images of what you see here and ill help if I can.

Adam

Thanks Adam, appreciated. Much to my surprise I found an artificial star amongst my bits and pieces that I must have bought a few years ago (and didn't know I had). I currently have a fixed set up and I may need to break this down to enable the artificial star to be aimed at the ASKAR set up. As soon as I have an image I will take up your offer of further help.

Regards Alec

22 hours ago, Adam J said:

could be tilt but also could be colimation, the only way I would be able to tell is with a star test. The fact that your RGB channels look out of alignment pushes me towards it being colimation though.

This is how its performing for me with a ASI1600mm pro and a L3 filter to cut down the blue. But I did need to tune the colimation as described to get to this result. I show you this so as you dont feel its just the scope design itself.

Another possibility with latteral CA is that of a de-centered lens element on the objective and thats not something that can be cured yourself.  The issue with amature scopes and amature astronomy equiptment in general accross the board is that of smaple to sample variation. Its unfrotunate, but not all of it is even the responsibility of the manufacturer with fast apos as all it takes is a jolt in transportation.

All I can say is get a artificial star, they are useful things to own in anycase.

Adam

Thanks Adam, appreciated. When it was tested for Astronomy Now, the out of shape stars did not appear, so somewhere down the line things have changed. I am now fiddling with the tilt adjuster, but it is all getting too much - doing my head in!!! last questions how far away does the artificial star have to be and did you simply fiddle with the spacer added to the red ring until the stars became more circular? Thanks again

On 25/06/2022 at 13:42, Adam J said:

This is the foil spacer I use. To be exact I used aluminium tape from B&Q, rapped around the ring one and a half times. 

It wedges the primary cell just enough to bring it into perfect alignment. 

Thanks Adam, only just spotted your image. I have now put a ZWO tilt adjuster in the optical chain with the spacing still at 55mm. Star field image attached. Comments on the misshapen stars welcome

I have had similar misshapen stars without the filter.

Thanks Adam, Astronomy Now

Thanks Adam, bought the ASKAR with very minimal use in Jan 2021 so not old. From new it had only been used to test and review it for a journal.

Before embarking on the use of an artificial star. I will produce some better images to show the star field for the examples above.  In the meantime is it possible that you could illustrate where/how you placed a foil spacer on the red ring between the front objective assembly and the helical focuser?

As I have run the set up with three different Canon cameras and now the ZWO294MC and always had poor stars it seems unlikely that tilt has nothing to do with the sensor end of the set up?  Thanks again for your patience and feedback