Massachusetts Institute of Technology
> George R. Wallace, Jr. Astrophysical Observatory

WAO 16-in (41 cm) Telescope
Information for Users



The following is intended to be a reference primarily covering the 16-in telescope and its dome, suitable for a user who's already familiar with the basics of observing with a small telescope (astronomical coordinates, manually acquiring target fields, guiding, etc.). It intentionally doesn't contain much information specific to particular instruments that may be used on the telescope, so be sure to find out what additional documentation may be available for whichever instrument you're using.


The WAO 16-in (41 cm) telescope and its two-story dome were built in 1971 as part of the original observatory. This telescope is a 16-inch Cassegrain originally manufactured by Ealing Optics Division, although the motor drives and control electronics have since been substantially modified. The telescope is electrically driven in both coordinates. Both mirrors are Pyrex, aluminized and overcoated with silicon monoxide. Instruments are mounted onto the ``saddle'', the large aluminum tailplate perpendicular to optical axis.

The telescope's mount is an asymmetric variation of the German equatorial type, whose baseplate is anchored in position by studs cast into its concrete pier. The asymmetric design of this mount means that the telescope is always used in one of two possible configurations with respect to the mount: it's either on the ``east'' side or on the ``west'' side of the pier. For most purposes the two configurations are equivalent because both permit complete coverage of the sky down to 20 degrees altitude (airmass approximately equal to 3). Normally this telescope is used on the east side.

For altitudes less than 20 degrees the two configurations are no longer equivalent owing to the interaction of the geometries of the mount and of the dome slot - it turns out it's not possible to point much lower than 20 degrees altitude on the same side of the pier as the telescope (normally east), while on the opposite side (normally west) one can follow an object right into the trees. Should you have the misfortune of having to observe below 20 degrees altitude near the eastern horizon, awash in extra light pollution from the city of Lowell, you'll need to change the telescope to the other side of the pier first.

Table 1: Summary of specifications
primary mirror: 41-cm clear aperture, f/3.2 parabolic
secondary mirror: 10.8-cm diameter, hyperbolic
focal ratio: f/11 (original Ealing info.)
f/10.9 (WAO manual, 1983)
field size: 7-cm diameter unvignetted
magnification: 110 to 880 diameters
resolution (Dawe's Limit): 0.29 arcsec
image scale: 46 arcsec/mm (original Ealing info.)
46.1 arcsec/mm (WAO manual, 1983)
focusing image plane range: 0.6-m
finder scope:7.5-cm wide-field refractor
weight: 1000 lb = 450 kg
maximum instrument load: 200 lb = 90 kg
original list price: $12,740.00


It's a Good Idea to familiarize yourself with the location and operation of everything listed in this section with the lights on (or during daytime) before you begin your first observing session.

The detailed instructions for multi-step procedures appear in the next section.

emergency information

The nearest telephone is in the dome on the upper level:

The circuit breaker panel for the 16-in dome is on the wall of the lower level, to the left as you enter the main door.

A type ``BC'' fire extinguisher (liquids & electrical) is mounted on the lower level of the 16-in dome, just inside the main door on the left.

The nearest type ``ABC'' fire extinguisher (paper/textiles, liquids, & electrical) is in the main building, just inside its main door on the left.

ground-level doors
The exterior hooks and eyelets are used to secure the door(s) open so they don't swing loose. (Unexpectedly walking into a metal door in the dark is painful and embarrassing)

light switches
The three lower level light switches are located just inside the door, to the right as you enter the dome:

The two upper level light switches are located on the dome wall, just at the top of the spiral stairs:

If you need to use the white lights during observing (e.g. when shooting dome flats) be sure the dome slot is closed first so you don't dazzle other observers at the site or contaminate their observations!

trap door at top of stairs

The ladders kept in the upper level can be useful for reaching the dome slot crank, finder scope, guidescope, etc.

dome slot crank
Dome is opened and closed manually using the hand crank at the lower right corner of the dome slot.
(Possible complications: can freeze shut in winter.)

dome slot position
Dome rotation is motor-driven, manually controlled using the 3-button heavy-duty control ``paddle'' mounted on the southwest corner of the pier: If you start the dome moving one way but want to change direction, you'll need to press STOP and then wait until the dome rotation has completely stopped before it'll go in the other direction.

