Background
I
consider myself a weekend amateur astronomer of 30 years with a main
interest in imaging under the skies in Arizona. My first imaging
experiences were with the Olympus OM1 film camera, followed by use of
the Starlight Xpress MX5C and MX7C one shot color cameras. Feeling
tied to using a laptop in the field for imaging; I divorced myself
from the entanglements of wires and connectors a few years ago and
settled on DSLR imaging with my TEC 140, C9.25 SCT and piggyback
using my Losmandy G11 mount. There are so many imagers out there
today and I know I will never compete with them, especially with the
high level of hardware available. But, I still enjoy composing and
capturing images the way I want and attempting to climb the image
processing learning curve. Wide field imaging has always intrigued
me but the cost of high-end equipment has been prohibitive. The
alternative was using camera lenses on CCD cameras but focusing was
always an issue. For the record, I have no affiliation with any
telescope or astronomy accessory manufacturer.
The Move Toward a Small Refractor
With
the introduction of relatively low cost, near APO, small objective
diameter refractors in the last 3 years, I found myself attracted to
purchasing one for wide field imaging. Knowing that the William
Optics and Astronomy Technologies product lines were at the forefront
in providing short focal length, fast refractors, I began my research
in picking my next telescope. I immediately realized how quickly
these scopes were introduced and then discontinued, presumably as
part of a natural evolution in perfecting the design driven by
competition. Special Dispersion (SD) glass, Extra Low Dispersion
(ED) glass, doublets, triplets and Petzval designs were all available
to entice the consumer to purchase one of these little gems. Aside
from the different objective lens design, all were solidly built and
finished, most with two-speed Crayford type focusers with SCT threads
terminating the focusing tube.
So, I
narrowed my search and zeroed in on a nearly new, AT66ED offered for
a great price on Astromart. The AT66 is a 66mm diameter cemented
doublet, 400mm focal length, f6 instrument. There are many reviews
available that detail the visual capabilities of the AT66 but I
wanted to concentrate here on describing the imaging attributes. It
is well known that field curvature is an issue when using larger
chips with refractors, so I planned on purchasing a field
flattener/focal reducer as part of the imaging train. Several
options are available, but good reviews of the Williams Optics FF/FR
0.8X Version II convinced me to purchase one. The FF/FR can be used
either by inserting the 2 inch barrel into a telescope or by
utilizing the native built-in SCT threads to fasten the FF/FR
directly to the AT66.
Although
supplied with a SCT to 1.25 inch barrel adapter, you would need to
purchase a SCT type 2 inch diagonal if you wanted to utilize any 2
inch eyepieces - not something you would want to do if you already
owned a refractor type 2 inch diagonal. Fortunately, Williams Optics
sells a female SCT threaded diagonal adapter that simply screws into
your refractor diagonal in place of the 2 inch barrel tube enabling
it to be used on these small scopes. The William Optics adapter not
only fits their own diagonals, but they advertise it will also fit WO
clones such as the Astro-Tech diagonal, which I own – and it
fit perfectly. William Optics also offers a SCT to 2 inch barrel
adapter, which is very difficult to find. One would think you could
use a refractor type diagonal with this adapter, however, in checking
with most telescope accessory suppliers, they claimed you would not
be able to reach focus due to insufficient in-focus travel. I took
their word for it.
This
combination would provide a flat field on my QHY8 APS sized chip and
converted the AT66 into a 320mm focal length scope at f4.8. A quick
call to a leading telescope accessory dealer provided me with the
proper combination of spacers to achieve the prescribed spacing of
56mm from FF/FR to CCD chip. The combination of the FF/FR and
spacers guaranteed a rigid set up with no flexure.
Imaging
with the AT66
Mounting
the AT66 piggyback on another scope can be challenging, as there
doesn’t seem to be any exact fit rings available. There are
guide scope rings for sale with the Delran tips that would work but
that would add substantial cost to the set-up. I chose to utilize
the mounting L-foot installed on the scope, fastening it to a
Losmandy camera adapter via the ¼-20 thread. After tightening
the screws sufficiently, a quick test of trying to twist the scope on
the adapter proved to me that no movement was evident and that the
mounting would not slip during imaging. The Losmandy camera adapted
was then coupled to the dovetail plate on top of my C9.25 allowing me
to position the AT66 to minimize weight of the camera wires pulling
on the camera. This added to the stability of the set up
considerably.
The
first light that passed through the AT66 onto the QHY8 One Shot Color
CCD camera was M8 and M20, beautifully captured in a very wide field.
I used Nebulosity 2.0 for image acquisition, flats and
pre-processing and PSCS2 and Noel Carboni’s Astronomy Actions
for post processing. I was concerned that with the very small
objective size of 66mm, it would necessitate me to acquire images
with lengthy sub-exposures but quickly realized when composing the
image and focusing the camera that the AT66 was providing sufficient
light. I made the normal exposures of 10 x 10 minutes each.
Becoming
excited about potentially capturing some very nice images with this
little scope, I quickly moved onto the Antares region before it
became too low in the sky.
Finally,
the next night I captured the Great Andromeda Galaxy when it was near
the Zenith.
All in
all, the AT66ED in combination with the WO FF/FR provides a great
wide field imaging platform with very good color correction and
nearly no blue haloes around bright stars. In my opinion, this set
up proves to be much more capable than a fixed focal length or zoom
camera lens attached to the CCD camera due to the ease of focusing
with the two-speed focuser on the AT66. If you have ever tried to
focus a camera lens on a CCD camera you know what I mean. At an
incremental cost of $375 (used AT66 and WO FF/FR), I added wide field
imaging capability to my existing platform. Add another $40 for the
SCT diagonal adapter and I now have a grab & go scope for wide
field visual use under Arizona skies. And with the summer Milky Way
on showcase, the views are spectacular.
Pros
Lightweight
Low
cost / high quality ratio
Very
smooth two speed focuser with lock (no creep with CCD camera)
Good
color correction
Cons
Focuser
needs to be extended nearly to end of range to achieve focus
SCT
threads at terminiation of focusing tube vs. 2” opening for
accessories
Summary
While
the Astro Tech 66 is no competition for the hight priced / higher
quality true APO’s, you will get very pleasing images both
visually and with CCD / DSLR cameras. The field is very large and
with a focal reducer such as the WO 0.8X, focal length drops to 320mm
@ f4.8. Stars are generally small with an even focused field across
the QHY8 6.1 MP chip. I was thoroughly amazed at how much light the
little scope could capture and how good the finished images came out.
For the price, I can’t see how you can beat it.
Clear
Skies
George
Kolb
Phoenix,
Arizona
www.pbase.com/geokolb
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