Revelation SCT Crayford Focuser Dual Speed

[cgarry]

I ordered this to improve the focusing on my Meade LX10 8" SCT. When it arrived the first thing I noticed was it was big and heavy, weighing just over 1Kg. The focus controls operate very smoothly giving the unit a real feel of quality.

The focuser screws directly onto the back of the SCT and the star diagonal plugs into the other end. The unit can accept 2" or 1.25" diagonals. Once installed the focuser allows 2.5cm of fine adjustment with the original SCT focuser still doing most of the work.

If the SCT is mounted on a fork mount then the focuser will prevent the scope pointing to or even close to the zenith. However, there is no problem when the scope is mounted on a GEM.

For me the main point of the focuser was for webcam imaging. On my scope the mirror shift while focusing would often throw the object of interest completely out of frame. This focuser completely fixes this problem and allows much finer focusing control in this situation too. It also allows finer focus control with high magnification visual observing, a nice bonus. For medium and low magnification observing this focuser is not required, but the original focuser works just fine with the Crayford in place.

So all in all, I am very pleased with it. It solved the mirror shift problem I had and allows much finer control of focusing at high magnifications. The downside is my setup is now over 1Kg heavier and the scope can not really be used on a fork mount, neither an issue for me.

Chris

[Nexus 6]

Very nice Chris, I looked at these when deciding what to put on my 925. I can hit the Zenith though, with the Moonlite on board, although I am not doing any astro imaging.

Alan

[brantuk]

Very useful review Chris thanks. I have the WO DS Crayford and, as you rightly say, they do add a fair bit of weight and length. Especially with a camera as well.

I'd be interested to know what's the maximum alt you can reach with this in place (didn't have time to try mine yet).

[cgarry]

I'd be interested to know what's the maximum alt you can reach with this in place (didn't have time to try mine yet).

I quickly put it on my 6SE to see how much it fouls the mount. A picture paints a thousand words, so:

While doing this I noticed another couple of issues that had not shown up using the focuser with my LX10 8" SCT.

Firstly the crayford focuser has to be turned slightly before it could be fully screwed in because the Crayford has a thumb screw at the bottom that fouls the original focus knob. But since the Crayford can be turned slightly to avoid this, then this is not really a problem.

Secondly, when in place the rubber of the original focus knob rubs against the top of the Crayford focuser making focusing with the original focuser difficult.

So I would not recommend this focuser for use with the 6SE. Something a bit smaller is needed.

Cheers,

Chris

[Sadr]

Yes, looks like a nice piece of kit, I've also been wondering about the clearance of the barrel and the focuser knob on my STF Mirage 7D. What is the diameter of the ring that screws on to the scope?

I have about 88mm clearance - would this be OK?

Thanks guys

[cgarry]

The ring that screws onto the scope has a diameter of 90mm. So 88mm would not be enough.

Chris

[Sadr]

Thanks for that, could have made an expensive mistake there.

The STF has no mirror slip, but it would be nice to have the fine focus.

[Luke]

Thanks, Chris, your review covered all the things I was wondering about plus some useful things to know that I had no idea about. Very helpful, thanks.

[paraman]

Very useful review Chris thanks. I have the WO DS Crayford and, as you rightly say, they do add a fair bit of weight and length. Especially with a camera as well.

I'd be interested to know what's the maximum alt you can reach with this in place (didn't have time to try mine yet).

I have one of these fitted to my CPC 800 and have found that if I use the primary mirror focus first with the revalation racked in, that, the amount of fine focus required by the revalation focuser is very small and even with a Williams diagonal and spc web cam if needed I could look vertically without hitting the body.

[ollypenrice]

I like mine as well, Chris. The only issue for imaging is respecting the chip distance with the reducer. On the Moonlite the reducer moves in the drawtube keeping the distance constant. Clever but not everyone needs it.

Useful review and thread.

Olly

[samtheeagle]

Well I'll chime in my support for this focuser too. I got one included with the 6" Mak I recently acquired. It needed a little bit of TLC, so I stripped it down and cleaned out a bit of black gunk, and it was transformed It takes bit of fiddling with the various hex screws to get the tension the way you like it, but it's running like a dream for me now.

I tend to rack it out to 50% of it's travel and then use the standard focus knob to get close to the mark, and from then on use the crayford. Works a treat!