Motorised Focusers

mick pinner · #1 04-03-2009, 07:01 PM

l'm looking for recommendations on the best motorised focuser for a reflector, price is irrelevant. thanks.

gbeal · #2 04-03-2009, 07:36 PM

This will open that can of worms Mick.
In my case, Feather Touch. OK, I have a problem, I have three, but two of them have the motor permenantly attached, as they are predominately imaging scopes. The other is the 16" truss newt/dob.
The focusers are well known, and the motor system just as good, I am constantly amazed at how good.
Add auto-focus with FocusMax and it is almost too easy, well it seems like it.
Gary

[1ponders] (Paul) · #3 04-03-2009, 07:44 PM

I have a JMI attached to my SCT and I'm not too impressed with the 2" compression ring. It doesn't hold my ST 7 orthogonal to the scope, there is always a little bit of sag which shows up as out of focus stars in my dec axis. I can't say if it would be the same for a reflector but it is something to be aware of.

marki · #4 04-03-2009, 08:39 PM

I have a moonlite with stepper motor on my LX. I use a cercis controller. Auto focus routines in Maxim Dl are a breeze and the controller allows 2 focusers (Main + guide scope) to be connected simultaneously from one box as well as an optional temp sensor which adjusts the focus automatically during exposures. Only problem being that the setup is too slow for visual work (I am an impatient sod). The unit holds everything where it should be and is rated to lift 3.6kg. They are also available for newts.

Ciao Mark

Quark (Trevor) · #5 05-03-2009, 12:01 AM

Hi Mick,
I have a JMI Moto Focus on my 16" Newt. Have had no problems with it and it really comes into its own with my Saturn imaging. The only time I use it as a moto focus is when I am imaging.

I rolled some quarter inch thick aluminium plate to the same curvature as my tube, did this for the OD and ID. The JMI Moto focus bolts through both aluminium plates sandwiching the tube. The plates are approx 6 inches square, they spread the load on the focuser over a larger area and I think this alleviates flexure along the axis of the focuser.

Regards
Trevor

Dennis · #6 05-03-2009, 08:48 AM

Hi Mick

I have a couple of older JMI NGF’s and a Moonlite motorized focuser.

The JMI’s a very good for the price, but I have to be very careful with seating heavy accessories such as my ST7, as the weight is too much and can lead to sagging, much as Paul described.

The Moonlite was more expensive and is a step up in rigidity from the JMI’s. It does not sag with the ST7 and CFW8 filter wheel.

If I were only using my scopes visually, the JMI’s would be fine as they would not be over stressed.

Cheers

Dennis

bird (Anthony Wesley) · #7 05-03-2009, 06:09 PM

JMI for me, I'm very happy with my existing 2" model, have had it since 2004 and given it a real caning.

Just bought the new 3" model, waiting for it to arrive :-)

The JMI models allow you to switch easily to manual focussing by loosening a spring-loaded knob. I've seen other manufacturers where you can't switch between manual and motorised without dismantling it.

cheers, Bird

rogerg (Roger) · #8 06-03-2009, 10:20 AM

On my LX200 I use a JMI NGF-C which is permanently equipped with a RoboFocus unit. Unbeatable. Using FocusMax focusing is a 1 button exercise, taking usually about 45 - 70 seconds on a Mag 7 star. It's easily scripted in to automation each night.

The RoboFocus has been having a few heat issues lately, not sure what's going on. It's been working solidly since about 2003.

On my Megrez I have an Orion Acufocus. It's sufficiently "fine resolution" to accurately focus easily, but doesn't have the PC interface of the RoboFocus so lacks the auto-focus capability. For the money it's great, but if money is irrelevant I have no doubt I would get the RoboFocus instead.

The RoboFocus has absolutely no backlash or slop. It's accurate to an extremely high level, really I can't fault it at all except for the recent issues with heat which I expect are due to such constant usage for 5+ years.

Back when I bought my RoboFocus I chose it over the JMI equivalent because it was reported to be of higher procision due to it's usage of stepper motors and temperature compensation. Certainly it is useful being able to exactly position the focuser at position 186 if you know that's exactly where it should be (range for my JMI is about 5000 positions from fully in to fully out).

Roger.

[1ponders] (Paul) · #9 06-03-2009, 05:58 PM

There must be something wrong with the compression ring on my NGF-C then 'cos the sbig sags like it's got a rubber crutch.

rogerg (Roger) · #10 06-03-2009, 06:15 PM

Quote:

Originally Posted by [1ponders]

There must be something wrong with the compression ring on my NGF-C then 'cos the sbig sags like it's got a rubber crutch.

Hmmm..

Do you have a motor on your JMI? I would think if you have a motor on it, the only way it would slip were if the pressure against the tube was far too light such that the tube can slide without the focusing shaft rotating.

Dennis · #11 06-03-2009, 07:45 PM

Quote:

Originally Posted by [1ponders]

There must be something wrong with the compression ring on my NGF-C then 'cos the sbig sags like it's got a rubber crutch.

Hi Paul

I have not enjoyed much success with compression rings and heavy cameras.

My JMI NGF-CM had a single locking screw and a brass compression ring that appeared to work fine on eyepieces. As soon as I began to use the ST7, I noticed a sag although it appeared to be a “fixed” sag rather than vary over a session.

So, I removed the compression ring and drilled & tapped 2 further holes at 120 degrees for an extra two locking screws. My main concern with this modification was the potential for tilting the inserted adapter in the draw tube if I did not tighten each screw the same. However, this has not appeared to be a problem, so far.

My problem with the Moonlite/Tak eyepiece adapter combo was that the Tak 2” adapter was very shallow and by sheer coincidence, the compression ring of the Moonlite just nipped the grub screw cut-out “lip” of the Tak adapter, making it rock in situ, as its shallow insert depth did not provide sufficient longitudinal stability that a longer length adapter would have provided.

Cheers

Dennis

[1ponders] (Paul) · #12 07-03-2009, 09:53 AM

Hi Roger.

Quote:

Do you have a motor on your JMI? I would think if you have a motor on it, the only way it would slip were if the pressure against the tube was far too light such that the tube can slide without the focusing shaft rotating.

It's not a slipping, I have an optec FR attached to the camera and I can lift the camera up and down with noticeable movement in the focuser tube of the JMI.

Thanks for the info Dennis. I'll pop my JMI in the mail this week. When can you have it back to me with the new grub screws.

Just so I don't take over Mick thread, I'll start a new thread on this issue later on after I take a few photos of the problem. Sorry for the off topic Mick.

mick pinner · #13 07-03-2009, 10:36 AM

you can continue here Paul, it all adds to the info l'm looking for.

[1ponders] (Paul) · #14 07-03-2009, 10:41 AM

Cheers Mick.

Dennis · #15 07-03-2009, 11:52 AM

Quote:

Originally Posted by [1ponders]

Thanks for the info Dennis. I'll pop my JMI in the mail this week. When can you have it back to me with the new grub screws.

Hi Paul

Drilling and tapping the additional 2 holes proved a bit of a challenge on two fronts:

There isn’t much tube length to work with and the internal groove for the brass compression ring makes the focuser tube walls thinner in that region, so I had to be very careful where I drilled the additional holes.

Cheers

Dennis