"SuperDoc" Contax Hacking Page...

With thanks to Mr Okayan's  Hack Contax Page

  The "SuperDoc"  Universal Contax Lens/Hood Shadecap

  35mm Lens Hood ?

  28mm Lens Hood

  46mm Heliopan Hoods

  Sunken Lens Release Button

  Wrong Colour Filters & Hoods ?

  QED - Hood Graph Measurements

  Parallax Errors - Nagging Doubts & Workarounds

  "SuperDoc" Universal Contax Lens/Hood Shadecap - Contax designed their lens hoods to be used with only one filter at any one time.  As these hoods are cylindrical they only work at maximum effectiveness at the corners of the rectangular film plane with other areas being less effective.  Yashica used to provide rectangular lens hoods for their 'ML' and earlier lens range.  These were attached to the lens body by a neat clamp.  These were very effective and were beautifully made.
    NB - It should be noted that the G1 & G2 auto-focus may not work if the diameter of the cylindrical lens hood is greater than 55mm.  (There is therefore more leeway vertically if one uses a rectangular lens hood.)  
    Problem - How does one get a simple SINGLE rectangular hood shade effective for 21, 28, 35, 45 and 90mm lenses without spending a fortune on a bellows hood which would anyway screw up the auto-focusing?
    Take it Away...
    Contax/Kyocera have already done all the computing for you by (hopefully) optimally fixing the lengths of the three hoods for the three lenses, 28, 45 & 90mm (see below for 35mm lens).  All one has to do is buy a Contax hood cap (GK54) or better and a lot cheaper generic plastic 57mm cap and cut a rectangular hole in it.  The ratios are: 2 : 3 : 3.6 (H:W:Diagonal).  So for a 55mm diagonal, the height of the hole is 30.5mm and the width is 45.8mm.
    Cut a rectangle (H = 30.5mm W = 45.8mm) of stiff paper and using this as a template, mark out your plastic hood (you are practising first aren't you?).   Start cutting with your Stanley knife taking all possible precautions against removing digits, flaps of skin etc. Remember to cut slightly too small a hole and then gradually enlarge up to your marks if you are in doubt. Chamfer the outer edges of the hole very slightly.
    Mark the top centre with a dab of red marker ink so that you can always correctly align it with the black mark just in front of the aperture ring.   Paint the outside to a colour of your choice and check that the inside surface of the cap is painted black before use. 
    Slip your new hood cap onto the front of the hood, align and voila even more protection for your lens from stray light. It works with all five prime lenses (not including the Hologon) using optimally one filter or filter ring in place and the correct Contax lens hood or just one filter in the case of the 21mm lens.

 28mm Lens Hood - If you are not using any filter then the deeper GG2 hood works well.  The GG1 is computed for using one filter in combination with the GG1 hood. (See graph)

 35mm Lens Hood ? - Contax/Kyocera have been (query ??) a bit slack suggesting that the 28mm GG1 hood is OK for the 35mm lens.  For un-thinking perfectionists this will definitely not do.
    Take it Away...
        1.) When measured on graph paper the GG1 is fine.  The reason being that that the 28mm lens has a smaller diameter glass front lens than the 35mm lens and as the angle of view is greater with the 28mm lens the hood depth for each can be the same.  (See graph)

  46mm Heliopan Hoods - If you decide to use these narrower diameter lens hoods then you will need to shorten them quite a lot.  The measurements are as follows (without thread depth):

    If you are definitely NOT using filters then add 4mm to the above figures. (See graph)
   Depending on one's skill cut down the hood to the required length.   How you do this is up to you - either buy a dozen and practice or if still in doubt use a local machine shop.

  Sunken Lens Release Button - To speed up lens changing this button needs to be more easily found without fumbling (Look at any Minolta or Canon release button).  At DIY stores there are little self-adhesive round pads that stick on cheap kitchen units to deaden the sound when the doors are closed.  Paint if required (though they seem to come in clearish plastic) and stick one on the lens release button.  They come off reasonably easily and any residual glue can be removed without damage to the finish.
(NB As your adhesive is likely to be different from mine and this 'hack' involves direct action on the body of the camera, test carefully on say the base of your own camera first in case you can't get it off easily.)