Click here
for a printable version (Requires Acrobat® Reader)
DGM Opticsä
OA-Seriesä instruments
offer some of the finest optics and innovative mechanical design utilized by
any telescope available to the amateur astronomer today. Outlined here are basic procedures to
help you attain optimal performance from your OA-Seriesä
telescope.
Once you have received your
OA-Seriesä
telescope carefully unpack all components and inspect for any damage that may
have occurred during shipping. Although it is rare for damage to have occurred
during shipping, it is very important to contact DGM Opticsä so a
claim can be filed as soon as possible with the shipping company.
Depending on your model, all the
OA-Seriesä
telescopes require some assembly. The OA-4.0ä is
easiest of all the OA- Seriesä telescopes
as far as assembly and requires only that the primary mirror is installed in
the tube assembly and the split yoke is secured around the circumference of the
tube assembly. To install the primary mirror, carefully unpack the primary
mirror and remove the (3) machine screws that are attached to the large
platter. Then, with the small orientation hole in the large platter aligned
with the focuser, gently slide the entire assembly into the tube and, using the
predrilled holes in the tube attach the mirror cell and primary to the tube
assembly. Next set the tube assembly in the “Split Yoke”. Placing the split
yoke assembly around the tube assembly and securing it by clamping the
adjustable draw latch on the split yoke does this. Caution: Adjust the
draw latch only as tight as is needed to hold the tube assembly securely. Then
place the split yoke and tube assembly onto the mount struts. You can now
proceed to the alignment step.
If you have purchased the OA-5.1
ATSä, the OA-5.5ä, the OA-6.5
ATSä, or the OA-7.0ä, you will
need to attach the large base plate to the small base plate and strut assembly.
To do this, find the (2) 3/8” nuts and 3/8” fender washer attached to the 3/8
machine screw and bushing assembly. Then, remove the 3/8” nuts and 3/8"
fender washer attached to the machine screw. Next, carefully insert the
bearing/machine screw assembly on the bottom of the small base plate and strut
assembly into the bushing on the large base plate assembly. Now, place the
fender washer through the 3/8” machine screw and thread the (2) 3/8” nuts onto
the machine screw. Tighten the first 3/8” nut “finger tight” against fender
washer, then with an adjustable wrench hold the first 3/8” nut in place and
tighten the second 3/8” nut down to “lock” the assembly in position. If you
find that the mount has excessive play, repeat the procedure described above to
attain the desired motion and “free play” in the bushing/bearing assembly.
Also, note that this procedure may have to be repeated several times until your
mount has been “broken in”, or with seasonal changes in relative humidity and
temperature. You can now follow the basic primary mirror installation as
described for the OA-4.0ä and proceed to the align step.
The OA-Seriesä telescopes secondary mirrors are permanently mounted and
aligned prior to shipment and rarely require anything more than to be checked
prior to aligning the primary. Here is the procedure. First, you will notice
that a small indelible ink mark has been placed in the center of the primary
mirror. This mark provides a visual reference to the center of the primary when
aligning the secondary mirror. Using an empty film can, with a ¼ inch hole
drilled in the center and placed in the barrel of the focuser, the mark on the
primary mirror should be centered when viewed with your eye on top of the film
can. Next remove the film can and with your eye remaining centered over the
barrel of the focuser move your eye back to approximately 6 inches away. Repeat
this step at distances of 12, then 18, then 24 inches. At each step the
secondary should appear concentric and centered with regard to the barrel of
the focuser with your eye remaining centered on the optical axis as you move
farther from the focuser barrel. If it appears that the secondary is not in
correct alignment you can manipulate the secondary by carefully bending the
brass rod that attaches the secondary to the “L” stalk that supports the whole
assembly to the interior of the tube. If you cannot achieve a satisfactory
alignment contact DGM Opticsä and I
will be happy to assist you. If your secondary mirror appears to be in correct
alignment you can proceed to “part B” of the alignment.
