ASAHI Pentax one

jaimeb82 · Mar 28, 2009

just received an ASAHI spotmeter Pentax. It is the one without the light, I have no experience with spotmeters. The 9v battery is new. I went outside this morning, nice and sunny NYC today and the needle goes all the way to the highest number 18 or 19. It ia almost impossible for me to find something in the outdoors that will give me a lower EV number.

Inside of my apartment, the EV values seem to be more reasonable. Am I doing something wrong? Did I buy a broken/non-calibrated spotmeter?

thanks in advance, Jaime

chriscrawfordphoto · Mar 28, 2009

The older ones had a dual range system. You had to choose either the high or low range. If you chose the low range, it would show everything as the highest number in bright light.

Arvee · Mar 28, 2009

I may be mistaken but I believe that unit takes two batts, the 9V and a button cell. Google for a manual and possibly more information. I seem to remember that the button is a mercury cell and if it was replaced with an alkaline, your readings will be high.

-F.

jaimeb82 · Mar 28, 2009

thank you guys, that seems to be the case, haven't tested yet, but there is a 1.3V mercury battery (Mallory RM640, Eveready E640 or equivalent)--for high-light range. I can't unscrew the battery housing cover, it is really hard! may need some W4 or a large screwdriver.

Found the manual here:

http://www.butkus.org/chinon/pentax/spotmeter_iii/spotmeter_iii.pdf

Thanks again

resummerfield · Mar 29, 2009

jaimeb82 said:
.......I can't unscrew the battery housing cover, it is really hard! may need some W4 or a large screwdriver. .......

That Mercury battery has corroded and welded the cover on. Yes, use some penetrating lube (just a trace) and let it set and penetrate. But be careful with the large screwdriver..... I've seen several cameras with the bottom plate twisted and completely destroyed by using too much force.

jaimeb82 · Apr 1, 2009

I finally opened, it is all green and corroded but it seems like mercury batteries were discontinued, I knew $50 for this spotmeter was to cheap to be true.

winger · Apr 1, 2009

I think the camera should still function without the batteries and meter. You'll just need to meter with something else or use the sunny 16 rule. I have an even older Pentax (no meter at all) and that's how it's been used.

jaimeb82 · Apr 1, 2009

Oh no, it is not a pentax camera, it is a pentax spotmeter. I shot with mamiya and speed graphic

naeroscatu · Apr 1, 2009

I finally opened, it is all green and corroded but it seems like mercury batteries were discontinued, I knew $50 for this spotmeter was to cheap to be true.

There are adapters that you can use to replace the mercury battery in your spotmeter with ready available silver-oxide.
You don't mention what type of mercury cell battery it uses but in most cases they deliver 1.3 V. The adapters have diodes built in that lower the output from 1.5 V of equivalent silver-oxide batteries and deliver a constant 1.3 V. Few options are out there including B&H. Oh, you are correct about the price to good to be true... however I don't think replacing a mercury battery is a bad problem on a Pentax spotmeter. Even if you spend $40 additional on the adapter you will probably end up with a good spotmeter for $90 instead of $150 regular on the market.

Anscojohn · Apr 1, 2009

jaimeb82 said:
Oh no, it is not a pentax camera, it is a pentax spotmeter. I shot with mamiya and speed graphic

********
Some creativity in battery might be in order. If I recall correctly, that RM640 battery was as thick as a coupla "regular" 1.35 vbatteries--so you have room to play with. Something as simple as a wooden plug, with a hole drilled in it so as to take a zinc/air hearing aid battery, with some aluminum foil stuffed in either end of your home-made plug might do it for you. Be creative.

If you find this is beyond your interest and technical skills, I'll be glad to give you 51 dollars for it so you can make a profit!!

aeronaut · Apr 2, 2009

Some comments:

1) The appropriate way to remove the mercury battery cover is with a $0.05 tool called a nickel. It fits perfectly in the groove, and won't mess up the bottom. Now, if the old cell has corroded the cap on, there may be trouble - use penetrating oil. But the nickel is the best way to open the cap.

2) While 1.35 V cells are out there, it's not that hard to build a circuit that will take the 9v from the bigger cell and step it down to exactly 1.35 V. As long as the 9V cell is above 1.35+1.2= 2.55 V, it should replace the missing mercury cell with no additional battery needs. The circuit consists of a LM317 voltage regulator and 2 resistors. I'm gonna try to install one into my meter in the spaces in the handle.

3) While I'm at it, the possibility of illuminating the scale is tempting - a LED should do the trick nicely. Again, can be powered off the 9v cell, with a current limiting resistor. Should be cake.

I'll report on how these mods go when I finish them.

Regards,
Martin

jaimeb82 · Apr 2, 2009

Anscojohn said:
********
with some aluminum foil stuffed in either end of your home-made plug might do it for you.

Is the aluminum acting as a transmitter of electrical current? kind of connecting the bottom with the top (negative to the positive?) I can definitely try something like that, as far as the cost is $1

jaimeb82 · Apr 2, 2009

aeronaut said:
Some comments:

1) The appropriate way to remove the mercury battery cover is with a $0.05 tool called a nickel. It fits perfectly in the groove, and won't mess up the bottom. Now, if the old cell has corroded the cap on, there may be trouble - use penetrating oil. But the nickel is the best way to open the cap.

2) While 1.35 V cells are out there, it's not that hard to build a circuit that will take the 9v from the bigger cell and step it down to exactly 1.35 V. As long as the 9V cell is above 1.35+1.2= 2.55 V, it should replace the missing mercury cell with no additional battery needs. The circuit consists of a LM317 voltage regulator and 2 resistors. I'm gonna try to install one into my meter in the spaces in the handle.

3) While I'm at it, the possibility of illuminating the scale is tempting - a LED should do the trick nicely. Again, can be powered off the 9v cell, with a current limiting resistor. Should be cake.

I'll report on how these mods go when I finish them.

Regards,
Martin

The 9v is for low light situations. Wouldn't you kill the ability to read in low light situations if you make that 9v battery to become a 1.35?

In any case, are you in NYC?, could you do all that to mine? Please!

ASAHI Pentax one

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