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Thank you very much for the welcome and for your comments, Ian. After quite a long time searching, I did recently acquire a used Celestron MicroGuide eyepiece. Luckily for me, it is in like-new condition. I have not used it much yet, but I am looking forward to comparing and contrasting it with the filar micrometer method in terms of ease of use, precision, repeatability, etc. I will share any details in this thread, of course, and I hope that you will critique and supplement my finding. Clear skies 🙂

Hi Everyone: I hope it's alright that I am cross-posting a topic that I created on CloudyNights a few weeks ago. I am just very much interested in sharing and learning from people in the SGL community, as well 🙂 Recently, I have been working on adapting several microscope filar micrometers for use with my various telescopes. My efforts have been documented in this thread in the Equipment forum started by Josephus Miller entitled "Adventures converting a microscope micrometer to astrometric purposes". I will continue to participate there and post my design and modeling updates. But over the past few months, I have been accumulating notes on some more generalized observations. My purpose in starting this topic is to explore a separate, much broader discussion....and I did not want to hijack Josephus' thread! I have learned quite a bit over the past 6 months about a number of challenges that must be overcome in order to adapt these instruments for astronomical use. This thread is for the purpose of sharing what I have learned to date (and to seek clarification/corrections on my knowledge), but also to hear from others in the community about their experience on the subject. Please forgive the long-winded introduction of this first post. I am simply trying to frame the topic as best I can, and to provide some background as to where my current efforts have taken me. I am not an expert on astrometric filar micrometers. I am, however, quite knowledgeable regarding the filar micrometers employed in microscopy. I used them for many years doing biomedical research. About six months ago, I decided that a filar micrometer eyepiece was the the one accessory I wanted most for my newly resurrected 127mm Meade ETX-125 telescope. My son and I have been wanting to train our glass on double stars recently, and I thought it would be fun to see if we could measure separation distances and position angles. As it happens, I have a few decent microscopes -- including a high quality vintage Bausch & Lomb. The scopes seemed like the perfect testing ground for evaluating microscope filars, and how they might best be suited for astronomical use. There were four overarching goals/requirements for me in building the adapter, namely that it should: 1. Function independently of the choice of telescope. It must be easily portable between a 70 mm refractor, a 90 mm MCT, a 114 mm Newtonian equatorial, a 125 mm MCT, and a 200 mm Dobsonian. This requirement more-or-less dictates a focuser-based solution, and excludes a pre-objective solution (e.g. two of the scopes have neither a dew shield nor spider vanes to attach an LED). 2. Function with any of the micrometers in my library. Some of them have differences that need serious design considerations such as novel barrel attachments, differing nosepiece configurations and lengths, etc. Some of the differences are more minor, but still need attention (the microscope barrel set-screw locations and clearances, for example). 3. Include an integrated 360-degree protractor to allow position angle measurements of double stars, comet trajectories and magnetic field orientations of sun spots and solar prominences. My desired measurement precision is +-30 arc minutes. 4. Work equally well with my homemade 1.25” astrometric reticle eyepiece (thread link here) or any other 0.913" reticle microscope eyepiece that I want to use. If you've read the earlier postings in Josephus Miller's thread, you know that the conversion projects for all of us contributing have been interesting...and at times somewhat frustrating! There are no companies currently producing filar micrometers for astrometric use. And if you could find one, they would likely be prohibitively expensive. This pretty much leaves us hobbyists to either build/print one from scratch....or to adapt one originally designed for microscopy. During my journey, there was a critical evaluation process to determine which designs are most easily adaptable for astrometry, and a bunch of challenges that need addressing. OVERALL CONDITION It is worth mentioning at this point that I ended up ordering 17 different micrometers over the past five months. I did not keep them all, but I did end up purchasing a few. The reason I assessed so many is because of the appalling condition that many of the micrometers were in. For example, I received micrometers that had: 1. No filum line whatsoever (the slide was either broken or missing) 2. Dial gauges so far off that they could not be calibrated 3. Scales that were out of linear alignment with the filum 4. Scales wandering or not well-attached to the sled 5. Internal mechanisms corroded, damaged or otherwise compromised. 