swapping lenses in shutter

[john_cooper9]

<p>I have a 100mm f:3.5 Zeiss Tessar in a Compur 0 shutter. I have replaced the elements with those from a Mamiya 50mm f:6.3 lens for 6x9 (a Zeiss Biogon-like copy). Looking through the open lens I closed the aperture from fully open to just when the blades appear around the lens - the setting is between f:5.6 and f:8 i.e. about f:6.3. Is this coincidence or am I correct in assuming that the shutter's marked apertures of f:8 thru f:22 are accurate enough for the new lens?</p>

[bob_salomon]

Either see if you can find the correct scale or have a repair company make you a proper scale.

[thirteenthumbs]

<p>fs=Fl/ep<br>

fs- f stop<br>

Fl- lens focal length<br>

ep- entrance pupil- the diameter of the aperture opening as viewed through the front of the lens.<br>

ep=Fl/fs<br>

ep=50/6.3<br>

ep=7.94mm</p>

<p>Your shutter's aperture may open much wider but the image quality will be poor until the f6.3 aperture is reached. Some shutters blocked the aperture opening wider when used with slow lens. </p>

[john_shriver]

<p>You should check that the shutter you moved the lens cells into is the same thickness as the shutter you removed them from.<br>

You do need to make, or have made, a new aperture scale.</p>

[john_cooper9]

<p>The original shutter is a Seiko 0 inside the mamiya housing for the Press 6x9. My experience is that for all practical purposes shutter sizes of 0 1 and 3 are the same "thickness". The Seiko for the 50mm f:6.3 is stopped down at the f:6.3 mark i.e. it will not open any further. I should measure the opening at the various marked apertures and compare them with those of the "new" Compur 0. I intend to do a film test at the various apertures using Provia 100. This should be proof enough!</p>