Oversized 2" dovetail fitting?

[badhex]

Hi all

Many moons ago I got what was listed as an Orion Optics 2" focuser taken from a 10" dob, for a telescope I'm still in the process of building(!). It also came with both 2" and 1.25" EP adaptors. At the time, I thought it odd that there was a 2" adaptor with it, but I was a somewhat greener in my experience so I didn't think too much of it.

Having just acquired a Bresser AR-152 'frac with 2" fitting, I dug out the 1.25" adaptor, only to find that both it and the 2" adaptor have a dovetail flange type fitting at the bottom, and only fit inside the (obviously bigger than 2") focuser that they came with, and don't fit in a normal 2" EP fitting.

So now I'm even more confused than I was all that time ago!

Can anyone shed any light onto what the point of the annoyingly oversized adaptors etc. is?

PS. I have just found what I think it a very similar focuser here: http://www.astroshop.eu/focusers/skywatcher-1-25-2-rack-pinion-focuser/p,16122

plus a 2" adaptor which appears identical, labelled as follows: http://www.astroboot.co.uk/images/astroboot/dynamic/800w-532h/20130308174953_59_Image59.JPG

"Sky Watcher 2" eyepiece adapter to fit most Sky Watcher focusers. The barrel is 2" female push-fit at one end and 56.8mm OD dovetail flange at the other. Please note: this is note a 2" extension tube - it is an adapter to convert and reduce the over-sized aperture of the standard SW focuser."

[ChrisLX200]

Such a flange is used to allow for unlocking and rotation, and tightening screws which bear against the flange will both stop it rotating and snug it up against the matching female housing. It is actually a good quality feature and better than a simple parallel tube clamping mechanism.

ChrisH

[John]

I think the issue here is that Orion Optics were at that time using Skywatcher focusers so the 2" and 1.25" adapters you have are Skywatcher ones and these are rather different from the ones that virtually all other focusers use, probably including the Bresser which will be more like a Meade I reckon.

I may be wrong but I think the Bresser focuser will take 2" eyepieces without the need of an adapter. To fit 1.25" eyepieces an adapter like this would be your best bet:

http://www.firstlightoptics.com/adaptors/2-to-125-eyepiece-adaptor.html

Trying to use the Skywatcher 1.25" adapter in the Bresser focuser may well not work too well because of it's Skywatcher-specific flange fitting design.

[badhex]

Hmm thanks Chris. There's a different assembly on my Mak102 which does a similar thing, allowing for rotation without unscrewing the two screws so your EP/diagonal setup does not fall out completely. Initially I was thinking that you could still achieve a dovetail fitting which fit inside standard 2" EP holders, but this would only be suitable for a 1.25" adaptor without encroaching on the internal diameter of the EP barrel and reducing FOV.

[badhex]

Thanks John. Yes, I came to this conclusion all too quickly! The flange is too wide for any normal 2" fitting, mostly an issue because of the fact that now I have nearly everything I need to get the Bresser up and running - bar the EP adaptor - and was hoping to get first light this weekend