techie question

[lhuchison]

Are there any restrictions to the type of focuser used on a newtonian? i,m asking about the draw tube length really.

i have a low profile crayford type fitted recently on my SW200P with a draw tube of 24mm.

the newt is a 8in, is there enough back focus ( there is an adjuster ) for it to function

Ive tried focusing on an object about 3 miles away but am unable to bring to focus. I cant try stars yet as we,ve had cloud every night since i fitted it!

I can return it but was wondering on the technical side of things before changing it.

It does state that it for newtonians of 8" to bigger.

[Uplooker]

Depending on which brand of focuser and whether or not it accepts 2" & 1.25" EPs you could fit a Baader fine tuning ring to the bottom of the 1.25" adaptor. This would allow you to move the 1.25" adaptor further out. I had to do the same when I fitted a Revelation Dual Speed Crayford focuser ro my SW 150P newt

If you can or do go down this route i would recommend getting the 28mm ring - see link

http://www.firstlightoptics.com/baader-planetarium/baader-hyperion-finetuning-ring.html

Ian

[steppenwolf]

Is the problem of focus one of not having enough inwards travel? This is a common issue with Newtonians and is normally resolved by use of a low profile focuser. From your description, it sounds as though you have bought the Sky-Watcher Low Profile 2 speed Caryford?

If the problem is one of not enough outwards travel then a simple extension tube can be used to resolve this.

[rfdesigner]

If you need to get the image plane a bit further outside the scope the best point to attack can be the main mirror cell.

The cell will usually be attached to the tube by only a small number of bolts/screws and by drilling some new holes an inch or so further up the tube you will push the image plane outside the tube by the same amount.

Of course you will suffer from a slightly more vignetted field as the secondary mirror really needs to be enlarged by a small amount, but it can be a fairly quick and easy thing to do and is reversable without cutting huge holes in the tube which is what needs to happen if you move the focusser. (been there got the T-shirt)

Derek

[jason.p]

Having a similar problem with a new 8mmEP for my 6" Newt.