Hasselblad PME3 issue with longer focal lengths

[Photomultiplier]

Hello

I acquired an PME3 metering prism some time ago and noticed the following behavior:

Conditions:
- New 6V lithium battery, voltage measures to spec according to manufacturer datasheet. Current consumption of PME3 approx. 22mA when in use.
- 500C/M with 42165 Acute-Matte and 500C/M with standard screen for comparison
- Evenly lit white wall with reference measurements taken with two Sekonic meters that agree to within 0.1EV
- Stray light was shielded from the eyepiece as good as possible

First i used the PME3 with the Acute-Matte, i even bought the screen because i wanted the prism.

With the 2.8/80 CF Planar, everything works fine. MAX is set to 2.8 and ISO to 100.
With the 4/50 C Distagon, it also works, and of course, MAX is set to 4 in this case.

Things get weird when using the 4/150 CF Sonnar anf 5.6/250 CF Sonnar.

4/150 CF Sonnar + Acute-Matte + MAX set to 4: Meter reads +1EV high
5.6/250 CF Sonnar + Acute-Matte + MAX set to 5.6: Same as above

This was the point where severe head-scratching started.

When turning the MAX and ISO knobs, the reading moves in an linear and consistend way across the scale in the increments of the knob. So no linearity problems apparent.
Same with the light level.

As impossible as it sounds, it seems as if with the 150 & 250 Sonnars, there is more light coming through than the max aperture would permit.


After that, i counterchecked things and used the standard screen. As expected, everything is -1EV down, which is also stated in the manual. I set ISO to 200 to compensate this.

2.8/80 CF Planar at MAX 2.8: Works fine
4/50 C Distagon at MAX 4: Works fine
4/150 CF Sonnar at MAX 4: Works - This is different to the test above with the Acute-Matte
5.6/250 CF Sonnar at MAX 5.6: Reads +1EV higher than it should

Does anybody have an idea what is going on? The Acute-Matte came in an original Hasselblad plastic box, but as it has no number on it, i have to believe that it really is an 42165 screen. It only has the crosshairs which appear to be scribed or molded into the fresnel plate. Anyhow, they are NOT painted and if the screen is held into the light, the rainbow spots phenomenon occours, so after all that i know, it should be a 42165. It definitely is not the D type because the notches are missing.

If it would be an different and incompatible screen that causes this behavior, at least the standard screen should give consistent results with 150 and 250mm too, albeit with the necessary compensation at the ISO setting, but it also shows +1EV error with the 250mm.

Chris

 

[Sirius Glass]

Hello

I acquired an PME3 metering prism some time ago and noticed the following behavior:

Conditions:
- New 6V lithium battery, voltage measures to spec according to manufacturer datasheet. Current consumption of PME3 approx. 22mA when in use.
- 500C/M with 42165 Acute-Matte and 500C/M with standard screen for comparison
- Evenly lit white wall with reference measurements taken with two Sekonic meters that agree to within 0.1EV
- Stray light was shielded from the eyepiece as good as possible

First i used the PME3 with the Acute-Matte, i even bought the screen because i wanted the prism.

With the 2.8/80 CF Planar, everything works fine. MAX is set to 2.8 and ISO to 100.
With the 4/50 C Distagon, it also works, and of course, MAX is set to 4 in this case.

Things get weird when using the 4/150 CF Sonnar anf 5.6/250 CF Sonnar.

4/150 CF Sonnar + Acute-Matte + MAX set to 4: Meter reads +1EV high
5.6/250 CF Sonnar + Acute-Matte + MAX set to 5.6: Same as above

This was the point where severe head-scratching started.

When turning the MAX and ISO knobs, the reading moves in an linear and consistend way across the scale in the increments of the knob. So no linearity problems apparent.
Same with the light level.

As impossible as it sounds, it seems as if with the 150 & 250 Sonnars, there is more light coming through than the max aperture would permit.


After that, i counterchecked things and used the standard screen. As expected, everything is -1EV down, which is also stated in the manual. I set ISO to 200 to compensate this.

