A fairly fuss free field microscope concept.

[apochronaut]

So, this is at the concept stage so far, but far enough along for me to have made some optical trials. It wasn't going to go very far, if the optics hadn't panned out but I so far , am reasonably pleased.
One of the basic tenets I am working from is to reduce the complication of the instrument down to as basic a form as is possible, yet retain as full functionality in the form of a wide binocular field, a magnification range from 50x to 800x with no liquid immersion required, a built in rechargeable illumination system, coarse and fine focus, a mechanical stage and as small a size and light a weight as is possible. I would like the option for dry DF as well but that is going to be a project on it's own, after the basic microscope is completed.

Field microscopes are myriad but none I have seen, are capable of fully duplicating the potential of a bench microscope. Some of the very sophisticated small ones are very good or reputedly so; the various McArthur designs, Swift FM 31, the Nikon H and HP and the Chinese Army Field Hospital microscope, maybe the Tiyoda too but some are limited to 400x magnification, others require oil immersion to obtain a full high resolution and none have a truly full wide field image. All are monocular and unfortunately, all are expensive to buy second hand.

An option, is to take a very small conventional microscope and convert it for field use. Most really small microscope frames have sub standard sized optics and so the practical possibility of converting one to a laboratory grade optically, would be low. Even if I decided to re-machine the nosepiece and fit a wider ocular tube to one, the optical pathway is likely too narrow for wide field and too short for good optics.

Larger student grade microscopes that will carry RMS optics begin to get too big or are limited by virtue of their conventional horseshoe base design and they are as far as I can see, all also monocular. I haven't come across one that had or has a binocular option.

I don't have anything against monocular microscopes; in fact I have used them regularly since 1964 but in this case I decided to make a binocular microscope for the field and as convenient and fuss free a one as possible.

The starting point of all this was my realization long ago, that an objective I have had in my possession for about 15 years already, would be an ideal complement to a field microscope but that no field microscope I knew of was capable of accepting it. I set out to find other complementary objectives to it and have recently completed a set of 5, with which to build a microscope. I have further conducted trials with as many eyepieces as I could lay my hands on, in order to find one that most perfectly corrects the objectives, yet renders as wide a field as possible.

The objective in question has no brand on it and is simply marked 80X .90. There is no other designation, such as it's tube length, whether it is cover slip corrected or not or who made it. It was sold to me as a Hacker and from some small amount of research, I have satisfied myself that it is in fact made by Hacker, currently a brand of the the small German company Gerhardt Optik und Feinmechanik GmbH in Hessen. At one time Hacker might have been the brand of the company Hertel and Reuss, of Kassel. Through some testing, I have determined that this is a dry objective, is cover slip corrected, has a parfocal length of 37mm and that it works well with a 160mm tube length.

Recently I acquired 2, n.o.s. CBS ( Christoph Beck and sons...quit business in 1981), objectives to complement it. They are also 37mm parfocal, corrected for 160mm and a .17 coverslip and they look so similar to the Hacker, as to seem as though they might be from the same factory. Whether they are or not, they were new, are virtually parfocal with the Hacker, have excellent N.A.'s and most importantly have a magnification spread that I like for this application, being 10x .30 and 30x .55. My ideal was 5x( which I have: marked only 5x .11 Wetzlar 160mm), 10x, 30x, 60x, 80x; all dry. The 60x turned out to be a problem, for a while. For some time, my searches turned up nothing, until I remembered that I had a very old Leitz Wetzlar 62x. It turns out that, even though it is 170mm, it seems relatively unaffected by the shorter tube, at least not that I can see terribly obviously, and only suffers from a reduced magnification to about 58x, even better for my purposes. I may yet find a better 50x, which might be a better option. This Leitz objective is probably from the 1930's and has only 62x marked on it. There is no N.A. but when compared to other similar objectives, I would guess it is .85. An added bonus is that it is within about 2 um of perfect parfocality with the 30x .55 C.B.S. objective and the Hacker 80x .90 needs only about 8 um of downfocusing to match the focus position of the Leitz.
None of the objectives in any sequence of rotation contact the slide and in using them incrementally, focusing is smooth ,slick and predictable.

