What is this blemish?

Conn Buckley · Post by **Conn Buckley** » Sat Nov 10, 2007 9:34 pm

I was out on Thursday night last with scope /camera. I took this image of an out of focus Mirphak. Anybody know what the blemish is at about the 5 o'clock position? Presumably it is small but i wonder where it is in the system. Conn

John O'Mahony · Post by **John O'Mahony** » Sun Nov 11, 2007 8:30 am

That scope is well collimated! I'll bet the optics are first rate too.
It could be a speck of dust on the corrector. I see these all the time but they are never the same each time I set up the scopes.

Dave Lillis · Post by **Dave Lillis** » Sun Nov 11, 2007 9:50 am

Thats is a spec of dust on the cmos sensor in the camera, with very careful cleaning with something like a cotton bud you can remove it, you can make things worse if you 're not careful.

Frank Ryan · Post by **Frank Ryan** » Mon Nov 12, 2007 1:08 pm

As Dave says, they are 'dust doughnuts', vey common and very annoying, especially if you are taking any shots near twilight or dawn. There are ways to remove them in post processing but the techinques are convoluted and (for me) not warranted. I usually photoshop them out but I gues the best way to sort it out is to clean the chip. Very dangerous work as any mistakes could make an even bad situation worse.
I just put up with them.
I must give the processing removal techniques a go to see how long it takes.
There is an feature in this months Sky at Night about it in the section
'Building a Flat Field Box'

Conn Buckley · Post by **Conn Buckley** » Thu Nov 15, 2007 9:55 am

Lads thanks for the helpful comments. Sorry about the delay in responding but between golf and our marathon day in Birr I am only catching up.
John, I have to thank Dave for the excellent collimation job. Yes, I am really pleased with the LX 200R. I get out as much as possible and just like the ETX 90 I find that the Meade manual can be a bit scattered e.g. when it mentions the mirror lock it will refer to a later page 'for more on the mirror lock' and even that page will refer to some other page, so it does not read easily.

Conn Buckley · Post by **Conn Buckley** » Thu Nov 15, 2007 9:57 am

Dave, thanks for the cotton bud tip. When the webcam had this problem you told me how to clean it and it worked out very successfully.