M O D I F I C A T I O N
So after a month of research, planning and refreshing the UPS tracking page - the MF finally arrived. Fully functional and clean as a whistle. I guess that's the good thing about being stored in a hospital closet for 40 years.
Following some assessment, it was clear that it was going to require more than just a swapped focus screen to unlock its full potential. And just because I can change my own oil doesn't mean I can do an engine swap. So I reached out to Sam over at Sam's Camera Bench for a little help. He's got a knack for Pentaxes and his K1000 teardown lead me through my first repair.
We spent about a week tossing ideas around and anticipating solutions for anything that could come up. But even still, the unknowns were numerous and some quirks of this camera may always be a bit of a mystery. A massive thank you to Sam for his expertise, enthusiasm and incredible modification work on this. Dude's a legend.
Alright, let's get into it -
focus screen
This one is no surprise. The primary issue is that the magnified screen doesn't allow you to see what's in focus. Regardless of the focus position on the lens, the image through the viewfinder remains unchanged and always in focus. And since zone focusing isn't the most satisfying or accurate way to go, a ground glass replacement was needed. Thanks to Jeff, I knew an ME or ME Super would be a suitable donor but the hopeful side of me wanted to see if the 45° split-image screen that I love so much from my P30T would fit and wouldn't ya know it.
The magnified screen was fully transparent and not ground - meaning the image was clearer and brighter than your average SLR. This meant swapping to a ground focus screen would actually cause the meter (which is calibrated for a transparent screen) to think the scene was slightly darker than it actually was, resulting in a slightly overexposed image. Maybe only by 1/3 stop but still, let's address the meter.
light meter
Taken prior to any mods, test roll #134 is a good representation of the results the spot meter will give. While not impossible to deal with, accurately spot metering requires extra time while shooting and crucially - it's helpful if you know what shutter speed you're metering for. Plus with no meter lock and only AUTO mode, you're stuck metering off what's directly in the center of your frame.
The lens under the light sensor for the spot meter plus hand wiring to the eyepiece
The magnified screen's rounded corners and the unlabled LEDs
One of the early mysteries of this camera was the meaning of the lights in the finder. The spot meter displays a vertical row of red LEDs with no values next to them. No shutter speed overlay, no +/-, nothing. They do react to different lighting conditions but without knowing the values or even the range of the LEDs, it was gonna be a challenge.
So in order to be sure of the shutter speeds and swap to a center-weighted meter, the main PCB was removed and replaced with one from an ME. This included the eyepiece, light meter, and viewfinder LEDs. The pentaprism was also swapped over to fit the ME's metering cells.
Fabrication test using brass shims soldered to the full-frame mask
New pentaprism with custom mask(left) and old pentaprism(right)
frame mask
There was still the problem of not having shutter values displayed next to the LEDs. Without any backlight, inserting the ME's shutter speed overlay in front of the half frame mask wasn't of much use. We suggested the idea of using a full-frame mask and adding marks or posts to help with framing and leave it Sam to say "brb" before fabricating a brand new mask with full length vertical half-frame guides and overlay attached!
Custom half-frame mask with shutter speed overlay and 45° split-prism focus screen
lens mount
The need for this particular modification stems from the specialty lenses intended for use with the MF. Communication between the lens (endoscope) and the camera's light meter was routed only through the x-sync port. Meaning that if I wanted to use manual focus lenses, the meter would have no way of knowing my chosen aperture.
Because there was no lens mount connection needed, a number of parts were omitted entirely. First, the tab on the aperture coupling ring was removed (more like snipped off). Then the variable resistor behind the top of the lens mount which measures the movement of the aperture ring was left out. Thankfully the mounting holes for it were in place so the ME could donate some more blood.
Above - Old aperture ring without tab
Below - New ring with tab
Lens mount assembly - ME(left) and MF(right)
However, because the aperture coupling ring was no longer a moving piece, they removed not just the return spring but the post that holds the spring in place. Ugh.
Unbothered, Sam's solve was to epoxy a new hook in place of the post and it works like a charm.
Custom attachment of the return spring
Less of a headache but similar to the aperture coupling ring, the spring for the stop down lever wasn't needed so wasn't included. The lever itself was there as it's integrated into the mirror mechanism so a relatively easy add.
odds & ends
With the bulk of the functionality mods out of the way, there were just a few things left to do -
The mode dial was interacting with the power switch slightly differently than normal. Instead of cutting power to the shutter and firing mechanically in 1/4 mode, the MF continued to power the shutter and perform some metering/electronic timing. The wiring of the timing switches to the metering circuit was also different so the ME's shutter was swapped in too.
The plastic lever above the frame counter controls the power switch in different modes. Minor profile change between the MF(white) and the ME(black) kept the shutter powered on the MF.
Frame counter assembly - MF(left) with locking tab to lock advance lever and ME(right) with beveled tab
This is a quirky one - the advance lever was only able to be seated flush with the camera body when the camera was turned off in the locked position. My guess is this was just part of Pentax's design philosophy for their industrial product line. The reminder to the user to switch the camera off when finished feels like something baked into an SOP of some kind. Or maybe it wouldn't fit in the case with the lever in the stand-off position...
Maybe that's just all they had around.
I'm not a left-eye shooter but there are plenty of instances where I'll want the back of the camera flush to a wall or mount. So another donor part from the ME to remove the advance lever lock.
And finally, some side-by-side comparisons
Underside of the film counter mechanism showing the finely pitched sawtooth gear of the MF(right) compared to the same gear on an ME Super(left)
Advance gearing - ME(left) and MF(right)
Above - Top of the exposure compensation dial showing the ME Super's full stop incriments(left) and the MF's half stop lowercase/uppercase lettering(right)
Below - Underside of the same dial. Notice the locking detents on the ME Super(left) and the tighter beveled teeth on the MF(right)
If you've made it this far - wow. Ya nerd.
While there aren't any other custom mods just yet, there's definitely more on the way. And if you have any ideas for future projects or want to know more about the MF, reach out and let's do some problem solving.