Two positions for the dome are marked by alignment arrows at the boundary between the movable dome above and the fixed wall below. When the dome arrow lines up with the wall arrow marked ``H'' (west of south) the dome is in its ``Home position''. Similarly, lining up the dome arrow with the wall arrow marked ``F'' (east of south) puts it in its ``Flat-screen position''.

(Possible complications: can freeze in winter.)

telescope power and drive control units
Locate the three separate electronics boxes which together make up the drive control system. All three are mounted on the underside of the built-in desktop on the east side of the upper level. On the left are two stacked ``Daedal'' motor controllers, and on the right is a Commodore SX-64 ``executive computer''.

Step-by-step instructions for powering up and shutting down the telescope appear in the next section. Most importantly, you'll need to make very sure the Daedal boxes are powered off when you leave for the night so that the telescope doesn't track itself around into its concrete pier.

finder scope
The finder scope for the 16-inch telescope is located on the top of the telescope's ``saddle'' and has a field of view diameter of 5.7 degrees. Transparent field overlays with the finder field size drawn are available at Wallace in the red binder labelled ``WAO 16-in'', for use when observing with the star atlases at the observatory.

(Possible complications: mount doesn't permit easy position adjustment, so tolerating small misalignments may be more time-efficient than trying to recenter super-precisely)

RA and Dec clamps
This telescope is slewed manually. Locate both clamps, which look like black wheels: the declination clamp is located on the west side of the telescope mount, and the RA clamp is located at the south (lower) end of the polar axis. Both clamps release counterclockwise and clamp clockwise. Release and clamp the clamps smoothly in order not to jar the telescope position.


For the above reasons slewing this telescope is really a two-person procedure, for which instructions appear in the next section.)

setting circles
Setting circles are located behind plastic windows in the telescope mount near the manual clamps. Once the telescope is powered on, dim red illumination of both setting circles is controlled by a small silver toggle switch, located on the west side of the telescope mount between the declination clamp wheel and the main counterweight.

The setting circle around the polar axis is marked in hour angle rather than right ascension. (HA = LST - RA) The markings run from 0h to 6h, then back to 0h, then back to 6h, so you need to mentally account for quadrant ambiguity.

motion/focus control paddle
Controls for fine motions and focusing of this telescope operate when telescope power is on and are located on a control box (``paddle'') connected through a wire to the base of the telescope. The arrangement of controls is shown here:
[control layout diagram]
Figure 1: Motion/focus control paddle for 16-in telescope

(Possible complications: paddle cable getting wrapped around and caught on things; accidentally stepping on paddle)

objective baffle
A baffle made of sheet metal is bent around the open end of the telescope tube and held in place with metal bands with screw closures. It's designed to block stray light which would otherwise get into the telescope's optical path and contaminate observations, and so will normally be left in place when observing. This is just as well because messing with the baffle is a real annoyance!

The only known circumstance in which observers have to deal explicitly with the baffle is flat-fielding for a CCD instrument, because the baffle self-shadows the flat screen. Instructions for shooting ``dome'' flat frames appear in the next section.

C8 guidescope
The C8 offset guidescope permits use of guide stars several degrees away from the field being imaged, useful because the large field of view increases the chances that a brighter guide star can be found. This rectangular ``guidescope capable area'' extends 4.5 degrees north of the target of the 16-in telescope, 4.5 degrees east, 1.0 degree south, and 6.0 degrees west; its boundary is indicated on the atlas overlays for the 16-in telescope. The guidescope's focal length is 2000mm. Schematically, the guidescope has the following appearance:
[guidescope diagram]
Figure 2: C8 offset guidescope

Instructions for using the guidescope appear in the next section.

flat-field screen
A white screen target for ``dome flats'' is fastened to the inside of the dome, to the right of the dome slot. Instructions for shooting dome flats with a CCD instrument appear in the next section.

other telescope accessories
Smaller accessories such as eyepieces are kept in the dome in a black plastic case. The 16-in case is ``Kit A'' and contains the following:

star atlas
A laminated copy of Sky Atlas 2000 lives in the dome.

A speaker on the upper level brings in one channel of the vintage Wallace stereo. There's a crude volume control hung inline on one of the speaker wires.


