Suitable low power eyepieces for a F4 dobs

Sounds like the eyepieces needs to be further from the scope, if you cant move the focuser up the scope then what you need is something like
www.telescope.com/jump.jsp?itemType=PRODUCT&itemID=51

Do a quick search in google, I'm sure you'll find exactly what you're looking for.

William,

I'm with what the guys said about the focus problem.

I too have an f/4 newtonian. One essential piece of kit for a scope that fast is a coma corrector. I use a Baader MPCC and it is very good. This will give you sharp stars out to the edge of a low power eyepiece. Other wise all you will see out there is elongated blobs.

That will be a lovely scope once you got it all sorted.

appreciate all the sugestions, lads. I'll look into it further (pardon the pun, ha, ha) and back on the result

William --

If funds allow, I'd check out some sort of coma corrector first. f/4 is pretty fast, and wide-field eyepieces are going to suffer for it. Tele Vue's Paracorr is a far better choice visually, but I believe it's also more dear. As Dave suggested, there's also Baader's MPCC.

The coma corrector (because it goes in front of the eyepiece and because it slightly slows the focal ratio) *may* solve the focus travel issue as well. But if it doesn't (or funds don't allow), I think the extension tubes are going to move the eyepiece *too far* out. Another option would be to add a barrel extender and a parfocalizaing ring to the two eyepieces in question so that they can be extended out of the focuser by an arbitrary amount.

Here's a link for a barrel extender:
www.scopestuff.com/ss_epe2.htm

and one for a parfocalizing ring:
www.scopestuff.com/ss_par1.htm

There are other vendors that sell both items; I list ScopeStuff only as an example.

-- Jeff.

PS: one note: the eyepiece must have filter threads on the barrel end to use the barrel extender. But most do these days....

PSS: oh, and if that's not enough, there's one more trick: check to see where your collimation screws are in their travel on the main mirror. If all three of them have the needed 5 to 10mm of travel left, you may be able to simply move the primary forward a bit and re-collimate.

PSSS: it's probably at this point that I should note that I don't actually own any Dobs. But I seem to be full of advice anyway.

Hmm... forgot to state the "other" obvious...

If you don't fancy cutting a new focuser hole (if you have a metal tube, say) you can always move the primary mirror cell up or down the tube instead. This involves drilling just three screw holes. The balance of the scope shouldn't be affected significantly if the shift is just a few milimetres.

Think laterally!

Phil.

Also be aware that an MPCC will move your focus plain another 10mm or so outward so you'd definitely need an extender to reach focus. I'd definitely get the MPCC though - It even made quite a difference on my old F5 so I guess it would be essential at f4. The standard MPCC doesn't come with the adaptor to use eyepieces (just threads for cameras) so if you order one you'd need to tell them that you want it for visual use and need the eyepiece adaptor.

If you have a barlow you could unscrew the lens assembly and just use the tube as an extender.

Trev