Next comes the easy part: the
primary. To provide a constant reference, the primary mirror alignment should
be done with the scope pointing on the horizontal looking at a white
background. Looking into barrel of the focuser, with no eyepiece, and your eye
centered over the barrel of the focuser, you should see only the primary with
no image of the secondary visible. Next, if you have a standard OA-Seriesä scope or
optics sets (OA-4.0ä, OA-5.5ä, or
OA-7.0ä), move
your eye slightly towards the rear of the scope, (the six o’clock position if
the front of your scope is twelve o’clock). If the instrument is correct in
alignment you should see a small “sliver” of the secondary mirror at the twelve
o’clock position on the primary mirror. The key to aligning an off-axis
Newtonian telescope is in the fact that off-axis primary is actually a segment
taken from a larger “parent mirror” and it is beneficial to think of it in that
way. When looking into the focuser barrel, think of an imaginary “center line”
running through the primary from twelve o’clock to the six o’clock position on
the primary. This imaginary line runs from the thickest to the thinnest part of
the primary and it also points back to the center (apex) of the old “parent
mirror”. If the alignment appears incorrect, use any needed combination of the
primary mirror cell adjusters (wing nuts) to bring the image of the secondary
mirror to the correct position on the “center line”. The procedure for the ATS
scopes, or optics sets, (OA-5.1 ATSä, OA-6.5 ATSä, and OA-9.0ä) is
different only in that the “sliver” of the secondary will be at the six o’clock
position, instead of the twelve o’clock position. Other than that the procedure
is the same.
The star test is the final confirmation of the correct
alignment of your OA-Seriesä
telescope. The test consists of centering a bright star, beginning at low
power, and observing the in and out of focus star images, then repeating the
test with progressively higher power eyepieces. In all cases, with the star
centered in the field of view, the image should be round and concentric with no
trace of astigmatism or coma, (elongation of the star image), both inside and
outside of focus. If you find that the image is not concentric when centered in
the field of view then using one of the (3) primary mirror cell adjusters (wing
nut) will need to be adjusted. To do this examine the in and out of focus star
images around a circumference around the edge of the field of view. Once you
find the area of the field of view where the star test is most concentric then
use the (3) primary mirror cell adjusters to bring the “sweet spot” to the
center of the field of view. Once you have established the correct alignment by
star testing you can note the visual position of the secondary
"sliver" and quickly perform accurate alignments.
Some
additional hints for star testing are as follows:
1. If possible use
lower quality eyepieces. The reason being that well
corrected eyepieces have better off-axis correction and seem to make
the task of determining where the "sweet spot" is in the FOV more
difficult.
2. When you get to the point of examining the in and out of focus star images high power star test images be sure to examine it first with about 3-4 diffraction rings, then progressively reduce the number of rings until there is only the bright outer ring with a dark dot in the middle. With the image that close to focus the sensitivity of the star is very good and will show even a small degree of miscollimation. Also keep in mind that local seeing conditions will have an effect as to how well defined the in and out of focus star images are and will limit the magnification and/or how close to in focus you can interpret the images.
3. Once you have established optimum alignment with the
star test a laser can be used to align your OA- Seriesä
telescope thereafter. Do so by constructing a translucent film which can be
placed over the open end of the scope, as you would with an over the aperture
solar filter. Be sure to place an index mark on the holder so it can be placed
in the same position each time with regard to rotation. Then with the laser in
the focuser activate it and place a mark exactly where the beam strikes the
translucent film. Then all that needs to be done to achieve optimum alignment
is to use the primary adjusters to bring the laser beam onto the mark on the
film.
4. Also, be sure that your scope has reached complete
thermal equalization before performing the star test(s). If you are confident
that all alignment steps have been completed correctly and still are not sure
if the alignment is optimal please feel free to contact DGM Opticsä for technical support.
Cleaning the optics should be performed whenever the
primary or secondary mirrors have an excessive amount of foreign material on
the optics, or when the optical performance is obviously degraded due to
surface contaminates. DGM Optics uses the technique described, but other
methods may be used if preferred.
Start by removing the primary
mirror and cell from the tube assembly. Do not remove the primary itself from
the mirror cell as the method described can be done with the mirror in place.
1. Prepare a
solution consisting of 20 parts distilled water and 1 part mild dish washing
soap.
2. Using, unscented,
plain white, bathroom tissue, take 10-12 two-ply sheets and fold into
a square pad, then fold the square pad in half and set on a clean oil-free
surface.
3. Then, set
aside 6-8 cotton balls on a clean oil-free surface.
4. Next,
with the mirror facing up, place the mirror cell assembly under running, room
temperature water for about (1)
minute.
5. Turn the
water off and pour a generous amount of the premixed distilled water solution
over the surface of the primary mirror.
6. Then take
the cotton balls and saturate them with the premixed distilled water solution
and lightly swirl them on the surface of the mirror. You don’t
have to swirl the mixture so as to create a lot of bubbles on the surface,
agitate it only enough to see a hint of the soap in the solution. That will
usually be sufficient to remove most stubborn dirt or stains on the surface.
7. Next,
with the mirror facing up, place the mirror cell assembly under running, room
temperature water for (1) minute, except after one minute turn off the water
and quickly flush the surface with a generous amount of distilled water.
