Takahashi Epsilon 180ED Review
https://www.astromart.com/reviews/article.asp?article_id=571
Takahashi Epsilon 180ED
The Takahashi Epsilon 180ED is an astrograph boasting ultra fast f/2.8
optics and a flat photographic field. Introduced in late 2005, this
Epsilon 180ED is latest in Takahashi’s famous Epsilon line. This review
details my experiences with this astrograph in the area of DSLR
photography.
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| Imaging Setup |
Vital Statistics
The Epsilon 180ED is fundamentally a highly corrected Newtonian with a
fast hyperbolic 180mm (effective aperture) primary mirror and a two
element “ED” corrector located in a rotating focuser assembly. The scope
is attractively clad in an outer tube powder-coated with a rich warm
yellow color. The construction is solid and heavy duty. You should not
expect collimation loss once properly set unless you plan to parachute
out of an airplane with this OTA.
The OTA is around 22lb, but throw in the various accoutrement such as
rings, finder, dovetail plate, camera, and you have the working weight
quickly ballooning to over 30lb. With my DSLR astrophotography setup, I
am loading about 34lb onto my mount. CCD users can easily approach 40lb.
While this is not exactly hernia city, you need to be aware of lifting
and mounting such masses at shoulder level. What this also means is your
mount and tripod become important factors if you are considering this
astrograph. I view the Takahashi EM-200 (which I had) as on the
borderline of inadequacy except on calm imaging nights. The Takahashi
NJP, Astro-Physics Mach1GTO (which I currently use) and the Losmandy
G-11 are sensible options.
Optically, you are looking at a fast f/2.8 system with a published 44mm
image circle. As claimed, I found star images to be impressively pin
point across the entire edge of my APS-sized Canon 20Da chip.
In Action
First off- do not buy this scope for visual use. It is meant to be used
as an Astrograph. There are cheaper and more optically suitable options
for visual use (although none of your options are banana-yellow). Sure,
you can look through the Epsilon 180ED with the attached ocular
accessories, but it is not any better than an Orion reflector costing
thousands less.
Attachment to my Canon 20Da DSLR is easy and simple, using the Takahashi
wide mount EOS T-ring which is the same one used for the Takahashi Sky
90 II. There is provision here for my IDAS LPS 48mm filter. I’m not a
rabid fan of the Tak wide mount accessory- it is two pieces mated and
held by a set screw that serves little function except to be
accidentally released in a tired stupor at 4 am when one’s logical
reasoning and fingers report to different departments in the brain.
Adequate cool down is necessary for the optics to reach thermal
equilibrium. Do not set this OTA up in the sun (even the late afternoon
sun) as the interior heats up fairly quickly and then take its own sweet
time giving up the Joules. Images do look pretty bad if the mirror is
not at equilibrium.
My imaging setup involves a DSLR mounted on the focuser and a SBIG STV
head (in eFinder mode) on the top accessory plate. The Takahashi rings
and top accessory plate are well made and recommended. I also attach a
7x50 finder to the OTA.
Focuser Gripe
The focuser is a low profile Crayford configuration with a removable ED
corrector element. The outer assembly is held captive at the base by a
large “Captain’s wheel” that allows free rotation for image framing when
loosened. I found this construction inadequate. When the Captain’s
wheel is loosened, the focuser tube can rock. If you are not aware of
that happening, you run the risk of re-tightening the adjustment wheel
with the optical train now out of alignment. With the fast optics, you
really do not have any room for error here. On my first night of
imaging, I loosened the adjustment wheel and under the weight of the
camera, the focusing tube sagged out of alignment. I ended up with a
frame with only 20% center stars pin point and the rest horribly
deformed, stretched and out of focus.
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| Pelican, 3x3min exposure |
A web search shows some of the expert CCD users have fashioned their own
alternative focusers assemblies to securely hold their CCD cameras. For
me, I do have a work around: when you loosen the spoke wheel to adjust
the camera angle, apply a light inward pressure to the focuser (I gently
press my camera inwards). This will prevent the camera and focus
assembly from tilting out of alignment. Of course, do be sure that your
focus lock is screwed tight so that you do not change critical focus. It
takes a bit of practice to do this but now it is habit with me. Happy
to say, all my images are currently and consistently spot on sharp edge
to edge. I might also venture a note that as I have one of the earlier
editions of the 180ED, improvements might have been instituted since
then.
Imaging Characteristics
While star images are relatively sharp to the edge, the optics is not
flat field. What this means is that I have to use flats in my processing
workflow. Absolutely must. What is more, the area of illumination is
not centered and symmetrical, thus the flats are dependent on the camera
angle. Using the good ‘ol white T-shirt approach and a suitably cloudy
day, I have build up a set of flats according to 9 possible camera
positions. I just keep track of the camera position in my notebook
during imaging. I have found this to be adequate in my processing work.
True, it is a bit of a pain to set up a multi-position flat library but
it is a once-only thing, and the results of good flat field processing
are always rewarding. Imaging software such as ImagePlus and MaxIm DSLR
handle flats, bias frames and darks in an automated manner.
Fine Focusing
Ah yes, unless you have been gifted with the hands of a Swiss cuckoo
clock maker, you will need the Takahashi 10:1 fine focuser to prevent
mental breakdown. It works very well indeed with the Epsilon 180ED.
Installs in seconds.
Collimation
Initially when I was not aware that the focuser was tilting out of
alignment, I thought that the optics were out of collimation. Picking up
the instruction manual, I found the “Engrish” anguishly unintelligible.
Even after the aid of some cold beverages, the hidden DaVinci code did
not reveal itself to me. Thankfully my optics turned out to be in
perfect collimation. If it ain’t broke, don’t fix it. And if it is off
one of these days, it’s headed to Art and Fred at Land, Sea, and Sky.
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| Stitched mosaic from 4 composite frames. Individual exposures of 2.5 min. |
So is f/2.8 nice?
Sure it is, although I believe that speed in imaging is not everything.
Optical characteristics (such as focal length) of your imaging
instrument must be carefully matched to your camera chip for a
particular class of object you are interested in imaging. For me, the
Epsilon 180ED does satisfy my wide field work. Let me explain: I only
get to go up to the mountains once or twice a month to image. Time up
there is very precious, factoring a 2.5 hour drive there and back. The
Epsilon 180ED allows me to image and build complex mosaics in a
reasonable and productive manner given my very limited imaging time. I’m
very happy with how this scope performs, and I am impressed with the
edge-to-edge performance of the optics. A quick note here- unless you
are out in the major boondocks, sky fog and sky gradients become a
consideration with fast wide field optics. On the Blue Ridge Parkway,
sky fog limits exposures on my Canon 20Da at ISO1600 to around 2.5 to 3
minutes. I used to image at 6 min with my refractors at f.4.5.
Conclusion
I’m happy with the performance of this astrograph. While I would have
preferred a different camera angle adjustment design, it works fine with
the measures I mentioned above. For wide field astrophotography in the
500mm range, this tubby yellow OTA affords outstanding imaging
performance at a very reasonable price point. It’s a keeper.
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