[ 3.1. Powering up | 3.2. Slewing | 3.3. Changing side of pier | 3.4. Guiding | 3.5. Dome flats | 3.6. Shutdown checklist ]

3.1. Powering up the telescope

  1. Turn on the AC power outlet strip mounted on the outside of the right-hand support of the built-in desktop.

  2. Turn on the power switches of the two drive controller boxes. (the switches will light up)

  3. Unlatch and remove the Commodore computer's front panel to reveal its keyboard. (The Commodore should have powered up when you turned on the AC power strip on because the computer's inconveniently-located power switch, located on the left side of its back panel, is normally left ``on''.) If you need to adjust the brightness and/or contrast of the Commodore's display screen, find the controls behind a door to the right of the disk drive.

  4. Find a 5 1/4-inch floppy disk labelled ``16" Driver Disk'' in the Commodore's disk drive.

  5. To load and run the program, simultaneously press the ``Commodore key'' (bottom left) and the ``Run/Stop'' key (just above it). Alternatively, type load "drive",8 then type run

  6. The display screen should clear and then read ``PRESS CTRL-SHIFT-SPACE TO CHANGE SETTINGS,'' and you should hear the telescope RA motor start running. The rates are initialized to the following defaults:

    Table 3: Initial settings for telescope motion rates
    RA track = 14.32
    RA guide = 3
    RA set = 15
    Dec track = 0
    Dec guide = 3
    Dec set = 15

    The control program is menu-driven, so to change any of the rates just follow the instructions!

    If you temporarily leave the dome unattended it's prudent to to turn off the tracking by using the control program to set the track rates to 0, so that the telescope doesn't track itself around into its pier if you unexpectedly don't come back in time.

    (Quirks: The telescope paddle controls don't operate while the program is in a ``change settings'' menu. Also, suspicion that the units of the rate settings aren't really the ``arcseconds per second'' they claim to be, because if they were then the correct RA track rate would be something like 14.97.)

3.2. Slewing the telescope

Slewing this telescope is really a two-person task because the location of the RA clamp makes it impossible for a single person to simultaneously control both clamps while continuously keeping the firm grip on Dec counterweight bracket needed to prevent the unclamped telescope from swinging away out of control when aiming.

  1. Get a helper, who will act as voice-interface to the RA clamp! Have him/her take position at the base of the polar axis and prepare to operate the RA clamp. Here's what the helper needs to know about operating the clamp: The observer meanwhile needs to speak up to be heard by the helper over the noises of the tracking motor.

  2. Turn on the red perimeter lights so that you can watch where the telescope is going when slewing, and avoid collisions.

  3. Gauge where you'll need to stand in order to be able to do all of the following: Usually you'll need to be on a strategically-placed ladder to reach everything.

  4. To start the slew, take your position and use your left hand to hold the telescope firmly by the horseshoe-shaped Dec counterweight bracket attached to the telescope's ``saddle'' mount. Maintain this hold on the telescope continuously whenever either or both of the clamps have been released, because letting the telescope ``go free'' can lead to dangerous surprises.

    Assume the telescope has been left way out of balance until and unless you personally determine otherwise! When properly adjusted after an instrument change it'll be only somewhat out of balance, intentionally, to improve tracking and guiding by taking up mechanical backlash. But you can't determine the balance just by looking, and you need to understand that if it's not properly adjusted it could be strongly torqued, in which case loosening a clamp without keeping a firm grip on the telescope could lead to a serious accident when it swings away very rapidly.

  5. Carefully release the Dec clamp with your right hand.

  6. Ask your helper to release the RA clamp. Helper should verbally confirm when the clamp has been released.

  7. Now that both clamps have been released you can carefully point the telescope toward your target, sighting along the upper-right corner edge of the saddle and/or viewing through the finder scope.

    Take it slowly! Not only can the telescope and/or instrument collide with stuff in the dome near floor-level (mainly the telescope mount, the pier, people, and ladders left in the way), but the telescope-plus-baffle combination is oversized for this dome and can easily hit the hoist hanging down from the inside of the dome ceiling, high opposite the dome slot.

  8. Acquire your field and have your helper clamp the RA. Hold the telescope steady so the act of clamping doesn't shift the pointing. Helper should verbally confirm when RA has been clamped.

  9. Once your helper confirms clamp in RA, you clamp the Dec, again holding the telescope steady. Alternatively, you can ask your helper to come around and lock the Dec if you're having trouble holding the telescope position while clamping.

  10. One last step before turning off the red lights is to make sure the telescope has a clear path to move east-to-west about the polar axis as it tracks your field. Move ladders out of the way, and make sure any wires, cables, or hoses aren't going to get caught on anything.
Use the paddle fine-motion controls to line up your instrument exactly on your object, and then collect photons at will!

