CCD Weirdness

[Shelster1973]

Am putting this in the beginners section because I am still very very new to CCD imaging.

Having finally managed to get out tonight, I am running into a few issues.

1st you will see from the attached is one of focus.  Have had my verniers out and marked and measured the distances that I am supposed to have between my come corrector and CCD, but still cannot achieve a sharp focus.

The second is a bit more bemusing.

The 1st image was a 15 min grab with a lum filter and the 2nd is the same target with same filter but only 1 min.

The question is what is going on?  Am I exposing for too long and this is what is giving me the weirdness?

As for focusing, am guessing I am going to have to get my OTS off the mount and get it somewhere during the day where I can have an experiment with getting the right distances between all the optical train elements

Image 1

Image 2

[geordie85]

The difference in images could be due to high level cloud. I'm unsure about your skies but mine are very murky at the moment. Not sure about the banding though. Maybe due to a power drop? I get banding like that on my 383l when my battery is running low.

[Shelster1973]

Made some progress.

i emailed Terry at SX last night and he had a look at the fits images.  He thought that I may have in issue with the anti-blooming level so asked me to take a picture of the insides and send it to him.  This confirmed his suspicions and he suggesed that I adjust the potentionmeter controlling it.  Followed the instructions and am now waiting to try it out.  WIll give it a go on my flats box as hopefully I will be able to get exposures greater than 1/1000th of a second without seeing the strange artifacts.

Also triple checked my distances today too and it is spot on at 55mm.  In a weird way am now hoping that when the moon shows itself again in a few weeks it is clear and will use that as a traget of opportunity to check my spacing and focus.  May try and see if I can get the OTA onto a distant target, but there is nothing at a suitably great distance that is visible from my imaging location in the back garden

[MattJenko]

Focus issues are not the same as spacing issues, so you should be able to get good focus in the center of your images even if the spacing is not right between sensor and corrector.

Not sure if you have tried it before, but CCDCalc is a great way of helping to get spacings right without a lot of the guesswork. It costs though... 

[Shelster1973]

14 minutes ago, MattJenko said:

Focus issues are not the same as spacing issues, so you should be able to get good focus in the center of your images even if the spacing is not right between sensor and corrector.

Not sure if you have tried it before, but CCDCalc is a great way of helping to get spacings right without a lot of the guesswork. It costs though... 

Cheers Matt

Do you have a linkie ot the CCDCalc please?  My GoogleFu is weak today

[Waldemar]

24 minutes ago, MattJenko said:

Focus issues are not the same as spacing issues, so you should be able to get good focus in the center of your images even if the spacing is not right between sensor and corrector.

Not sure if you have tried it before, but CCDCalc is a great way of helping to get spacings right without a lot of the guesswork. It costs though... 

CCD Calculator is Freeware since 2005, so the only cost is time to invest

[Shelster1973]

24 minutes ago, Waldemar said:

CCD Calculator is Freeware since 2005, so the only cost is time to invest

Free is my favourite price...and I'm not even a Yorkshire man either

Will have a look later on tonight when I get home and can see it.

Was thinking of giving CCD Inspector a run too.  Noticed on the website that it says it has a fully functional demo, so can throw one of my images into it and see what it comes back with

[MattJenko]

Sorry, my bad - I meant CCDInspector!  I should know as I have it installed and use it for my spacings and have done recently....

[Shelster1973]

5 minutes ago, MattJenko said:

Sorry, my bad - I meant CCDInspector!  I should know as I have it installed and use it for my spacings and have done recently....

Do you fancy sorting mine out for me ?

[Shelster1973]

Right

Downloaded and installed CCDI last night and the 30 day clock is running.  Have to say I am a bit overwhelmed and bemused, but as far as I understand it I need to do the following

• Setup as normal
• Point scope to star field that contains no large 'celestial objects'
• Take a fair few images of said star field (thinking 25 - 30) at suitable exposure so as not to saturate stars butlong enough to give decent amount
• Point CCDI at said images
• Select them all them 'measure'
• Bring up a few plots and pretty 3d images and then scratch head at what to do next

Does that seem correct?

Have also had a minor adjustment to my imaging train too.  I moved the spacer so that it is behind the filter wheel now.  So I now have MPCC>Filter Wheel>7mm spacer>0.5mm Delrin Ring>Camera.  Prior to having the filter wheel, I hac the MPCC connected via longish spacer to the camera and my Ha filter screwed to the front of the MPCC and managed to get a sharp image, so know I can achieve focus.  Part of me is thinking of moving it all behind the filter wheel and having a 2" nose piece attached to the front of the filter wheel so that I can fit into focuser, but have a feeling I will be putting a fair bit of stress on joints and introducing possible issues with flexure.

[MattJenko]

The way I do it is to take 2 or 3 images as you describe for an average (not to stack etc, but to ensure that they look similar). Do the measure all and then look at the 3D curvature graph. I use a Baader variable adjuster which makes things easier, so I can then make a little in or out adjustment and repeat and see the difference. Basically, you need to work out which direction to move the spacing to go from concave to convex. When I did my TS60/x0.79 spacing, I managed to get it so that the edges were flattening as the center was starting to bulge, meaning I was unlikely to get a perfectly flat image, but could get it pretty even.

 

[Shelster1973]

Unfortunately due to the minimal distacnce I have, the 7mm is the only main spacer in there and have not found an adjustable one that small.  Will keep looking but feel I am down to using the delrin rings to get the fine tuning done.

[MattJenko]

Its tough to judge things when changing the spacing is such a dismembering process and delrin spacers are all well and good if you have long threads. I get concerned when the connecting threads get smaller and smaller :). Curse of the 55mm spacing requirements that a lot of correctors have I guess. Post up your 3d images you get. With an SX694, it should be a little more tolerant than my 1600 because of the sensor size.

[Shelster1973]

A few CCDI plots from tonight and one of the images used to create it

Not really knowing what I am looking at...I feel that I may have a wee bit of tilt and the CCD plane is not parallel.....

[MattJenko]

Looks tilted, all the stars are angled top left to bottom right. Looks pretty good other than that though, as fix that and I reckon it will look much better. Also, if you rotate the camera in the tube, is it tilted in the same way? With a newt and coma corrector, it generally is a push fit, so might be the way in which the CC is locked into the drawtube.

[Shelster1973]

The focuser is the one that came with the scope and has been off for when I flocked the tube.  Is a 2" tube, but fitting is just a case of sliding it in and then the cc is held in place by two thumb screws at 12 and 4 o'clock around the tube.  Have not rotated the ccd to see if the titl moves.

Have been contemplating upgrading the focuser to either the moonlight CR2 or the baader steeltrack one.  The one last night flet a bit 'gronky' when moving it to get focus.

[Shelster1973]

Just doing some more reading and it appears that I have not taken into account the fact that using filters adds to my spacing distance.  So having got it all set up for 55mm I now need to re-adjust for 56mm.  Break out the rings