Olympus OM-10

Basic information:

The Olympus OM-10 is an ideal SLR camera for a beginner on a budget. Prices are very reasonable for used bodies (they went out of production long ago). OM-fit lenses are readily available.

Features:

• 35mm film, 25 to 1600 ASA.
• Aperture priority.
• Auto-exposure (with +/- 2 stops control).
• Bulb exposure.
• Self-timer.
• Manual adapter available, but scarce.

Building a manual adapter:

The manual adapter is a simple resistive device which plugs into a mini-jack on the front of the body. The following table gives resistor values against exposure time:

Exposure    Value
1000          7k6
 500         15k2
 250         30k3
 125         64k0
  60        121k6
  30        249k5
  15        494k0
   8        972k0
   4         1M96
   2         3M91
   1         7M92

The design of a simple manual adapter, giving between 1/1000 and 1/15 plus bulb exposures follows:

Jack ----------------------------+
     ^---+                       |
         |                 __    |
         |            o---o  o---|
         +---/\/---o       S2    /
             R1     \ o--------->\ R2
                    S1           /
                               

R1 = 8k protective resistor
R2 = 500k log pot
S1 = SPDT toggle switch
S2 = Push-to-make momentary switch

This gives a switchable system. In one mode, the potentiometer controls the exposure, between 1/1000 and 1/15; in the other, the shutter opens on pressing the shutter release, and then closes on pressing the momentary switch.