Cleaning secondary?

[Devon Oxford]

   Last night I tried imaging Jupiter with my 12" LX200GPS with a 2X Barlow... it was promising, but I could see many 'spots' of various sizes in the image. This is the first time I've noticed these. OK, I sez to meself... I've got some dust on my CCD / filter / Barlow lens... Checked them. Cleaned the Barlow. Same problem. Found that I can rotate the whole camera with Barlow and the 'spots' are stationary... no other lenses in the optical path. The corrector has a few minor dust spots, but nothing that should be noticeable at all. The only thing I can figure is that there are dust smudges (possibly from condensation?) on the secondary. Opinions...?
   If I MUST clean the secondary, does anyone have any cleaning techniques that will be helpful?

   Thanks!
                   Devon

[lindendave]

Hello Devon,

I've never had to do that with my scope but the thought has crossed my mind while cleaning other optical parts attached to the scope. Fortunately your question has been posted where you will get the best advice on the planet!

[Devon Oxford]

   About the LAST thing I want to do is touch the mirrors on this thing. The 'spots' don't really show up with visual use, or really even without the Barlow. But, with the Barlow, they are far too intrusive... and I'm trying to do some planetary imaging. I did a 'capture' of the 'spots' (inside lighting, no Barlow) which shows them quite well... but I'm not sure how to post them here (or if they would be wanted on here).

   Thanks!
                   Devon

[drclay]

I am doubtful that even spots or dust on the secondary would be "focusable" and still would be suspect of the Barlow or camera CCD chip.  Typically the light path will focus beyond resolution points of any debris on the optics EXCEPT debris located very close to the focal plane:  eyepiece, camera, barlow, etc.  How about filters....do you have filter in place?

Any objects on the secondary would have to be about 1/4" diameter to be seen on the imaging plane.

Check again .... rotating the equipment is the best way as you have done, but try it again and make sure that you rotate everything at the back end of the telescope.

Dr. Clay

[Devon Oxford]

   I agree, Dr Clay... My 'camera' (modified QuickCam Pro 3000) has a filter threaded on the nose, so it rotates with the cam. Using the thing live, I can rotate the whole assembly... the picture rotates, but the 'spots' do not.  There are no other optics or glass in the chain. In my test capture, they look kind of like something you would see in a microscope: in my attempted shots of Jupiter, they looked more like the classic 'dust mote' on the CCD chip or window. The largest spot resembles a 'ghost donut'  .... I'm not sure if I'm overlooking something...

   Thanks for your help on this...

               Devon

[drclay]

Look at the reflection of the secondary by aiming the OTA out of a window in daylight; you will see the secondary shining on the primary mirror....if there is anything large enough to cause this on the secondary it will be seen to the eye.

Once done, open up the back end of the scope (take off all accessories) and examine visually through the rear port.  If you still do not see anything on the secondary, then put in an eyepiece (low power will be best) and aim the scope at the daylight sky, being careful of course to not look at the sun......if the secondary is causing the problem, then you will see the spots....again, rotate any eyepiece to eliminate that as the source.

Next, take it out this week and aim at the MOON and examine with medium power.....start with the scope in focus and then turn it slightly out of focus; any debris will show up as darkened blobs in the visual field.  If you do not see anything, then attach the camera and once again aim and focus at the moon.  Look at the image coming out of the camera and once again examine out of focus.

Keep us posted.
IF YOU MUST CLEAN the secondary, the corrector should be remove with most caution, making sure to index its position in the cell and returning it exactly as it came out.  DO NOT REMOVE the secondary....clean it in place and use ONLY pure (96% or higher) isopropyl alcohol and white unscented Kleenex tissue...apply with one tissue, using plenty of alcohol and remove quickly with a dry tissue....as the tissue crumples and flakes, throw it away and quickly grab another and always keep a dry, flat surface against the secondary.  NEVER rub hard....just light finger pressure the entire time!

Dr. Clay

[Ron]

   About the LAST thing I want to do is touch the mirrors on this thing. The 'spots' don't really show up with visual use, or really even without the Barlow. But, with the Barlow, they are far too intrusive... and I'm trying to do some planetary imaging. I did a 'capture' of the 'spots' (inside lighting, no Barlow) which shows them quite well... but I'm not sure how to post them here (or if they would be wanted on here).

   Thanks!
                   Devon

Devon,

Pictures are certainly ok here, they are easy to post and embed with your messages.  All you need is a storage site such as the one I have, Fototime, there are also other frees sites out there that will let you link your images.

If you decide to embed some images with your messages just let me know and I will try to help guide you through the process.

Ron