Newt f/ratio vs collimation difficulty?

[casstony]

I've only recently introduced myself to the world of dobs/newts and I'm thinking that I'll be ready for a larger one by the time GSO gets around to producing f/4 mirrors. Is it much more difficult to collimate an f/4 versus an f/5 dob?

[wavelandscott]

The "act" of collimation is the same...however, the tolerance for accuracy is a bit different.

I don't have the figures at my finger tips but the precision needed is greater for the faster scope. It is possible (and I have seen them) to determine how tight the tolerances are for the different scopes...

In either case, the more accurate your collimation the better the views!

There are many different tools/techniques available to help in this respect...ranging from a rather simple collimating eyepiece to a barlowed laser to a Cats Eye (or other) Autocollimator etc.

For a faster scope I believe that the more precise tools will give you more "benefit" than they might in a slower scope...however, as I mentioned earlier, the better your collimation, the better the view.

Clear Skies!

[janoskiss]

GSO is already producing f/4s. Collimation procedure is the same, but faster mirror is less tolerant to error, ie you need to get it closer to perfect for it to be good enough. But basically if you can collimate an f/5 you can collimate an f/4.

[Satchmo]

They allready make some 8" F4 mirrors. I doubt you'll ever find large F4 mirrors from them because they are too labour intensive and China is about selling big volumes of stuff at low margins.

[casstony]

The GSO 16" is f/4.5; do you think it would not be possible for them to make an f/4 with their current production techniques and standards, or would it simply take a lot more time to make each mirror?

Thanks everyone for your replies.

[Satchmo]

Theres a 25% increase in asphericity between F4.5 and F4 and the tolerance envelope is much tighter. I would rate the increase in difficulty at perhaps 50%. I doubt the 'masses' would pay the price difference to lose 8" on a eyepiece height. The premium mirror market allready has all that specialist stuff covered anyway. And F4.5 is probably the cut-off point at which you can `get away' with not needing a coma corrector, so there is some wisdom in stopping at f4.5 in the mass production market.

[casstony]

Thanks for your explanation Mark. Looks like I need to get the Paracorr promotional thread back up and running and convince everyone of the benefits of seated viewing to give GSO a market :)