8. After the
surface has been flushed with distilled water quickly turn the mirror cell
assembly on its side to drain off excess water. Then take the bathroom tissue
pad and lightly and gently blot the remaining water
from the surface.
9. Next,
using a paper towel, carefully wipe up the water on the large and small
platters of the primary mirror cell. Avoid turning the assembly upside down,
and avoid touching the freshly cleaned mirror surface. Inspect and repeat
procedure if necessary. Reinstall mirror cell assembly in tube assembly.
Because of the crucial nature of
the secondary mirror alignment, it is advisable to remove and/or clean it only
if there is an excessive amount of contaminants on the surface. To remove the
secondary, loosen the hex nut/threaded rod assembly that secures the mirror
itself to the "L" shaped stalk. If you need remove the secondary for
cleaning be sure to measure the exact distance that the second hex nut
is threaded into the brass rod. That will mark the position when the secondary
is reinstalled. If possible, use cleaning methods that allow the secondary
mirror to remain in place. Try blowing the surface off with low pressure air or
wiping the surface with a soft camel hair brush and then gently rake the
surface with a bathroom tissue pad dampened with a small quantity of alcohol or
methanol. And as always, DGM Opticsä will be
glad to give technical support if needed.
DGM Opticsä OA-
Seriesä
Dobsonian style mounts are manufactured by a professional furniture making
company and offer some of the smoothest tracking and most comfortable viewing
possible with a Dobsonian mounted telescope. The optical tube assembly is set
in DGM Opticsä Split
Yokeä. The
Split Yokeä allows
the tube to be balanced and rotated for comfortable viewing of any portion of
the sky.
All bushing, bearing and trunion
parts are custom made using Teflon (TFE) and Ultra-High Molecular Weight
Polyethylene (UHMW). These materials feature excellent friction coefficients
with high chemical and temperature resistance. The wood is a beautiful, high
grade, Atlantic Birch triple coated with a clear polyurethane finish that will
last for years. The finish can be cleaned and polished with any commercial wood
preserving products any time you want to bring back the "new finish"
shine.
As for Teflon (TFE) and
Ultra-High Molecular Weight Polyethylene (UHMW) components, they need only to be
kept free of abrasive materials, which may inhibit the Alt-Azimuth motion(s) of
the mount. Clean these components by wiping the surfaces with a clean cloth
that has been lightly dampened with acetone or alcohol. Note: It
is recommended that chemical resistant gloves be worn when using such solvents.
Also, the vertical bushing/bearing assembly should be periodically treated with
machine oil such as WD-40, or similar products, to inhibit corrosion of the
machine screw and double nut locking assembly.
The OA-Seriesä mount
utilizes a black anti-static Ultra-High Molecular Weight Polyethylene (UHMW)
disc on the large base plate with the small base plate/strut assembly riding on
Teflon (TFE) pads. Periodically the base plates can be disassembled and cleaned
of any debris, and then treated with WD-40 to increase the smoothness of
azimuth motion. The OA-4.0ä mount
features, believe it or not, vinyl LP records as the surface the Teflon pads
ride on.
The OA-4.0ä is now
offered with a "Teflon strap clutch". This simple, inexpensive,
device is built in to one of the struts and applies controlled friction to the
trunion bearing and prevents the tube assembly from "falling down"
when various eyepieces are used. This device requires no special maintenance.
However, a thin coat of WD-40, or machine oil, can be applied to the assembly
where the components contact, the trunion bearing, and the Teflon strap. When
additional clamping is applied, the smoothness of the altitude motion is
enhanced. Also, the "Teflon strap clutch" is available with any of
the OA- Seriesä
telescopes, and can be easily retrofitted to your scope if you need more
friction with the altitude bearing motion. Contact DGM Opticsä for more details.
1. Do not
loosen the "split yoke" draw latch with tube pointing up. Doing this
can result in the tube sliding down on the small mount platter and damaging the
tube assembly or the mount.
2. Do not
store the Standard OA-4.0ä for long periods (2+ hours) at
temperatures greater than 140
degrees Fahrenheit. The Standard OA-4.0ä uses PVC (Polyvinyl Chloride)
tubing for the optical tube assembly and is rated for that temperature.
3. If
possible try to bring your OA-Seriesä telescope into an intermediate temperature area after observing in cold weather. This
will help inhibit "sweating" on the optics that can be harmful to
thin film mirror coating.
4. And, Finally, Do Not Look Directly at the Sun
with your OA- Seriesä, or ANY Telescope. DOING SO WILL RESULT IN INSTANT BLINDNESS!!!
Clear Skies!