Crayford on SCT - How much of a pain is it?

NightCal · #1 01-01-2007, 04:16 AM

I'm currently exploring my options for providing fine focussing on a tight budget for my 8" LX200 Classic. At the moment I'm leaning towards buying a JMI Motofocus to attach to the main focussing knob in conjunction with a Peterson EZ focus conversion kit and FocusMax autofocussing software when imaging. Whilst this set up should reduce image shift, it will not be eliminated and may stay problematic.

The obvious answer is a Crayford focusser mounted on the rear cell of the LX200, but this will cause problems as I will not have enough clearance to use the scope near the pole (about 15-20 degrees radius around Polaris). My perception is that this would be a major pain in the neck; but is this perception correct?

So, calling all you who have a Crayford mounted on an 8" LX200 Classic (or similar); what do you think?

[1ponders] (Paul) · #2 01-01-2007, 09:57 AM

Hi Nightcal, I have the JMI motorised crayford on a Meade 8" OTA and I wouldn't be without it. (I can even swap it over to my Orion ED80

). I don't like fine focusing with the main focusing knob. Too much movement.

My OTA is on an equatorial mount though. That was the reason I sold my original 8" LX200 GPS, not enough clearance through the forks for polar imaging with a 300D.

Striker (Tony) · #3 01-01-2007, 10:06 AM

I totaly agree putting a decent size Crayford could severely affect imaging near the poles but would a meade 2" electric focuser do this considering there smaller in profile....???

Worth a look.

Harb · #4 01-01-2007, 01:35 PM

I use a 10:1 Williams Optic Crayford Focuser on my CPC 11" Celestron.
It does limit you somewhat, but a wedge soon fixes the problem......
Other than that, it is the best thing.
I am going to upgrade it to a JMI motorised focuser, soon as the shops are open again after the Christmas break.

cheers

NightCal · #5 01-01-2007, 09:52 PM

Quote:

Originally Posted by Striker

I totaly agree putting a decent size Crayford could severely affect imaging near the poles but would a meade 2" electric focuser do this considering there smaller in profile....???

Worth a look.

The Meade 1209 microfocusser would fit, just! By my calculation it would only fit if I rack it all the way in. I'm really worried that one night I would forget to rack it in and cause some serious damage to my scope, eyepiece, camera etc. I really cannot afford that as I am working on a very tight budget.

The idea of having a single motorised Crayford that I can move between my LX200 and Orion 80ED has some appeal and is worthy of further investigation.

My concerns about this would be:
a) a very high initial outlay or a relatively low initial outlay on the Crayford on it's own, then having to wait for a year or more before I could afford to motorise it and get the relevant adaptors made.
b) a lot of hassle swapping over focussers.
c) it still doesn't address the issue of fork clearance!

allan gould · #6 01-01-2007, 10:10 PM

Apparently WO are going to release a motorised focusser for their SCT focusser (rumour). I have one on my 8"SCT and wouldnt do without it.

[1ponders] (Paul) · #7 01-01-2007, 10:17 PM

Swapping the focuser over is very easy. Takes about a minute.

NightCal · #8 02-01-2007, 03:51 AM

Quote:

Originally Posted by [1ponders]

Swapping the focuser over is very easy. Takes about a minute.

Which focusser are you using? A description and/or some photos of the swap over process would be really handy to give me an idea of what is involved.

[1ponders] (Paul) · #9 02-01-2007, 09:35 AM

I'm using the NGF focuser (the older -CM type I think it is)

The first photo is my standard setup for the Orion ED80 or my Celestron 102. This should work with any refractor with a 2" focuser. The middle adapter will come with the focuser and has a female C thread to screw onto the back of your sct. The right hand adapter is called an SC Adapter and you can order it with the focuser (it comes as a standard accessory with the Meade microfocuser).

Some nights I have to make other arrangements if I'm alreading using the SC adapter. The second photo is of an Orion 2" Prime Focus Adapter ($40 from bintel I think). This unscrews to leave a 2" barrel with a C thread on one end that can be screwed into the focuser adapter instead of the SC adapter or used without the focuser adapter as in the third image.

To swap over from SCT to refractor involves loosening the three grub screws in the focuser that hold the middle adapter in, remove the focuser, screw the SC adapter into the middle focuser adapter, put them back into the focuser, tighten the grub screw again and slide the whole lot into the refractor 2" focuser and tighten the refractor retaining screws. Done!