3.3. Moving telescope to opposite side of pier

As mentioned earlier it's not usually necessary to to switch the telescope from the east (usual) side of the pier over to the west side, but if you do need to switch it this is the sequence of slews to do so:

  1. As usual, turn on the red dome lights while you slew.

  2. Unclamp in RA, slew until the HA = 0 (due south), and clamp. Your helper will be able to guide you to the position of HA = 0 by reading the HA setting circle.

    You're about to move the telescope to a rarely-used orientation, in which hitting the hoist with the baffle and yanking out wires connected to the instrument is especially likely.

  3. To avoid these problems, temporarily disconnect (if possible) any wires, cables, or hoses to the instrument and take the next 3 steps very slowly:

  4. Unclamp in Dec, slew carefully until the Dec = +90, and clamp. Use the Dec setting circle to determine the position of Dec = +90. Watch out for the hoist.

  5. Unclamp in RA, slew carefully 12h forward (rotate 180 degrees) until the HA equals the ``other'' 0, and clamp. Watch any wires, cables, or hoses you couldn't disconnect; they're going to be wrapping around the telescope mount and you need to make sure they have the slack they need to not get yanked off. Also watch out for the hoist.

  6. Finally, unclamp in Dec, slew carefully back down to Dec = -48, and clamp. Did we remember to tell you to watch out for the hoist?

    Presto changeo, you now have the telescope in the ``home'' position but on the west side of the pier!

  7. Reconnect any wires, cables, or hoses to the instrument.
Note that the instrument is now ``upside down'' which means the directions of the N and S paddle motions will be opposite what they were on the east side.

When you're finished observing, reverse the procedure to return the scope to the east side of the pier.

3.4. Guiding with the off-axis guidescope

Past experience with this telescope has been that all but the shortest exposures need to to be manually guided in RA. The polar alignment was very good though the last time it was checked so corrections in the Dec direction shouldn't generally be needed for exposure times shorter than about 10 minutes.

Here's a recommended approach for choosing and acquiring a guide star with the off-axis guidescope:

  1. [While planning]
    Use a properly-scaled ``field template'' overlay of the guidescope-capable area with a star atlas to identify the brightest several candidate guide stars before you go to the telescope.

  2. [At the telescope, before acquiring the target object]
    If the guidescope isn't already aligned to point parallel to the 16-in then slew to a bright star and ``make it so''. This simplifies things later because it guarantees that guide star acquisition starts from a known place and that the guidescope will have full travel in both directions.

  3. [Also before acquiring the target object]
    This is also the time to make sure the guidescope's finder is properly aligned with the guidescope: install the C8's visual back and the 40mm eyepiece (for 50x, to get the widest field). Focus the C8 and confirm that the bright star on the finder's crosshairs appears in the visual field of the guidescope. Finder orientation can be easily adjusted now if needed.

  4. Locate your target field with the 16-in telescope and acquire the object in the field of view of the instrument you're using, and clamp in both directions.

  5. Move the guidescope using the RA and Dec gear wheels to acquire your brightest candidate guide star in the guidescope finder. Center it on the finder's crosshairs.

  6. ``Fine-tune'' the pointing of the guidescope to center the guide star in the 50x visual field of the C8.

  7. If you're using a CCD instrument you can make sure your instrument's still seeing the target field by shooting a short unguided test exposure. If it isn't then you probably disturbed the 16-in telescope pointing while fiddling with the guidescope. You'll have to re-acquire your object and try Steps 5 and 6 again. (Just as well you find this out now rather than guide a several-minute exposure on the wrong field...)

  8. Replace the 40mm eyepiece in the visual back of the guidescope with the higher-power 12mm (170x) illuminated crosshair eyepiece, and refocus the guide star. Use the control paddle to make the small adjustments needed to center the star in the field.

  9. Now add the 2x Barlow lens from the accessory kit between the 12mm illuminated crosshair eyepiece and the visual back, for a final guiding magnification of 340x. Refocus and recenter once more on the (now increasingly blobby) image of the guide star. Make sure the eyepiece and Barlow lens are firmly attached to the guidescope and to each other.

  10. Illuminate the crosshairs of the 12mm guiding eyepiece by plugging its cord into the blue 3-volt battery pack from the accessory kit. The crosshairs are illuminated by a red LED mounted in the side of the eyepiece housing. Use the brightness control on the battery pack to adjust the brightness of the LED to a level suitable to see them with your guide star, but no more intensely than necessary.

