My 4" refractor is an Irving?

[John]

... It has the letters "Ora " and the marking "//\\" on it too....

I think the second markings are the ones you use to align the two lens elements correctly with respect to one another. A partially rotated lens element can cause spherical aberration in a refractor, conversely though, deliberately mis-aliggning them can, through experimentation improve the SA.

Refractor collimation can be checked with a cheshire collimator as set out in the link you have found on the topic. The focuser needs to be square on with the optical axis of the scope before checking the collimation and this can be tested with a laser collimator in the drawtube - the beam should emerge right in the centre of the objective lens. If not you need to find a way to adjust the tilt of the focuser to achieve this.

[philj]

Just picked up this thread when doing research into my latest acquisition, a 4" F11 refractor with Wildey Lens and Irving focuser purported to be an early Fullerscopes. Having stripped the lens and cleaned it, it is indeed a Wildey objective from 1987 as per the signature and date that Henry put on most of his optics, that Im pleased with. However in 87 Fullerscopes were not putting Irving parts on their scopes anymore as the BC buy out meant that they were producing their own focusers and mounts. The scope came with a letter from A Woods of Welwyn Garden city re some eyepieces and accessories bought after the scope was purchased and I was told by the seller that the original buyer bought the scope from Mr Woods. So it all fits in nicely now, A Woods assembled the scope from Wildey and Irving parts. Its really nice to put names to people who have built your kit, you don't get that with Chinese and tiawanese scopes So thanks folks for all the useful info and here are a couple of pics of the scope

[John]

Ah, you went for that one then Phil

Nicely proportioned scope. I can remember those being offered new back in the 1980's in a small classified ad in some of the early editions of "Astronomy Now" magazine.

Is it F/12 ?

[philj]

No F11 John, its a heck of a lot lighter and easier to shift than my f15 almost grab and go actually, just doing the sums its F11.75 so more 12 than 11