6. Loose or frozen sled and/or diopter focus threads 7. Missing lenses, screws and/or other hardware The good news is that eBay folks are usually pretty understanding. Every micrometer that had a fatal flaw — or was in some way unusable — was refunded without incident. There were even a few sellers who told me to just keep the defective micrometers cost-free, which has turned into a real blessing. I now have examples of Bleeker, B&L and Unitron units that I’ve been able to experiment with worry-free. I've taken them apart several times now, a real boon to familiarizing myself with the interior mechanisms, and evaluating the construction quality. FILUM/SCALE SETUP I have an old Unitron 10x .01 mm filar micrometer from years back. A quick look at the 45 degree filum/scale setup reveals that not every microscopy filar eyepiece is well suited to astrometry. In fact, out of the 17 units I looked at from 8 different manufacturers, I dismissed six models outright due to the filum/scale orientations. The Unitron 10x 0.01, Nikon 10x, Zeiss Jena and one of the B&Ls had arrangements that do not seem well suited (the B&L filum/scale setups can vary within the same model, go figure 🙂 Here is a short compendium of the problems: 1. Scales toward the top or bottom of the field of view that would be difficult to use or even to drift-calibrate. You could probably get away with one of these, as long as the filum is horizontal. But I don’t think it would be optimal. The optics on most of these microscope filar micrometers are not of the highest of quality (with some exceptions), and making precise measurements at the extreme edges of a Huygens or Kellner eyepiece would seem an unnecessary handicap. Layout of the Nikon micrometer: 2. Filum at a 45 degree angle to the horizontal scale. These would be almost impossible to drift-calibrate or use against a dark sky. Calibrating an astrometric filar requires either a sidereal drift test along a straight axis, or a distance measure between two stars of precisely known angular separation. With a 45° filum, the first of these tests would be impossible, and the second would be difficult, at best. Layout of the Unitron 10x .01 mm and Olympus OSM micrometers. Some Zeiss Jena models also have this layout: 3. A filum and scale that never actually touch. On a well lit microscope stage you have the leisure of placing the filum at a starting/zero point, reading the scale, and measuring how far the filum moves to the endpoint....all while drinking a cup of coffee 🙂 Under such circumstances, it’s easy to imagine how a filum that is close to the scale but doesn't touch could be fine for microscopy. But stars and the entire sky move constantly. Which means we need to have a fixed zero point on a horizontal scale, and then be able to place the filum at the end point of our measurement all the while insuring that the zero point is still correctly placed. That really requires a horizontal scale and vertical filum that intersects it (refer to the Nikon image above. It's a good example of this). On the other hand, here are some examples of filum/scale setups that work well for astrometry: Bleeker / Bausch and Lomb: Unitron 10W: WEIGHT Here is a table of weights of the various micrometers that I have available: American Optical 10x .......... 161 grams Bausch and Lomb ............... 196 grams Bleeker .............................. 231 grams Leitz Wetzlar ...................... 353 grams Unitron W10 (Mitutoyo) ....... 306 grams Zeiss K15x ......................... 412 grams OPTICAL QUALITY Not surprisingly, the quality of the optics varies widely among the models. I’m only going to offer general impressions here, mainly because the age of these units may play a significant role on the residual quality of the optics. I’ve only seen a few examples of each particular manufacturer (and sometimes only one), so other folks may get a unit that is in much better condition than mine, and their optics might be exceptional. In short, my real-world experience is limited to only a few examples, so I will keep it honest 🙂 Here is a list of the best to the worst based on my collection: 1. Unitron and Bleeker are tied for #1. Both appear to have excellent ocular and field lens sets. I actually have seen three different Unitrons and two different Bleekers, and they are all outstanding optically. 2. Zeiss does not disappoint in any way. If the K15x unit that I have was not so heavy, I would not hesitate to use it or recommend it. On the other hand, I am still evaluating some interesting features of its novel, hybrid-45 degree scale and filum setup, and may eventually "light it up" to see how it fares. Strange filum/scale in the Zeiss K15x. A combination of perpendicular and 45 degree lines: 3. The Leitz Wetzlar optics are very nice. I have only seen one example, to date, but it is almost on par with the Unitron and Bleeker. The only negatives are the length of the nosepiece (considerably longer than any of the others) and, subsequently, the weight. 