Fitting a diagonal to a Konus

[tom714uk]

Hello all,

My Konus Motormax 90 (a Mak-Cass) has two places to put eyepieces - a built-in 90-degree socket and a 45-degree erecting prism that screws onto the back, where a diagonal would normally go on a Mak. A flip mirror alternates between the two.

I would like to replace the 45-degree prism with a standard 1.25" diagonal (which I have obtained courtesy of Astroboot) to enable easier and better viewing. I'll need some sort of adapter, however. I've read that the fitting on the back of the Konus is non-standard. Could anybody take a look at the attached photo and tell me if this is so, or if not, what type of adapter I'll need? If it's non-standard, I guess I'll have to see what I can rig up for myself.

As you'll see it has both an interior and exterior thread. The diameters of these are roughly 30 and 34mm respectively.

Many thanks in advance,

Tom

[tom714uk]

With some more determined digging on the web I've discovered it seems to be the same as that found on the back of a Meade ETX or a Celestron C90. So it should be quite simple to find an adapter!

Tom

[JamesM]

Tom, it is very dangerous talking to yourself, I should know as I seem to do it all the time in my household.

I hope your solution works out!

James

[tom714uk]

Hehe, I think I'll be going for the DIY here as the cheapest you can get the adapters seems to be about £25 and I'm trying to keep the costs pretty minimal. I'll post what I do in the end in case anybody in future wants to do the same thing.

Tom

[tom714uk]

Well, I have indeed found a minimal-cost solution. The only thing that came with the scope to attach onto that rear port was a 45-degree erecting prism. That had a retaining ring to attach to the scope and a 1.25" eyepiece holder on the other side, which I have unscrewed from the prism and superglued to one another (being pretty careful to keep them concentric!).

I was worried that the light path might end up too long to bring an eyepiece to focus once I had the diagonal in. But I gave this a very brief go yesterday evening and though I didn't have time to set up the tripod, I was able to focus on the moon hand-holding the scope! That was with a 25mm, hopefully it will still work with a 10mm (didn't fancy hand-holding with that...).

The other issue is of course that the diagonal, the eyepiece and half of my "adapter" are held up purely by glue. It seemed solid enough but obviously I didn't want to tug on it to see how solid. But the diagonal and eyepiece aren't heavy (being mostly plastic) and I won't be distraught if they fall on the grass (as they were cheap). And if the adapter does fall to pieces in the middle of an observing session, I can still use the internal mirror anyway!

Looking forward to some more comfortable and ever so slightly clearer viewing! I hope this information might be of use to another cheapskate with a Konus sometime.

Tom