Losmandy Dovetail and
the Skywatcher 804
Since I had planned to do some wide field imaging with my Nikon F, and wasn't
planning on buying a .63 reducer / corrector for the LX90, I
opted for a different alternative. I originally bought a Meade
camera adapter for the LX90 and used that for a few times. My
Nikon only has a 50mm f1.4 lens and was giving me very large
fields of view, far more than I wanted. It also picked up my
Meade dew shield attachment thumbscrews in it's FOV.
Attaching the
Nikon at prime focus was too narrow for wide field, so I
decided to buy a short tube 80 refractor. Looking at all the
suppliers (Orion, Celestron, Skywatcher and others), it seemed
the ST80 was pretty much the same OTA, just painted and
branded for each company that was selling them. I chose the
Skywatcher 804 simply for aesthetic reasons - the color matched
my LX90 OTA perfectly and makes it look like it was made for the
SCT. The Skywatcher is an 80mm f/5 (400mm fl) achromatic
refractor. Not only is it a great wide field scope for the LX90,
but on it's own tripod it makes an excellent terrestrial /
wildlife scope. The ST80 was taken apart, and minor tune-ups done
(ST80 tune-ups). While
disassembled, the gray enameled parts were repainted flat
black.

Skywatcher 804 on the Meade
camera adapter
This was prior to disassembling the ST80 for tweaks and painting
I originally attached
the 804 to the Meade camera adapter. This was fine for visual use
but there was no way it would support the Nikon F as well.
It also was a pain to collimate to the LX90. The Skywatcher
weighs in at 3 pounds and really put the maximum amount of weight
on the camera adapter. After looking around at alternatives, I
decided on the Losmandy dovetail system.

The Skywatcher 804 from the
front, both DA plates on the dovetail
I opted to use the
Skywatcher's original rings, as they provided a secure quick
release mount, and once on the dovetail are only slightly out of
collimation to the LX90. Slight adjustments when mounting the DA
plate to the dovetail finalizes collimation.

Rear view of the 804 with the
two DA plates on the dovetail
Losmandy was chosen
because they have an impressive array of adapters that can
be used with the dovetail. Installing the dovetail required the
removal of the Meade camera adapter. The Losmandy dovetail
was used with the "DA" adapters for the Skywatcher 804,
as well as with a piggyback camera adapter for the Nikon.
The Nikon could be slid on the dovetail with the Skywatcher still
in place.

The Losmandy
Rail on the LX90
The Losmandy DM8 system
for Meade 8" SCT's includes the dovetail, two mounting
blocks and required hardware. The mounting blocks attach to the
front and rear of the scope using the supplied mounting holes on
the Meade OTA. Losmandy supplies stainless replacement allen head
cap bolts for this purpose. The dovetail is attached to the
mounting blocks in a similar fashion, again with supplied
replacement bolts. Two 1/4-20 thumbscrews are supplied as safety
screws - to prevent accessories on the dovetail from sliding off
if the female plate accidentally loosens. Machining is of very
high quality and all surfaces are polished and black anodized.
All edges are round finished with no sharps anywhere. Everything
lines up perfectly with one another, and with the scope itself. I
was pleasantly surprised at the quality of work in this mounting
system, even after having been highly recommended to me by many
people.

The Losmandy "DA"
plate/adapter
The DA adapters are made to accept a wide
variety of accessories. They have 7 holes (countersunk from the
bottom) in an "H" pattern. The DA plate has a hand set
screw on one side that tightens against the dovetail to secure it
in place. DA adapters are two piece, each side of the
female dovetail is split, the smaller of the two has the hand
tightened set screw. I assume this is to make it adaptable to
different width male dovetail plates. Fit and finish on the DA
plates is as high a quality as the dovetail itself.

Nikon F piggybacked on the
Losmandy dovetail
My second DA plate contains a 1/4-20 stud
for the Nikon, to replace the Meade camera adapter. This
arrangement works well, but the DA plate must be attached to the
camera first, then slid on the dovetail. The Skywatcher can stay
mounted while the Nikon sits at the front of the dovetail. A
small readjustment of the Meade weight set is required when
the Nikon is mounted up front.

Nikon F at prime focus on the
804
The only potential problem from
installing the dovetail, was the needed space for the corrector
heater. Luckily, there was just enough room between the dovetail
and Meade dewshield to allow for the coil to be placed at the
corrector's edge within the OTA. Between the heater and the dew
shield, I rarely have to call it a night due to the corrector
fogging up or frosting. The heater is a home made 12 watt, 1 amp
device, made from an old electric blanket's nichrome wire, and is
powered off a separate 17ah battery.

The corrector heater mounted between the
dovetail and the dew shield
This arrangement gives me the best of both
worlds. I now have a wide field scope that I can use without
changing EP's around or using a focal reducer, and which
doubles as a wide field lens for the Nikon. I also retain a
piggyback camera mount and it can be slid on the dovetail at a
moments notice. The options are available to me now for a
multitude of other arrangements (weights, tube rings, telephoto
lens supports). The Losmandy system is very well built and
machined, and it's a beautifully designed system as well. Being
able to slide the accessories along the dovetail makes balancing
the OTA a snap, and setup / teardown is easier and faster than
before.
Updated 12/01/01 The two split rings that came with the ST80
have been replaced with a single 4" PVC pipe
coupler. 6 holes were drilled and tapped for 1/4-20
thumbscrews at 120� offsets, and two holes were drilled
and tapped to attach the PVC coupler to the Losmandy
rail. All thumbscrews have a rubber thread guard to
protect the ST80 OTA from scratches. This new addition
allows for more precise collimation to the LX90 OTA, and
seems to be a little more study than the original rings. |

The new PVC tube ring on the Losmandy rail,
showing the 1/4-20 thumbscrews
Losmandy web site
|| Back
to Contents || Wedge
adapter || Focuser
|| Azimuth adjuster
|| Weight Set
|| Dovetail
||
|| Compass
|| Polar
|| Pinouts
|| Tours/Ephemerides
|| LED Markers
|| Balance
|| Focuser
Bearings ||
|| Corrector || Encoders
|| Firmware ||
|