M13 + problem

[adamsp123]

Hi

Here is my attempt at M13 on 28/05/09 before being overwhelmed with Dew and Fog! Note Hair dryer sounds awefully loud at night even on low setting!

Canon 1000D + SW LP filter + Baader MPCC

ISO 1600 20x30secs + 6x1min. Unguided

Meade 10" SNT

I have noticed triangular shaped stars which I got a horrible feeling MAY be the MPCC any other ideas/comments most welcome.

[Ant]

I had a conversation with Steve yesterday about some problems that I have and he mentioned triangular stars - apparently they are caused by pinched optics.

You could check to see if the little clips that hold the main mirror in place are too tight.

You should be able to pass a business card through the gap between retaining clip and mirror (although that's a guide to the gap required and I'm not suggesting that you actually use a business card ).

Hope that helps

Ant

[adamsp123]

thanks for that Ant, I wonder if I have over tightened the lock screws on the main mirror after a recent re-collimation?

[Ant]

I do not think that collimation screws would cause pinched optics.

Collimation moves the entire mirror cell (which the mirror sit's within), it's the little clips that keep the mirror in place in the cell that's the issue.

Cheers

Ant

[MartinB]

Great M13 though, despite having your optics nicked.

[Tim]

It's a great image regardless, star colour is lovely.

Are the stars triangular all over the image in the same direction? If the stars were rounded before but are now like this, then you may well of overtightened the locking screws, possibly even on the secondary.

Cheers

TJ

[RobH]

Hello Pete,

I'd not have noticed the triangular stars at first viewing, what I did notice immediately was the rich star colour and overall vibrancy of the image.

Very nice

Cheers

Rob

[Tim]

Hmm, just noticed the 'unguided' bit. Are the stars the same shape even with a very short exposure, say 5 secs?

[adamsp123]

I am almost certain I have overtightened the main mirror locking screws, as it is an SNT design the secondary doesn't need collimating (more or less) once it is set correctly, just the main mirror and all the stars are 3 point distorted the same across the view, so I think I will loosen the lock screws and see what happens.

Thanks for all the ideas and kind comments on the picture.

Pizza Pete