4. The Bausch & Lomb‘s are very good. They’re really not always that great out to the edges (I have seen 5 of them), but they are definitely better than the American Optical and Nikon. Overall, I would say they’re completely acceptable. 5. The Nikon optics were decent, but nothing to write home about. Due to the poor filum and scale layout, however, I would never recommend one for astrometry. 6. I’ve seen two examples of the American Optics. They’re OK, but they don’t seem to be a very sophisticated lens set. I get a lot of kidney-beaning, and the focus tends to drift radically as you get toward the edge of the field. CHALLENGES 1. Diameter of the nosepiece barrel/tube - There are two issues to deal with regarding the nosepiece. The first is pretty simple: Microscopes have a 23.2 mm (0.913") inside-diameter barrel. Likewise, we need an adapter to bring it up to the standard telescope barrel size of 1.25” (or 2" in some cases). Years ago, this was probably a significant hurdle to overcome unless you had a machine shop (or knew someone who did). Today, eBay has the answer. You can order one of these adapters for $8 delivered. It will work for most filar micrometers, but not all. The second nosepiece/barrel problem has to do with differing methods of attachment. Some of them have a nosepiece that slips into the microscope tube (most common), and others have a nosepiece that slips over the tube. Still others have a very narrow radius/space within which to slip an adapter. The B&L, Bleeker and American Optical (with minor modification) all work well with the aforementioned eBay adapter. For others, you need to construct a suitable adapter by either machining it or coming up with some sort of "Rube Goldberg" solution. 2. Illumination of the filum and scale - Microscopes have plenty of light coming from beneath the "stage" (the platform where the slide sits). But when pointed at a dark sky, there is no light at all to illuminate the filum and scale. This is a significant challenge, but there are several ways it can be overcome. If you are curious about the ways that I and others have solved the issue, feel free to read the thread linked in the first paragraph of this post. There are many other useful posts elsewhere on other sites, and from other CN members. My initial desire was to develop a “dark-field” solution (i.e. delivering illumination in a perpendicular direction to the long axis of the telescope so as to minimize longitudinal scatter from the light source). A quick review of my posts on the subject reveal that my dark-field experiments were not very successful. Planting micro-sized LEDs in the body of a micrometer was not terribly difficult. However, the optical geometry of the components -- and the room available and obstructions within the micrometer bodies themselves -- made it very difficult to “light up” the slides etched with the filum and reticle scale. I have not given up totally on a dark-field solution, but it likely requires drilling small holes in the micrometer body and placing LEDs at optically strategic locations. Also -- while dark-field illumination may be optically preferable -- it lacks the convenience of mobility, since each micrometer would need to be "wired" internally to accommodate it. The current working model that I have provides "bright-field" illumination (i.e. from the direction of the primary lens/mirror). It is based on an inexpensive ($5 USD) Barlow body from SurplusShed.com. It works quite well, actually. It is my own design, but I drew from strategies that other folks had posted about and employed (such as this one from NinePlanets). Building it required relatively inexpensive hardware easily found on eBay, Amazon and/or the local hardware store (micro-LEDs, a small potentiometer, resistors, cyanoacrylate tape, soldering tools, etc.) For anyone interested on the evolution of my bright-field design, have a look at the posts starting here. 3. Addition of a 360 degree protractor scale - If you want to measure position angles of double stars or other things like that, you'll need a 360 degree scale and an accurate pointer. I am still working to perfect my own solution to that problem, but it's not a technically difficult task. You can see the current state of my modelling efforts in this post. Hopefully, I'll be making more progress on it in the next month or two. COST/QUALITY EQUATION In taking a few of these units apart and evaluating them from the inside out, it’s very clear that there are a wide variety of quality and cost prospects to consider. 