# Help with Mamiya 645 metered prism finder



## snark

I recently bought a Mamiya 645-1000S with a metered prism finder.  I cannot find any user's manual that addresses this particular model of finder, and cannot even identify it for sure; apparently there were a number of versions manufactured: PD, CdS, AE, AE-S, etc.  I've looked through all the stuff available online and all I've seen have a shutter speed set knob on the finder, but this one does not.  It has only the film speed set knob and an "on/off" knob with a white button in the middle of it.  There are no LEDs in the viewfinder but a needle that indicates shutter speed, so it must work as aperture priority only.   Anyone know where I can get a manual for this?  The one on Butkus's site is the wrong model.

Maybe someone can advise me:  I just ran a test roll through it.  The meter readings are accurate when compared to my hand-held meter readings, and in manual mode I got good and consistent exposures at all shutter speed/f stop combinations from 1/8 to 1/500 sec.  The automatic mode does not seem to work - negatives got progressively thinner as I stopped down.   I've covered all the obvious bases; the lens and shutter speed select are both on auto and the linkage fork/pin on the lens is engaged.

I may be missing something here - like what the heck is the white button supposed to do?


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## webestang64

Does this help..... http://www.mamiyaleaf.com/assets/files/documentation/M645_1000S_v4.pdf


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## snark

webestang64 said:


> Does this help..... http://www.mamiyaleaf.com/assets/files/documentation/M645_1000S_v4.pdf


This is the same user's manual that's on Butkus' Oprhan Camera site, and the viewfinders covered in it both have shutter speed setting dials.  Mine has none.  Only film speed.

Thanks, though...


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## tirediron

Is yours an actual metered prism?  I'm not aware of Mamiya having done it, but there were a lot of cameras in the days before universal built-in meters that had an ASA dial just as a reminder of what speed you had loaded.


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## snark

Yes, it's metered.  In the viewfinder is a needle that indicates the appropriate shutter speed as you adjust the lens aperature.  It is accurate.  There is a symbol on the shutter speed knob on the left side of the camera body (a red circle with a red dot in it) that is supposed to actuate the exposure meter, and I guess to link it to the camera body and synchronize the shutter speed to the lens opening.  The meter is off (the needle in the viewfinder does not actuate) if the shutter speed is not set on that position.


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## tirediron

Hmmm... you've got me there.  I'm not familiar with that at all.  Sorry.


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## snark

This may help - I found an identical finder on EBay, so here's what mine looks like.   The Ebay seller says his works fine, but his is on a 645, mine on a 645-1000S; I wonder if they are incompatible?  
And check out the white button in the middle of the on/off knob.  When I push it I can hear a metallic click, but nothing seems to change.  What is it supposed to do, I wonder?

Mamiya M645 Camera Metered Prism A Mode 80 2 8 Lens Teleconverter More eBay


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## Derrel

I think that button is for finder display illumination, using an internal "grain of wheat" type bulb, as they were called. Many older 1970's era metering prisms, like the various Photomic prisms made by Nikon, used the grain of wheat bulb and a similar external button so the shooter could see the settings in dim conditions.


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## snark

Oh.  Now I feel dumb.  That makes perfect sense.  As that's now cleared up, I am even more convinced that the finder is not compatible with my camera body.


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## compur

If it fits your body it's compatible.

I think you're expecting too much from your finder. It's just a metered finder showing what shutter speed for _you_ to set. It's not an AE (auto exposure) finder that sets it for you.


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## snark

I am sure you are correct, it is definitely aperture priority and not auto exposure, but I cannot believe it was designed this way.   To take a meter reading, one must turn on the meter, set the shutter to Auto, take the reading, then change the shutter speed dial back from Auto to the desired speed. This has to be done every time a reading is taken because the exposure meter circuit is only completed when the shutter is in the Auto mode, and in Auto mode I have no idea what speed the shutter is set on.   

Again, it would not be the first time I missed seeing a forest for the trees, that's why I'm asking.  Just doesn't make much sense to me; it's far easier to use my hand-held meter.


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## Derrel

This is a camera designed over 40 full years ago. The first model hit the streets in 1975; your 1000s premiered in 1976...at that time, the mechanical buckhorns-on-the-lens and mechanical "pin" on the prism housing was Nikon and Mamiya's high-tech way of mechanically relaying lens f/stop information from the aperture ring to the metering prism...this camera was made in the early days of metering systems for medium format rollfilm SLR's.


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## snark

I understand the mechanical linkage between the meter and the aperture ring.  At risk of being obtuse though, I gotta say it's beyond odd that the shutter "auto" setting does nothing but turn on the meter.    It makes sense that when I select an f stop and the needle in the viewfinder moves to a certain shutter speed, the shutter would either fire at that speed or allow me to select that speed without deactivating the meter and going to full manual mode.  

