Minolta XD-5

connloyalist · Joined: 22 Jul 2020 Posts: 355 Location: the Netherlands

In my collection of lenses one of my goals is to have at least one film camera body for that lens mount. Preferably in working condition Smile

So a few months ago I picked up a Minolta XD-5. But, that was just before a bleak and very grey winter set in and I was not inspired to go out and give it a try.

With spring now properly here I shot my first roll with it. I had a roll of Portra 160 that I had picked up on sale and that I needed to use, so this has turned into a dual test: checking if the XD-5 is good (light seals for example), and my first experience with Portra 160. Yes, a bit of an expensive test roll.

I handed the film in the other day, should be back any day now so at this moment I don't know yet how the undoubtedly uninspiring pictures will have turned out. But from the perspective of using the XD-5, that is a really, really nice camera. I can see myself becoming a fan of Minolta, combined with the really nice lenses (ignoring my early experiences with iffy Minolta lenses). The only niggle is that I haven't yet found a way to comfortably hold the heavier lenses since the XD series cameras don't have any grip for your right hand (and none available that I know of?). Probably more a question of carrying the weight of the lens and camera with your left hand. It's not what I am accustomed to doing, so that will take a little getting used to. I am discovering that I really like using 135mm on full frame and the 135mm 3.5 is easily light enough so no problem there.

I don't know if these XD's are known for any particular failure mode that will cause it ti become a paper weight (electronics possibly?), but while it works I am going to thoroughly enjoy this XD-5.

Regards, C.

Doc Sharptail · Joined: 23 Nov 2020 Posts: 1308 Location: Winnipeg Canada

This thread is useless without some pics of the camera Wink

Been watching an XD-5 for over a year here on the local marketplace, and it hasn't moved in all that time.
It's quite over-priced for what it is.
Nice looking camera though.

-D.S.

connloyalist · Joined: 22 Jul 2020 Posts: 355 Location: the Netherlands

RokkorDoctor · Expire: 2025-05-01

connloyalist · Joined: 22 Jul 2020 Posts: 355 Location: the Netherlands

RokkorDoctor · Expire: 2025-05-01

RokkorDoctor · Expire: 2025-05-01

As promised, a short write-up of the exposure system of the XD series cameras by Minolta.

I typed this up quickly; it may be full of typo's and maybe there may be one or two inaccuracies, my apologies in advance, but most of it should be correct and it will give you some idea of how the XD exposure system works and how it came into existence (incl. the SR /MC / MD mount variations)

Also, the following web pages may be useful (I didn't check them for 100% accuracy):

https://www.rokkorfiles.com/XD11.html
https://high5cameras.com/all-articles/camera-reviews/minolta-xd-series/

Now on to the exposure system of the XD series cameras (XD7/XD11/XD5). I will avoid the math here Wink

In order to understand how this system came into existence, it is important to consider that the “MD lens mount” introduced with the XD cameras was a backwards-compatible modification of the original Minolta “SR” mount. In fact, it still is the “SR” mount with an additional couple of meter-coupling levers (“MC” & “MD” coupling levers) located outside of the mount itself.

The second important point to consider is that the aperture actuation mechanism introduced with the original SR mount does not allow for the camera to mechanically set an accurate aperture on the lens. The travel of the aperture actuation pin is short, too short to enable it to be calibrated as a specific amount (stops) of stop-down for a given travel distance of the aperture pin. This means that the SR mount aperture actuation mechanism as per the original design really only allows the camera to reliably switch between either the full open aperture on the lens, or the aperture set on the lens’ aperture ring. (This was revised in the following Minolta autofocus “A” mount, where there is a dependable relationship between aperture pin travel and number of stops aperture stop-down.)

With the introduction of the SRT camera, Minolta added the “MC” tab to the mount, which is essentially coupled to the lens’ aperture ring and it tells the camera the difference in stops between the lens’ wide open aperture, and the aperture set on the lens’ aperture ring. This means that the camera only knows the stop-down of the lens set by the user (in number of stops), it does not actually know the actual aperture selected by the user. But that is all the exposure system needs to know; with 1) a light-reading taken at full aperture, 2) the number of stops exposure reduction when the automatic aperture closes as indicated by the MC lever position, 3) the shutter speed set on the camera and 4) the film speed, the camera has all the information it needs to indicate the exposure in the viewfinder. On the SRT camera series this was all implemented with cables, pulleys, levers and cams. On later cameras the exposure was calculated electronically and the MC lever operated on a logarithmic linear resistance track (potentiometer) rather than a mechanical cable pulley system.

This system used in the SRT worked perfectly fine for the semi-automatic lollypop-and-needle exposure system found in those cameras. And even for later cameras which only offered electronic AE exposure in aperture-priority mode (XG, XM, etc.) the MC coupling lever is all that is required for exposure calculations, since no active control of the aperture is required.

However, with the XD series cameras, the smart engineers at Minolta found a way to implement both aperture-priority and shutter-speed priority modes whilst keeping the mechanics of the SR mount aperture actuation compatible (in fact, they implemented a semi-hidden “program” mode, likely the first of its kind). The key to making this feasible was the switch from the rather slow CdS (Cadmium-Sulfide) light sensor used in the SRT to using a much faster Silicon photodiode (SPD). What the engineers realised was that whilst the aperture actuation mechanism was essentially still a binary aperture open / aperture closed control only, the photodiode was fast enough to track the diminishing amount of light coming through the lens as the aperture was closing down. This allowed them to implement a pal & toothed gear break mechanism that would instantly lock the aperture actuation lever inside the camera body against any further movement towards closing once the lens had reached the required stop-down.

