Best battery solution for Pentax Spotmeter V?

Discussion in 'Large Format' started by e_b|7, Mar 15, 2005.

  1. I really like the sweeping needle of this analog spotmeter, but in
    addition to the 9 volt for low light levels, it requires a E640N 1.3
    volt mercury battery, which is no longer available. Options seem to

    1. Use an alkaline 1.5
    2. Use a Wein 1.35 with a spacer of some sort
    3. Use a hearing aid battery with an adapter

    Does anyone have any thoughts on what works and what works best?

    Thank you all in advance.
  2. Are you sure it's a Spotmeter V?

    Earlier Spotmeters used that battery set-up (and I think some of the early Spotmeter V's as well?? - anyone?)

    Most/current Spotmeter V's use 3 x 1.5 cells
  3. I doubt if it is a Pentax Spotmeter V. It sounds awfully like my old analog Pentax spotmeter. I found the Wien 1.35 V battery with an appropriate holder and spacer was the best solution. But it is far from perfect. I was still off at various levels, up to half a stop or more, but varying according to where I was in the high range. Also, the battery would start to fail without warning, so it required regular checking against another meter. The usual check to test the 10 reading on low and high scales wasn't reliable for checking the condition of the battery. I finally gave up and got myself a Pentax Digital Spotmatic.
  4. has 1.5v replacement alkaline batteries for the E640N Mercury batteries. They sell them 2 for $10. Check their web site and scroll down to the "Alkaline Mercury Replacement" section.
  5. Replace it with the Digital Spot. It`s ten times better anyway and smaller.
  6. Thank you all for your help. You are correct, in that I have the old Pentax analog spotmeter and not the Spotmeter V. My apologies for that inaccuracy. I've got a 1.5 volt alkaline on the way. I'm going to compare the results to other meters, and go from there.

    True, it sounds like I'll eventually need a new spotmeter, but, I can always use a 35mm camera body with spot metering mode in a pinch.

    Thanks again everyone!
  7. I have the Honeywell/Pentax 1/21 spotmeter which has this combination of batteries. I bought a pack of hearing aid batteries and put a spacer with it. I find that it reads about a half stop high based on shooting some slides and comparing it to various other meters I have. Here's the thing though, I think it consistently meters a half stop high. If you put a 1.5V alkaline it will only read correctly for the brief moment when the discharge curve of the battery matches 1.3V. The zinc-air batteries have a very flat discharge curve until they drop off very quickly, like someone mentioned. I bought an eight pack and they don't begin reacting until you remove the little cover. I just carry a bunch of spares around. Good luck and happy metering!
  8. For the Pentax III and the Honeywell/Pentax/Asahi spotmeters, I make and sell an electronic regulator that, along with a 3V lithium coin cell, produces a calibrated, rock-steady, regulated, 1.35 volts to the spotmeter's high-range circuit. The regulator is not a diode, but a real voltage regulator, and the output is constant for the entire life of the lithium cell. Go to for information on this regulator solution.
  9. Duane: $30 each!!

    You gotta be kidding. That is more than my meter cost.
  10. $30 is more than reasonable for this kind of gadget.

    You should not compare such things with mass-produced electronics assembled by a combintion of automated machines and low paid workers in the third world.

    The hour or so it would take to assemble this gadget easily justified the price tag. In fact in real terms it is cheap.

    You should rather compare this with the price of a later spotmeter costing $100's and performing much the same task.

    As for the digital meters being better, I can't comment, but in general I find digital meters harder to read and interpret. As to accuracy, the means of indication has little impact on the accuracy of the reading.

    I would think this device is a realistic solution to the problem, offered at a very low price.
  11. It is indeed a great article, and I think a reasonable price considering that my partner to fight back to life in full and not half as walking and without having to spend hundreds of usd in digital spotmeter that not even taste therefore very much because people still do this favor to those who need, thanks Duane
  12. I've developed a new type of regulator device. It is for twin-px624 stacked series mercury battery applications, like the Gossen Luna Pro light meter. It uses the same real regulator technology as the first regulator, but regulates two silver cells down to 2.69 volts (2 x 1.345V). It is now also available at . This device was developed at the suggestion of someone who bought one of my spotmeter regulator adapters. It is offered at less than the B&H solution.[​IMG]

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