  11. You'll find it helpful to orient the crosshairs so that movement along one crosshair corresponds to RA and movement along the other corresponds to declination. Use the control paddle for the main telescope to nudge the telescope gently back-and-forth to determine orientation without losing your field.

  12. Use the control paddle to make the final small adjustments needed to bring the guide star to the intersection of the crosshairs. (Some eyepieces have double crosshairs, which some beginning observers find more convenient as they form a ``box'' in which you can put the star.)

You're set to start your guided exposure! Set the control paddle at ``guide'' speed, and make sure you know which way each paddle button will move the star before you start.

When guiding an exposure it's critical that you not smear your exposure by bumping or leaning on any part of the telescope or mount. The proper viewing distance will keep the crosshairs sharp and will reduce the danger of accidentally leaning on the telescope.

After you're finished observing, please realign the guidescope with the 16-in telescope as part of the shutdown procedure in preparation for the next user.

3.5. Shooting dome flats (CCD instruments)

The idea here is to aim the telescope at the flat screen and illuminate it with the white dome lights so you can shoot your flats. The complication is that the light baffle at the open end of the telescope brings the end of the tube so close to the flat screen that its shadow makes it impossible to uniformly illuminate the screen. The workaround is to temporarily remove the baffle when shooting dome flats.

Although it's possible for an experienced user to perform the following steps by him/herself, two people are recommended because removing the metal baffle wildly unbalances the telescope, and getting it back on the telescope is an unwieldy process.

(Possible complications: This process was improvised at the end of a night of observing when Steve S. discovered the just-installed flat screen was unexpectedly being self-shadowed. As such it makes seemingly random use of things that happened to be available in the dome on that night: the taller ladder, the blue battery box from the accessory kit, and the particular location of the red weights on the Dec counterweight bracket. As user you should be aware that if the red weights have been moved to a different place on the bracket as part of rebalancing after an instrument change, you may need to re-improvise for the step in which you prop up the back end of the unbalanced telescope at the correct angle to point it at the flat screen. This would be a good thing to check before you begin observing to avoid a surprise just as you reach what you thought would be the end of a long observing night!)

  1. Close the dome slot, and turn on the white perimeter lights.

  2. Turn off the telescope tracking (set the track rates to 0 using the control program) so it doesn't track off the white screen while you're trying to shoot your flats.

  3. Move the dome to its home position by lining up the dome arrow with the ``H'' arrow on the wall; this will position the dome slot toward due south.

  4. Slew the telescope back to its home position, south and horizontal (HA=0, Dec=-48). Getting the HA right at 0h is especially important.

  5. In anticipation of the telescope becoming very unbalanced in the next step, bring the taller wooden ladder up to the back (instrument end) of the telescope and position it so that the horseshoe-shaped Dec counterweight bracket rests on and is supported by the top of the ladder as shown in ``A'' of the following figure:

    [step A] [step B] [step C]
    A B C

    Figure 3: Pointing telescope at flat screen

  6. [2-person step] With the back end of the telescope tube supported by the ladder use a flat-head screwdriver to loosen the metal bands securing the light baffle at the open end of the telescope tube, and then carefully remove the baffle by sliding it forward off the tube. (Your helper's very important job during this step is to make sure the ladder stays safely put under the back end of the telescope.)

    As you pull off the baffle make sure you don't hit the now-protruding secondary mirror mount, since doing so would ruin the optical alignment of the telescope.

  7. Move the dome to its flat-screen position by lining up the dome arrow with the ``F'' arrow on the wall. This will position the flat screen toward due south, slightly above where the (now much shorter-looking) telescope is actually pointing at the moment.

    Next you'll have to tip the telescope a bit upward to aim the telescope at the flat screen, always keeping in mind that the telescope is now very unbalanced and ready to plummet.

  8. [2-person step] The taller and/or stronger person should stand solidly on the floor, hold the telescope by the Dec counterweight bracket, and lift up the (now much heavier-seeming) back end of the telescope just enough to get it off the ladder support.

  9. In the meantime the shorter and/or less-stronger person moves the ladder underneath the telescope slightly to the left so that the (relatively small) red cylindrical weights on the Dec counterweight bracket line up vertically with the top of the ladder, as shown in ``B'' of Figure 3.

