Pentax Honeywell Spotmeter 3º/21º
Introduced in 1960 as the world's first spotmeter the co-branded Pentax Honeywell sold for $99.50 USD with a
leather case. The spotmerter's name references the 3º metering area and the 21º viewing area. Produced in a
few variaties over three years it was replaced with by the Ashai Pentax Spotmeter 1º/21º which provided a
higher degree of measurement accuracy. Subsequently, most spotmeter produced thereafter had 1º measurement
areas.The spot meter consists of an objective lens (100mm, f/2), a 45º split meter relfex viewing system, an
eyepiece and the photo conductive cell.In this case the photo conductor is CdS (Cadmium Sulphide) cell.

Left ViewRight view

How to Use the Meter
While looking through the viewfinder place the circle (3º measurement area) on the subject you wish the meter. Partially depress the reading button, or half-press,to sample a high light intensity area and read the LL (light level) from the H(igh) scale (numbered 10~18). If the need does not go past the 10 on the H scale, fully depress the reading button and read the LL from the L(ow) scale (numbered 2~10).

If the meter is subject to high light levels when the meter reading button is fully depressed (inteded for low light levels only), the needle may become stuck on the far right of the scale. Meter with the lens cap on or meter on a low light area while fully dressing the meter reading button. This should return the needle to it's zero position.

Reading the Results
Calculation rings
The ASA, aperature, speed and LL rings are located on the barrel of the lens. Set the ASA righ the the matching film speed you are using. To do this rotate the ring so that the ASA appears below the red dot found on top of the meter's body in front of the viewfinder. Set the subject's meter number no the LL ring to the red dot found on the top fron the the lens barrel. Presented are the combinations of shutter speeds and f/stops suitable for using as an exposure setting.

The LL (light level) numbers are specific to the meter, they can not be related directly or indirectly to cameras using EVS or LVS systems.

The calibration screw is located behind the viewfinder on top of the meter. Turn
the screw, while not depressing the meter reading button, so that the needle
rests in line with the H and L marker on the left of the scale.

Low Light Level Conditioning
For low light level readings where the lens cap has been left on for an extended period of time, the cadmium sulfide crystal will reach a proper reading in about 2 to 3 minutes. It is possible to "confition" the meter by viewing, no need to actually take a reading, a subject of slightly greater brightness then the subject of interest. Or simply take off the lens cap a few minutes prior to taking a low level reading so that he CdS cell "warms up". It is also possible to over compensate low level readings if the meter has been left un-capped and viewing an extremely bright subject and then attempt to meter on a low light level subject. In this case the CdS cell would need to "cool down."

Colour Correction
The reflex viewing system and the CdS cell have a coating which corrects for colour sensitivity. The meter provides a compensated measurement for exposure when either colour or neutral density filters are attached to the lens (46mm thread). There is no need to adjust exposure for a filter's exposure factor.

The Unlike modern meters the 3/21 uses two batteries for the high and low level metering. While the Eveready 22.5v is still available in the U.S., the 5.6v Mercury battery is no longer availble due to environment reasons. The 5.6v Mercury, PX23 Silver Oxide, is used for the high light level intensity metering. The 22.5v Dry Cell, Eveready 412, is used for the low light level intensity metering. Unlike later models there is no check battery function, meter readings can become un-reliable over time. The original mercury battery was expected to last for about 1 year. The 22.5v tends to last longer.

Type of measurement: Reflected light meter reading H(igh) and L(ow) ranges for half-press and full button presses.
Angle of view: 21 viewing° (diagonal)
Angle of Acceptance of CdS:
Photo conductor
3° spot
Sensitive element: Cadmium Sulphide CdS cells
Light Level Range: 3~18 (for 100 ASA)
Measurement range: (L)ow: 2~10; (H)igh 10~18
Range sensitivity of film: 3~6400 ASA
Range of diaphragm: f/1~ f/128
Speed Range: 8s~1/8000s
Batteries: 5.6v Mercury, PX23 Silver Oxide is a viable replacement
2.5v Dry Cell, Ever Ready 412
Dimensions: Height 130mm, length.135mm, width. 62mm, weight 420g

Two other sources of information on this meter can be found at James Ollinger's site and at Michel Carrère-Gée's site.