Ok you Dob people....

I've moved from the Lightbridge 12" to 16".
I'm finding a problem in that the 16" is not as sharp as the 12".
In particular stars tend to be "smeared" rather than pinpoints.
I've collimated the ass off it, but without any further success.
In particular, objects that need sharpness just aren't sharp.
For example, Saturn isn't anywhere as clear as it was.
I understand seeing can be responsible for this, but even on good nights..like last night...it wasn't really any different.
So, I guess I'm looking at maximising the scope's alignment.
Any hints on how to get my stars pin-sharp and get the maximum detail out of my targets?

Is this across the field or just towards the edges of the field? Also, remember you have increased the magnification for any given eyepiece - is the effect the same if you use a longer eyepiece to achieve the same magnification? Is the secondary clean?

You've also gone from f/5 to f/4.5. You may just be seeing increased coma from the faster mirror. Are you using a coma corrector (such as a Tele Vue Paracorr)? It would help even the f/5, but the f/4.5 is probably really in need of it.

There's a review on CloudyNights here: www.cloudynights.com/documents/paracorr.pdf .

-- Jeff.

There's increased coma and there's increased coma.
A Paracorr is on the cards, but I didn't expect to be using one yet unless I was using 30mm eyepieces and greater...which I'm not.
The widest I'm using is a Panoptic 27mm.
Previous results with a 12" were excellent...some coma only at the edge of the field.
The smearing of stars makes close doubles almost impossible to separate.
In the F5 to F4.5 transition I'd have expected a more graduated coma increase, instaed of what I'm seeing now.

Eamonn,

Although it was nice and transparent here last night. The seeing was not very good at all. My focus metrics were reporting figures twice as bad as an average night. Maybe that was the issue?

I'm not sure that it's a single night issue, Dave. I've noticed it over maybe six nights, with some consistency. That's why I'm looking for anyone who has had a similar problem, or who has a good proven methodology of getting the best they can, in particular looking at the vagaries of secondary mirror alignment, and how I can ensure it's spot on.
However, i'm sure that seeing may be an additional issue. It's just that with so very few nights...and too widely spaced out... on which to compare viewings it can be difficult.