Newtonian Focusers

[Grant Privett]

I’ve recently got the network for my Orion Optics VX12 / NEQ6 combination to the point where I was confident enough in it to start using an OAG (off axis guider) and, in a change from my previous approach – a 114mm reflector strapped to the main tube – I have decided to use a Starlight Xpress filter wheel that I bought.

Now, until I took the Midi wheel out of the box and attached the CCD+corrector lens I had not appreciated how much the whole lot would weigh – I wouldn’t want to drop it on my toe. I got some half decent pics but, looking at them, I am a little suspicious that the weight is making the focuser – an ACU-2s – tube droop slightly. I have started to wonder if this is a standard problem and what others do to counter it. I’m thinking the knurled nut used to lock the focus might help a little if slightly tightened, but that seems a bodge. There are 4 other bolts around it, but I am not sure they should be adjusted.

Has anyone else had this sort of problem? What worked for you? I’m kind of expecting the words “Buy another focuser” to rush toward this conversation, with perhaps a side order of “Get a lighter filter wheel”. 🙂

[Mr Ian David Sharp]

Hi Grant,

I own 3 of those SX Midi wheels and also a larger one for 2″ filters and I have only had the droop issue when I was connecting one to a small WO71 APO with a fairly heavy ATIK CCD. I think it was the CCD that did most of the drooping in that case!

The other scopes I use have much more robust focusers such as Moonlite on my C9.25, and the Tak focuser on my Tak 85. These focusers are designed to carry much heavier loads.

I don’t think that the SX Midi FW is a particularly heavy example of a filter wheel, so I don’t think I can say anything that will help with your current setup. I think I would have to fall in the ‘buy another focuser’ camp!

Cheers
Ian.

• This reply was modified 1 year, 6 months ago by Mr Ian David Sharp.
• This reply was modified 1 year, 6 months ago by Mr Ian David Sharp.

[Grant Privett]

Thanks for the reply.

Yes, I did look at the SX Mini wheel but it doesn’t accept 2″ filters and weighs pretty much the same as the Midi anyway – 800gms or thereabouts.

The Trius 694 clocks in at 450gm. I doubt if the Lodestar guider makes much difference.

So the whole thing is a decent weight – which seems a lot at the end of a thin Newtonian tube. 🙂

I will try tightening the central screw by tiny amounts every evening and see how it gets on.

BTW the Midi wheel can take 2″ filters – it has two wheel options.

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