Pentax MX

Asahi Optical launched the Pentax MX in 1976, together with the more automatic ME. Both were Pentax's answer to a shift Olympus had started in 1972 with the OM-1: the full-size SLR, made small. The MX is usually described as a smaller, lighter successor to the Pentax KX. The MX is the manual one of the pair. Its cloth focal-plane shutter is fully mechanical. Two small silver-oxide cells run the meter and nothing else. Asahi's own manual says the camera can still be operated when the batteries have worn out. According to Hamish Gill of 35mmc, the camera was aimed at professionals. Asahi built a system around it. There were eight interchangeable focusing screens, a data back and a magazine back. The Winder MX ran at 2 frames a second, the Motor Drive MX at 5. The meter has no needle. Five LEDs sit beside the finder image: green for correct exposure, orange for half a stop off, red for a stop or more. The way it switches on is the detail owners remember. You pull the advance lever out 20° to its stand-off position, then press the release halfway. Push the lever flush against the body and the meter is off. Size is the other part of the story. Asahi gives 135.5 x 82.5 x 49.5 mm and 495 g for the body. Gill calls it, as far as he can work out, the smallest fully mechanical metered SLR ever produced, slightly smaller than the OM-1. Ricoh Imaging, which owns the Pentax name today, lists the Asahi Pentax MX under 1976 in its own Silver Series timeline. Production ended in the mid-1980s. Camera-wiki and Kosmo Foto give 1984; other references give 1985.

A first manual SLR that keeps working when the battery dies. Every speed from 1 second to 1/1000 runs without power; only the LEDs go dark. Travel and walking, where a 495 g body with a short lens makes a difference by the end of the day. The Pentax K mount, with a large pool of manual-focus SMC Pentax and Pentax-M lenses. The 40mm f/2.8 and the 50mm f/1.7 were among Asahi's own standard lenses for this body. A bright finder at 0.97x magnification, with the shutter speed and aperture both visible while you shoot. The focusing screen is interchangeable through the lens mount. Where it falls short: manual exposure only. There is no aperture priority, no program and no automatic flash. The meter gives dots, not numbers. Five LEDs in half-stop steps are quick to read, but they do not tell you how far off you are beyond one stop. 1/1000 top speed and 1/60 flash sync are modest. Fast film in bright sun will run out of shutter. Lenses without an aperture ring cannot set their aperture on this body. Small controls. 35mmc found the shutter speed dial stiff. The advance lever in its stand-off position also gets in the way of anyone who shoots with the left eye. There is no mirror lockup control.

First pull the advance lever out to its stand-off position and press the release halfway. The meter is off when the lever sits flush, which catches out many new owners. If nothing lights, fit two fresh cells and look at the battery contacts for white or green crust. A dirty or bent meter switch is the next suspect.

Push the advance lever flush and watch the finder. The LEDs must go out. If they stay lit, the meter switch under the base plate is out of adjustment. This is a common and small repair, described under the faults section.

Fire the camera at 1 second, 1/2, 1/4, 1/8, 1/15 and 1/30, with the back open and the lens off. Each should close by itself in roughly the right time. A shutter that stays open at the slow end, while the fast speeds work, points to dried lubricant in the slow-speed governor.

Fire at every speed and watch the mirror. It should drop straight back. A mirror that stays up, usually at the slow speeds, is a known MX fault. Winding on often brings it down, but the cause needs attention.

The lever winds, the counter moves, and the frames come out blank or overlapped. The take-up spool's slipper clutch is a known cause. Load a test roll you do not care about and check the rewind knob turns as you wind.

Try the hot shoe and the sync sockets separately at 1/60. A flash that fires from the socket but not from the shoe points to the contacts, not the flash.

Run a cotton bud along the channels around the back door. Foam that is black, sticky or crumbling has failed. Look at the mirror bumper foam in the mirror box too.

Owners and repairers describe the same pattern: the mirror sticks at slower speeds. The usual cause is the mirror timing mechanism in the bottom of the camera, gummed up with residue, often from decaying foam. iFixit's guide adds a dirty mirror return latch, or a closing curtain too slow to trip it. The repair is a clean, lube and adjust. It is technician work, and on a body this compact it should include new foam seals.

Speeds from about 1/30 down to B stay open while the fast speeds work. One owner traced it to a seized escapement wheel in the slow-speed mechanism, freed it, and cleaned out the dried grease with solvent. Owners report doing this at home. The forum advice is still to send it to a Pentax specialist, because solvent and oil in the wrong place cause new faults.

A common electrical fault on the MX. A simple set of brass contacts under the base plate forms the meter switch. Over time their adjustment drifts until the meter never switches off. The fix is to remove the base plate and reset the contacts. That means bending them gently, or moving a small screw in a slotted plate. Owners describe it as a short job. If the meter still stays on afterward, the fault is in the circuit and needs a technician.

Rule out the cells first. iFixit lists corroded battery contacts, dirty switch contacts and broken internal wiring as the causes of a dead meter. Light corrosion cleans with vinegar or isopropyl alcohol on a cotton bud. A meter that reads but reads wrong needs calibration on a bench.

The cloth curtains travel at a set speed, and that speed drifts over decades. The result is uneven or wrong exposure at 1/500 and 1/1000. A technician measures the curtains with a shutter tester and adjusts their tension. This is not home work.

iFixit lists foam around the rear door, the mirror box, the front lens board and the viewfinder. Door seals behind the back are the most accessible part of the job. Foam inside the mirror box and behind the lens board is harder, and its residue is linked to the mirror fault above.

iFixit traces this to bent contacts near the eyepiece, or a dirty X-sync contact under the winding plate. The eyepiece contacts can be reshaped carefully. The sync contact sits behind the front lens board and is technician work.

iFixit links this to a failed slipper clutch in the take-up spool. The symptom is blank or stacked frames partway through a roll. It needs the camera opened.