Flats showing up possible alignment issue?

[CedricTheBrave]

finally have got round to sorting out some flats

shows that the image is not centre so I am guessing my colmination is off although it looks ok through the cheshire!

could this be the focuser not being square on the OTA?

[alacant]

Hi

How does the flat frame look if you rotate the camera 90º?

How do the flat calibrated images look?  i'm guessing good since you mention that collimation via the Cheshire looks good. If the latter has cross hairs, then even more confirmation. 

OTOH, if the stars look distorted, time to investigate.

Firstly, be sure to read the collimation myths. then, to help us diagnose, post a shot through a simple central hole collimation cap and also through the Cheshire. (links to) A light frame and a flat frame, the camera you used and its orientation would help nail it if necessary.

Cheers and HTH

 

Edited June 18, 2020 by alacant

[CedricTheBrave]

2 hours ago, alacant said:

Hi

How does the flat frame look if you rotate the camera 90º?

How do the flat calibrated images look?  i'm guessing good since you mention that collimation via the Cheshire looks good. If the latter has cross hairs, then even more confirmation. 

OTOH, if the stars look distorted, time to investigate.

Firstly, be sure to read the collimation myths. then, to help us diagnose, post a shot through a simple central hole collimation cap and also through the Cheshire. (links to) A light frame and a flat frame, the camera you used and its orientation would help nail it if necessary.

Cheers and HTH

 

thank you very much

i am going to have a look at this later and try and get some diagnostic images up

[CedricTheBrave]

interesting first change! rotated the DSLR by 90 degrees

[alacant]

Now rotate it back and take another frame. Push the camera tight up against the focuser each time.

Edited June 18, 2020 by alacant

[CedricTheBrave]

looks like its slightly different every time but not consistent

i am going to look at tightening the focuser tube a little to see if that helps

i have been thinking for a while that its not very sturdy 

[alacant]

What focuser is it?

[CedricTheBrave]

It's the stock skywatcher dual speed 

Think I will upgrade to a moonlit or steeltrack

[alacant]

Ah, ok. There's the third thumbscrew at 120° trick but even so, I've never had consistency with it on either an ed80 or a 130pds.

Not sure what telescope you have but the items you mention are likely to cost more than the telescope itself whereas the old sw 63mm single speed rack and pinion focusers are much better at holding heavy loads than the ds will ever be. They also  bolt straight onto the existing baseplate.

Have a look here.

Cheers.

Edited June 18, 2020 by alacant

[CedricTheBrave]

35 minutes ago, alacant said:

Ah, ok. There's the third thumbscrew at 120° trick but even so, I've never had consistency with it on either an ed80 or a 130pds.

Not sure what telescope you have but the items you mention are likely to cost more than the telescope itself whereas the old sw 63mm single speed rack and pinion focusers are much better at holding heavy loads than the ds will ever be. They also  bolt straight onto the existing baseplate.

Have a look here.

Cheers.

I have a 200pds

I do like the fine adjust but it's always struggled with my dslr

[ollypenrice]

How do you orientate your focuser? Do it like this. Pieter Vandevelde knows what he's doing.

What a nice location, too! 🤣

Olly

Edited June 21, 2020 by ollypenrice

[CedricTheBrave]

On 21/06/2020 at 18:56, ollypenrice said:

How do you orientate your focuser? Do it like this. Pieter Vandevelde knows what he's doing.

What a nice location, too! 🤣

Olly

wow

[CedricTheBrave]

I went for a steel track managed to fit it ok although drilling holes in the OTA was a bit nervy!