KODAK’S 170mm (= 7ins) f6.3 Anastigmat lens seems to be a bit of a curiosity. At first I understood it to have been cannibalised from a 1920s or 30s Kodak Autographic 3A folder and pressed into service with my 1964 Crown Graphic. However, today I noticed a faint but definite bloom on the lens as it reflected the afternoon sky.
Lens coatings were not introduced until the late 1930s and this lens certainly seems older than that. Is the bloom the result of some natural oxidation or did someone like the lens so much they had it coated in later life? Or does it just happen to have been made in the two or three year gap between Kodak introducing their first coatings and bringing in their alphabetical lens date-codes?
It is clearly a four-element lens: the back group unscrews easily and quite obviously comprises more than one lens. It is also obvious at that point that there are a couple of lenses in front of the aperture diaphragm.
Shining a pen-light into the back group at a slight angle shows pairs of reflections, indicative of two lenses separated by an air space. The front group has similar reflections. So it seems that this Anastigmat is a four lens design, with the lenses all separated by an air space – a design known as a dialyte.
The pre-war Kodak anastigmats fell into three groups – triplets, Tessars and dialytes, so the result is in line with that, though no official details seem to be available anywhere for the 170/6.3.
Users’ views on dialytes seem to be rather mixed, some report amazing results, others have had versions that disappointed. The f7.7 203mm Kodak Ektar, which is a dialyte, is very well-regarded so hopefully this smaller sister will turn out to be equally good. Everything seems to be fine on the ground glass – but time and use will tell.
The main problem in using it, apart from the lack of filters, is that the Ilex shutter’s measured speeds topped out at about 1/37s (for both 1/50 and 1/100 on the dial). So with 100 ISO film in normal daylight I will already be looking at apertures of between f/22 and f/32. In daylight, ISO 400 will be out of the question.