F-Stop Printing with EPOI Printol Enlarger Timer

[Dan Rainer]

Hi all,

I recently decided to try f-stop printing and I'm trying to figure out if my EPOI enlarger timer would work well with that workflow. The switch on the bottom says "SECONDS" and toggles between "X1" and "X-1". I'm assuming that this refers to seconds and tenths of seconds. Based on that assumption, the knob on the right does seem to do tenths of a second when in "X-1" mode. However, the left knob gives very inconsistent results.

In X-1 mode, 10 on the left knob gives about 1 second. 10 = 10/10 = 1, seems simple. However at longer times, this breaks down. Set to 90, I got over 2 minutes of light. Does anyone have any insight into how this timer works? Bonus points if you have any info on EPOI, I can't find anything about the company online.

 

[reddesert]

It's actually "x .1", a decimal point not a dash, so your assumption that it should multiply the time on the dials by 0.1 is correct. I don't know why it's not giving you the right time. Do both dials give you the time in seconds in "x 1" mode?

Maybe one of the dials is dirty. I have one of these timers, although I don't have access to it at the moment. IIRC, to inspect the components / wiring, you just need to loosen the screws at the corners and lift the faceplate out of the box. (Unplug it first, obviously.) My instinct would be to shoot some electronic contact cleaner into the dials and switch and work them back and forth a few times.

EPOI stood for Ehrenreich Photo Optical Industries. Joe Ehrenreich/EPOI was the original distributor of Nikon in the USA, and also distributed other brands - for ex Bronica. In about 1981, Nikon (Japan) acquired the company and turned it into Nikon USA.

 

[Nicholas Lindan]

I second Mr. Desert's advice - open it up, give the switches at the back of the knobs a spritz of contact cleaner and work the knobs back and forth. It doesn't matter which cleaner you use, they are basically all the same - some just add red food coloring as a marketing gimmick - even a very light spritz of WD-40 will work in a pinch.

If that doesn't get it working again then it is time for a new timer. Some timers make f-Stop printing much easier than others.

 

[Ian C]

E.P.O.I. (Ehrenreich Photo Optical Industries) was for many years the sole distributor of Nikon cameras and lenses in the U.S. I don’t know whether it made any of the products it sold to dealers.

https://www.shorpy.com/node/23083

https://www.ebay.com/itm/184447801880

Cleaning the switches with tuner cleaner as mentioned is a good first step. That might fix the problem.

I’m not familiar with the inner workings of the EPOI timer. Many timers of that era used capacitors of various values to establish the time standard for enlarger timers. This is based on the constant charge/discharge rates of capacitors.

As they age, capacitors can change internally leading to increasingly inaccurate times. By replacing the capacitors—if they are at fault—the normal time function can often be restored. A capacitor usually must be unsoldered to remove it from the circuit to test it with a multimeter to determine whether it’s at fault.

There might be other electronic components that have aged and failed in addition to the capacitors. An electronics technician could diagnose it. It might be cheaper to look for another timer in good working order.

 

[Nicholas Lindan]

As Ian mentioned, the time will be set by the charging time for a capacitor-resistor circuit. The knobs will usually change resistor values and the X.1 X1 switch will change capacitors. You have to be careful in changing the capacitors in the timing circuit - you want ones with close tolerances. Many capacitors are made for filtering purposes and have a -20/+80% tolerance band.

Capacitors get a bad rap. The problem started in the late 80's with electrolytic capacitors from China that were both small (good for compact electronics) and cheap. Consumer goods like TVs and CD players were failing left and right. The capacitors were too small and too cheap - a combination that does not make for a high quality product, think Yugo. Miniaturization costs money, big time.

Capacitors made in the US (Mallory, Sprague, CDE ...) in the 1960's are generally still good and within tolerance. Modern high quality brands are Panasonic, Kemet, and Nichicon.

 

[koraks]

Many timers of that era used capacitors of various values to establish the time standard for enlarger timers.

It's also possible they used logic IC's (74xx series etc.; decade counters and the like). Timing might have been an R/C, but then I'd expect everything to be off. It's also quite likely the actual time base was taken from the grid AC frequency, so 60Hz in the US and 50Hz in Europe.

If you open it up and post some good photos of the innards the general concept will show itself, no doubt.

 

[ic-racer]

I have one of those I got in 1975. Still works fine today, so I have never opened it up. It is a newer design than the Omega timer that only has a single silicone device (one transistor). My guess is that there is an IC in the EPOI.

