jason_greenberg_motamedi Posted April 5, 2003 Share Posted April 5, 2003 I recently picked up a B&L 5x7 (4 1/2") f/18 barrel mounted Protar V. After examination I see that the maximum aperture of the iris is smaller than that of the glass, meaning that open all the way at f/18 a small amount of the iris shows. Well, being the fool I am I opened the thing up and removed a small strip of brass which prevents the aperture from opening all the way up. What is the reason for this bit o brass? is it to prevent focus shift? Should I replace the brass right away and forget I ever saw it or do some film tests? Thanks in advance... Link to comment Share on other sites More sharing options...
hans_berkhout Posted April 5, 2003 Share Posted April 5, 2003 Clive Russ might know the answer; cliveruss.com Link to comment Share on other sites More sharing options...
peter_mcdonough Posted April 5, 2003 Share Posted April 5, 2003 Hi Jason, I have a symmetrical wide angle that had waterhouse stops from appx f/16 to f/64. When I had it removed from its original housing and mounted into a shutter, the aperture was increased to f/5.6. At this increased aperture a great deal of spherical aberration was introduced. The resulting image displayed a beautiful glow and softened appearance. Stopping down eliminated this effect. Without the brass stop your lens may be brighter but softer. Stopping it down would correct the softness. Peter Link to comment Share on other sites More sharing options...
dhananjay_n Posted April 5, 2003 Share Posted April 5, 2003 Many old lenses were designed to be used at a certain minimum aperture for acceptable performance. To avoid folks complaining about poor results when using it wide open, the apertures were probably restricted to what the designer held to provide acceptable performance. You probably can open it up for brighter focussing as long as you remember to stop down but keep in mind you might have zonal spherical aberrations that can result in focus shift etc. Cheers, DJ Link to comment Share on other sites More sharing options...
sjmurray Posted April 6, 2003 Share Posted April 6, 2003 I also have a B&L Zeiss Protar V, f18. Mine's about a 175mm focal length. I have shot at wide open and found that there is a nice double image in the outer areas of the negative. You have to stop it down at least to f18. F22 or more would probably be better. The sharpness is pretty good when stopped down. Even looking through the ground glass carefully when aimed at some bright lights you will see the aberration wide open. As soon as you stop down it goes away. Do some test shots. Look at the attached image. I took it with the Protar wide open or f18. Look at the left side of the image. On the structures there you'll see some ghosting or doubling of the image. That will disappear when stopped down. Link to comment Share on other sites More sharing options...
sjmurray Posted April 6, 2003 Share Posted April 6, 2003 Oops, here's the image. Its a water tower.<div></div> Link to comment Share on other sites More sharing options...
Troll Posted April 6, 2003 Share Posted April 6, 2003 Don't forget to re-focus when you stop it down. Link to comment Share on other sites More sharing options...
joe_photo Posted April 10, 2003 Share Posted April 10, 2003 wOw what a shot!!!! Link to comment Share on other sites More sharing options...
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