2.8/80 CF Planar at MAX 2.8: Works fine
4/50 C Distagon at MAX 4: Works fine
4/150 CF Sonnar at MAX 4: Works - This is different to the test above with the Acute-Matte
5.6/250 CF Sonnar at MAX 5.6: Reads +1EV higher than it should

Does anybody have an idea what is going on? The Acute-Matte came in an original Hasselblad plastic box, but as it has no number on it, i have to believe that it really is an 42165 screen. It only has the crosshairs which appear to be scribed or molded into the fresnel plate. Anyhow, they are NOT painted and if the screen is held into the light, the rainbow spots phenomenon occours, so after all that i know, it should be a 42165. It definitely is not the D type because the notches are missing.

If it would be an different and incompatible screen that causes this behavior, at least the standard screen should give consistent results with 150 and 250mm too, albeit with the necessary compensation at the ISO setting, but it also shows +1EV error with the 250mm.

Chris

I have no problems with longer lenses, 150mm, 250mm, 500mm or 500mm + 2XE and the PME prism. My only grip is that with the Accumat D screen Hasselblad NJ could not only calibrate it so that I have to reduce the ISO by a factor of 2 to be correct. So for ISO 400 film, I have to set the PME on ISO 200 for the exposure to be correct. A pain in the ass so I have placed blue painter's tape with a reminder note on the PME.

 

[Photomultiplier]

So in your case it just works like the manual says? With MAX set to 4, 5.6 or 8 according to the lenses aperture.

What puzzles me most is that even when one would assume that the Acute-Matte screen is in fact something different, it behaves as if there was MORE light coming through. Even if it was some effect caused by the angle of incidence of the lenses light rays at the fresnel?

But even if it really is not the 42165 that it was sold as, why do i have the +1EV error with the 250mm when using the standard screen? There is nothing mentioned in the manual. Only the overall compensation because the standard screen is less bright.

When stopping the lens down, the reading moves accordingly. So it is definitely no problem with light sensitivity or linearity.

@Sirius Glass: How does your PME behave when using the non Acute-Matte standard screen? Despite having to compensate the ISO by factor 2, does it work with MAX = 5.6 when using the 250mm?

 

[Sirius Glass]

So in your case it just works like the manual says? With MAX set to 4, 5.6 or 8 according to the lenses aperture.

What puzzles me most is that even when one would assume that the Acute-Matte screen is in fact something different, it behaves as if there was MORE light coming through. Even if it was some effect caused by the angle of incidence of the lenses light rays at the fresnel?

But even if it really is not the 42165 that it was sold as, why do i have the +1EV error with the 250mm when using the standard screen? There is nothing mentioned in the manual. Only the overall compensation because the standard screen is less bright.

When stopping the lens down, the reading moves accordingly. So it is definitely no problem with light sensitivity or linearity.

@Sirius Glass: How does your PME behave when using the non Acute-Matte standard screen? Despite having to compensate the ISO by factor 2, does it work with MAX = 5.6 when using the 250mm?

With the Accute-Matte D screen twice as much light gets to the eye piece and it is advertised as such. Hasselblad NJ stated that they are unable to make that adjustment so they calibrate as normal and told me to use half the ISO. The 250mm lens still is set to work at MAX = 5.6.

 

[Photomultiplier]

It behaves the same with the sky and all other scenes i throw at it. And i do not see this behavior with any other camera and with Sirius' equipment it also works as it should. (For the 4/150 he uses MAX=4 and for the 5.6/250 MAX=5.6)

The handheld meter also has a wide FOV and it matches exatcly with the spotmeter in my test setup with the wall.

And remember, we are talking about an 1 stop metering error with an center weighted meter. If that would really be caused by the optics alone and be intrinsic to the lens technology itself, there would be no such thing as a perfectly exposed slide.
This cannot be normal behavior. Nothing is stated in any manual or book and i never heard of anybody having to use some other MAX setting than the aperture of the lens.

There must be something wrong, but i do not have a second meter or body to cross-check and i know no one personally who has an Acute-Matte and/or the PME3.

Maybe there is some bizarre optical effect caused by deteriorating anti-reflection coating of the unused sides of the pentaprism that becomes apparent only when the rays fall on the screen in a steeper angle like in the longer lenses?
But i can hardly imagine it to cause errors that large. The optics look fine, except for a bit blotchy looking unused sides. e.g. the triangle shaped surface that is visible when one looks into de prism from below.

@Sirius Glass: How does your prism look when viewed from de side that faces the screen? Namely the black painted unused surfaces of the glass prism that are not used in the optical path.

 

[Photomultiplier]

No, they are wide open.

