The optics on my
Vixen ED80Sf refractor were sufficient for my wide-field imaging
needs, but I soon found that the weight of my Canon 40D DSLR was too
much for the stock Crayford focuser. With no locking mechanism I
would lose focus over the course of a couple of hours. Therefore, I
started the hunt for a replacement. My requirements for the focuser
were fairly simple:
It must have a 2” tube
with a 1.25” adapter
Dual-speed with a fine focus
ratio of around 10:1
Brake/lock mechanism to hold it
in place while imaging
Use of a compression ring
instead of a screw to hold eyepieces and the camera
(Optional but desired) The
later addition of a motor drive should be easy
On the short list
were the GSO Dual Speed MicroFocuser, Moonlite 2” Crayford
(Synta) with options to meet my criteria, Starlight FeatherTouch 2.0”
Dual Speed, William Optics 2” Synta focuser, and JMI Event
Horizon EV-1r. I did initial research by comparing prices and basic
focuser properties as shown below:
Based on the price,
weight capacity and feedback from others, I decided to order the JMI
on September 25th, 2009. The first thing I liked about the
JMI was that the $350 covered all of the options I needed. With the
Starlite and Moonlite, I would have had to start with the base model
and add options to come up to the same level of functionality as the
JMI. This may be misleading to potential customers who think they can
get a Moonlite for $275, but don’t realize that it is a $125
option to add a dual-rate control with a shaft lock, or that adding
motor control later on requires you to send the focuser back to
Moonlite for the upgrade.
There was a longer
than expected delay in shipment, apparently due to a vendor, so the
focuser didn’t ship until October 21st (almost a
month). I would have appreciated status e-mails to let me know that
there was a delay. Instead, I had to call twice. When I did call,
however, I immediately got a real person on the phone and did not
have to step through a bunch of automated voice commands.
The unit arrived a
couple of days later and was packed very securely. Included in the
box was the focuser itself, basic installation instructions, and a
bag of different thumb screws, set screws and hex wrenches. This
thing was noticeably heavy and extremely solid-feeling. I called it
“the beast”.
The JMI EV-1r is
rotatable and lockable, so there were thumb screws to hold it in
place. With the extra screws that came with the unit, I could choose
to use either metal or nylon, based on needs. If I didn’t need
the force of using metal, I could opt for the nylon and keep from
scratching the base. The unit also came with a 2”-to-1.25”
adapter and I was pleased to see that it was of the same high quality
machining as the rest of the unit and used a compression ring.
Replacing the stock
focuser could not have been easier. The JMI was a perfect fit for the
80mm refractor tube and the holes lined up perfectly. The JMI came
with the body screws and a hex wrench that fit. My finder scope also
fit perfectly in the built-in holder of the EV-1r, though I did have
to work a bit on the alignment of the finder (this could have been
because the holder was way off on the stock focuser; I’m not
sure).
The dual speed knobs
had a very nice, heavy secure feel to them. There was no slop
whatsoever. The EV-1r had bearings on both sides of the tube
providing an even tension that made it very stable. The graduated
scale on the main focuser knob was a plus that some of the other
focusers didn’t have. This would allow me to switch from the
eyepiece to the DSLR and be able to get close enough to focus to
start fine focusing with software.
While the focuser
was rotatable, I did not feel very confident when I loosened the
thumb screw because the draw tube felt like it was going to fall out;
especially with a heavy DSLR hanging off of the end. There was a deep
groove around the tube to allow for rotation without the tube falling
out, of course, but there seemed to be a lot of play as soon as the
thumb screw was loosened the least little bit. I may try the metal
thumb screw here to see if it is any better, but I don’t want
to mar the surface. Therefore, I may just rotate the DSLR and leave
the focuser locked.
The first night out
allowed me to enjoy the performance of the Ev-1r’s dual-speed
control. I noticed no shakiness or shift while focusing – even
while focusing at high magnifications in preparation for drift
alignment. I noticed no drift in the focus, even though I had
forgotten to lock it down before starting an imaging run. It was able
to hold the DSLR stable from around 30 degrees to zenith, where I
stopped for the night. The first images were as sharp as the last
ones. Below is the result of 10 minute subs over the course of three
hours.
I just placed an
order for my second JMI, this one for the 8” reflector.
Pros:
Cons:
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