[rochler]

Hmmm... I just went thru this a while ago! What you need to do depends on exactly what the difference is between the old focuser & the new one.

What you should do is measure the distance between the outside of the OTA and the base of the drawtube when it is fully racked in (old focuser), and then rack it out and measure the distance again (old focuser). That will tell you height of the drawtube from the OTA (i.e. the profile of the old focuser) + how far it racks out (i.e. the drawtube length of the old focuser).

Repeat with the new focuser, so you can determine what the difference is. This should tell you whether you have problems with in-travel or out-travel (i.e. whether you need to get a spacer inserted between the crayford & the OTA, or whether you need to get a drawtube extension). Does that make sense? You shouldn't need to refit the old focuser to measure this, it should be straightforward.

Since your old focuser focussed o.k. then the problem can only be either that the new focuser has a lower profile, which is causing you problems in racking in far enough to reach the focal point for your EP, or if the profile is the o.k., then it must be that the drawtube can't travel out far enough. Either way, you should be able to get either an adapter/spacer for the focuser so it sits up higher, and/or an extension tube.

What you are trying to achieve is to get a very close match to the old focuser in terms of profile and drawtube length.

Of course, that may present problems with finding longer suitable socket head cap screws to fit. You may need to source from a wholesaler like 'Coventry Fasteners' - they do up to 50mm in M3, M4 & M5 (stainless, zinc or HT).

PM me if you need any clarification....