Focusing SCT options - Steel track v JMI motorfocuser - Vote :-)

[Telescope40]

Hi All.  Looking at options to fine focus my C9.25.  Completely split between the following. 

1-  Baader Steeltrack Focuser

2- JMI Motorfocus unit.

I like the look of the Steeltrack and have tried out at a couple of Astro meets.  Very nice. Lovely engineering.

However like the fact the JMI will mean not touching the scope at all and results in no Bad Beach Boy impressions  --  Bad Vibrations  !!! 

Which one would you go for. Quick vote and any comments more than welcome

John

[Ikonnikov]

I've just ordered the JMI Motofocus to go with the Feathertouch SCT micro focuser that was already installed on my C8 when I bought the scope. This is primarily to help get good focus for Hyperstar imaging where an additional (crayford) focuser on the visual back is not an option.

I believe these are more desirable for planetary work (at long focal lengths and therefore small fields of view) as they give minimal image shift in contrast to moving the of the primary mirror (which the JMI will still do assuming you're referring to the SCT versions).

Paul

[RobertI]

I'd be interested in people's opinions as I have been struggling with the same dilemma myself. The problem I have is mirror shift when focussing at high 'magnification' to image the planets - the image diappears off the sensor everytime I turn the focussing knob - its not vibration from my hand, it's movement of the mirror when focussing.

I concluded that a Rack and Pinion focusser was the way to go as using the normal focussing knob to move the mirror, even motorised, will cause mirror shift.

Even if you do not do much planetary imaging, I would have thought the Baader Steeltrack or similar R&P focusser would be a good future proof solution. Having said that i have not had the courage of my own convictions yet!

Rob

[Telescope40]

Hi all again. My observing is visual but happy to read all wisdom either visual or imaging.

Regards John

[CodnorPaul]

I believe steel track and similar focusers on back of SCT limit fov don't they?

[JamesF]

I believe steel track and similar focusers on back of SCT limit fov don't they?

Given that the Steel Track will take a 2" eyepiece I'm really not sure how it would restrict the field of view beyond what was already compromised by the baffle tube.  It may be that to achieve focus with a diagonal and an external focuser you extend the effective focal length beyond that quoted however, so in that sense it might reduce the FOV.

James

[JamesF]

What you go for may well be determined by how you use the scope.  If you focus using the primary mirror alone then you will get problems with mirror shift whether you focus manually or with a motor.  That's unavoidable though may not be an issue for visual use, but it can be a royal pain in the Derry Air for imaging.

The Steel Track is machined specifically to take an HTD drive belt, so should motorise very neatly whether you buy Baader's system or make your own and it does mean that the fine focusing doesn't involve mirror shift.

For visual only I think I could live with the mirror shift and not bother with a secondary focuser.  For imaging I'd take the secondary focuser every time and motorise it myself if I had to.  (Oh, I have

James

[Stu_2011]

Hi

I have one of the standard Skywatcher 2 speed Crayfords on my CPC 925 and it's great. It has a JMI motorised focuser driving the Crayford and it works really well.

If I was buying an external focuser now I would look at the Steeltrack or possibly the Revelation rack and pinion version.

It's a good mod for SCT's and planetary imaging.

Thanks

Sent from my iPad using Tapatalk

[perfrej]

I used to have a late model EdgeHD 925 and found it to be utterly useless because of the mirror shift. I only image and I need to have the mirror unlocked so that automation can do its thing and focus at will. Simply doesn't work. The only solution is an added focuser at the back and that was not a very good option with the EdheHD as it has a corrector lens there and distance to sensor would change.

For visual use I would definitely get an extra focuser and lock the mirror, or weld it in place. Optically, these are great scopes but the mirror assembly leaves a lot to be desired.

/per

[Steve 1962]

I've owned a 925 with a Steeltrack and was very pleased with both. The Steeltrack is a thing of beauty except the nylon rotator grub screws which are easily replaced. I've used the Steeltrack both with a home made bracket and a Skywatcher focus motor and latterly with Lakeside focus motor - both worked well.

[Peter Drew]

I would avoid any system that relies on primary mirror movement for fine focusing of a catadioptric telescope.

[Mr Spock]

I use the feathertouch on my C9.25 and it is a fantastic piece of kit. The C9.25 I have doesn't have any mirror shift so maybe that makes a difference, I don't know, but I couldn't be happier with mine.

[ollypenrice]

I believe steel track and similar focusers on back of SCT limit fov don't they?

No, I don't think so. I used a Steeltrack on a 14 inch ODK for DS imaging. It's fairly good but not premium, but it's good value. If you don't want to move the primary then a conventional focuser on the back is the only way. 

Olly