The first fly in the ointment here remaining was that the Minolta exposure system was still to take exposure reading at the full-open aperture. The “MC” tab only communicates stop-down to the camera, not the actual aperture set on the lens’ aperture ring. This means that in shutter-speed priority mode the camera would have no way of knowing how fast the lens was at wide-open aperture, and no way of indicating the expected aperture for proper exposure. This is why the “MD” tab was introduced. For operating in shutter-speed priority mode, the user would have to set the lens’ aperture to the minimum aperture. This would activate the MD tab which was really a four position switch:

0) switch open (minimum aperture not set on the lens)
1) minimum aperture set on lens, which is f/16
2) minimum aperture set on lens, which is f/22
3) minimum aperture set on lens, which is f/32

These four different positions were encoded in the space of travel of a single (minimum) aperture stop on the lens’ aperture ring. Hence only three minimum working apertures were ever available on “MD” lenses, and there were no half-stop click stops between the smallest aperture and the one above it. It simply would have been impossible to add more minimum stop-encodings on the switch within such a short mechanical travel distance.

With the number of stops stop-down indicated by the “MC” tab, and the minimum aperture set as indicated by the “MD” tab, the camera now has all the required information to indicate the exposure in the viewfinder, including the expected aperture in shutter-speed priority mode. For switching between aperture-priority mode and shutter-speed priority mode there was a mechanically actuated mask which either set a scale of shutter speeds against the exposure LEDs, or a scale of apertures against the same LEDS. The actual aperture set on the lens was also visible through a Judas-window (except for the budget XD5 model, which lacked the Judas window).

Another fly in the ointment is aperture overshoot/rebound. Minolta apertures for the SR mount lenses, to be fair, aren’t the most precise in world, although it depends on the lens series (older Rokkor and Auto-Rokkor and some MC lenses can be quite accurate). On later models (mostly MD, MDIII) the apertures achieved can easily vary by 1/3 to 1/2 of a stop or so from the value set on the aperture ring, especially on the smaller aperture settings. It is a consequence of aperture blade topology and the need to make aperture mechanisms as low-inertia as possible for the “MD” exposure system to work. This is why in the XD series cameras just before firing the shutter and whilst the mirror is still in the down position a final exposure reading is taken to make any necessary adjustment in shutter speed in order to achieve an accurate exposure.

The actual exposure sequence of the XD worked is thus as follows:

In Aperture priority mode:
- the user sets the desired aperture on the lens
- the camera takes a light reading at the full open aperture
- together with the “MC” stop-down info, light reading, and film speed it can calculate and indicate an expected shutter speed for proper exposure. This exposure is locked in memory (capacitor charge value)

In Shutter-Speed Priority mode:
- the user sets the minimum aperture on the lens (could be locked on most MDIII lenses)
- the user sets the desired shutter speed on the camera
- the camera takes a light reading at the full open aperture
- The “MC” stop-down info (now really the difference in stops between the lens maximum and minimum apertures since the lens is set at minimum aperture), the “MD” switch minimum aperture info, light reading and film speed give the camera all the information it needs to calculate an indicate the expected aperture for proper exposure. This exposure is locked in memory (capacitor charge value)

When the shutter button is pressed (in either aperture or shutter speed priority mode) the following sequence happens:
- the aperture actuation lever inside the camera is released and a spring starts to move it across so the aperture is allowed to start to close
- a pneumatic delay holds down the mirror
- in shutter-speed priority mode the exposure value is tracked by readout of the SPD (photodiode) until it equals the value stored in the memory capacitor, at which point the brake is applied and the aperture actuation mechanism is locked against further movement
- in aperture priority mode the aperture is allowed to close down completely to the user’s set value
- a final exposure reading is taken and final shutter speed is calculated. This is to allow for any overshoot/rebound in the actually achieved aperture
- the pneumatic delay of the mirror is released and the mirror swings up
- the shutter is fired at the calculated “final exposure reading” speed and the film is exposed

Note that regardless of aperture-priority or shutter-speed-priority modes, the camera always takes a final exposure reading at the closed-down final aperture value and uses that for setting the final shutter speed. This means that any inaccuracy in the final aperture achieved (in either aperture-priority or shutter-speed priority mode) will be compensated for and hence XD series camera exposures are very consistent. It also means that in shutter-speed priority mode any inaccuracies in achieved aperture will translate in an adjustment in shutter speed; so in shutter-speed priority mode it would be wise to assume the shutter speed won’t be 100% spot-on but may vary by up to half a stop or so from the value set by the user.

connloyalist · Joined: 22 Jul 2020 Posts: 355 Location: the Netherlands

Fascinating! And very clever by the Minolta engineers. Thank you for this explanation Smile

Might your post about how the Minolta exposure system works be a candidate to be pinned somehow?

Regards, C

stevemark · Joined: 29 Apr 2011 Posts: 4324 Location: Switzerland

Thanks for that extensive summary - I was faminilar with the facts since the excellent books by Josef Scheibel have very accurate information on the SR-T, the XM/XK/X-1, the XD/XG series, and the X-300/500/700 series.

Books highly recommended for anyone being able to read German ...

S