Even if they were stopped down, the reading would move down, not up. I used the DOF switch and aperture to validate the linearity of the meters values.

 

[reddesert]

I am not familiar with these focusing screens or Hasselblad meter prism specifically. Generally, focusing screens can behave differently with different lenses, because the angle that the rays exit the lens is different. In technical terms, some lenses have their exit pupils more forward or rearward, and the screen "sees" the light as coming from the exit pupil. Focusing screens have their fresnel grooves and focusing aids (microprism or split image) set up as some compromise to work with the majority of lenses, but if you use a lens that is toward the extreme of what it is designed for, then the visibility in the focusing aid, or the brightness of the screen, may change.

Normally I would expect odd cases to be discussed somewhere in a manual (but it's unclear to me how many different kinds of Hasselblad screen there are). Just as an example, there are an enormous number of Nikon focusing screens, and some of them (especially with microprisms) came in several models for different focal length ranges: http://www.mir.com.my/rb/photography/hardwares/classics/michaeliu/cameras/shared/ff2screens.htm I realize this doesn't mention metering, it's just evidence that the focal length and the focusing screen do interact.

Old Gregg, I don't agree that reflected light meters are necessarily off for wide angles. Meters measure surface brightness. The corners of the view in a wide angle are farther away, but when something is further away, there's more area within the field of view, so surface brightness, unlike point source luminosity, does not change with distance. If you meter an evenly lit wall at 5 feet away and at 10 feet away you should get the same number.

 

[Sirius Glass]

It behaves the same with the sky and all other scenes i throw at it. And i do not see this behavior with any other camera and with Sirius' equipment it also works as it should. (For the 4/150 he uses MAX=4 and for the 5.6/250 MAX=5.6)

The handheld meter also has a wide FOV and it matches exatcly with the spotmeter in my test setup with the wall.

And remember, we are talking about an 1 stop metering error with an center weighted meter. If that would really be caused by the optics alone and be intrinsic to the lens technology itself, there would be no such thing as a perfectly exposed slide.
This cannot be normal behavior. Nothing is stated in any manual or book and i never heard of anybody having to use some other MAX setting than the aperture of the lens.

There must be something wrong, but i do not have a second meter or body to cross-check and i know no one personally who has an Acute-Matte and/or the PME3.

Maybe there is some bizarre optical effect caused by deteriorating anti-reflection coating of the unused sides of the pentaprism that becomes apparent only when the rays fall on the screen in a steeper angle like in the longer lenses?
But i can hardly imagine it to cause errors that large. The optics look fine, except for a bit blotchy looking unused sides. e.g. the triangle shaped surface that is visible when one looks into de prism from below.

@Sirius Glass: How does your prism look when viewed from de side that faces the screen? Namely the black painted unused surfaces of the glass prism that are not used in the optical path.

 

[cowanw]

So I set up my PME 90 and tried the 80mm, 150mm, 250mm, and 350mm. I have a 42215 Acute Matte D split/micro and used the Integral setting on a plain white wall. The 50 and 150 read 2/3 stops faster than the 250 and 350. Not exactly your setup but the setup is newer and in good condition. I believe it functions as it should. My Pocket Spot reads as per the 50 and 150.

 

[Photomultiplier]

@cowanw: Thank you for the tests with your equipment. So i am not the only one wo gets different readings.

@reddesert: i am also pretty sure now that the angle of incidence at the screen because of the exit pupil diameter is the cause of this behavior. With the Hasselblad Flexbody for example, you have to use correction slides with your focusing screen if you tilt the back. Otherwise the screen gets very dark if you look at it perpendicilarly. The slides
are fresnel plates with linear grooves that deflect the light in a more usable fashion. As you sad above regarding design compromises, the correction slides are also a compromise. One for ~10° tilt and another one for ~20°

It would be interesting to use a ground glass without any fresnel optics, just for experimentations sake. The image would be dim, but all those angle of incident related effects would be gone.

Maybe it's time to once again use good old kentucky windage: https://www.microwaves101.com/encyclopedias/microwave-slang (just search for it on this page)
I will just have to live with it and dial in the MAX values with 1Stop offset when using the Sonnar lenses. Important to me is that there is apparently nothing broken and it is just an systematic error that can be compensated for and the reading is reliable otherwise.

