Topical Tips 2

 

I'm sure we've all acquired tips, techniques, 'tricks of the trade' or perhaps made simple gadgets while pursuing the fascinating hobby of amateur microscopy. Why not share some of yours with us? They don't need to be original, but I'm sure they'll be of interest to others who may not have come across them. Just send us a short note in an email (contact in footer), enclosing a scanned picture or drawing if you wish and we would be pleased to compile, upload and acknowledge your contributions.

 

Topics covered - scroll and scan titles to find:

 

Useful magnifiers and mini-portable microscopes from old projector lenses

A highly effective magnifier for lab or field work is a 2-inch f1.2 wide barrel l6mm projector lens, such as found on Bell & Howell and Eiki motion picture machines. I have a 2-inch f1.2 Eiki lens to which I added a screw-in 48 mm Canon close-up lens to give a total magnification of 7X (approximately). It also provides an extremely sharp, bright wide-field view. Such lenses can be found occasionally in science surplus stores, garage sales, flea markets, camera stores having used equipment, etc.

The lens should be an f1.2 for the wide field. The f1.6 lenses (standard on projectors) have a much narrower field of view but also work as a magnifier. I have also used some Bolex 16mm extension tubes, attached a 25mm f2.5 Wollensak lens on one end and a 15X microscope ocular on the other. You can use several or just one or two extensions. I figure mags of 20 to maybe 40-50X.

One can also take a microscope ocular and an objective lens and mount to a Bolex 16mm extension tube (make as short or as long as you want) to make a mini-portable microscope. I made one from an old 10X objective and an old 15X eyepiece--can achieve about 30X on up to almost 100X depending on tube length. Supposed to be used with 160mm tube length but works quite well with surprising resolution. Only problem is holding very still because it is a hand-held device. One could make some kind of holding device I suppose.

Chuck Huck, Warrenville, IL, USA

Editor - thanks Chuck for sending these useful tips.

Infra-red filters

If you own a black and white video camera e.g. the security type and you use it for normal video microscopy, make sure you have an infra-red filter in the light train. Most B&W cameras have a significant sensitivity to infra-red which will be detrimental to obtaining a good video image. IR filters can be bought from larger photographic outlets, or blocks of special heat absorbing glass are available.

If you don't know if your B&W video camera is sensitive to IR, point a video or TV remote control at the camera and activate the buttons. If bright flashes are seen on the video image, you need an IR filter for video microscopy! However, this infra-red senssitivity can also be exploited see the Micscape article on Infra Red Video Microscopy.

 

Polariser and analyser filters

The polarising filters supplied by microscope makers can be expensive, but it's very easy to make your own which are quite adequate for most work. I made mine from a pair of $4 clip-on polaroid sunglasses (for prescription spectacles) from a local drugstore. (Since buying a more expensive set I can detect no difference in the quality of image obtained). High extinction polaroid sheets are also available from microscope dealers to make your own.

By the way, the polariser for the eyepiece is often conveniently inserted on the stop plate inside the eyepiece (the top element usually unscrews). The problem with this is that a filter here has to be squeaky clean as it is usually imaged in the image plane. I prefer to just lightly stick the filter on top of the eyepiece with 'Blu-tak' or plasticine when it is needed. Any slight dirt or blemishes on a less than perfect filter is then out of focus.

The Micscape Articles Library has many articles and image galleries showing the stunning results obtainable from a simple pair of polarising sheets. Enter 'polar' into our Library Search Engine to view them.

 

Getting the most out of achromatic objectives

If like me you have a modest student microscope supplied with the basic set of objectives they are probably achromatic objectives. These are more than adequate for the undemanding studies many amateurs are likely to do. If you want to do work with achromatics where resolution is more critical but have no wish (or the budget) to invest in the better corrected optics like fluorites or apochromatics - you can get the best out of achromatics by putting a green filter in the light train. The residual chromatic and spherical aberration of achromatics is removed for this colour of light.

 

Don't discard the water from a defrosted fridge

Distilled / deionised water can sometimes be hard for the amateur to source or expensive for general microscopy. A good supply of quite pure water can be obtained when you defrost the fridge which will be adequate for many uses. The water condensing on the outside of the fridge compartment (as long as it's kept clean) has been condensed from the air so should be essentially free of hard water impurities, although the higher purity of deionised/distilled is advisable for permanent slide mounts

Out of interest I measured the conductivity of water defrosted from my fridge and compared it with my tap water, which is soft so already low in inorganic impurities. The 'fridge water' was 10-20 units and the tap water 150 units so is far superior to even soft water. (A lower conductivity value shows there is less ionic inorganic impurities i.e. the main component of hard water. The 'units' are mS/cm).

 

Extend your range of objectives

If your compound microscope has the standard objective thread you can add objectives. The set often supplied can jump in large steps eg 10x, 40x, 100x is common. You may find in your studies this set is too restrictive - I find a 5x or less and a 20x extremely useful. The former gives good views of e.g. insect parts and larger organisms like water fleas where often 10x is too high a magnification. The 20x is also handy where the higher mag of 40x and it's poorer depth of field and field of view is a disadvantage. You don't need to spend a fortune on objectives; achromatics are more than adequate for many amateurs requirements. You may wish to consider a 'plan' achromatic which gives a flatter field at say the 5x where the field of view is quite large. (Note if you are planning to 'mix and match' different makers objectives, eyepieces and microscopes, ask the dealer if the combination you plan to use is OK, some makers combinations won't work properly!)

 

Photographic enlarger lamps

If you own a microscope without an internal lamp, you will need a good external light source. There are few external microscope lamps available new nowadays and are often silly prices. The domestic light bulb with pearl or frosted finish are OK at a pinch in a suitable desk lamp (for visual work) but they often have writing on the front which will be seen in the field of view or they have less than perfect frosting. A much better bulb is that designed for photographic enlargers. It gives a whiter light and is very evenly 'frosted'. Most photographic outlets should sell them in ca. 60-75W in the domestic bayonet or Edison screw fitting. (Warning: if making your own lamp / housing or replacing bulbs in lamp housings, check with a qualified person it is safe regards bulb wattages, ventilation, overheating, earthing etc.).

I find the enlarger lamp very useful for low power work with a 3.5X objective where microscope lamps often struggle to provide good even lighting over a wide field of view.

 

Photography and video down the microscope - watch out for 'flare spots'

When setting up a homemade system for photography or video down the microscope it is well worth inspecting the projected image quality (with all the adaptors to be used in place) to spot flare spots caused by unwanted light reflections etc. that may not be noticeable with the camera in place. This can easily be checked with a mounted piece of tracing paper held at, below and above the 'image plane' in a darkened room with the camera absent and microscope set up and focused on a subject slide and the slide then removed. These flare-spots may only appear for certain objective, eyepiece, lighting combinations so check the image quality with all combinations you may use.

When I first bought an adaptor to attach my video camera to the microscope I obtained very poor image contrast. A quick inspection with tracing paper in the image plane revealed flare spots. In this case they were easily removed by putting a smaller stop in the video adaptor as the stop supplied wasn't small enough to cut down flare in my setup.

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Note that a variety of articles on simple techniques and home made projects for the amateur microscopist can be found in the Micscape Library (look under 'Novice' or 'Techniques').

Disclaimer: these tips are given in good faith, but no responsibility is accepted by
Microscopy-UK, Micscape or its contributors for any damage to property or persons on using these tips. It is up to the reader to judge if a tip is appropriate and safe.

Compiled by Comments to the author sent via our contacts page quoting page url plus : ('dwalker','')">Dave Walker.

 

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