So we're going to photograph our slides. We will of course need a camera, with interchangeable lenses, because the standard lens will generally not be suitable. So, in addition, we’ll need a lens, a light source and a support for the slides.
In order to obtain a quality comparable to a specialized scanner, a lens is required, the main qualities of which are the absence of distortion (image deformations), chromatic aberrations (coloured fringes) and vignetting (darkening of corners). To avoid all this, it is better that the lens has a fixed focal length: it will not be a zoom. On the other hand, it does not need to have a very large aperture. As for the focal length, it can range from 35 (for an APS-C sensor) to 100 mm. This description corresponds perfectly to that of a “macro” type lens.
Personally, I have remained faithful since the silver period to the same brand, Pentax not to name it, the interest being that it is the only brand, together with Nikon to a lesser extent, to have retained an almost total compatibility of its equipment for about forty years. So I did not have to renew all my equipment to go digital. But I admit that if I had gone from zero to digital, I would have chosen another brand, probably the one I have just quoted…
So, among this
pre-historical pre-digital era equipment, I
kept a 100 mm f/4 macro bellows lens, with no focus ring, because
it is designed to fit on a bellows with a very vintage look.
Advantages: it is easy to adjust its tirage (distance
between the camera body and the lens mounting plate) on a
graduated scale, and it has a precious diaphragm ring that no longer
have modern lenses. Disadvantage: its rather long focal length which
requires to use a bulky tube for the slide holder.
Under this name there existed in heroic times an accessory which permitted to re-photograph slides. I was inspired to make mine. Note: I found a similar device not too expensive on Amazon, not long ago, equipped with a tube fitted with a lens and a film holder. The latter was of an entirely correct quality; but the lens, whose purpose was to obtain a shorter tube and therefore less cumbersome, was on the contrary lamentable: distortion, aberrations, everything was there. Return to sender. I still give you the reference page, but I will have warned you.
This support consists of four elements:
The main tube is covered inside with black velvet flocked vinyl adhesive to avoid any parasitic reflection. For the same reason, the inner side of the slide holder is painted in matt black.
You’ll find the dimensional diagram of the slide holder (4) in this PDF document. Note that the length of the PVC tube must be adapted to the focal length of the lens used.
It lacks a strip film holder that would allow me to digitize negatives. Even some reversal films that I had more or less missed development, and that I had for this reason left in strips, proved to be exploitable in digital.