[ausastronomer (John Bambury)]

Hi Graeme,

The news I bring isn't what you want to hear.

Essentially the FOV of an eyepiece is determined by the field stop. In this situation with a narrow focuser drawtube and the bottom of the drawtube further away from the focal plane than the eyepiece field stop, the bottom end of the focuser drawtube becomes the field stop. If you were to use 1.25" eyepieces in this scope they would have to be short focal length ones. With plossls or othoscopics you could possibly get away with <15mm focal length eyepieces. If you wanted to use wide field eyepieces you would be restricted to even shorter focal lengths of < 10mm. It's very easy to use .965" eyepieces in a 1.25" or 2" focuser, it doesnt go very well the other way around.

I was going to suggest before you buy new eyepieces, you replace the focuser on your scope with a GSO 2 speed crayford for about $100. This would have given you "free reign" with any eyepiece purchase.

Unfortunately, I remembered this scope was one of the very few scopes to be sold commercially with a "sled" or "slide" focuser. A sled focuser, whilst an excellent concept that has some advantages, makes it exceptionally difficult to change the focuser for someone who is not an experienced ATMer. A sled focuser has the secondary mirror attached to the focuser sled by a single spider vane and achieves focus by sliding the eyepiece and secondary mirror (as a single unit) closer to or away from the primary mirror. The only way to change the focuser on this scope is to replace the secondary mirror with a new one with fixed vanes. You would then have a gastly hole in the side of your tube which would need to be repaired.

This is all a bit of a pity really because optically these scopes are very good and are built like a tank. I think your best options are to use the eyepieces you have for a few months and if you are serious about the hobby again sell the scope and buy one with a 2" focuser. Another option is to try and find an ATMer who could change the focuser and secondary mirror for you but this will cost you between $200 and $300 in itself. It may not be worth spending that much money on, I am guessing an early 1980's scope, when you can buy a good GSO or Synta 8" dob with 2 inch focuser for around $400 brand new.

Cheers,
John B