1. The B&Ls seem to be real workhorses. The construction quality is pretty good, and the mechanisms seem to hold up well over time. On the other hand, the micrometer wheel components and internal construction are not the absolute highest quality (cast threads, stamped dial gauges, exposed springs, etc.) BUT (and this is a very big “but”) the materials used and the way they are constructed makes them among the lightest of all the brands/models I’ve tested so far (beat only by the American Optical 10x). Since astronomy geeks like us need to balance these hunks of metal off the end of a focuser, that weight difference could be a very big advantage. The other nice thing about the Bausch & Lomb is that they are plentiful (at least here in the U.S.) I’ve been finding them advertised at prices as low as $30 shipped. To me, that means that — should you choose to use a B&L for your conversion — one could build up a library of spare parts fairly easily and inexpensively. 2. The Bleeker has the feel of handmade quality across-the-board. They are very nicely kitted out, with beautiful optics and well-made components. The dovetail sled that carries the filum slide itself is a thing of engineering beauty. The micrometer screw is a little nicer than the B&L. They are, in fact, very close in weight to the Bausch & Lomb. All of the other units I’ve tested have been heavier than these two. 3. The two Unitron models (10x .01 and W10 0.001) are both exceptional in every way. Only the W10 has an adequate filum and scale layout for astrometry, but the quality of materials and craftsmanship for both is outstanding. The micrometer dials and screws are 100% machined and utterly professional. The downside is that they are not very plentiful, and I have not seen them come up for sale that often (only 3 examples of the astro-friendly ones have come up in the past few months). If you can get one of the W10 models, I’m sure you will not be disappointed. 4. Zeiss K15x - Not much to say about these, except....wow! VERY nice quality construction, optics and feature set. The scale/filum setup is a little weird (see photo above), but it could work. I am still evaluating this one. 5. American Optical - I have not yet had this micrometer fully open to evaluate the internal mechanism, but it seems to be reasonably well built. The micrometer wheel is professional quality, but the overall light weight suggests (maybe) that the internal mechanism is less robust than some. 6. Leitz Wetzlar - I have not yet had this micrometer fully open to evaluate the internal mechanism, but -- judging from the outside -- the construction quality is really exceptional....on par with the Unitrons and the Zeiss. CONCLUSION (for the moment) That about does it for my "intro" post. I hope that this thread will be a place to accumulate practical knowledge and recommendations for the acquisition, adaptation and use of microscope filar micrometers for astrometry. Thanks to everyone, in advance, for stopping in and participating. I look forward to reading any and all subsequent posts!

Just wanted to post a couple of star test updates for my illuminator. Here are some photos and comments from my first field test. And this was just last night at Valley Forge National Park.

Hello All: I just wanted to follow up with an update on my project status by way of some recent posts that I made on CN. If you’ve read my previous posts, you know that my initial desire was to develop a “dark-field” solution (i.e. delivering illumination in a perpendicular direction to the long axis of the telescope so as to minimize longitudinal scatter from the light source). A quick review of my posts reveal that my dark-field experiments were not very successful. Planting micro-sized LEDs in the body of a micrometer was not terribly difficult. However, the optical geometry of the components – and the room available and obstructions within the micrometer bodies themselves – made it very difficult to “light up” the slides etched with the filum and reticle scale. I have not given up totally on a dark-field solution, but I realize that it likely requires drilling small holes in the micrometer body and placing LEDs at optically strategic locations. For the moment, I’ve moved on to a "bright-field" model that works reasonably well. I would like to play it out through some live star-testing and ultimately (I hope) real-world astrometric measurements. Instinct tells me, however, that very dim DSOs and double-star pairs may get washed out by even the dimmest of bright-field illumination. When (or even "if") I get to that point, a dark-field solution may be the way to go. My methodology for adapting a microscope filar micrometer for astrometry is pretty straightforward. There were four overarching goals/requirements, namely that the adapter will: 1. Function independently of the choice of telescope. By that I mean that it should be easily portable from my 70 mm refractor, to my 90 mm MCT, to my 125 mm MCT, to my 200 mm Dobsonian. This requirement more-or-less dictates a focuser-based solution, and excludes a pre-objective solution (such as an LED attached to the dew shield or spider vanes, etc.) 2. Include an integrated 360-degree protractor to allow position angle measurements of double stars, comet trajectories and magnetic field orientations of sun spots and solar prominences. 