Whatever... thanks for your interest and assistance.  I guess I just have another camera without a meter.   Good thing I have a hand-held.  Disappointing - I apparently paid way too much for it.


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## Derrel

Well...here's what I was able to piece together; I will not vouch for all of this. Some of this I know as fact, from the manual; later, there are some suppositions and hunches!

First, I mentioned the mechanical linkage system because it's a lot like "early 1960's Nikon Photomic technology", only in 1976...it's a mechanical system. If you look at Pages 35 through 37, on the PD and the CDS prisms: the PD prism forces the user to put the camera shutter speed dial at the NULL position, between 1/1000 second and Bulb, on that little dot; the other finder, the CDS model, forces the user to adjust and center the light meter using the shutter speed dial on the prism and THEN use the BODY's speed dial to set the shutter to the meter's indicated speed.....OMG...can we say clunky? In fairness...it took Nikon years, and a special, bulky, externally mounted automatic aperture controlling mechanism add-on device to do ANY automatic camera metering and setting, for years. Medium format cameras were never really designed to have any kind of metering systems, and the engineering systems in the pre-electronics era were verrrrry kludgy in the Mamiya brand.

The "A" prism is the AE prism, as I understand it. it works off the camera body battery, so the body battery MUST be good for the prism to actually set the speed. This is where things get a bit fuzzy, from here on down.

I looked around tonight and found these threads:
Prism Finsder for Mamiya 645 1000S - Photo.net Medium Format Forum

From what I understand, that little white dealy might have to do with the AE lock for the metering works; but more importantly, the prism YOU seem to have is, as I understand it an *Automatic* prism; you set the f/stop you want, and the meter is supposed to calculate the correct speed and set it automatically; it needs the battery in the camera to be good to do that (confirmed by multiple sources). See this thread: Mamiya 645j metered Prisms- Differences 

I thought the 645j is a much,much later, sort of stripped down 645 model; perhaps this prism's manual is online someplace, but not associated with the 645_1000 that you own. I think that might be why the original Mamiya 645_1000 manual only shows the two, earlier prism types: the AE prism came out LATER than your camera model did.

From what I can gather, it seems that over a 20-some-year span, the Mamiya 645 system had three types of prisms with metering: one setup that used a prism-enabled speed setting dial: a second system that required the identical speed to be set on both the prism AND also on the BODY-mounted shutter speed dial; and also a THIRD system of AE, the *"Automatic*" speed setting operation. So...yeah...this is a camera that used old-fashioned, 1960's-era Nikon-style buckhorn-and-pin lens indexing, and it had limitations, based on the aperture-indexing system.


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## snark

Derrel said:


> Well...here's what I was able to piece together; I will not vouch for all of this. Some of this I know as fact, from the manual; later, there are some suppositions and hunches!
> 
> First, I mentioned the mechanical linkage system because it's a lot like "early 1960's Nikon Photomic technology", only in 1976...it's a mechanical system. If you look at Pages 35 through 37, on the PD and the CDS prisms: the PD prism forces the user to put the camera shutter speed dial at the NULL position, between 1/1000 second and Bulb, on that little dot; the other finder, the CDS model, forces the user to adjust and center the light meter using the shutter speed dial on the prism and THEN use the BODY's speed dial to set the shutter to the meter's indicated speed.....OMG...can we say clunky? In fairness...it took Nikon years, and a special, bulky, externally mounted automatic aperture controlling mechanism add-on device to do ANY automatic camera metering and setting, for years. Medium format cameras were never really designed to have any kind of metering systems, and the engineering systems in the pre-electronics era were verrrrry kludgy in the Mamiya brand.
> 
> The "A" prism is the AE prism, as I understand it. it works off the camera body battery, so the body battery MUST be good for the prism to actually set the speed. This is where things get a bit fuzzy, from here on down.
> 
> I looked around tonight and found these threads:
> Prism Finsder for Mamiya 645 1000S - Photo.net Medium Format Forum
> 
> From what I understand, that little white dealy might have to do with the AE lock for the metering works; but more importantly, the prism YOU seem to have is, as I understand it an *Automatic* prism; you set the f/stop you want, and the meter is supposed to calculate the correct speed and set it automatically; it needs the battery in the camera to be good to do that (confirmed by multiple sources). See this thread: Mamiya 645j metered Prisms- Differences
> 
> I thought the 645j is a much,much later, sort of stripped down 645 model; perhaps this prism's manual is online someplace, but not associated with the 645_1000 that you own. I think that might be why the original Mamiya 645_1000 manual only shows the two, earlier prism types: the AE prism came out LATER than your camera model did.
> 
> From what I can gather, it seems that over a 20-some-year span, the Mamiya 645 system had three types of prisms with metering: one setup that used a prism-enabled speed setting dial: a second system that required the identical speed to be set on both the prism AND also on the BODY-mounted shutter speed dial; and also a THIRD system of AE, the *"Automatic*" speed setting operation. So...yeah...this is a camera that used old-fashioned, 1960's-era Nikon-style buckhorn-and-pin lens indexing, and it had limitations, based on the aperture-indexing system.