Finding a compatible eyepiece took some time, largely because I assumed my best choice would be one of the two versions of CBS eyepieces that I had on hand. While this turned out to be initially true, I eventually trialled several Leitz periplans that live in a cardboard box and had escaped my attention. These are from both the 170mm and 160mm incarnations of the Leitz designs and from previous testing, there is a large degree of incompatibility between them, even though all are marked 10x periplan. It turns out the shortest of the lot, yet with a respectable 18mm f.o.v. provides close to perfect edge to edge correction with the 3 higher power objectives and with excellent planarity , despite the fact that none of the objectives are plan objectives. Only the 5x and 10x have a degree of coma and lateral chroma, which is pretty normal for objectives of their era, especially pushed to an 18mm f.o.v.

If any one has another one of these in good shape, I would be interested in it, since I only have 1. It turns out that there are at least 2 versions of it. The one I have is 40.5mm top to bottom, including a black field lens carrier of 7.5mm depth threaded into the main chrome barrel, which is 29.5mm.There is a thin eyelens carrier of 3 .5mm, at the top. The eyelens is 10.5mm across. Others I have seen, have a narrower eyelens port.

I will follow up periodically with some pictures, as the project progresses.

[apochronaut]

Some preliminary pictures. It seems, I might be better going to a 50x(.85 if possible). There is very little difference in the resolution between the Leitz at 58x and the Hacker at 80x , for their dual use to be valuable.

The sample was live pond water, a little thick with a slightly floating cover, so .20-.22 , probably.

[apochronaut]

a few others.

[charlie g]

How do you configure the camera to the stand in the field, apo? What camera setup, what adapter for use in the field?

More and more I am enjoying a basecamp mentality...rather than a microscope outdoors where we hike, and where I collect.

The real commitment for me is to observe my collected specimens while the specimens are fresh from the field. Shame on me but I now sense a loss if I do not have image-capture ability as I make my 'fresh specimens observations' (not that my image captures are that good!).

I do see need for a microscope right at collection sites...but only if it has image-capture component.

Please share with us a few pictures of your developing field microscope...and thanks for your kindness,apo.

charlie guevara

[apochronaut]

Charlie G. Thanks for looking.
The purpose of the pictures I posted was to show the relationship of the objectives' magnification and also to show the relative image quality of the 80x .90 dry objective. It is easy to get used to thinking in terms of the possibility of 800x magnification as either a muddy image, coupling a 20x eyepiece to a 40x objective, or as an expensive proposition using a 40x high N.A. achromat OR a 40x high N.A. fluorite or apochromat with a 20x eyepiece. Using a 40x achromat is really pushing it and going to an apochromat, usually involves $, even though the results can be impressive. Either way, immersion is usually the route of choice but the use of a 20x eyepiece limits both the apparent f.o.v. dramatically and most importantly the eye relief. 20x eyepieces are just finicky and uncomfortable to use. This 80x .90 dry objective is a convenient and quite decent quality option, especially considering it is coupled to a high eye relief comfortable ocular with a nice wide field......and I can't put to fine a point on this: it is DRY.

The objectives were mounted on a 160mm stand, equipped with a trinocular head, in order to take the illustrative pictures, since I am still in process developing the correct light, small stand for my purposes. I don't think I would have any need for any kind of camera adapter on a field microscope. The sole purpose would be to edit samples, in order to bring back, only those that were useful. Since, my primary interest over the years has gravitated often to the very small, with many subjects under 20 um, a higher resolution dry field microscope is increasingly appealing to me.

[zzffnn]

Apo,

I think if you can deal with mono tube, the Tiyoda MKH or a clone/relative of it, may be ideal. Because Tiyoda can take RMS objectives and is very light - around 3 lbs I think. I don't know how good its fine focus is though.

Or that AO field microscope that Charles has that uses infinity objectives.

I think I have seen, in old AO catalog, tripod base folding scope too. But I cannot remember where and what.

None of them is cheap or easy to find though. Such a light weight stand with good fine focus and full condenser mount, is difficult to achieve. If you make/find such a stand for cheap, please let me know.

I actually train my eyes to work with mono field scopes, after our previous discussion (you were the person who persuaded me to drop the idea of having a bino field scope). It is not quite comfortable for my eyes, but doable and tolerable in the field.

I am not sure you can power dry darkfield at 800x total magnification with a portable battery-powered light source. 400x dry DF should work fine.

Is there any reason why you don't want to use immersion optics in the field? The short working distance of dry high objectives would require very good fine focus mechanism and thin slide preparation (with minimal water gap). Immersion objectives of the same NA (around 0.9) have much longer WD and are therefore much more forgiving.

