JMI NGF-S with extension tube:-
Borg 45ED II combined with 7508, Intes Dovetail, and JMI NGF-S:-
After selling my Borg 45ED with custom made tube, I immediately missed it and thus I ordered a new Borg 45ED II again. The new version feature 25mm more focal length than the old version, and everything otherwise remain the same. That means 25mm more back focus, that means slightly slower focal ratio, that probably means slightly better optical quality since a slower lens is usually easier to be made good, and slightly narrower field of view.
This time, I didn't go for a custom made tube, since the last one has to be used with a large and quite heavy clamshell. This clamshell is very robust and nicely made, and it's quite expensive too, the downside is it added the weight and bulk. The clamshell is not big, but it's big when used with a 45mm scope.
So, I go for a standard tube with is Borg part #6045, it comes with a drawtube plus a 1/4" socket for mounting purpose. For such a light weight scope, such a socket is more than enough. I also ordered a 7508 which is a 2" visual back. My NGF-S is installed via a 2"->SCT adapter, the SCT side is for NGF-S and the 2" side is for the 2" visual back. 7508 features two set screws which provide very secure connection to the NGF-S.
Apart from the 1/4" socket from the Borg 45ED II, the JMI NGF-S also has one. And I found it even nicer to mount the whole thing via that socket since most of the weight now come on the NGF-S.
Since it's a non-standard combination, I did some calculations before I order the parts. On testing the focus travel, I found it matches particularly well. Basically, the whole thing worksfor such configurations:-
1. 2" refractor diagonal with 2" 40mm Pentax SMC XL
2. 1.25" refractor diagonal with all my eyepieces, from a 7mm Ortho, a 13mm Nagler Type 6, a 20mm Japanese Widescan Type III, and with any sorts of combinations with barlows like Tele Vue 2x, 3x and 5x Powermate, too
3. DMK camera with and without diagonal (extension tube needed)
4. APM 1.25" Herschel Wedge with any eyepieces listed above, the Herschel Wedge requires a lot back focus which makes it a challenge even with my Tele Vue Ranger
Focusing is a snap with this setup. The first step is to roughly focus with the Borg drawtube and then fine tune with the NGF-S.
This setup is used for wide field imaging, and solar observation, the Borg 45ED II has aperture filter thread of 52mm which matches my Solarmax 40/BF10 very well. Given its short focal length, a full disc solar shot can be done without making mosaic.
The optical quality of the Borg 45ED II is superb, no color can be seen on a remote white lamp with a 7mm Ortho plus a 5x Powermate. You could see color when it's out of focus, but it's not a major issue indeed.
For this price, Borg 45ED II is a good 3rd or 4th scope, and it truely makes up an extremely portable setup such that it will never be left behind even for overseas trip. It can be placed inside the small bag which I bought to office everyday and still have rooms for a notebook computer and all other stuff.
When used with a JMI NGF-S plus a Shoestring FCUSB controller which I've described in a separate entry in this blog, it makes the cheapest and yet high quality remote contriollable setup in the world.
You could find images taken with this setup in this blog for your reference.