Tape with telescope balance position marks

[starguest]

Whether you have one or more scopes and need to remount them for every session, it's worthwhile putting some white gaffa tape on a suitable spot to indicate the balance point. Having the scope balanced for movement in its axes is an essential part of smooth and enjoyable viewing. This applies to owners of fracs, cats and newts on EQ or Alt/Az mounts and is a useful exercise for daytime or a well-lit room on a cloudy night!

Short version:

Balance a scope/EP/accessory combo, stick a piece of white gaffa tape somewhere and mark it with a pen; balance another combo, mark its position, both using suitable acronyms. Do I need to say that white tape marked with dark indelible ink is easily seen?

Oh yeah, before going to the end. It's so useful to have a couple of spots of tape on the moving DEC and RA parts and another pair on the head with a vivid mark at each where the parked home position should be.

Long version:

I understand there can be combinations of those with GOTO/non-GOTO mounts, eyepiece (EP) weights, binoviewers and those interested in imaging - dedicated or part-time - so making for a range of simple to complex marking requirements. This text is swayed more for general observing usage and, even if using a GOTO, should allow you to have fairly accurate marks when circumstances mean that you want to very quickly set up a given scope/EP and just manually move it to observe something knowing the balance will be ok.

There might be an argument for making notes on paper or on a page of your observing notebook where complex setups arise, but this text deals with using a roll of white gaffa tape and marked strips of it stuck onto suitable parts of equipment.

There are some smaller scopes whose mounting foot is not actually a fully "sliding dovetail", IOW it's notched in some way so it only fits on the mount head in one position. If one uses heavier EPs then balancing in DEC (declination, or pivoting the scope body around the axis of the counterweight shaft) may mean using some extra attached object to the front of the scope.

Of course that means there is a heavier load to balance in RA (right ascension, or when the scope and counterweight shaft are pivoted making the shaft horizontal) meaning a new counterweight position.

I just included that simpler style for completeness, to show that it can also benefit from some tape marking.

Doing the marking.

For the RA balance with 1 or more counterweights, one might be tempted to put a strip of tape around the shaft. This has its problems. The main one being when the weight(s) have to move past the tape and the internal gripper snags on the tape and begins to tear it. Or for shafts which slide into the mount body, the tape may mean it's too big to slide into its hidey-hole.

So, I suggest sticking the tape to the mount head and they all seem to have one or more suitably flat surfaces. This also means that you have space to make suitably annotated marks.

First, use a piece of plain paper and pencil to experiment with. You can easily rub out trials of line and letter size markings. Mark a box that is the same area as that to be used on the mount head.

Within the area corresponding to what's available on the mount, draw seperate boxes for each scope. Note that I happened to use 25mm wide gaffa tape and the mount could take 2x 120mm strips on one side. I could see that each strip could divide up into 3 or maybe 4 sections if you had that many scopes!

These sections 25mm x 40mm (or 30mm) are enough to have the little marking drawings be easily seen, though I need glasses to read such a close distance.

Sorry, not in a position to submit photographs.

Anyway, the idea is this:

strip 1 : S [newt][frac][cat]

strip 2: BV [newt][frac][cat]

Each section is for the scope type and will have a little drawing showing where the counterweight(s) will go on the shaft. The strips are for 'S' or Standard setups and 'BV' for Binoviewer heavier setups where the weight(s) need to be different. Section for Newtonian, Refractor and Cat (SCT or Maksutov) as examples.

The idea is to draw a horizontal line (A) representing the shaft length, and a block ( at one end of the line for where the shaft meets the mount head. You then draw a little vertical line on (A) where the counterweight should be. The distance from weight to mount head can be simply done using one's hand. Compare the distance to a hand-width and/or fingers - gloves might be important!

With 2 or more counterweights draw a separate vertical line and check distance from its neighbour.

Decide for yourself how to easily annotate the marks. I.E., for spacing of a hand-width or two - 1HW ,2W. Fingers, thumb, pinkie - 1F, 2F, 1T, 1P etc, etc.

I'm sure you know what I'm getting at, as there's the issue of marking space available. I don't intend to insult your intelligence.

Make a suitable acronym for the scope, use its name or model or type. If you have a Newtonian 200mm (8") and a refractor 120mm (5") then maybe using 200N, 8N, SW8N (skywatcher), 120R, 5ACH (achromat) is ok. Your choice!

I don't know if the formatting here will allow an above/below style to illustrate, but here goes to show what each little section on a strip might show. The [ represents the mount head ( above, and the -- is the shaft (A) above, with a c/weight shown by +.

S 200N

-+-+--[

P 1W

120R

-+--+[

4F

The S for Standard setup would be at left of strip then 2 sections: one for a 200mm Newtonian, the 1st c/weight is a hand-Width away from mount head and the 2nd c/weight is a Pinkie away from 1st. Then there's a 120mmm Refractor, the 1st c/weight is right next to mount, the 2nd is 4 Fingers away from 1st.

The marked section on the strip would have the 200N at top, the line drawing below and the spacing (P 1W) below that. The next section on the strip would be have same layout for next scope type.

That leaves us with the DEC marking.

Unless you don't mind putting gaffa tape onto the tube - which actually would be a bit imprecise - then a strip of tape will have to go along the dovetail side. Also, some mount heads, standard or 3rd party, have different ways of securing the dovetail and I don't know if the wider Losmandy type dovetail leaves a suitable flat area on its top side (not the dovetail gripped edge) that might allow a tape strip.

Anyway, as each scope will have its own dovetail ,there is minimal marking required. The 2 points that may affect where and how you use the tape strip are:

if tightening screws use the screw-head to bite into or drive a slab-side block against the dovetail edge;

which side of the mount the screws are placed so you can easily mount the scope and use one hand to steady and the other to tighten.

I'm assuming the screws are on left side of mount - West facing side with the correct tripod leg and c/weight shaft facing North (in the Northern Hemisphere). So, you will put the dovetail in the head puck and steady the scope with your right hand and tighten screws with your left.

If you had already put the tape strips for c/weight position on that left side then all the better.

If the tape has to go onto the dovetail edge itself then obviously that will be the left side. You now need to decide which end of the head puck is the reference, the front end toward North or the back end. Check how far the dovetail will slide depending on the accessories' weight.

The strip of tape needs to be cut to allow for the different positions of the dovetail. Probably the height of the dovetail edge is about 10mm, which is enough to make a vertical line on the tape and an adjacent acronym.

I.E. you might have |S |BV |C meaning this is Standard weight EP, Binoviewer, Camera position as appropriate. Or you could just use no acronym, a + mark, or a ++ mark. The | line will line up with the chosen puck head end. Again, your choice of mark.

I mentioned the tightening screws above and possibly they might bite into the tape strip at some point where you make a mark depending on setup. A possible way around this is to use both front and back puck edges, just see where the marks have to go.

That's it! I know it's a long and wordy post for a fairly simple aid but I wanted to lay it out as comprehensively as possible as I can't put up photos.