Derrel said:


> Well...here's what I was able to piece together; I will not vouch for all of this. Some of this I know as fact, from the manual; later, there are some suppositions and hunches!
> 
> First, I mentioned the mechanical linkage system because it's a lot like "early 1960's Nikon Photomic technology", only in 1976...it's a mechanical system. If you look at Pages 35 through 37, on the PD and the CDS prisms: the PD prism forces the user to put the camera shutter speed dial at the NULL position, between 1/1000 second and Bulb, on that little dot; the other finder, the CDS model, forces the user to adjust and center the light meter using the shutter speed dial on the prism and THEN use the BODY's speed dial to set the shutter to the meter's indicated speed.....OMG...can we say clunky? In fairness...it took Nikon years, and a special, bulky, externally mounted automatic aperture controlling mechanism add-on device to do ANY automatic camera metering and setting, for years. Medium format cameras were never really designed to have any kind of metering systems, and the engineering systems in the pre-electronics era were verrrrry kludgy in the Mamiya brand.
> 
> The "A" prism is the AE prism, as I understand it. it works off the camera body battery, so the body battery MUST be good for the prism to actually set the speed. This is where things get a bit fuzzy, from here on down.
> 
> I looked around tonight and found these threads:
> Prism Finsder for Mamiya 645 1000S - Photo.net Medium Format Forum
> 
> From what I understand, that little white dealy might have to do with the AE lock for the metering works; but more importantly, the prism YOU seem to have is, as I understand it an *Automatic* prism; you set the f/stop you want, and the meter is supposed to calculate the correct speed and set it automatically; it needs the battery in the camera to be good to do that (confirmed by multiple sources). See this thread: Mamiya 645j metered Prisms- Differences
> 
> I thought the 645j is a much,much later, sort of stripped down 645 model; perhaps this prism's manual is online someplace, but not associated with the 645_1000 that you own. I think that might be why the original Mamiya 645_1000 manual only shows the two, earlier prism types: the AE prism came out LATER than your camera model did.
> 
> From what I can gather, it seems that over a 20-some-year span, the Mamiya 645 system had three types of prisms with metering: one setup that used a prism-enabled speed setting dial: a second system that required the identical speed to be set on both the prism AND also on the BODY-mounted shutter speed dial; and also a THIRD system of AE, the *"Automatic*" speed setting operation. So...yeah...this is a camera that used old-fashioned, 1960's-era Nikon-style buckhorn-and-pin lens indexing, and it had limitations, based on the aperture-indexing system.



Boy am I impressed.  You did a ton of work to help me (until 02:00, it appears)  and I really appreciate it.  I think we are now the resident experts on Mamiya prism finders.  When these things were being built I was a troop in the army and no way could afford one.  I used to stare longingly at them in the PX and finally saved enough for a marked-down Kowa 6 (which turned out to be a magnificent camera).  Through all this I got the impression that Mamiya was the cutting edge of camera technology, and I never would have guessed how clunky some of their stuff actually was.

Anyhow, thanks again.  I will put a fresh battery in the camera and see what happens.  Also, that little white button may be the shutter speed set device that I could not believe was absent.  After reading your earlier post  I pushed it and looked for illumination in the finder screen and found none, and concluded the bulb was bad.   



Again, thanks for your help on this.  Anything I can do for you, just call...


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## Derrel

Always willing to try and help. I hope that a fresh battery is all this needs. Kowa 6...I remember those being in the magazines. As I recall, some fellow Moynihan had a medium format archive back in the earliest days of the internet...light blue pageswith black text, very "1990's world wide webb-ish", and he had an item in there on some system wide lens tests of a bunch of medium format lenses, and as I recall, resolution wise, the leading lens brand was not Hassy,not Rolleiflex, but Kowa.


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## Alexr25

This site http://www.photo-phil.org/Mamiya.pdf may also help as it lists which finders, backs etc are compatible with which bodies.


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## compur

I believe this may be the instruction manual for your finder:
http://www.cameramanuals.org/mamiya_pdf/mamiya_m645_pd_prism_finder_s.pdf


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