Thursday, January 21, 2021

Baader-Planetarium Micro-Guide Reticle

This eyepiece can serve any amateur astronomer who wants to make their own measurements of separations and positions of binary stars or the extents of features on the Moon. Given some facility with this little tool, you could probably measure anything you can see. 

It is called a “Log Pot Illuminator” because the brightness control is logarithmic: you have to turn the knob much to make it a little brighter or a bit dimmer. In other words, it delivers very fine control. (“Pot” is short for “potentiometer” an older word from the early days of electricity for a volume control, gain, or variable resistance.) You sharpen the image of the scales by turning the top screw mount of the ocular. It is very simple and intuitive. You focus the eyepiece as you would any other, by focusing your telescope.


The instructions are direct and easy to understand. From my point of view as an American technical writer I found some gaps in the narrative. (I have worked for German companies before, including Zeiss.) They tell you exactly what you need to know and not one word more. But everything was grammatically and syntactically correct. 

The Metrical View Plate

My three nights of use did not go well. 


First of all, things move pretty fast. The first two nights, my telescope was a Meade 10-inch “Advanced” Ritchey-Crétien (focal length 2500 mm) fork mount with manual controls. The challenge of targeting was like trying to snatch a housefly out of the air. My first projects were to measure the diameter of Mars, the width of the Trapezium in M42, and the separations of the brightest stars in the Pleiades. My eyes could not move fast enough to measure the objects against the tics. You might be more agile. But this really required a motorized drive to hold the telescope on target or a camera to record the view or both. 


Another of the procedures is to align the reticle with the celestial equator. The way to do that is to find a star and position the reticle so that the star tracks along the horizontal metric bar. I chose Rigel. Manipulating the reticle and the two axis controls was a juggling act. It likely would have gone better with the electric drive control paddle. Turning two knobs and twisting the reticle was hard work for a creature without a third manipulator. 

The next night, I tried a smaller telescope, an Explore Scientific 102 mm refractor f=660 mm with First Light mount (simple tilt-pan XY). I ran into a problem that I experienced earlier with this instrument: the focal draw cannot be short enough. In the earlier failure, I was viewing Venus; and to cut the glare, even a moon filter was not enough. I added another filter and hit a hard stop. The draw would not go in far enough to focus. (That morning, I was able to use two filters with my 70 mm National Geographic refractor.) The same thing happened here. With the diagonal in place, focus was impossible. Without the diagonal my posture was difficult to obtain and impossible to hold. So, I gave up.

$279 or €229 from Baader or a Selected Retailer


I have one more telescope that can work. (The National G 70 mm above is five years old and is held together with rubber bands. Nice as it can be as an f/10, it is too wobbly for consistent small moves.) 

Added 05 February 2021

(As reported to The Sky Searchers discussion board "Eyepieces" forum.)

I viewed the Trapezium in M42 and measured it as 1 division. It was pretty easy to align the Baader and let the stars drift across the scale. I did that several times. I calculated the size of Trapezium as 29 arc-seconds by 29 arc-seconds. Burnham's gives 12x13, but I am pretty happy with the first try. 

I also viewed Eta Cassiopeiae. They are close together, so I let them drift across the scale and measured them against the center between the two rows of divisions, which Baader says is 35 micrometers wide. From that, I calculated a separation of 10.3 arc seconds. I found online from a report at the Havering Astro club UK 13.4 arc-seconds. Again, I was satisified with the first attempt will try again another night.

The last instrument in my inventory is a Celestron EQ 130 f/5 Newtonian reflector. As an equatorial mount, manual tracking is with one hand once it is aligned. In fact, one of the calibrations that the reticle allows is to test and adjust polar alignment. But the telescope is resting in its cartons in the garage. If I decide to follow through on this, I will report it here.


I have one other unresolved problem. I still do not know how to change the battery. They have helps on their website, but no answers to the questions. They tell you which cell designation to use. They do not tell you where it goes. When I unscrewed the two pieces of the reticle itself—not the illuminator—I found a wire (which I accidentally tore out and had to re-solder.) So, at this point, I do not want to struggle with it any more. 

The instrument came to me on loan from a friend I met online, username JohnDonne on The SkySearchers. Of course, I bought him a new replacement. This one is is packed away. If I buy a telescope with a motor drive or if I buy a camera for astrophotography, I may take this up again, but I will most probably sell it at a discount to someone else in my local astronomy club and get my measurements from standard stellar survey catalogs.



Assign a Number to It, Said Lord Kelvin

Neutron-Irradiated Dimes

Blink by Malcolm Gladwell

Slow Down and Think

The Unit Circle

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