  10. Once the ladder is repositioned the first person eases the telescope back down, this time letting the red weights come to rest on the ladder and battery box, as shown in ``C'' of Figure 3.

  11. Now take a look at the flat screen and see whether it's lit uniformly. If it's obviously in shadow you may need to try and adjust the aiming of one or more of the white perimeter lights to get it better-lit.

    (Complication: getting truly uniform screen illumination with the existing lights in the dome is difficult.)

  12. Shoot your flat frames as appropriate for your instrument and observing program.

    When you're finished, the baffle has to go back on:

  13. [2-person step] Return the back of the telescope to its original position fully on the ladder (position ``A'' of Figure 3) by reversing steps 9, 8, and 7 above.

  14. Replace the baffle by sliding the baffle back onto the open end of the telescope tube and tightening the bands. Try to match the old position; you can tell where it was by the color difference between the uncovered (darker) and usually-covered (lighter) parts of the originally white telescope tube.

    This is probably the most annoying step of all because the baffle is unwieldy while at the same time its fit on the tube is very tight. The baffle has to go on dead straight because otherwise you won't be able to coerce it along the tube. Once it's started you can use the plastic-peen hammer from the tool rack (not the metal hammer!) to shimmy it slowly down the tube by rapping it smartly on its front edge, repeatedly cycling through the four different edge locations at the 12 o'clock position, then 3 o'clock, 6 o'clock, and 9 o'clock. Keep rapping at these four positions in succession until the baffle has crept far enough to reach its regular position. This involves lots of annoying banging noises. Take care not to hit the baffle so hard that you dent the metal!

  15. Clamp the telescope in Dec and move the ladder clear.

  16. If you're continuing observations, turn the tracking back on, turn off the white lights, and reopen the dome slot.

3.6. Shutdown checklist

  1. if you shot dome flats, is the baffle securely back in place?
  2. guidescope in ``home'' position, aligned with main telescope?
  3. telescope in ``home'' position, east side of pier, south and horizontal? (HA=0, Dec=-48)
  4. if you used any illuminated reticles, are they turned off? (so you don't exhaust the batteries)
  5. is the accessory box securely closed? (mice love the foam inserts)
  6. setting circles' illumination off?
  7. motor controllers off? (make very sure)
  8. AC power strip (and thus the Commodore SX-64) off?
  9. Commodore SX-64 keyboard/cover latched closed?
  10. covers on 16-in objective, finder scope objective, and both ends of C8 guidescope?
  11. dome slot in ``home'' position, due south? (blue arrows matching)
  12. dome slot securely closed?
  13. all upper-level lights off?
  14. all lower-level lights off?
  15. outside doors, both left and right, closed securely and locked?


Cassegrain focus
instrument last used
prototype medium-resolution CCD spectrograph 1998
visual back/eyepieces(*) 1999
Lynxx2000 CCD direct imaging(*) 1997
STAR-1 CCD direct imaging 1993
4-in x 5-in plate camera 1991?
35mm SLR camera(*) 1990

(*)'d instruments can also can be used on the C8 guidescope.

16-in finder                        (5.7 degrees)
16-in eyepieces on visual back      
16-in Lynxx2000 + PFE-1 0.5x        (acquisition eyepiece ~18', CCD ~3.1' x 4.1')
16-in STAR1 + its PFE               (CCD ~7.5' x 11')
16-in 35mm SLR camera               (~18.4' x 27.6')
16-in 4"x5" plate camera            (1.30 deg x 1.62 deg)
16-in Prototype Med. Res. Spec.     (slit 1.8" wide by [??]" long;
                                     25mm acquisition eyepiece ~14' diameter)
guidescope range of acquisition     (4.5 deg N, 4.5 deg E, 1.0 deg S, 6.0 deg W)
guidescope finder                   (4.9 deg)
guidescope eyepieces on visual back 
guidescope Lynxx2000 + PFE-1 0.5x   (acquisition eyepiece ~38', CCD ~6.5' x 8.6')
guidescope 35mm SLR camera          (41' x 61')


Idea is to print a hardcopy, draw in indicated field circle(s) with a compass, then photocopy onto a transparency.

Reproduction scales of sky atlases:

        Sky Atlas 2000 =  8.41'/mm = 505"/mm
      Uranometria 2000 =  3.23'/mm = 194"/mm
 Millennium Star Atlas =  1.67'/mm = 100"/mm
        Pickles charts = 0.285'/mm = 17.1"/mm
    (default settings)

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