I can't image tonight, as getting ready to do so, i kind of hurried and I tripped on the cable setting up and snapped the power connector on my mount.
Looking through the eyepiece now at sirius though, I get no ring like your photos. Tried a 24mm and a 12mm and an 8mm, don't get anything like in your photo. Is it that clear through the eyepiece?
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.[/QUOTE]
Thanks Paul, Ive been in contact with the dealer over there in the eastern states, and they said they would run some tests for me.
Quote:
Originally Posted by Poita
I can't image tonight, as getting ready to do so, i kind of hurried and I tripped on the cable setting up and snapped the power connector on my mount.
Looking through the eyepiece now at sirius though, I get no ring like your photos. Tried a 24mm and a 12mm and an 8mm, don't get anything like in your photo. Is it that clear through the eyepiece?
Peter, Im sorry to hear about your cable. Thankyou for your efforts. You said you could not see any ring visualy - to clarify, could you see a ring at all? I can see the ring visualy as crisp as they appear in the photo.
To clarify my previous post, I thought 144mm would place me well inside the baffle tube, but that may not be the case. I maybe at the back of the OTA. I will check.
I soldered up a new cable, didn't bother polar aligning properly, but took some quick shots with a Pentax DSLR on the back of the 10" ACF, I'm uploading the images now to see what we get.
Oddly, I did get a similar ring around sirius on my neighbour's C8 very early this morning, but it went away after we cleared the condensation from the corrector plate. I'm not sure if it was identical, but it looked very similar.
This one is a schmidt reflection from the corrector plate. If the scope is collimated accurately (centering of the secondary) it should fall in the shadow of the secondary and disappear from your picture. You can see in your shot that it doesn't trail with your stars. It's more or less static.
And a 30 second image. Bothe were taken with the Pentax K-r
Thanks for getting these Peter. If i look carefully in your second image i can just see a blue ring same as mine but fainter - can you see it?
Quote:
Originally Posted by Poita
Oddly, I did get a similar ring around sirius on my neighbour's C8 very early this morning, but it went away after we cleared the condensation from the corrector plate. I'm not sure if it was identical, but it looked very similar.
Interesting - thankyou
Quote:
Originally Posted by multiweb
This one is a schmidt reflection from the corrector plate. If the scope is collimated accurately (centering of the secondary) it should fall in the shadow of the secondary and disappear from your picture. You can see in your shot that it doesn't trail with your stars. It's more or less static.
Here is a link on these reflections aswell. follow the link.
Although i can see the ring photographicaly with an exposure long enough to show it up, I can only just see the ring when looking at Rigel Kent - the 3rd brightest in the sky. Stars less luminous than that, I will have to check to see what i can see visually - but my experience is that this is where it pretty much goes away. I will check.
Thanks for getting these Peter. If i look carefully in your second image i can just see a blue ring same as mine but fainter - can you see it?
Yes I can see it if I stretch the image a long way, definitely not visible in the eyepiece though no matter where I look.
I guess a test would be to use a fake star and see if the problem shows up.
It may be something inherent in these scopes, but it shouldn't be as obvious as in your photos.
I'm really interested in tracking down the source.
[EDIT]
I have tried letting the corrector dew up just a little bit, and the ring becomes far more prominent, just like in your images.
It could be a problem with the coatings on your corrector plate, I'd almost put money on it.
Or it could be a thin film of something on your corrector, maybe on the inside?
There are some spots on the corrector that only show up when moisture gets on it. Attached are 2 moisture free images of my corrector and 2 moisture laden images showing the CP spots. I have tried cleaning with pure Iso Alcohol but it did not clean sufficiently - the spots are still there. I gues there could be something on the inside, I have never taken the scope appart.
Maybe a trip over east to the dealer or Bintel is in order to see if they can clean it properly - I doubt the coatings have been damaged - I guess the dealer would soon tell me.
I think it just needs cleaning, either be very careful and do it yourself, or find out how much Bintel would charge to do so. I'd reckon there is a fair chance the ring will be minimised then.
I think it just needs cleaning, either be very careful and do it yourself, or find out how much Bintel would charge to do so. I'd reckon there is a fair chance the ring will be minimised then.
I think your right Peter, I had a go today and will inspect the CP more thouroughly later and also have a look at the stars to see if the ring is reduced. Warren from astro optical supplies has been good. He had a 8''and 10'' LX200 acf in the shop and he saw the ring increasing in brightness as the appature increased. Next week he has a 12'' coming in and he will look through that one aswell.
I tried again tonight, and as soon as I get the lightest condensation, that ring appears. I never noticed it before as I always use a dew-shield. But literally two minutes after taking the shield off, there it is!
Peter, do you think taking the shield off could have caused some stray light leakage? I know you said you let the corrector dew up just a little bit, and the ring becomes far more prominent, but is there a difference between having the dew shield on or off? having said that, i always use a felt linned dew shield.
I did think of that, and put the shield back on once the ring was evident. It didn't disappear, so in my case the ring is due to refraction of the dew layer on the corrector plate.
No dew, no ring. I guess any layer of gunk on the corrector plate could have the same effect, as could a faulty coating.
I swapped my C11 for a standard Meade 12" SCT recently and this Meade shows the same ring around bright stars visually. The C11 didn't show it and a Meade 10" ACF that I have doesn't show it.
One difference between the 3 scopes is that the 12" has glossy black paint in the baffle tube which is highly reflective while the other two have flat grey paint in the baffle.
The issue isn't important to me but I thought the report might be interesting to others. I suspect some flat black/grey paint wiped into the baffle from both ends might cure the problem, or perhaps a roll of flocking paper placed in the baffle.
I'd be curious to know if Joshua's old scope has flat or glossy paint in the baffle.