There is a LOMO 40x NA 0.75 water immersion achromat objective with a huge working distance. Around 1.8 mm, if I remember correctly. I actually think that WD is too long for cover slip (as that objective can be used for dipping without cover) - you need such a huge puddle of water above cover slip, such that immersion water may flood away your sample. Its image size is 18mm and oarfocal length is around 33mm. http://www.rafcamera.com/lomo-microscop ... miniscence

A 40x-60x oil immersion objective with a good WD should work quite well in the field, at least for those who don't mind use oil in the field.

[zzffnn]

Being in the same boat as apo, this is the portable scope that I use in the field:
https://www.amazon.com/My-First-Lab-Duo ... B000NOU54O

Yes, that is a plastic scope with mini objectives (small field) and without condenser. But I glued on a regular Abbé condenser and it works ok for 400x (total mag) oblique and 100x dry (DIY)
darkfield. Without condenser, image quality is junk.

Its pros include:
1) 2lb weight after adding condenser;

2) its only focus wheel actually works ok for 400x total magnification, once you get use to it;

3) usable and reasonable (though not very good) image quality, if you consider its used price of $30;

4) ergonomically and optically better than my other cheap pocketable scopes. Easy to use.

5) removable eye tube, which allows changing to a straight DIY tube (instead of the angled tube).

Its cons include:
1) poor image quality from its 40x objective, which also has a short working distance. Still usable, but poor;

2) focus wheel takes some getting-used-to at 400x total magnification;

3) poor build quality. All plastic.

4) its bottom LED died on me after 4 years of very light use.

5) only 3 objective slots. no 20x objective. Objectives are removable, but are smaller than RMS objectives. A mini 20x objective, which I am not even sure would fit or not, costs $50 on eBay.

My personal field use requires a very light weight scope, because we live in the hot Texas and I always carry drinking water for my family of 4. Thus I sacrifice image quality.

I have two pocketable scopes:
http://www.ebay.com/itm/micro-microscop ... 1830741617

http://m.ebay.com/itm/Meade-08025-Readi ... 1389206108

Neither of them has condenser. Their image qualities at highest magnification (400x and 160x, respectively) are not as good as the full-sized portable scope modified with condenser addition.

My LOMO Biolam scope weight about 7lbs in mono configuration and can almost work as a bench regular scope. But it feels too heavy for field use - yes, I have tried it - maybe I need to train my muscles more.

[apochronaut]

A monocular microscope would be perfectly fine for me, it's just that for this one, I want to make it binocular.

I have a very old Schutz microscope, made by Ruf and Co. in Kassel, around 1920, that I currently use sometimes and works fine for anything under 400x. It is quite minimalist in it's brilliant design and complete with it's wooden case( yes wood), it weighs just under 4 lbs. The microscope alone weighs 2 2/3 lb. Here is the clincher, it is made of cast iron and brass. The base is solid cast iron, the stage is solid plate brass, 4mm thick, the arm is solid cast brass and the focusing block, is solid brass. The tube length is 160mm, and it accepts RMS optics. Assembled, the microscope is 10 3/4" tall and the flared leg horseshoe base is 4"x 5". The stage is 2 3/4" x 2 3/4".
The design of the focuser is brilliant.
Coarse focusing is by virtue of a very smooth sliding drawtube, moving a brass tube inside a split collet that has an adjustable tension. It can be adjusted from just about allowing the tube to drop straight through, to lockup, with a brass two pin bevelled nut that impinges on the collet, compressing or decompressing it, depending on the direction of rotation. The fine focus, which is a coaxial knurled ring working against that collet, moves the entire collet and drawtube unit up and down a distance of 6mm inside the brass focus block, on an extremely fine helical thread. There are 50 graduations around the ring representing about 10 um per graduation but they are 2mm wide, so it is possible to get 1/5 of that or 2 um, easily.

The case is 5 5/8" x 4 5/8"x 8 3/8" tall and there is also another version of this with a lateral case, that is even smaller, and the microscope alone can be configured into a padded soft case that measures 5" x 4" x 8"

This model of the stand came with a 10x huygens ocular and a fairly simple stacked objective magnifying in 3 increments of 48x,96x and 224X. That is stated on the door for this model( # 1365) but there were clearly other arrangements on the basic stand and I have used other RMS objectives, which work well up to about 40x. There is no condenser but the understage space is sufficient for a small, stage attached one to be added and the arm has a sufficient bow to it , for a small 3 position nosepiece to be fitted as well. This would restrict the facility of removing the ocular tube, for packing.

