Hasselblad FE 50 f 2.8 diaphragm shape

Discussion in 'Medium Format' started by diegobuono, Mar 22, 2014.

  1. Excuse me if I go back on something related on the same matter

    http://www.photo.net/medium-format-photography-forum/00cS83

    But I notish that the diaphragm shape is pentagonal from f8 and smaller, instead for the larger aperture the diaphragm is decagonal but
    the shape become more irregular (I mean that the sides are of different lenght, and so the shape is not regular) the more I stop down
    from wide open to f6.3. It is a normal behaviour or it is another wrong repair issue (see the above link). Thank you in advance.
    Diego
     
  2. The aperture opening should be an equal sided geometric shape from wide open to fully closed down. The shape will depend on the number of blades that make up the aperture.
    Irregular sides or shapes indicate the aperture needs servicing as one or more blades are not moving smoothly and are sticking or hanging up on something.
     
  3. That indeed is the way it is supposed to be, Diego. No worries.
    (Though the shape should be regular. But maybe it is, and it's just that you were expecting a regular right sided pentagon? The opening at wider apertures is regular in it's complexity.)

    At wider apertures the shape is more rounded, from f/8 and smaller it's a pentagon.
    Set the DOF preview lever, and watch through the rear of the lens at the aperture blades, and see how the blades work.Looking through the front too you'll see at f/22 that it's not just a matter of five straight sided blades. The diaphragm of this lens (and of a lens like the f/2 110 mm) is an intricate affair. Much more so than that of C(...) series lenses.
     
  4. Q.G., I don't have the possibility to shot some picture unfortunatly (if you can and can post it , it would be much
    apreciated); when I say "irregular shape" I mean that not all the side of the ten-sides diaphragm shape are
    of the same lengh. I.e. at f 6.3 I see: one side about 1 centimeter long, the opposite side is about 0,5 cm long, the side
    next (on the left) to that long 1 cm is about 2,5mm, the next on the right is about 3mm. And then there are 2 sides that are long
    about 6mm, 2 sides long about 4mm and so on. Furthermore I notish that when I stop down to f 8 the diaphragm is not
    pentagonal but shows one side more, even if very short (may be 2 or 3 mm). I hope the above description is quite clear.
    Thank you in advance.
     
  5. As QG says, but I'll add that my F lenses (50mm & 150mm) apertures are somewhat irregular. They may have been regular when new. I don't have these FE lenses (yet!) but they are essentially the same mechanisms with the added electronics.
    Many of the F/FE lenses have a compound aperture, the secondary blades make the aperture rounder when it is larger than ~f/8, beyond which they have no effect. The idea is to produce rounder specular highlights in the out of focus regions (something people mistakenly call bokeh).
    Here is the aperture of my 50F at f/5.6:
    [​IMG]
    The secondary blades are easier to see in the 150F (at ~f/5.6):
    [​IMG]
    This irregularity in the aperture is typical of the F/FE lenses I have seen.
     
  6. Yes, the diaphragm on my lens looks like that in the picture attached by Tom. So it seems that at least for this I should
    not be worried. Thank you all for the clarification.
     

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