MC and MD Rokkor lenses. What's the difference?

[malkav]

Hello all,
I was wondering what the difference is between the MC, and MD Rokkor lenses, and how does it effect usage on an SR-T 101 body?

Thanks,
Ed

[SidW]

Hi Ed,

They represent two stages in Minolta's development of exposure coupling between lens and camera.

The first step was the MC system. The lens aperture is set manually and the setting is read into the camera mechanically via a small tab that links the lens and camera and is coupled to the TTL exposure meter, provided the camera and lens are designed to work together like this (maybe late sixties or early seventies). Metering is done at full aperture.

MD was the next step a little later. An extra tab on the aperture ring enables the aperture to be set from within the camera. This requires a camera designed for this feature, maybe late 70s and early 80s until autofocus came along and changed everything.

Compatibility. MC and MD lenses will work like any other earlier lens when used on earlier cameras. An MC lens will provide MC aperture coupling on any MC or MD camera. An MD lens will provide MC coupling on an MC camera and MD coupling on an MD camera.

I'm not sure where the SR-T 101 fits in this progression. It might be an early MC camera. One of the others will know (e.g Randy, but there's a large Minolta clan here).

PS. I remembered I'd had an SR-T 100x and found the manual (dated 1975) - combined for 100x and 101b. The 101b was the same as the 100x plus shutter speeds were visible in viewfinder and a there was a selftimer. The metering is the MC type, but the manual says it will work with both MC and MD lenses, and that MD lenses are supplied with both as standard. That confirms that the MD system was around earlier than I thought and that MC lenses were no longer being made by 1975. Your 101 ought to be slightly older than the 101b.

PSS. Try this: jwhub.xtdnet.nl/mug/

[Randy]

An SRT will work with an MD lens like you say, but the second tab will make no difference. The only cameras that take advantage of the tab as far as I know are the XD Series...ie XD-5 through XD-11. The XG and up have no aperature priority, and neither do the XEs.

[Peter S.]

The MC/MD operation works like this:
The lens needs to be preset to the minimum aperture, but it is kept open by the camera.
Through-the-lens metering informs the camera on how many EV numbers the exposure needs
to be decreased w.r.t. the wide open lens and the selected shutter speed. Note that this is
the same for MC and MD operation. Moreover the MC tab informs the camera on how many
EV values will be lost by the closing of the lens' aperture.

In MC operation the shutter speed is adjusted by the camera, so that TTL-measurement minus
stop-down-EV decrement of the lens preset value just results in a correct exposure. A variant
of that method does a second metering when the lens is stopped down just a few milliseconds
prior to exposure. This is only possible with silicon photo diodes as light meters, as the reaction
of the older photo resistors was to slow for that mode of operation. I heared from a reliable
source, that the X-700 works like that. I don't know it for the XD. The second variant has some
advantage, when the relationship between the MC tab and the actual lens aperture is not
absolutely exact. The former method is better, when the lens is too slow, i.e. when the aperture
blades are still moving, when the second metering is done. (I will come to this later)

In the MD mode the TTL-measurement result minus the EV-adjustment for the fixed shutter
speed is used to evaluate for how many EV-steps need to be decreased by stopping the lens
down from the wide open TTL-measurement. Note that the cameras were build in a way, that
the shutter speed was increased, if a full open aperture was not sufficient to get the desired
EV value. Note also, that the trick with the second measurement for a camera with a fast light
meter works in the same manner.

So far, that MD lug is not used! And that's why MD operation is _possible_ with MC lenses.
And that is what the MD lug is used for: The MD lug tells the camera what is the absolute
aperture of the fully stopped down lens (i.e. F/16, 22, or 32, there are no other MD lenses) -
as opposed to the MC tab, which just give the relative number on how many F-stops the lens
should be stopped down for exposure. Now the camera can compute the F-stop of the open
lens by the difference of the stopped down aperture (from the MD lug) minus the number of
F-stops, that the lens could be stopped down (this it the MC lug information). And this is the
reason why MD operation want You to set the lens to its minimum aperture. Otherwise the
above difference would not give the wide open F-stop of the lens.

Now finally, the camera shows You the sum of the wide open F-stop plus the difference in EV
that makes a correct exposure, i.e. the F-stop that will be used for the exposure. To repeat
this: the MD lug is just required to get the viewfinder information on the selected F-stop.

As a consequence You can not trust the F-stop reading in the viewfinder, if You used a MC lens
in MD mode.

But now I want to come back to the second metering thing. With that feature the time a lens
needs to stop down to the working aperture has become a critical issue. For an old MC camera
it would make no harm, if the lens took all the time until the mirror had moved upwards. So
the stop down speed shurely had been checked - but a good amount of time was available
for the stopping down of the aperture.

When doing the second readout, the lens needed to be stopped down before the mirror even
started to move (otherwise the light meter wouldn't get any light, right?). So the whole firing
cycle gets longer by the stop down time (what before that could be done while the mirror
moved). So Minolta required their lenses to strictly meet the stop down time. As a consequence
the aperture mechanism (e.g. the shape of the aperture blades) had been changed (e.g.
look at the rolling blades of the MC Tele Rokkor-PF 2.8/135 and the straight one of the MD
Tele Rokkor 2.8/135). So if You got a sloppy lens, especially one with a large aperture (e.g.
a MC 1.7/85) then You might get some under exposure in the automatic modes. Of course
You can easily overcome this by using the manual mode - or by having the aperture cleaned.
All the reports I got, definitely state, that clean MC lenses work flawlessly on all the XD
and X bodies.

And as a small addition to Randy's comment: the X-700 is the other camera besides those
XD's that uses the MD lug.

I hope I found simple enough words to explain the issue - it is not that big thing in practice
however: I don't hesitate to use MC lenses on any SR-mount camera body. Btw, I found the
effects of the later coatings to be irrelevant - it increases price more than usability.

Best regards
Peter

[malkav]

Thanks for the replies. So I guess I can use MC and MD lenses on my SR-T 101.

[Peter S.]

Yup! You can use anything that You can screw into the SR mount...
P

[malkav]

Yay!!!