Repair and LED Conversion

Microscope normally comes equipped with a set of three or four objectives, a pair of 10X oculars, with intermediary image distance 10.0 mm designed for optical TL of 150.0 mm - mechanical TL - 160 mm, with simple immovable condenser fixed onto the stage, declared NA of 0.9 capable only of  bright field observation, with additional swing in/out single lens element for use with low magnification objectives. Detailed description of all the options are given in the user's manual¹. It is interesting to note that objectives do not have any traces of delamination, that is otherwise quite common for Zeiss optics of the period.

The condenser is a very simple, plastic construction with glass elements, declared NA of 0.9, screwed to the stage with no ability to focus, or replace it with a more versatile device. The iris was messed up a bit and needed intervention. The only "luxury" is the additional lens intended to provide illumination for low magnification objectives, however, there is no provision of any kind to allow proper centring of condenser within the optical path. The illuminator collector, single lens, is built in the base with a frosted glass filter above it, with no field aperture.

Burned out Zeiss West KF2 Power Supply, epoxy sealed assembly. 

The built in illuminator power supply was burned out with no option of repairs, so I have simply built a replacement working on low voltage AC supplied by the external unit containing a mains transformer, which provides galvanic isolation from mains. As the simplest solution, I converted illuminator for use of 3W neutral white LED with intensity control, more than sufficient for bright field observation. 

As an added extra with this power arrangement, the microscope illuminator can be powered from a 12V car battery connected directly to the power connector at its backside, even a 24V battery will work nicely, or a 12V lantern battery cell pack such as Rayovac 926C or similar.

Since the original lamp holder was missing and because of LED conversion I've made a new lamp holder instead, which served as holder as well as an additional heatsink for a 3W LED, providing ample light for the microscope using the 100X immersion objective, without any problems with light to spare and if necessary one can use neutral density filter.

Replacement of the missing fixed ocular tube

Microscope assembled and fully operational

Excerpt from the Zeiss pamphlet "41-114 e Zeiss KF2", page 8³,

Microscope with a condenser that cannot be focused. Illuminator, consisting of a single lens collector (unfocusable) built in the base with a frosted glass above it, and no field aperture cannot be called K�hler!

There is no question about it, Zeiss West KF2 microscope is INCAPABLE of K�hler illumination. 

After carefully reading Zeiss description I began to wonder about what was their aim by claiming K�hler illumination. Perhaps to hide the fact that KF2 is equipped with only critical illumination, counting on the lack of knowledge by the modern day end user, whom they have taught through decades that the only "proper" illumination is K�hler and thus it was difficult for them to now contradict it? 

Going as far as to say: "K�hler illumination is often quite bothersome to accomplish, even for experienced microscopists."

Also, claiming the NA of the condenser as 0.9 is a fair bit stretching the fact when the condenser is a cheap uncorrected Abbe design, which at the best is hardly over the aplanatic 0.4 NA. I did not even bother to measure it!

Personally, I see Zeiss West KF2 not in any way different, nor better, than any of the cheap Chinese, or Indian, made microscopes. The obvious. and the only, difference being the higher cost, of course just by parading the brand name.

2. Power LED Driver using LM2596S module - by Dushan Grujich Feb. 2014 

3. 41-114 e Zeiss KF2 - Pamphlet English language