Rescue and Modification of a Ricoh Auto Half


I’ve restored this cute little Japanese half-frame 35mm digital camera with a metering conversion from selenium to CdS, and the addition of adjustable focus. Right here’s the story.

My assortment consists of completely different cameras for various functions or moods. Generally it’s nice to gradual the method down, and agonise over the exact technical particulars of each shot. Different occasions it’s extra applicable to simply go snap, snap, snap and seize the second. This tiny Ricoh is nice for the latter. It was launched in 1960, and featured clockwork motor wind that’s good for a dozen or extra photographs in a single go. Being half-frame, it allowed you to snap away for as much as 72 portrait-format exposures.

On most variations, the main focus of the 25mm f2.8 lens was fastened. The shutter launch was initially on the entrance of the digital camera, and fires the shutter at about 1/125s when there wasn’t a flashgun related. Computerized publicity metering used a selenium photocell behind the acquainted ‘bubble window’ across the lens, driving a hidden publicity meter and trap-needle mechanism that managed the opening of the 2-bladed aperture.

Later variations added all kinds of bells and whistles. The shutter launch was moved to the highest plate, a self-timer was added, and there have been a number of fancy colored finishes from Ricoh and a number of other different licensed manufacturers. A couple of acquired fiddly-to-use zone focus, adjusted by turning the entrance of the miniscule lens rim with downwards stress out of your fingertips. The highest-of-the vary SL mannequin acquired a a lot larger f1.7 lens with correct zone focus, and battery-operated metering with a CdS sensor, but when you will discover a working one it’ll be eye-wateringly costly.

I acquired my digital camera cheaply on eBay earlier this yr, in good beauty situation and undeclared performance. It’s the primary model, 1960-63. Unsurprisingly, the metering didn’t work. Disassembly and investigation confirmed that the selenium plate produced solely a tiny flicker on the metering needle when uncovered to shiny gentle. All of my efforts to enhance it failed.

I didn’t wish to hand over although, so I regarded for options. Some individuals have had success changing a selenium plate with a photo voltaic panel out of a calculator, and re-calibrating the circuit. Probably not an choice right here, as a result of all of the panels I might discover had been a lot too broad to slot in the slender housing below the lens.

The subsequent choice was to make a battery-powered CdS system to drive the Ricoh’s meter. I had some CdS photoresistors from defunct SLRs in my spares field, and the quite simple 1.5 volt circuit diagram utilized by the previous screw-mount Praktica SLRs is out there on-line. Earlier than lengthy I had rigged up a take a look at circuit, utilizing potentiometers mounted in an previous takeaway tub, and a CdS sensor positioned in entrance of my calibrated LV gentle supply. Within the digital camera I eliminated the viewfinder for entry and positioned a bit of masking tape subsequent to the meter needle path. That enabled me to mark the seven positions that produced apertures from f2.8 to f22 when the trap-needle was operated.

Circuit testing. Energy provide & voltmeter on the left, then my gentle supply which is calibrated for LV.

Now I might experiment to find out what altering the resistor values would truly do. It was an iterative strategy of attempting a set of resistance values and noting how the aperture worth within the digital camera modified because the sensor was uncovered to various gentle ranges. Plotting the leads to Excel enabled me to see how the resistances within the circuit modified the gradient of the graph, and its vertical offset. After a little bit of fiddling, I had a set of resistor values that ought to work.

Getting it to suit was the following problem, as a result of it is a palm-sized digital camera. I designed and 3D-printed a brand new entrance housing that’s barely wider than the unique, so far as attainable whereas nonetheless being symmetrical across the lens and never interfering with the shutter launch button. The CdS sensor sits above the lens, behind an enlarged viewfinder window constituted of an previous CD case. The circuit and battery are in a compartment under the lens, behind a sliding cowl.

It is a tiny digital camera, so the electronics are a decent match.

The opposite sensible addition it wanted was an on/off swap, to stop the battery draining when the digital camera shouldn’t be in use. There actually wasn’t any room for it under the lens. Ultimately I constructed one into the digital camera, so it operates with the shutter lock mechanism. When button on the skin of the digital camera is slid ahead to unlock, the opposite finish of the see-saw locking lever strikes backwards to disengage from the shutter launch. That finish now touches towards a springy brass electrical contact I made, and completes the meter circuit. Sorted.

The brass contact (high left) is related to the white wire, and grounds the meter when the shutter is unlocked.
Word the pencil marks towards the meter, from f2.8 to f22.

Including front-element adjustable focus wasn’t too troublesome, as a result of the present housing for the entrance factor screws out and in. It’s set to a distance of about ten ft on the manufacturing unit, and locked with three grub screws. I eliminated the grub screws, and glued the housing right into a 3D-printed lens hood, which has an honest grip and a focusing scale. A detachable brass tab contained in the circuit compartment is used to set the infinity cease, and in addition prevents the lens being unscrewed multiple flip.  As a result of lack of house, I had so as to add a white-painted steel pin to a recess within the entrance housing to point the main focus.

The main target scale as-seen when in use, seen by a recess with a white needle to point the centre.

The one tough bit is that there is no such thing as a ‘B’ setting, which might make focus calibration simpler. As a substitute I labored out the place I wanted to shove a little bit sliver of plastic into the shutter launch mechanism, to jam it mid-cycle with the shutter open. Then calibrating the main focus was easy sufficient, utilizing an previous SLR split-prism focusing display screen held towards the movie rails.

Assembling and testing the digital camera appeared to point that it labored, because the aperture opening modified in keeping with the sunshine stage.  That justified becoming some new gentle seals on the rear movie door, which is eliminated utterly when loading movie.

The rear movie door is absolutely detachable. Shutter lock is on the suitable hand finish of the digital camera.

I loaded a roll of Ilford Delta 100 into it and took it on a few photograph walks — one round Norwich, and one across the North Norfolk coastal village of Burnham Overy. It’s probably not appropriate for covert use, as a result of the quiet click on of the shutter launch is adopted by a ‘ZZZZZZUUP!’ noise as you launch your finger and the clockwork winder does its factor. Winding the spring makes use of a silent ratchet although. I acquired 79 exposures out of the movie, and will have gotten 80 if I’d have loaded it at nighttime.

Elm Hill, Norwich.

The well-known Norwich Keyboard.

Model on Norwich Market.

Boat at Burnham Overy Staithe.

Millstream, Burnham Overy.

Tower Mill, Burnham Overy.

The outcomes had been pleasing. Exposures had been fairly near the mark, though it’s nonetheless wise to make use of a detrimental movie with first rate latitude. Having the ability to focus the digital camera allowed for lots extra image alternatives than would have been the case with fastened focus. All of the element is there, and it’s a really usable digital camera to maintain in your pocket.

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