PME Metered Prism and Acute Matte screen

Discussion in 'Medium Format' started by graham_martin|2, Dec 12, 2009.

  1. I have read that the PME metered prisms are for the older type focusing screen and that when combined with an Acute Matte screen that it throws the meter off by one stop. Can someone confirm that for me, and let me know what steps one has to go through to get it to meter it correctly? From what I have found so far it seems that one first uses a hand held meter to see what the exposure should be and then make some adjustments to the ISO and max aperture.
    Is this fairly easily done, or should I look for a PME3?
    If it helps, the serial number of the prism I am looking at starts with RP. According to the Hasselbaldinfo.com website that means that this is probably a pre Acute Matte metered prism.
    Thanks
     
  2. I use a PME with acute matt screen on my 500c/m and I have no trouble at all with reversal emulsions. It also works just fine on my 500 body with an original screen. Where did you see the claim that there's a problem?
     
  3. I used a PME45 with an Acute Matte D which came with the 503CW. It was spot on whenever I used it. If you use a grid screen, it will affect the meter, and you will need to compensate for it. I use a grid on my H3D and it requires adjustment to the metering. On Sony and Canon DSLRs that I have used there is an adjustment of some sort to tell the metering what screen you are using. The Hasselblad has no such feature.
     
  4. The PME45 has a mode in its program setting that allows you to correct for global exposure adjustment. It's P5 - named 'permanent exposure correction'. This can be utilised to compensate for different focusing screens.
    The Hasselblad branded Acute-Matte D types and standard type screens (including microprism, split image and grid screens) require no correction - they're accurate. If you get an older fresnel screen, or an OEM screen, then you can use the meter adjustment feature to dial in permanent compensation.
    The correction Jeff describes above for grid screens is needed only if using spot metering with the microprism oriented vertically. If using it horizontally, or with center weighted metering and the microprism in either orientation, then there's no problem.
     
  5. Thanks Neil, I'm happy to stand corrected. Memory is an uncertain companion at times.
     
  6. Very nice answer Neil. It's been a worthy visit to the forum today.
     
  7. In response to H.P. here is where I read that there is a problem:
    http://www.hasselbladinfo.com/forum/archive/index.php?t-1625.html
    and here:
    http://www.photokb.com/Uwe/Forum.aspx/photo-medium-format/602/Hasselblad-PME-which-one
    and here:
    http://www.photo.net/medium-format-photography-forum/00Bxyc
    My question is, do I need to go to at least a PME 3 or can I use the PME and make adjustments as I originally mentioned?
    Thanks
     
  8. Graham's prism is not an PME45, so anything said about that doesn't necessarily apply to his.
    Besides, it's not the grid that could cause problems, but the clear parts of the split image rangefinder.
    Graham's PME is indeed callibrated to work with the old style screens. The Acute Matte screens are one stop brighter, and you do need to adjust for that.
    You do that by either setting an one stop slower ISO value, or an one stop slower maximum aperture on the prism.
     
  9. Thanks Mr. de Bakker. Having you confirm what I read elsewhere makes me feel a lot better. Do you know if it comes with a diopter adjustment?
    Thanks
     
  10. Graham,
    No diopter adjustment.
    You need to add correction lenses to the lens already in the eyepiece. There is (or should be) a retaining ring above the eyepiece lens, the purpose of which is to hold such a correction lens in place.
    Hasselblad sold correction lenses, and you could find some still. What i did however was ask a local optician (or whatever those people are called - the ones selling prescription glasses) to get me some in the power required (the same as you need in eyeglasses for a distance of a meter or two), and grind them down to size (from memory, 28 mm).
    Just as good as the original ones, but a lot cheaper.
    P.S.
    The "qnu" on Hasselbladinfo is me. "semmelblad" is another Photo.netter, called Ulrik Neupert. A very knowledgeable chap.
    So i haven't really confirmed, only repeated what you read elsewhere. ;-)
     
  11. I have a VCF/6 and it is correct that you have to compensate for the acute matte screen. In my particular case I found that I got better results with 1 and 1/3 stops. I recommend you perform tests with an external meter.
    Regarding diopter correction, hasselblad sold complete eyepieces (you had to substitute the original eyepiece). You can see them here. They come in fixed increments (+1,+2, etc.) and are not useful if you happen to have astigmatism. Having a custom one made as Mr. de Bakker said, will be the best solution.
    Another option is to get a viewfinder magnifier, which has an adjustable diopter correction. It is expensive and is not practical if you shoot handheld.
     
  12. I currently use a non-metered HC4 which has a diopter range from minus 5 to plus 5. My setting is minus 2. That might help me get the right eyepiece. Otherwise I could look into getting one custom made. In looking at the manual I see that it has a built in 3x magnifier which, when combined with the Acute Matte split screen, may be all that I need for correct focus.
     
  13. Replacing the entire eyepiece, instead of just adding correction lenses, was something Hasselblad came up with later, with the PME5.
    Perhaps to prevent people doing what i did, and get diopter correction lenses elsewhere. ;-)
    When you have an eyepiece with retaining ring, just go the optician and order a lens for it. Much cheaper, and easier than trying to find a complete eyepiece.
    If not: the lens in the PME5's eyepiece of course also comes out. So in my PME5 i had it replaced. The optician has a thing that tells him the diopter strength of any lens. Add the correction needed, and you'll know what lens to get in a jiffy.
    The viewfinder magnifier is nice if you want an extra close look at the screen. But is of limited use when composing. So if you use that thing for it's diopter correction, though focus will be very accurate, you will still be looking at a fuzzy viewfinder when composing.
    So whether it is usable depends on how badly you need a diopter correction. If you can make do with how you see the screen without correction, only need the correction to improve focussing, it might work.
     

Share This Page