charlie g wrote:
Hi, fibreoptix, I find it odd that these new and unbranded chineese objectives do not list their: 'tube length' as a spec!? : 160 tube length...sigh, they are RMS standard: about???34mm?? length Charlie Guevara finger lakes/US
Charlie G. It is not unusual for student grade optics to be unmarked as to the total optical path length( specimen to top of the eyepiece tube). Your Nikon Labophot isn't marked , either. It is in fact 160 + 45= 205mm. 185mm was in some ways a student microscope standard, although many objectives designed for a 185mm system had threads, other than R.M.S. The notice by the seller of 185, was enough to warn a knowledgeable buyer that these objectives would be short: 25mm parfocal, by deduction.
There is NO R.M.S. standard for objective length, only for the standardized R.M.S. thread that is most commonly used on microscopes. The mechanical tube length standard is D.I.N. 58887, by which Deutsches Institut für Normung,, established that the distance from the objective shoulder to the intermediary image should be 150mm and that the intermediary image should be 10mm below the top of the eyepiece tube, totalling 160mm. The length of the objective is not included in this standard. Various systems have existed based in this standard, as well as deviations from this standard; most notably that of Leitz and their cooperative companies( Seibert, the main one), and the early Japanese both of which used a 170mm tube. If the mechanical tube length is 160mm, then the objective parfocal length needs to be added to that, in order to find the total length. Lomo would be 193mm, AO 194, Baker( early) 194, J.I.S. based on a 170mm tube length is 206, Leitz 170mm system was 207mm; the 160mm system was 205mm, Bausch & Lomb 196.7mm, Reichert 197mm, PZO 205mm, Vickers 205mm, most Chinese 205mm. Zeiss for many years was non-conformist as well, with a total length made up of 147mm( instead of 150), 13mm( instead of 10) and 33mm for a total of 193mm. The more modern Zeiss are 205mm.
There is another D.I.N. standard associated with the 45mm parfocal distance utilized concurrently by many manufacturers and the tube lengths associated with infinity microscopes are a whole other thing altogether.