But as i often try to use the small backpack, i think the PME3 will stay at home more often than not because it is relatively heavy (approx. 0.5kg/1lbs) and almost doubles the height of the camera so that it does not fit anymore.
On the other hand, i really enjoy the ease and speed of working with TTL metering. I liked it in my 35mm days and would like to use it with MF also more often.

 

[Photomultiplier]

The metering prism madness goes into the next round...

Today i used the 80mm Planar with my 55mm macro extension tube. When using the handheld meter, i compensate by +1.5 stops for the 80mm in combination with the 55mm extension. This value has been calculated with
the close up calculator on the hasselbladhistorical website and it has been confirmed with countless macro shots over the last 14 years.


I noticed that the PME3 does not change its reading when the 55mm tube is in place. It should change by 1.5 stops but it does not. This behavior was reproduced with a evenly lit white wall.

This is getting more and more enigmatic and maybe ruined some of yesterdays shots

The light intensity MUST decrease according to the inverse square law, but the reading does not change, at most a fraction of a stop.

In the manual it is explicitly stated that the meter compensates for bellows extension. Yes, it is clear that it should work like that, but why it does not work in my case?


Either it is not the 42165 screen it was sold as, the PME3 is out of whack regarding its photocell alignment (but i checked it) or my setup employs a new kind of physics (or everything together^^)

Anyway, i am at my wit's end.

 

[Michael Mutmansky]

Here’s a video to help you identify the screen you have.



He has done a bunch of other Hasselblad videos and they are all quite excellent.

 

[Photomultiplier]

Yes, he has great videos!

I always wanted the D with split screen but only was able to obtain the non-D acute-matte with the fine crosshairs. P/N 42165
It exactly looks like how a 42165 should look like. Rainbow pattern when held against the light, fine grooved crosshairs (not painted).

Funny enough: Yesterday i tried the whole thing again with the Flexbody and its focusing screen. The screen is not changeable, but it seems to be
quite like the acute-matte.
I inserted the prism and the behavior was the same. No reduction in the EV reading when using the 55mm tube where it should read -1.5EV low.

I am inclined to make a day-trip to vienna with a friend of mine who wants to buy a rollei TLR or something similar and visit the camera shop there
and ask if i may cross check things with their bodies and metering prisms. IIRC i even bought the prism from them online

Maybe inside the prism there is something off, like the angle of the sensor or antireflex coating or whatever, but i had it already disassembled and everything looks
pristine and properly aligned. Nothing shifted out of position.

 

[Michael Mutmansky]

I'm no help beyond that, but only to suggest that these ground glass screens do use optics to make the GG appear brighter by redirecting the diverging light rays back towards the eye (into converging rays) and they may just result in errors with the meter when the light rays are more parallel coming in (from the longer lenses and the extension tube).

A talk with someone who knows the Hasselbald gear really well (a dealer who should have had training on things like the function of the metering prisms and interaction with the screens) may prove very useful. I somewhat suspect that you will have to put together a crib sheet of adjustments for using that meter with the screen and certain lens combinations.

This is actually one reason I decided to not get a metering prism. I felt that unless it were perfect with respect to these possible interactions, I'd be all messed up and chasing my tail trying to figure out where the errors were occurring. I'd rather do it manually from a spot meter from the start. Let me say that I didn't know there whould be issues, but I figured there might be because I had read about recalibrating older meters for the newer screens...

I did get a PM45, but not a PME45... not sure how much I'll use it as the gear is all new to me these past few months, but I did decide to not get meter version because I felt I may have issues with some lenses and with extension tubes and exposure consistency. Having used LF gear for many years, I didn't feel I needed any help with calculating exposures that the metered prism would solve.

 

[Sirius Glass]

Here’s a video to help you identify the screen you have.



He has done a bunch of other Hasselblad videos and they are all quite excellent.

Thank you. I never knew that the two bars will move out automatically, I have always had to fight them. I prefer the AcuteMat-D without the focusing ring and with vertical and horizontal cross hairs to allow me to line up verticals and horizons.

 

[Michael Mutmansky]

Thank you. I never knew that the two bars will move out automatically, I have always had to fight them. I prefer the AcuteMat-D without the focusing ring and with vertical and horizontal cross hairs to allow me to line up verticals and horizons.

