Friday, March 20, 2015

The Nikon F2H

The Nikon F2H is a limited production run of Nikon F2T (titanium) camera that were modified to enable high frame rates (up to 10 fps).  The system comprised of three major components, the F2H body, MD-100 motor drive, and MB-100 battery pack.  The F2H was introduced in 1978 with a limited production run and a second run was made in 1984 in time for the Olympic games.  Serial numbers usually begin with “78” for the bodies.  Both runs combined saw a production of about 500 units.  The back has the serial number of both the body and the paired motor drive printed on the take up spool side.  In this way, having the back with the two different numbers matching the body and the drive will tell the owner if it is a matched set.

The F2H camera body is modified in several ways to enable pairing with the high-speed MD-100.  These changes to the camera features were required at the time due to engineering limitations that were not overcome until the 21st century.

The most important change is the use of a pellicle mirror.  This is a semi-transparent mirror that allows two-thirds of the light to pass through the mirror to hit the film plane while one third of the light is reflected into the pentaprism for viewing.  Since only 2/3 of the light makes its way to the film plane, there is an effective loss of 1/3 of a stop when compared to a normal SLR.  The easiest way to compensate for this light loss is to rate the film 1/3 of a stop slower than you would otherwise.  For example, ISO 100 film should be rated at ISO 80 when using an external meter or mental exposure.  The 2/3 stop of light loss to the viewfinder also makes focusing more difficult, especially with slower lenses.  To help overcome this, a P-screen is standard.  The P-screen lacks a split rangefinder that would tend to go dark with slower lenses.  If a photomic finder is fitted instead of the standard DE-1 finder, then the ISO should be de-rated a full stop: 1/3 a stop for the light loss to the film plane, and 2/3 of a stop for the reduced light hitting the metering cells.  The fixed mirror also helps with shutter bounce and noise when used without the motor drive.  Since the mirror is fixed, there is no fear of mirror-induced vibration and the camera is notably quieter than a standard F2.  Of course when the drive is attached, the motor winding noises will more than make up for any loss of mirror noise.  Finally, the fixed mirror allows for observation of the scene during exposure, something missed by SLR’s.  It harkens to the days of rangefinder cameras. 

The second most obvious modification is the shutter.  The shutter has been changed to eliminate  the slower shutter speeds, Bulb, Time, and 1/2000th of a second.  The shutter range is 1 second to 1/1000th with a flash synch of 1/80th of a second.  The elimination of the slower speeds goes along with the elimination of the self-timer but the loss of 1/2000th of a second is unfortunate.  There does not seem to be any published reason for the loss of the speed.  There is at least one F2H that had be modified with a new shutter returning the 1/2000th of a second to the camera.  I suspect that the F2H shutter was replaced with a standard F2 shutter.  My only thinking is that the standard F2H shutter is more robust or modified somehow for the higher frame rate, however since higher shutter speeds above the synch speed are done by reducing the width of the slit of the shutter curtains, there should be no issue with needing faster curtain speeds.

As mentioned above, the self-timer lever has been eliminated.  No particular reason is published, but the lack of the self-timer lever foregoes both the self-timer function and the 2-10 second shutter speeds offered by the standard F2.  This lack of lever is one of the most obvious physical traits of the F2H.

The Depth of Field (DOF) preview button is also different, both is shape and function.  The high frame rate would wear the mechanical iris controls in the camera, so Nikon engineers opted to have the iris remain closed during exposures and winding.  The iris is therefore “normally closed.”  To enable focusing at full aperture, the DOF button was slightly enlarged and the locking lever was removed.  When depressed, this button opens the iris instead of closing it.  Shooting therefore requires a finger to press the button, focus and exposure is obtained, the button released to close the iris, and then the exposure is made. 

The remaining features of the F2H body are essentially the same as the F2T, but the internal mechanics are probably a bit more rugged to deal with the high speed operation.  The F2H is arguably the toughest mechanical cameras out there.

The motor drive of the F2H system is called the MD-100.  The drive is similar in shape and layout of the MD-2.  There are a few cosmetic features that differ as well as the internal makeup.  The MD-100 is the heart of the system, and when fitted with the appropriate power supply, can provide 10 fps when the shutter speed is between 1/250th and 1/1000th of a second on the “H” setting. 

