Jump to content


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


JMI's NGF-C manual focuser short report.

This topic has been archived. This means that you cannot reply to this topic.
2 replies to this topic

#1 Tim13


    Viking 1

  • *****
  • topic starter
  • Posts: 577
  • Joined: 07 Aug 2004

Posted 09 October 2005 - 12:21 AM

I had my first night out with my LX200 8 inch classic and it's new NGF-C manual crayford focuser. I never really realised how annoying the mirror shift in a SCT was until tonight. I wish that I would have made this upgrade much sooner.

I purchased the focuser through OPT, and it arrived ahead of the estimated delivery date. Not bad for free shipping. The only negative of the whole purchase situation was when I called OPT to ask a question about the focuser before buying. After answering my question, he told me that he felt that it was a decent focuser, but that it used set screws instead of compression rings. Now, I'm not concerned about set screw marks on my ep's, so it really didn't matter to me. Much to my surpise, the focuser uses compression rings instead of set screws. I realise that OPT carries hundreds of astro accessories, but I guess that I expected more familiarity with the products that they sell, based on their reputation. I'm glad that I didn't hold off on buying this based on the misinformation.

The focuser is packed nicely in a box with foam cut outs, and is very well protected for even the most finicky buyer. I couldn't help but rack the focuser in and out to get a feel for it, and I was a little concerned. It was smooth, but not what I had hoped for. Now, my frame of reference here for what a quality focuser is, happens to be a Feathertouch mounted on a refractor. After playing with the JMI for a little bit, I set out to mount it on the scope. Attaching it took all of about 5 minutes. The included hardware and allen wrenches made installation a snap. I was very pleased with the low profile of the focuser, as I use my scope strictly for visual use, and only in Alt-Az mode, so vertical clearance though the forks is important to me.

Tonight was the moment of truth. After doing a quick allignment, I put in a diagonal, along with an eyepiece. I don't know why this made a difference, but racking the focuser in and out was much, much smoother than when I was just holding it in my hand. I set the focuser at the midpoint of it's travel capability, and then focused with the scope's focuser. After that, I then used the JMI to fine focus. Since Vega was my only alignment star, I was close to the double-double. Getting a sharp focus and clean split was a snap with the JMI. I moved on to Mars for a quick peek. It's really nice to be able to focus without any image shift.

My overall impression is that for the cost, the JMI performs as advertised. The initial reservations that I had while hand holding the focuser and feeling the movement, quickly evaporated once I was able to witness it in action attached to the scope, and loaded with a diagonal and eyepiece. After the first night out with it, I am very happy. The lack of image shift is wonderful, and the feel of the focuser is nice.

As a side note, I've owned this scope since November of 2000, when it was purchased new. One of the main reasons that I decided on the JMI was because of it's low profile compared to other SCT focusers. Unbeleivably, tonight I had my first (and hopefully only...)runaway slew. The scope was at about 70 degrees elevation, and after a goto command was entered, it started moving up through the vertical. Because of the low profile of the JMI focuser, I was able to shut the scope off without the diagonal striking the bottom of the fork assembly. It's strange that this would happen for the first time, after buying a focuser with just this scenario in mind.


#2 Rat8bug


    Surveyor 1

  • *****
  • Posts: 1,749
  • Joined: 07 Jan 2005

Posted 09 October 2005 - 10:39 PM

Tim, I also have this focuser for use with my C8 OTA mounted on a Vixen GP-DX. When everyone was buying William Optic focusers, I opted for this one becase of the lower profile and much lighter weight. another benefit of using the auxillary focuser is you get sharper images. That is because a compound optic is optimized for a fixed primary to secondary mirror seperation; not a range. I bought mine directly from JMI....



#3 Eddy



  • *****
  • Posts: 1,355
  • Joined: 30 Sep 2004

Posted 10 October 2005 - 03:32 AM

Nice report Tim,
It is just how I feel about the focuser. I just upgraded the manual focuser with the motofocus system. Very nice upgrade and easy to install.
I thing though. I bought mine as well through OPT (beginning of this year) and mine came with setscrews. So, maybe JMI just recently changed their systems. I do prefer compression rings though. I have the impression that it holds the EP's better (apart from the setscrew marks).

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Recent Topics

Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics