PME metered prism can I use it with AcuMat screen

G

Gregarpp

I bought a 45° PME prism.
I assume this is one of the older prisms.

How can I tell what the prism is calibrated for?
Acu-mat or the original screen?

Will the serial number tell me?
 

qnu

Banned
The serial number may be of use, yes. Especially if there are letters in it.
I have to check, but i believe the PME3 and all the later prisms also have their type printed on them as well.

The quick and easy way to find out is to compare the reading you get with prism and screen to what another meter says it should be.
 

semmelblad

New Member
Starting with the PME-3 the Hasselblad prism finders were calibrated for Acute Matte screens by the factory. But older prisms may have been recalibrated for the bright screens or newer prisms may have been recalibrated to match older screens. You never know. Compare with a handheld meter to have a starting point and then spend a slide film to see and document what you really get.

Ulrik
 

lmenzin

New Member
I have a PME prism that happens to work well with an Acute Matte screen. I bought it used and thus don't know its service history, meaning that perhaps it was recalibrated by a previous owner. The best way to compensate for screen brightness differences (if you don't send it out for recalibration) is to use the ISO setting.
 

qnu

Banned
Pete,

Your prism isn't one of the clunky ones with a needle display?

What is the serial number? The PME3 (the first one factory calibrated to work with Acute Matte screens) appeared in about 1989. The previous model was first made in 1980/1981.
So the letter codes (in front of the serial number on the bottom plate) that would indicate the old prism would be RS, RV, RH, RP, RI, RC, RT, RU and RR. RE is difficult, may be either, though i guess an RE one will already be a PME3.

But as was said, the early prism may have been recalibrated, so if you find your prism is indeed the early type, you still need to test against another meter.
 
G

Gregarpp

Mine is the original PME prism.
The internal display is all in EV readings.

I have a Minolta V meter.
If I were to use my spot 5° attachment and point both at a wall, they should read the same?

This would be a reflective type reading?
 
R

Rustyx814

Per the manual for my 501C: If the PME has not been recalibrated for the Accute-Matte, use the following formula to receive an accurate meter reading from the PME Prism:

Reduce the ASA/ISO setting to 1/2 the film
speed value as indicated on the film package.
or
Increase the MAX lens apeture setting one full
stop.
or
REDUCE the EV reading one full step when
setting it on the len's EV scale.
(pg 24 Hasselblad 501c Instruction Manual)

Of course, it is best to use another meter to check for accuracy using this method. If you spot meter the wall and then compare with the PME's} meter, you should be able to tell whether the PME is calibrated.
 

qnu

Banned
Pete,

Just to satisfy my curiosity: what is the serial number, or rather, what is the letter code in the serial number?

Yes, if you point the camera with prism at a wall, do the same with a hand held meter, the reading should be the same.

That is, they should be more or less the same.
I never found two meters that did agree exactly, and i have tried a few. And there is bound to be a slight difference due to different areas metered, etc.
So don't let small differences worry you. look out for the big ones.

And provided you use all the correct settings on both meters, of course. ;-)
Don't forget to set the right aperture on the PME, and meter with the aperture fully open!
 
G

Gregarpp

I will post the serial number tonight.

When you say meter wide open, I thought my 80mm lens stops down to f4 when it is not set to 2.8

Do I need to compensate for that?
 

qnu

Banned
Pete,

The 80 mm lens stops down to f/4 when not set to f/2.8?
I don't quite follow. None of the lenses i know does that, nor should your lens. Unless, of course, the lens happens to be set to f/4, and the aperture is closed down manually. ;-)

(By the way: what version 80 mm lens do you have? C, CF, CFE?)

As long as you do not have the aperture closed manually (using the appropriate lever/tab) the lens should be fully open (i.e. f/2.8 in any 80 mm lens), no matter what aperture is set.

And should you indeed have closed the aperture manually, the lens will be stopped down to whatever aperture happens to be set on the aperture ring.

Anyway, yes, if a lens is stopped down to some aperture, that very same aperture number must be set on the meter as well. The meter must know through what size aperture the light it is metering is coming.
Any mismatch will result in wrong readings, incorrect exposure.

The usual drill is to keep the lens wide open (not just for metering, but for focussing as well), and set the maximum aperture of the lens in use on the meter.


Knox,

The meter doesn't care whether the screen used is an Acute Matte or an Acute Matte D. They are the same as far as brightness is concerned.
 

knox

New Member
I was curious, so I looked in my PME45 VIEWFINDER manual . . . page 15 says "the accu matte D series is strongly recommended as the exposure system is calbrated according to this type" the older accu matte "will work for lenses only and in the F/2-F/4 range provided the split image line is in the horizontal position"
 

qnu

Banned
Knox,

There are two issues here.

First, the meter is calibrated for Acute Matte screens. It really doesn't matter whether Acute Matte or Acute Matte D type.
The non-D type being discontinued, the manual talks about Acute Matte D screens.

Second, one half of the split image rangefinder will darken with lenses of f/4 or slower.
This is a problem when using the spotmeter mode in the PME45 (not present in the earlier PME prisms).
And this problem is with the rangefinder, not (!!!) with the type of screen it is in.
A similar problem arises with screens having micro prism arrays. You can not use the spot meter with either type of focussing aid, no matter whether in a D or non-D Acute Matte screen (or non-Acute Matte screen).

The Acute Matte and Acute Matte D screens are equally bright, and there is no difference as far as metering is concerned.
 

knox

New Member
Thanks for taking the time regarding this. I bought a 45 a couple months back and have yet had a chance to spend much time with it, so all info is appreciated.
 
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