They have made every effort to make the cased microscope compact and well protected. A padded block on the door, locks the base down and the top of the focusing tube is so close to the top that they have chiseled a relief for it. The case is made of butt jointed 10mm thick softwood, which accounts for it's lightness.

I think these were imported and marketed by Bausch & Lomb. Here is a front view of one https://ixquick-proxy.com/do/eu/show_pi ... 9f921abaec

[zzffnn]

Thanks, apo.

I am sure there are similar monocular scopes that are small and light. The problem is finding one at a reasonable (not "collectible") price.

I have seen several like that one on eBay, all of which cost more than $200. Not worth it for a field user, in my opinion.

[apochronaut]

Were the ones you saw similarly made with the compact helical tube focus?...or were they actual Schutz field microscopes , selling for over 200.00?

[zzffnn]

Did not find any "Schutz" microscope. Of those field scopes that I have seen, some seem to have compact helical tube focus, but most probably don't.

Some reasonably-priced helical focus telescope tubes may be used for DIY modification, if everything else fits and works well.

[billbillt]

Being in the same boat as apo, this is the portable scope that I use in the field:
https://www.amazon.com/My-First-Lab-Duo ... B000NOU54O

Yes, that is a plastic scope with mini objectives (small field) and without condenser. But I glued on a regular Abbé condenser and it works ok for 400x (total mag) oblique and 100x dry (DIY)
darkfield. Without condenser, image quality is junk.

Its pros include:
1) 2lb weight after adding condenser;

2) its only focus wheel actually works ok for 400x total magnification, once you get use to it;

3) usable and reasonable (though not very good) image quality, if you consider its used price of $30;

4) ergonomically and optically better than my other cheap pocketable scopes. Easy to use.

5) removable eye tube, which allows changing to a straight DIY tube (instead of the angled tube).

Its cons include:
1) poor image quality from its 40x objective, which also has a short working distance. Still usable, but poor;

2) focus wheel takes some getting-used-to at 400x total magnification;

3) poor build quality. All plastic.

4) its bottom LED died on me after 4 years of very light use.

5) only 3 objective slots. no 20x objective. Objectives are removable, but are smaller than RMS objectives. A mini 20x objective, which I am not even sure would fit or not, costs $50 on eBay.

My personal field use requires a very light weight scope, because we live in the hot Texas and I always carry drinking water for my family of 4. Thus I sacrifice image quality.

I have two pocketable scopes:
http://www.ebay.com/itm/micro-microscop ... 1830741617

http://m.ebay.com/itm/Meade-08025-Readi ... 1389206108

Neither of them has condenser. Their image qualities at highest magnification (400x and 160x, respectively) are not as good as the full-sized portable scope modified with condenser addition.

My LOMO Biolam scope weight about 7lbs in mono configuration and can almost work as a bench regular scope. But it feels too heavy for field use - yes, I have tried it - maybe I need to train my muscles more.

Hi zzffnn,

How did you like the compact Meade microscope?.. I have looked at these "pocket" scopes for years and wondered if they worked well... I like the size of the Meade...

Thanks!,
BillT

[apochronaut]

Did not find any "Schutz" microscope. Of those field scopes that I have seen, some seem to have compact helical tube focus, but most probably don't.

Some reasonably-priced helical focus telescope tubes may be used for DIY modification, if everything else fits and works well.

The snag there is that a twist focus telescope tube would not have as fine a screw. The Schutz fine focus is a micrometer screw. Although the little stand resembles other small brass stands from the same era, the combination of precision of manufacture coupled with extreme light weight sets the instrument apart somewhat.

The original Schutz company was founded around 1900 in Cassel, by Carl Schutz an optician specializing in binoculars,microscopes and telescopes. In 1912, the name was changed from Carl Schutz & Co. to Carl Schutz Optische Werke AG. In the mid-20's he merged with Ruf & Co. , into Schutz Ruf & Co. Cassel, the spelling of which was changed to Kassel in 1926. They were known for very small and compact porro prism binoculars, as small as 3x15, something unheard of in those days. During W.W. II, they made binoculars and as a result, even their ordnance code couldn't keep them concealed and they were bombed out.

[zzffnn]

BillT,

Ergonomics of the Meade is not very good for my application (pond ciliates). The Indian one is more comfortable to use and has higher magnification. Neither offers good imaging above 80x/100x total magnification.

Apo,
Thank you for your comments. Yes, the telescope focus that I have is not that precise. I imagine other telescope focus mechanisms may not be that different.