View Full Version : barrel G Claron 150

Luca Merlo
15-Feb-2006, 14:59
Sorry for the ignorance, but I am wondering if the barrel G claron 150 can fit the Copal 0 of Nikkor M 200 and W 135 without changing the aperture scale. In other words, I consider to buy a barrel G Claron 150, unscrewing the front and back cells and assembling them on these Nikkors Copals when I will need it. Will I have any problem ?

Luca Merlo
15-Feb-2006, 15:04
Sorry for teh second posting. It just slipped ......

15-Feb-2006, 15:21
because the focal length of the nikkors is not 150mm, then you need to rescale the fstop. You can compare the plots of FL/fstop of those three lenses to help you rescale the fstop.

tor kviljo
16-Feb-2006, 01:54
It will probably be nearly spot (only 10% difference in FL) on when assemblied on the 135mm's shutter, as the difference of focal lengths here is the smallest. The 200mm will be about 1/3 stop away, possibly making a new pointer necessary. However, confirm this using a vernier caliper to check the physical aperture openings on the barrel-aperture of the G-Claron and the aperture on the 135mm Nikkor shutter unit: the f 11 is supposed to be about identical for those lenses, but if the 135mm is of a odd design, aperdure diametresmight not correspond directly. I have used aperture-units with other than the lenses they were calibrated for, just by adding a new pointer. From the new pointer, all aperture values will be correct as a movement from f 5.6 to 11 or from f16 to 32 represent a physical reduction in aperture diametre by 50% regardless of what diametre the aperture mechanism initially were made for.

Ernest Purdum
16-Feb-2006, 18:21
Front cells magnify the iris. How much magnification differs a lot from one lens design to another. It isn't the actual diaphragm size that determines the f number, but the apparent aperture as viewed from the front. For this reason, your question could only be answered by someone who had very full specifications on both lenses. If you search above for "apparent aperture" you'll find a lot of discussion of this situation and what can be done to deal with it.