For f-stop printing I do the following with a hand-held calculator:

1 stop = multiply or divide by 2
0.5 stop = multiply by or divide by 1.4
0.333 stop = multiply or divide by 1.26
0.25 stop = multiply or divide by 1.19

 

[albada]

Capacitors get a bad rap. The problem started in the late 80's with electrolytic capacitors from China that were both small (good for compact electronics) and cheap. Consumer goods like TVs and CD players were failing left and right. The capacitors were too small and too cheap - a combination that does not make for a high quality product, think Yugo. Miniaturization costs money, big time.

Capacitors made in the US (Mallory, Sprague, CDE ...) in the 1960's are generally still good and within tolerance. Modern high quality brands are Panasonic, Kemet, and Nichicon.

I heard that the "capacitor plague" (search the Internet for that phrase) was caused by defective electrolyte made in China using an incorrect formula which they stole from a company. I've seen computer motherboards with multiple blown caps, and have replaced some myself. The EPOI will not have this problem, but its caps might have dried out enough to cause intermittent failures.

Some timers make f-stop printing easy because they calculate seconds for you. And @Nicholas Lindan himself manufactures and sells such a timer; his website is http://www.darkroomautomation.com/da-main.htm
. The RH Designs Stopclock and Analyzer Pro are two more such timers.

Mark

 

[RalphLambrecht]

I have one of those I got in 1975. Still works fine today, so I have never opened it up. It is a newer design than the Omega timer that only has a single silicone device (one transistor). My guess is that there is an IC in the EPOI.

For f-stop printing I do the following with a hand-held calculator:

1 stop = multiply or divide by 2
0.5 stop = multiply by or divide by 1.4
0.333 stop = multiply or divide by 1.26
0.25 stop = multiply or divide by 1.19

not bad idea or just use a

I have one of those I got in 1975. Still works fine today, so I have never opened it up. It is a newer design than the Omega timer that only has a single silicone device (one transistor). My guess is that there is an IC in the EPOI.

For f-stop printing I do the following with a hand-held calculator:

1 stop = multiply or divide by 2
0.5 stop = multiply by or divide by 1.4
0.333 stop = multiply or divide by 1.26
0.25 stop = multiply or divide by 1.19

not a bad idea or use a handy table

 

[mshchem]

Don't waste your time with this timer. I bought one of these brand new in the early 70's. Quit working reliably after a couple years. I tried contact cleaner etc. Just a turkey.
There's several new f stop timers available, one is an advertiser here

 

[Dan Rainer]

Thanks for all the helpful replies!

I opened up the box and admired the colorful array of capacitors and resistors (pics below). No immediate signs of leaking/bulging/corrosion. I sprayed a bunch of contact cleaner and wiggled the knobs a ton. Each knob position has its own individual resistor.

I reassembled and did some more testing. The right knob feels dead-on timing wise, but the left knob is still off and the timing drift gets progressively more noticeable with each subsequent click of the dial. (At the 90 and 100 positions, I'm not sure the enlarger light ever actually turns off. I waited several minutes before losing patience and resetting the timer.) It also drifts in full seconds mode, but the drift is far less noticeable. 100 seconds yielded 104. Not ideal, but pretty impressive considering the age.

From my testing and the info in this thread, I'm pretty sure there's a specific timing capacitor for the left knob in X.1 mode that has gone sluggish, particularly at longer exposure times. I think I'll hold onto the timer and take it to a friend with more electrical engineering and soldering experience. Could be a fun project to located a replace the culprit.

In the meantime, I'll start looking into upgrading to a modern, electronic timer. I know f-stop printing can be done with just about any timer, but I want the precision of accurate fractions of a second. The timers from @Nicholas Lindan and RH Designs both look promising.

Looking forward to more accurate printing going forward!

 

[Nicholas Lindan]

Looks like it uses 1% Dale resistors in the timing switches - which are high quality components. Good chance the IC is a 555 timer. The black and orange wires from the x.1 and x1 switch should each go to a capacitor. As you surmise, it is the capacitor connected to the x1 position that is likely the culprit.

 

[RalphLambrecht]

maybe it's time for a new f/stop timer?

 

[mshchem]

These timers are 50 years old. I bought one new, it was like a months salary stocking groceries. Beautiful thing, started acting crazy after a few years. I felt like I had been robbed. One of the best days was when I finally gave up and binned it!

 

[MarkS]

OTOH, I also bought an EPOI Printrol in the mid-'70s- it cost about $50 then, a stretch for a college student.
It worked fine from '75-'80, and then from 1989 until about 2005, when the 'expose' button quit working. I gave it to a friend who was an electronic tinkerer, but it just added to his large collection of 'broken things I can't be bothered to fix'. I consider that I got my money's worth, but today? Find a timer that will do what you want.