Re: CCDT67


ccoop974
 

Hi Maarten,
I plan to Just make something up 
That will extend the length of the baffle instead of enlarging an already big central obstruction. This should also eliminate the problem.
Good luck,
  Steve


On Jan 18, 2015, at 9:50 AM, "Maarten Vanleenhove maarten.vanleenhove@... [ap-gto]" <ap-gto@...> wrote:

 

Tnx Rolando, I geuss I'll stick with the extra obstruction untill I can get a camera with bigger pixels so I don't need a reducer anymore ...

Maarten

chris1011@... [ap-gto] schreef op 15/01/2015 om 18:34:
 

The reason that you have extra light coming in is because the telecompressor increases the field size. Your telescope baffle was calculated for a smaller field. If you want to see how this occurs, remove the camera and telecompressor and place your eye at the back of your focuser. Now when you look up the focuser tube, you will see the secondary when your eye is at the center of the focuser. Then when you move your eye off-axis to the edge of the focuser, you will see a small sliver of light directly from the sky on the opposite side, which gets bigger the farther your eye goes off-axis. This is quite normal in all Cassegrain designs. It is always a compromise between maximum baffled field size and minimum central obstruction size.

Rolando




-----Original Message-----
From: maarten.vanleenhove@... [ap-gto]
To: ap-gto
Sent: Wed, Jan 14, 2015 5:32 am
Subject: [ap-gto] CCDT67



Hi,

I have a question on the CCDT67. I am currently using it with a GSO RC 16" f8. I get nice round stars around the field but, however it came to my attention that the primary baffle is no longer sufficient to block direct sky light. The ccd can see the sky directly even when this light should be blocked. I came to this conclusion due to the fact that on flats/images I was seeing a dark patch in the middle of the image and around the edge, the image brightens up considerably. We have a lot of light pollution here, I geuss the problem would be far less noticeable in darks skies. Adding 1 cm of extra obstruction on the secondary baffle solves this problem completely. I've wrapped a piece of foam hiker mat around the secondary baffle.

Would this be cause due to the fact that the CCDT67 decreases the distance from the back of the telescope to the camera ? (without it I need to add extra spacer rings) Is it know exactly how much that distance decrease is ?
Would you have suggestions in fixing the problem ? Adding extra obstruction isn't nice, but narrowing the primary baffle seems tricky as well (the question is what material can be used to do that)

kind regards,

Maarten 



Join main@ap-gto.groups.io to automatically receive all group messages.