Eyepiece - Back to the camera.

This afternoon I reached the point of being able to test the Raspberry Pi camera module against one of the eyepieces from the microscope.

In order to do this, I kludged together an illuminator (using four white LEDs) and a printed image that sits in the graticule tray - an object that is in focus at the same time as the image from the microscope objective.

By holding the objective to the camera, I was able to estimate the separation between camera lens and eyepiece required for the best possible image - as well as to determine whether any intermediate lenses would be required.

The test was unexpectedly an immediate success. With the camera sat against the built in eye-cup on the eyepiece (a Vickers x10 Complan), the (circular) test image almost filled the height of the rectangular image - meaning that with a little tweaking and with the creation of a suitable adaptor, the camera is essentially able to be used as-is.

The graticule image - this was scaled down to a 19.5mm diameter.

In the graticule image above, the edge of the graticule mount covers the edge of the image - the fine, black line representing the expected limit of the vignette.

First Test - captured image through the eyepiece

As you can see, the test image is rather grainy - this is because the image is of a tiny picture printed out using an ink jet printer. There is also some distortion, but this is mainly due to the graticule being somewhat misshapen.

A blurred artifact (from the 3 o'clock to the 6 o'clock position) is the visual effect of some de-lamination in this eyepiece's optics.

The image is not properly centred because the test system was simply being held together in my hand. The pale mark in the lower left of the image is a reflection off of the inside of the eye-cup.

Conclusion:
This test was more successful than anticipated, and will warrant a proper adaptor being made in the near future.

Next steps:
A paper and card prototype adaptor will be used to perform more sophisticated testing and adjustment of the optical system. An acrylic design will follow, which will be capable of supporting the camera and associated computer while attached to the eyepiece.

Some festive thoughts on LED lighting.

As someone with a collection of things that I would like to photograph, I have long considered the question of suitable lighting.

For close-up work, including macro-photography, good daylight is unparallelled but, being Britain, good daylight is at a premium. When we have it, I want to be outside enjoying the sunshine and not indoors photographing small bits of rock.

Anyone who had done any macro-photography knows that the lighting is the most difficult part to arrange of the whole set-up. Flash tends to bleach out highlights and to cast stark, black shadows; incandescent light tends to be too yellow-orange and fluorescent light produces some weird colour casts.

Enter the LED.

For a while now, ice-white LEDs have been widely available in hand torches (flash-lights), work-lights and so on. While excellent for blue and green minerals, these LEDs produce poor earth-tones and dull reds, oranges and yellows.

Recently, warm-white LEDs have been available. These give a much better colour rendition for most subjects, but need to be combined with Ice White LEDs for a better overall effect.

Now comes the problem - buying warm-white and ice-white LEDs is a problem - they are generally advertised simply as white - and finding LEDs labelled by colour usually means expensive.


Today, I was shopping, and looking at Christmas Lights, and specifically cheap strings of LED lights. Lo and behold, there were strings of Ice White and strings of Warm White LEDs, as well as a range of other colours. I bought a string of ice white and a string of warm white (as well as a couple of other colours) - they were £2 per string of 20, batteries not included.

Now, LED fairy lights, instead of a dome-shaped lens, have a dimple in front of the chip to spread the light so that it is visible through a 270° angle.

What results is a pleasantly diffuse light similar to a coloured (or not) incandescent light with the appropriate colour tone.

A little time with a soldering iron and strip-board would quickly turn a string of festive LED lights into a macro-photographer's flood-light. Switching LEDs in and out could change the colour cast, brightness of illumination etc. - and all at 10p per LED. You even get a free battery box and switch with each pack of 20!


Incidentally, I have to say that the warm white LEDs are a little warmer than I would have expected, and really would make excellent display lighting without the starkness of the ice-white LEDs that are more commonly encountered.