Looking to replace my Compur electronic 5FS with a Compound V I checked the measures of the former.
First the front and rear inside diameters _are_ different. While the rear is more or less 82.5mm - and hence most likely the 82.77 of the Compound V that Ole reports in this link - the front has a diameter of about 85.5mm. The tube length of the 5FS I have is about 49mm.
This 5FS is coming with an Apo-Lanthar 300mm mounted on it. However, there is an adapter ring that screws on the front of the shutter that changes the measurements as follows:
1. It reduces the diameter from ~85.5mm to ~82.5mm
2. Extends the length of the tube to 60m.
This tells me that the two Apo-Lanthar cells should be mounted without any modification on a Compound V. In fact, it seems clear that they were produced for a Compound V and Compur (or some metalwork shop) produced the ring adapter so that a 5FS could be used.
What I do not know though - a company data sheet would be most useful - is whether these two measurements, i.e., front diameter and tube length - are truly representative of a "standard" 5FS or are those of my specific sample.
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