I know, right? It's as if Hasselblad thought through the design of the system pretty well! It's an auto-lock that eliminates the possibilty of a screen rattling around and giving you poor focus.

 

[Arthurwg]

All very interesting. I would love to hear the answer.

 

[Sirius Glass]

I'm no help beyond that, but only to suggest that these ground glass screens do use optics to make the GG appear brighter by redirecting the diverging light rays back towards the eye (into converging rays) and they may just result in errors with the meter when the light rays are more parallel coming in (from the longer lenses and the extension tube).

A talk with someone who knows the Hasselbald gear really well (a dealer who should have had training on things like the function of the metering prisms and interaction with the screens) may prove very useful. I somewhat suspect that you will have to put together a crib sheet of adjustments for using that meter with the screen and certain lens combinations.

This is actually one reason I decided to not get a metering prism. I felt that unless it were perfect with respect to these possible interactions, I'd be all messed up and chasing my tail trying to figure out where the errors were occurring. I'd rather do it manually from a spot meter from the start. Let me say that I didn't know there whould be issues, but I figured there might be because I had read about recalibrating older meters for the newer screens...

I did get a PM45, but not a PME45... not sure how much I'll use it as the gear is all new to me these past few months, but I did decide to not get meter version because I felt I may have issues with some lenses and with extension tubes and exposure consistency. Having used LF gear for many years, I didn't feel I needed any help with calculating exposures that the metered prism would solve.

Metering through the lens works for all the lenses and with the 1.4X and 2X extenders plus compensates for the extension tube and bellows.

 

[MattKing]

Meters that read off of the viewing screen can definitely be affected by how the viewing screen is designed, because those meters are often quite directional in how they work.
The two usually need to be designed together.

 

[McDiesel]

@Michael Mutmansky Hasselblad metered prism finders are designed for specific focusing screens, and work beautify regardless of lens or extension tubes. Some prisms require an older matte screen, while others require AcuteMatte. PME-45 is designed for AcuteMatte screens, I do not remember the model names for the older prisms but you can look them up. This KEH description says that PME51 is designed for AcuteMatte screens as well.

 

[Sirius Glass]

I know, right? It's as if Hasselblad thought through the design of the system pretty well! It's an auto-lock that eliminates the possibilty of a screen rattling around and giving you poor focus.

Metering through the lens works for all the lenses and with the 1.4X and 2X extenders plus compensates for the extension tube and bellows.

Meters that read off of the viewing screen can definitely be affected by how the viewing screen is designed, because those meters are often quite directional in how they work.
The two usually need to be designed together.

@Michael Mutmansky Hasselblad metered prism finders are designed for specific focusing screens, and work beautify regardless of lens or extension tubes. Some prisms require an older matte screen, while others require AcuteMatte. PME-45 is designed for AcuteMatte screens, I do not remember the model names for the older prisms but you can look them up. This KEH description says that PME51 is designed for AcuteMatte screens as well.

I always use my 45° PME with my Hasselblad 503 CX since I bought it and use it for my 30mm Fisheye through my 500mm with a 2XE extender. The WLF just sits on the shelf by itself mopping and crying.

 

[Photomultiplier]

And the extension tube (55mm with an 80mm Planar in my case) does influence the reading by -1.5EV with your equipment?

Info: my PME3 says on its label that it is designed for P/N 42165 which is the plain acute matte screen that i bought (it was sold as 42165 and also looks like it according to the already mentioned telltale signs)

 

[bdial]

FWIW, the PME can be calibrated for use with a standard screen, I had that done on mine.

 

[Photomultiplier]

I know, but that is not de problem in my case. The standard screen is 1 stop dimmer than the newer ones. So it can be adjusted internally or one can select the ISO one stop off to compensate. I have been looking for circuit diagrams but found none. Maybe i reverse engineer
the circuit board when i have time, because i would like know what circuit topology they have chosen. (And what role each of the trimmers play^^)


I have tried the standard screen also. Same behavior, just 1stop lower as expected. The strange things with the different focal lengths not indicating correctly despite correct setting of max aperture persisted. (See initial post)

 

[Sirius Glass]

FWIW, the PME can be calibrated for use with a standard screen, I had that done on mine.

I had mine done by Hasselblad for my 45° PME and my Acute-Matte D. They did the calibration, however they could not accommodate the newer screen, therefore, per their directions, I now set the ISO to half the value on the PME.