"We" recently tried (very unsuccessfully) to find a way of using a 4/3 camera in combination with an Olympus NFK projective on a BH-2 microscope. http://www.photomacrography.net/forum/v ... sc&start=0
Olympus NFK projectives use direct projection onto the film/sensor. The smallest magnifications available are the NFK 2.5x and the NFK 1.67x. To get a good coverage of the microscopic image, the NFK 2.5x should be combined with a full frame camera (which are expensive) while for the smaller APS-C sensors, an NFK 1.67x is required, which is very expensive. So either way, the upfront costs are considerable. http://www.alanwood.net/photography/oly ... scope.html
For smaller camera sensors, like m4/3, the coverage is even worse. Olympus offered the MTV-3 0.3x adapter for smaller fields; however, this adapter is reported to have an image field of only 16 mm, too small for m4/3 http://www.alanwood.net/photography/oly ... scope.html
The obvious way around this would be to use the afocal method (visual eyepiece + camera prime objective). However, this would require a modification of either the BH-2 phototube or the eyepiece, as Olympus visual eyepieces don't fit into the narrow top of the BH-2 phototube (as far as I know). The afocal method doesn't work on the NFK projectives without the need to re-focus the microscope.
During the discussion I got a PM suggesting that the MTV-3 adapter works like a negative teleconverter and that I might be able to get the same effect by placing a camera objective abnormally close to the camera.
So I started a quick test with the results shown below. I don't own an Olympus microscope, so I won't pursue this any further. But maybe someone feels inspired and takes the idea further.
Basic Set-up:
Zeiss Standard microscope with trinocular tube; both binocular tubes and phototube have canonical 160 mm tube lens
Canon EOS 500D (APS-C sensor, 26.8 mm diagonal approx.)
Olympus NFK 2.5x projective
Zeiss Planapo 25/0,65 (I don't have Olympus Plan objectives, but the Zeiss Planapo 25 works quite well together with the NFK; there are colour fringes at the edge of the field in this test; the colour fringes are due to the Zeiss-Olympus combination; there are no colour fringes when using an Olympus 20 LWD achromat, so the fringes are not introduced by the camera objective)
Polaroid Tominon 105 mm 1:4.5 camera objective in Copal 0 shutter mount (4 element (Tessar) type, used in gel imagers or MP4 copy stands http://www.everythingretek.com/PRDLibra ... 4SERVC.PDF) Normally the Tominon produces an image > 20 cm behind the lens. In this test, the rear lens was placed just inside the EOS camera body
Three different set-ups were compared:
(4) Direct projection: NFK 2.5x projects image directly onto the APS-C, about 150 mm above the projective (as designed by Olympus).
Visual eyepieces (binoculars) and LiveView image (NFK) were parfocal when taking this image.
(3) Afocal method: Zeiss Kpl 10x high eyepoint and 40 mm camera objective.
Visual eyepieces (binoculars) and LiveView image (NFK) were parfocal when taking this image.
(2) Tominon as relay lens: The Tominon was placed approx. 2-3 cm above the NFK (regular front lens facing the NFK) (see image below). The EOS camera was placed directly onto the Copal shutter mount, so the back lens of the Tominon protruded into the camera body without touching the mirror.
Visual eyepieces (binoculars) and LiveView image (NFK) were parfocal when taking this image.
Below is a comparison of the results from (2) - (4), showing a stage micrometer across the entire image frame. (4) and (3) are good quality and almost perfectly plan. (2) is good in center but has image curvature at the sides.
(2) also has some barrel distortion and shows some vignetting [I didn't perform background subtraction on this image to show the extend of vignetting]
Field coverage (allow 5 % error with the drawing): Circle in light blue shows the field visible through 10x/18 eyepieces. Direct projection (4) covers a small portion of the overall field. (3) Afocal gives excellent field coverage. (2) covers a large field, probably already excessively large, although the Zeiss Planapo is plan up to field numbers of 25. It would be interesting to find out how an Olympus SPlan would perform in this test. The field covered is equivalent to that of an "NFK 1.3x". The exposure time is greatly reduced compared to direct projection (4).
Suggestions for further tests:
The Tominon 105 mm might be excessive for APS-C cameras, especially since it introduces field curvature at the edges.
An objective with a longer focal length (125 mm, 150 mm) might be worth testing. However, it might cover the sensor of m4/3 cameras quite well.
The distances between NFK and Tominon and between Tominon and camera might be optimised to reduce distortion, field curvature and vignetting.
It might be worth testing other optics as relay lenses, like enlarger lenses or even simple afocal reducers (from astrophotography).
Regards, Ichthy
