Ive noticed a blue ring around bright stars eg sirius. Check the picture bellow. this is sirius at prime focus and the ring around the star would cover about 1/2 the width of the image. (sorry about the crop - its not ideal but i didnt know how else to reduce the image size bellow 200Kb as it was shot in RAW mode).
Im using a lx200 acf 12" and the ring is there whether its through the eyepiece or photographicaly. Does anyone know the source of this.
I was browsing Paul Haese's website, and noticed here that he had something simillar. Do you think its caused by the same thing?
Hi josh.
It LOOKS similar and certainly appears to be some sort of internal reflection, but you need to say what sort of scope you are using to be sure!
could the ring be light getting past the baffle tube thats not from the mirror?
these images show some light leakage when trying to look for it however if i look straight at the secondary mirror i can not see any, BUT, i dont have the diagonal in place with these shots and when it is in place, i cannot see any light leakage as it is shown in these images.
Also could it be bafffle reflections, in image 740 the light from the baffles is just visible if you look carefuly.
I should also point out that just before the bright star is in the FOV, i can see the ring from it in the eyepiece.
thanks
Josh
edit:
I have now been informed that when looking off axis and without a diagonal in place i.e when looking close from the rear of the OTA, i should see what the pictures show. however i shouldnt see it when there is more length off the back of the OTA such as when using a diagonal - which is the case.
Last edited by Joshua Bunn; 23-12-2011 at 03:52 PM.
Would someone with a 12" lx200 ACF or R scope mind looking at or photographing the brightest stars in the sky such as sirius, rigel Kent, or canopus. I need to see if other scopes like mine have the same result as the ring that can be seen in the first post.
Ive been asked to check this out by astro optical supplies so they can help judge if its my scope or not.
Sorry I don't have a lx200 so can't help you there.
I did once have a Celestron CPC1100 though.
Like yours I could see light leaking around the outside of the baffle tube as shown in your above photos.
However I never saw any blue rings through the eyepiece
so I am doubting that that would be the cause.
Also I think you would probably see this leakage in most commercial type SCT's.
Thanks for your reply, I described what i saw there about the light leaks around the baffle tube to someone with much experience in this field and they said this was normal. I must also say that there were no accesories on the back of the scope when those images were shot, ie no visual back or focuser, and that was taken into consideration when i described what i was seeing re. the light around the baffle tube.
Joshua, I don't think it is exactly the same problem. That being off axis light getting down past the baffle. It looks more like a standard reflection to me. The blue line is concentric with the star and not distorted.
It looks more like a reflection off you sensor window. What sort of camera are you using? Are you using a reducer? If so which company made the reducer?
A bit more information will make it a little easier to ascertain. Can you reduce the size of the image down to 900 x 900? Try using PS or your stacking program to do that.
Thanks Paul,
It looks similar to what you had with your GSO if im not mistaken.
Ive pretty much rulled out cameras and accesories and i think its the scope. I have not used a reducer or any additional glass in the optical train.
The image in my first post was taken with a canon 550D
The image i have attached to this post is sirius again, a full frame 2 sec. exposure. the optical path is optec tcf-s focuser screwed onto the back of the OTA and an stl 11000 mono camera. the image was taken through a clear filter.
Is the 3.25" to sct reducer still in place on the back of the scope? If so check that it is flat black inside rather than shiny anodized (this was a problem on my 9.25 celestron).
Ive changed the reducer (not telecompressor) from the standard one that comes with the scope to the one that mounts the optec focuser to the back of the OTA directly and it hasnt changes anything. the one that came with the scope is flat black and i can still see the ring.
Ive been looking down the focuser tube when the scope is pointed at a bright light indoors and can see various reflections.
The dealer who i bought the scope from have contacted meade and meade basicaly said this is normal. But Dr Clay, who ive been corresponding with about this says its not normal after i sent him the images.
I can post the reply Meade gave if anyone wants to see it.
I'm just waiting for a clear sky to test with my meade, last two nights have been gale force storms, and it is clouding over again now.
The moment I get a piece of clear sky with sirius in it, I'll take a look.
The good news is that it seems to be concentric with Sirius and therefore not a baffle tube problem. So you can rule that out. Good to know that no reducer is in place to cause problems.
Different cameras show the same problem so yes it is likely that the reflection is coming from within the scope.
Off axis reflections will not show up like this. That type of reflection shows up like on the experiments I did.
I tend to think this is caused because Sirius is so bright and some reflection coming back is normal. Could you try imaging Hadar or Acrux or Beetleguese for me? If the reflections are not overly evident in those images or not evident at all it is a minor reflection problem.
Thanks everyone for the input.
Kal, I entered some figures into this calculator, 9 micron pixels, f/10 system, and diameter of about 1600 pixels, and it said the replection was 144 mm from the ccd. This would suggest the baffle tube, but i think I already eliminated that by placing a rolled up piece of felt in there. The ring was still there so i removed it. Thankyou all the same.
Thanks Peter, It will be interesting to hear the result.
Paul, I will try imaging them when i get my scope out next. Before then, on saturday night i imaged Delta crux, 6 sec exposure (2.75 mag star) and i still saw the ring. Bear in mind, the camera was binned 3x3. see attached image.
Im in contact with the dealer where i bought the scope and they are doing what they can to see if this is normal or not aswell.
Paul, I will try imaging them when i get my scope out next. Before then, on saturday night i imaged Delta crux, 6 sec exposure (2.75 mag star) and i still saw the ring. Bear in mind, the camera was binned 3x3. see attached image.
Im in contact with the dealer where i bought the scope and they are doing what they can to see if this is normal or not aswell.
thanks
Josh
Yes looking more like an issue rather than just an errant minor problem.
Delta Crux showing is going to mean other stars of the same magnitude will produce the ring. Binning just shows what a 1x1 would look like after several minutes anyway.
Don't bother imaging the stars I requested. Maybe send these images to the dealer and ask them to explain it. If the dealer via Meade cannot explain the reflection then ask to have it replaced.
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