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How-to Make an Astonomical Eyepiece out of Microscope Eyepieces



One of the best eyepieces I have in my collection for astronomical use is a Zeiss E-PL 10x/25 highpoint microscope eyepiece ( Zeiss # 44 42 36 ). This eyepiece provides a razor sharp, high contrast image when used with my 80mm f6.5 Brandon APO refractor. The apparent field of view seems to be between 55 and 60 degrees with an eye relief of about 20mm and a focal length of 25mm. I would match this eyepiece in quality with any astronomical eyepiece I have ever used.

Like telescope eyepieces, microscope eyepieces come in a couple ( 2, as far as I know ) standard sizes. The larger size eyepieces, such as the Zeiss I own, is designed to fit in a 30mm ( 1.181" ) tube. The smaller eyepieces fits a 23.5mm ( 0.935" ) tube.

The 30mm microscope eyepieces are about 1.75mm smaller in diameter than the standard 1 ¼" size used for telescopes. While the 30mm microscope eyepiece can be used in a standard 1.25 inch eyepiece holder, the fit leaves a lot to be desired.

Found the perfect adapter ... all you have to do is cut the bottom off a 35mm, plastic film can. The inside of the can provides a snug fit for the microscope eyepiece and the outside fits almost perfectly in a 1 ¼" eyepiece holder.

Its just a tad loose, about ¼ mm smaller in diameter than a standard 1.25" telescope eyepiece. You could take up the slack by wrapping some adhesive backed plastic film, such as mylar, around the film can. Personally, I didn't bother with it.

Note that there are differences in film cans from different manufactures. Of the dozen film cans my local camera store gave me just for the asking, one was an oddball that was not suitable for this purpose.

I wish I could provide some photos, but at this point my camera is about as useful as your average boat anchor. Getting it fixed is on my list of things to do.

A disadvantage to the film can adapter is a standard filter for a 1.25 inch eyepiece could not be screwed into it. But it should not be too hard to modify the basic idea to hold a filter.

I have not attempted to adapt 23.5mm eyepieces to a 0.965 inch eyepiece holder as I do not have one. The difference in size is about 3/4mm. While this amount of slop might be acceptable, I think I would try to make an adapter. One possible solution might be some brass tubing available at your local hobby shop. Another possibility could be tubing made for model rockets.

I have found microscope eyepieces are readily available on ebay ( www.ebay.com ) for quite reasonable prices if you are willing to be patient and sort though a lot of candidates.

For those of you who are not familiar with ebay, its the world's largest flea market and auction. With millions of buyers and sellers, you can find just about anything you want. Like all auctions, some deals will be better than others, you just have to pick and choose.

I bought two identical Zeiss E-PL 10X/25 eyepieces in two different auctions. I paid $150 for one of them and about $50 for the other.

Other examples: I saw a working, scanning electron microscope auctioned off for about $2500. I also saw a completely decked out Astro Physics 7" refractor and mount worth about 20 grand sell for $7000. Sigh ... such things are only dollars away.

Ebay provides search capabilities to allow you to zero in on what you want. To find microscope eyepieces you can search for "microscope eyepiece" or "microscope eyepieces". Note that searching for the singular "microscope eyepiece" will not find items listed under "microscope eyepieces". Searching just for "eyepiece" or "eyepieces" will return a list of eyepieces for all kinds of things; telescopes, microscopes, cameras, and things you never heard of.

It also pays to search for "microscope lens" and "microscope lenses". A number of people who sell items on ebay have absolutely no idea of what it is they are selling and list the items using terminology not normally used by people who know what they are looking for.

Many people who are looking for microscope eyepieces do not think to search for them as lenses. As a result, you can quite often get excellent bargains because there are less people who know what they are doing, picking over the items listed under "microscope lenses".

The Zeiss E-PL10X/25 eyepiece I paid $50 for was advertised as a "microscope lens". The one that cost me $150 was described as a "microscope eyepiece".

One final word about ebay, it's also an excellent source for all kinds of optical and photographic equipment. Searching for "telescope" will typically reward you with 600 - 800 items for sale.

Another excellent source of microscope equipment is Tottleben Scientific ( www.tscmicroscopes.com ). They sell all sorts of used and demo equipment for quite reasonable prices and regularly auction items on ebay. Eyepieces are not normally listed individually on their web site, but if you give them a call you will find they always have a number on hand.

The rules for picking microscope eyepieces are somewhat different than for astronomical eyepieces:

  1. Typically, microscope eyepieces are not listed by focal length, but by power. All eyepieces with the same power will have the same focal length. ( The total magnification of an image in a microscope is calculated by multiplying the magnification power of the objective times the magnifying power of the eyepiece. For example, a 40X objective paired with a 10X eyepiece will magnify the image 400 times). Common eyepiece powers are 10X, 15X and 20X. I have also seen 3X, 5X, 8X, 12.5X, and 25X. The powers assume the microscope has a focal length of 250mm. To determine the focal length of the eyepiece divide the eyepiece's power into 250. For example, my Zeiss eyepiece is a 10X. That makes its focal length 250mm/10 or 25mm. The second number on the eyepiece is the diameter of the field stop in millimeters. In the case of my Zeiss eyepiece, the field stop is 25mm.
  2. Many microscope eyepieces, especially older ones, will have very narrow fields of view. You will want to look for eyepieces that are listed as being wide angle. Also, the eye relief can be very short, again especially in older lenses. You will want to look for eyepieces listed as high point. They are designed to be used by people who wear glasses. These eyepieces will quite often have a picture of a pair of eyeglasses on them.
  3. Like telescope eyepieces, there are a lot of poor microscope eyepieces out there. Department store microscopes ( Gilbert, Tasco, etc. ) tend to be even worse than department store telescopes. I know its hard to believe, but its true. Like with telescope manufacturers, they are good and bad names. In general you will do OK with Nikon, Olympus, Leitz, Leica, and Zeiss, to name a few. Bausch and Lomb used to make excellent microscope optics. My understanding is they are no longer in the business, but there is a lot of good Bausch and Lomb equipment out there.
  4. The descriptions for a lot of the eyepieces listed on ebay do not mention the eyepiece diameters. However, ebay provides you the means to ask the seller questions. I recommend you use it.While you do not have the wide range of focal length for microscope eyepieces as you do for telescopes, I believe the use of microscope eyepieces is a resource largely overlooked by amateur astronomers.

Some other uses I have found for film cans. My 1.25 inch diagonal did not have a lens cap for the eyepiece end. I glued the lid on to the bottom of the can I cut off to make the microscope eyepiece adapter. Just slipped it in the diagonal, tightened the set screw a bit, and voila ... a lens cap.

Guess what, didn't have a rear lens cap for my Brandon APO either. Glued the lid on another film can, slipped it in the rear, and tightened the screw a bit. Works great.

Finally, if you have other ideas that can flesh this article out or fill in gaps where I am ignorant. Send them in to the Cloudy Nights web master so he can update the information. After all, this web site is a collective effort.

Also, if you want to reproduce or publish any portion, or all, of this article ... don't bother to ask me if you can ... just go ahead and do it. As far as I am concerned it's in the public domain.




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