3. Function with any one of a number of micrometers in my library. Some of them have differences that need serious design considerations, such as novel barrel attachment configurations, differing nosepiece length, etc. Some of the differences are quite minor but may still need attention (the microscope barrel set-screw locations and clearances come to mind here). 4. Work equally well with my homemade 1.25” astrometric reticle eyepiece or any other micrometer microscope eyepiece that I want to use. The current working model that I have for an illuminator is based on an inexpensive ($5 USD) Barlow body from SurplusShed.com. It works quite well. Though I may well upgrade the Barlow platform once my design has been perfected 🙂 Building it required relatively inexpensive hardware easily found on eBay, Amazon and/or the local hardware store (micro-LEDs, a small potentiometer, resistors, cyanoacrylate tape, soldering tools, etc.) For anyone interested, please have a look at my detailed posts (links below) and provide comments here. I would also be very interested to learn about the direction you chose to go in, Shazzanne1963, and any progress you’ve made. Clear skies 🙂 Protractor Models (very preliminary) Illuminator - Version 1 Illuminator - Version 2 (to address a few design flaws)

Hi Folks: The filar micrometer adaptation project I have been working on is coming along pretty well. I just thought I would provide a link to my recent post on CN. Several of my CN colleagues also have updates in the thread that may be of interest. Clear skies 🙂

Thanks very much, Tomatobro. Please forgive a newbie question, but what is the Sharpcap forum? Edit: Never mind....I just did a search and I found it! https://forums.sharpcap.co.uk/

Just a quick note as I noticed the post by Tomatobro earlier in this thread which mentions the Unitron filar micrometer. I have three flawlessly operating filar micrometer eyepieces: Unitron (Japan), Bausch and Lomb (U.S.) and Bleeker (Netherlands). In this post on Cloudy Nights, I review the issues with the Unitron filar and scale setup for astronomy. In short, the reticle orientation and optics are excellent for microscopy, but the unit is severely handicapped for astrometric measurements. The Unitron has an "X" shaped moving reticle set at 45 degrees to the horizontal scale, and a 0 to 8 scale toward the top of the FOV (diagram below and a detailed explanation here). The 45 degree orientation makes it pretty useless for aligning a telescope with the NCP, and exceedingly inconvenient (being kind here) for double star measurements. The 0-to-8 scale does not help either way. The only application for which I would consider it adequate is lunar geological measurement. An Olympus micrometer that I found on-line but did not ultimately buy has the same problem, and Zeiss also produces filar micrometers with the same or similar scale setups. So....what's my point? (I frequently have none....that's part of my charm :-) Actually, I am just trying to add to the body of knowledge and help my fellow DIY astronomers. To summarize: Unitron, Olympus and Zeiss filar micrometers are not well suited for conversion for taking astrometric measurements (please see my clarification notes below). The Bausch and Lomb and Bleeker micrometers are much better, providing a 0-to-10 scale at the center of the FOV, and a filum set at 90 degrees to the horizontal. BTW - I have also run into problems that have nothing to do with the above filum "orientation" issue. Two of the micrometers I have are unusable in spite of being perfectly capable optically. Those problems range from cockeyed scales to out-of-calibration dial gauges to other vintage hardware related issues. Edit: 24 Feb, 2024 - Since I originally posted this, I have acquired a Unitron W10 micrometer as well as a Zeiss K15. I also tested a Nikon 10x micrometer. The filum and scale setup on the Unitron W10 is absolutely perfect for astrometry. It has an intuitive scale along the midline (horizontal) axis of the FOV, including a long vertical line at the center. The filum is an identical long vertical line that can move from one horizontal extreme to the other (this setup is almost identical to many astrometric filar micrometers). The Nikon reticle setup is exactly the same as the Olympus. Both are very poor choices IMO. The Zeiss reticle is interesting, to say the least. It is far too complicated to describe here in words (I'll provide photos one of these days). I believe, however, that it may be a good choice. I will continue to star-test it, and post my results here in the near future.

I just came across your thread, and I thought I would chime in since I'm in the process of adapting a microscopy filar micrometer for use on my ETX-125. Here is one of my posts in a recent thread on Cloudy Nights that discusses that project (hope it's OK to post that here :-) And this is an article from December of 1999 by a South African astronomer that may be interesting to you. It is about his/her project to design a filar micrometer for double star observation. I look forward to read any updates on your efforts! 🙂