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Question about the JMI NGF-DX3 Focuser

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#1 Tom L

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Posted 27 January 2004 - 01:29 PM

I posted this in the Equipement Forum but wanted to post it here also.

Does anyone have a JMI NGF-DX3 focuser and/or have commentary on it? I am considering one for my 8" refractor. All responses welcome!

Thanks, Tom

#2 Southpaw

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Posted 27 January 2004 - 06:13 PM

I just purchased a JMI NGF-DX1 M last week. I installed it last night. With just one night of learning how to use it I was amazed. It completely blows away the factory focuser. It is like night and day. I say go for it. It is machined very well. The presision for fine focusing is incredible. I am not familiar with your particular model but I can say if it is anything like what I got you will not use any other focuser again. ;)

#3 Tom L

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Posted 27 January 2004 - 06:26 PM

Thanks Chad. I need to see what the difference is between the DX1, 2 and 3. I'm pretty sure the DX2 has finer focusing control.

#4 Southpaw

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Posted 28 January 2004 - 12:53 AM

Well what I was told was the DX1 was the newest focuser by JMI and it has the fine focus and regular. It is also motorized. One knob is the regular fast ratio focus and the other one is a very fine adjustment focus. I do not know what the differences in gear ratio are but it is a great deal. According to the telescope shop I purchased it from it is the best one of them all. He could have been just telling me that but for $394 it better be good. For my application I had to also buy a 2" extention tube in order for all of my eyepieces and toucam to focus right. But from what I have read on JMI's web sight you can buy a focuser with the longer tube for a bit more money. I may do a review for it as soon as I learn the workings of it. I have imaged with it and so far I have been able to achieve greater focus than the factory focuser. The images are sharper and when focusing there is no shift in the image from slack. Hope this helps. I think once you buy one no matter what model you will be pleased with it. It is a great piece of machining. Good luck!

#5 Tom L

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Posted 28 January 2004 - 05:38 PM

Hey Chad, I did go do some more checking and the DX1 does have both normal and fine control, the DX2 has finer control than the DX3 and the DX3 is touted as being about 1.5x finer control over std R&P focusers. The DX1 and DX2 can handle 8# of equipement and the DX3 can handle 6#. Std focuer tube is 3" and that is what this one has I beleive. You can have JMI put a motor on all of these focusers for a price ($15-$20 installation cost as quoted on JMIs website). It is nice to know the motor upgrade is available and I will probably take advantage of it later on.

I found out that this is a focuser that is from a 18" starsplitter Dob. It was upgraded to a feathertouch!!! I'll pick it up tonight and make it fit on my Dob, since it has the flat base. Should be straight forward to make a wood block with a curve to fit my tube. I hope this will be the best bang-for-the buck upgrade for my scope in addition to putting it on a GEM. :jump:

#6 Stacy

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Posted 28 January 2004 - 10:54 PM

Std focuer tube is 3" and that is what this one has I beleive.


I think you will need an extension to get your ep's to focus. These low profile focusers generally do not have enough travel to directly replace an R&P without an extension. While your R&P may have two or three inches of travel, it starts at about 3 to 4 inches above the tube. The top of the JMI is about 1.6” above the tube (when racked in) I believe. The JMI DX3 with a 3” tube gives you a maximum height of 3.41” (plus the height of whatever base you come up with). Not enough to bring your ep’s to focus. Probably a JMI 1.5” extension would work well. :p

#7 Tom L

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Posted 29 January 2004 - 12:20 AM

Yep, I see what your talking about, Stacy. I do have my unused 1.25" Celestron barlow (which I don't like) that just happens to stand 1.5" off of the top of the focus tube and the barlow lens itself is easily removed! Since I don't have any 2" eyepieces (yet), this will work just fine! It will definitely let me know if this is enough travel. The fella I got it from had a curved base for a 12.5" Dob that I will use with some washers as shims plus some foam-like material that he had. Should look first rate!

This is a very nice focuser and I look forward to getting it on my scope and trying it out. I also got to admire his 18" Starsplitter Dob. :jump: What a beautiful scope! I hope I get to look through it one day.

#8 Tom L

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Posted 29 January 2004 - 06:55 PM

Here it is!

Posted Image

You're right Stacy, need to get the 2" extender to match the R&P focuser I have now. You'll notice the curved base. It is designed for a 12.5" Dob (14"+ diameter) and it will definitely need to be shimmed or not used. I hope the holes are going to match but I'm not ready to put it on yet.

#9 Stacy

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Posted 29 January 2004 - 08:55 PM

Gotta love those JMI's! :jump:

#10 Southpaw

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Posted 30 January 2004 - 12:58 AM

Glad you got it! I sure hope you will enjoy yours as much as I enjoy mine. Good luck!

#11 Guest_**DONOTDELETE**_*

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Posted 30 January 2004 - 10:55 PM

I got a DX-3 last summer and I am very pleased with it. I noticed the difference right away the first time I collimated the scope. With the laser on, I could rack the focuser in and out with no movement of the dot on the primary. With the factory focuser, the dot would move around a half inch.

The unit is adjustable for collimation which is a nice thing to have. The Crayford mechanism has very precise motions. You can move the focuser in very small increments with no backlash.

For a moderate priced unit I would rate it very well.

#12 Tom L

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Posted 31 January 2004 - 01:25 AM

I'm very impressed with the motion and the design. I need to get a base to fit my dob and the extension tube and I'll be a happy viewer!

#13 matt

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Posted 31 January 2004 - 02:36 AM

I have it on the Commandatore. It's very comfortable to use, with no play, backlash, slop, bumps, potholes, whatever. What is also good about it is that the design is lubricant-free, meaning you don't have to clean and regrease it, have grease either too sticky or too smooth, and grease finding its ay on your fingers and accessories.

My only peeve is that sometimes I bump the eyepiece, and as the thing is very smooth, it will push the focuser out of focus.


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