[n0wik]

I have a Pentax Spotmatic.
I put a new battery in it. The light meter works because when you change the shutter speed you can see that the pointer changes.
The problem is wrong pointing. It's 5 times too big. At f2.8 and iso 100 it takes 1/8 s (on camera with good lightmeter) but on Pentax it shows 1/250 s.
One of the batteries shows 1.35v, the other shows 1.41v but the meter shows the same values for each battery.
Is it the fault of the battery or the light meter is broken? What to do?

[stevebrot]

Welcome to the Pentax Forums!

Is it the fault of the battery or the light meter is broken? What to do?

What model Spotmatic do you own? Going on the assumption that your camera is one of the models that originally used a single PX 400 mercury cell (most did), the paragraph below should apply.

What type of battery are you using? The meter on your Spotmatic is not particularly voltage sensitive and should operate fine at 1.35v assuming that the battery is a fresh (newly opened) zinc-air cell. If the battery a 1.5v alkaline or silver cell, it may be close to depletion at that voltage and might not supply sufficient current to power the meter. You can check the battery as follows:

• Shutter speed on "B"
• Film speed on "100"
• While looking through the viewfinder, turn the meter switch on. The needle should rapidly (instantly) move from the slightly down position to full down.

Steve

[pentaxus]

Which spotmatic is it? What battery are you using? Some of the zinc air batteries for some Spotmatics can be installed incorrectly. That can give you weird readings. The best battery is an Eveready 387s battery. it is shaped just like the original battery and you can't put it in upside down. It is a 1.5 volt battery but the original spotmatic works just fine with a 1.5 volt battery. The Spotmatic, Spotmatic II, SP500 and SP1000 all use the 387s. Amazon and ebay both sell the eveready 387s with spacer ring which fits just like the original PX400.

[n0wik]

Welcome to the Pentax Forums!



What model Spotmatic do you own? Going on the assumption that your camera is one of the models that originally used a single PX 400 mercury cell (most did), the paragraph below should apply.

What type of battery are you using? The meter on your Spotmatic is not particularly voltage sensitive and should operate fine at 1.35v assuming that the battery is a fresh (newly opened) zinc-air cell. If the battery a 1.5v alkaline or silver cell, it may be close to depletion at that voltage and might not supply sufficient current to power the meter. You can check the battery as follows:

• Shutter speed on "B"
• Film speed on "100"
• While looking through the viewfinder, turn the meter switch on. The needle should rapidly (instantly) move from the slightly down position to full down.

Steve

It's Spotmatic SP

and this batteries:

[n0wik]

It's Spotmatic SP

and this batteries:

Imgur: The magic of the Internet

[n0wik]

You can check the battery as follows:

• Shutter speed on "B"
• Film speed on "100"
• While looking through the viewfinder, turn the meter switch on. The needle should rapidly (instantly) move from the slightly down position to full down.

I did as you wrote and it happened exactly the same.
The needle rapidly move from the slightly down position to full down.

[titrisol]

I did as you wrote and it happened exactly the same.
The needle rapidly move from the slightly down position to full down.

That is the battery check, so you should be OK on that
Now if the camera has been stored for a long time, lightmeter resistor might be a bit rusty.
In order to clear the thin layer of oxide move the ASA film dial from 100 to 1600 and back to 16 a few times
Check if lightmeter reads closer to what you have

If that doesn;t work you might have to send your camera for service

[stevebrot]

It's Spotmatic SP

and this batteries:

I did as you wrote and it happened exactly the same.
The needle rapidly move from the slightly down position to full down.

As noted above, the battery is good and it may be that the film speed resistor require a little "exercise" as described by member titrisol. If not, a routine clean, lube, adjust (CLA) by a service shop would be in in order.


Steve

[titrisol]

I assume you have looked at the service manual for the camera, if not find it here:
Pentax | Service Manuals | Learn Camera Repair

There is a section about the lightmeter adjustment but that is beyond my capabilities

[DanLee]

I tried the test above on my Honeywell Pentax Spotmatic, but instead of the needle going from slightly down, it went all the way up. What does that mean?

[Not a Number]

Polarity on the battery reversed?

[DanLee]

Thanks! I put the Wein cell in the way the sticker indicated, but upon examination it was the wrong way around in the holder. Someone goofed at the factory. Working fine now.

[titrisol]

Thanks! I put the Wein cell in the way the sticker indicated, but upon examination it was the wrong way around in the holder. Someone goofed at the factory. Working fine now.

Wein cells are expensive, after it's done keep theplastic spacer and you can use hearing aid batteries (I think 312-Brown is the right size)

[stevebrot]

Thanks! I put the Wein cell in the way the sticker indicated, but upon examination it was the wrong way around in the holder. Someone goofed at the factory. Working fine now.

Wein cells are expensive, after it's done keep theplastic spacer and you can use hearing aid batteries (I think 312-Brown is the right size)

...and after that use a silver cell (Renata or Eveready 387S). The meter is not voltage sensitive. When the battery runs out, reuse the collar and replace the cell with a 394 silver cell. This is what I use on my SP and SPII.


Steve