The drive controls include a fixed shutter button on the grip.  This differs from the MD-1/2 which allows for remote control.  The knob near the shutter button allows for locking the system, single exposure, or continuous exposure.  In the locked setting, the drive cannot be used to fire the camera, but the button on the camera will still work along with the manual advance.  In the single fire setting, the shutter will trip with the motor drive’s button and will wind once the button is released.  This allows for delayed winding when the noise might be objectionable.  On the back of the drive is a lever that allows the back to be released. There is also a button and lever to engage the rewind motor.  A red-LED pilot light blinks with each frame that is wound.  A dial that is raised and twisted sets the frame advance speed along with a label that displays L, M1, M2, M3, and H along with the minimum shutter speeds required for each setting.  A slide to activate the film sprocket release is next that allows for multiple exposure and allows for rewind of the film.  The last dial is a film frame countdown dial that stops the drive after a set number of frames have been exposed.  The default is 40 exposures which is the typical setting for a 36-exposure roll of film, but the dial can be set from any number of frames from 1 to 40.  This allows for a specific number for a sequence and ensures that the drive will not rip the film out of the canister unless the dial is reset.  The underside of the drive has a 5-pin female plug that mates with the MB-100.  Finally in the front is a 3-pin remote control and external power port.

As with the MD-1/2/3, there is no electrical communication between the camera body and the drive.  The shutter speed must be set appropriately, or the two will get out of synch.  The speed dial on the motor drive itself activates timing circuits to vary the delay between exposure and winding action.

The frame rate with MN-1 Ni-Cd battery packs at full charge are as follows:

CH: 10 fps 1/250th +
M3: 7.5fps 1/125th +
M2: 6 fps 1/60th +
M1: 3.5 fps 1/60th +
L: 3.0 fps 1/30th +
If using Alkaline cells, the frame rate diminishes a bit.

The MD-100 is a later model drive in the F2 system and suffers from a manufacturing change in the production history.  MD-1 and earlier MD-2, used metal drive gears while later models, including the MD-100, used plastic (nylon) drive gears.  These gears tend to split and become non-functional but can be replaced if required. 

The MD-100’s internal circuits are a bit misunderstood in online and published write ups.  It is often claimed that the MD-100 uses 4 MN-1’s in the MB-100 power pack supplying 30 V to the drive.  This is not true.  Examining the circuit diagram, and also taking meter readings on the MB-100 tell a different story.  The drive use one MN-1 (7.4-8.0V) to power the control circuits, then two additional MN-1’s in series, for a total of 22.4-24V to drive the motor in the advance direction.   A separate MN-1 is used to power the motorized rewind (7.4-8.0V).  Greater detail on the voltage supply from the MB-100 will explored below.

The MD-100 is also not compatible with standard MF-1, MF-2, or MF-3 backs.  There are a very few (10 or so) known modified F2H cameras that can use special 250-exposure MF-1’s at reduced frame rates, but none are compatible with the 750-exposure MF-2 backs.  The MF-3 back, which keeps the film leader out, required contacts to work, and the MD-100 lacks these contacts.  F2T and standard F2 backs work as normal.

The power supply to the F2H system is the weakest link and least understood part of the rig.  It is best to understand the standard MB-1/2 pack before delving into the MB-100.  The MB-1/2 consists of two hinged doors that are fitted either with rechargeable MN-1 battery packs or AA cells in a pair of MS-1 battery holders.  The MN-1 is rated at 7.4 volts but has a fully charged voltage of 8.0.  Each MS-1 takes 5 standard AA-cells (LR6) for 7.5V per pack.  In the MB-1/2 the cells are wired in series and then the packs themselves are wired in series.  The power is transferred to the motor drive via 2 pins at 14.8-16V and about 250 mA for the MN-1’s. 

At first glance, the MB-100 looks like a pair of MB-1’s stacked on top of each other.  Additionally, a strap loop is fitted between the packs, and an external button and LED are fitted as a battery check light.  The pack fits four MN-1/MS-1’s and it often assumed that since the frame rate is twice that of the MD-2, and that there are four packs rather than two, then the voltage must also be doubled.  The first hint that the power supply is a bit different is that there are five pins instead of two.  Tracing the pins starts to tell the story, and the circuit schematic tells the rest of the tale.  Two of the pins supply power from the lower, right pack in the MB-100 into the motor drive at a nominal 7.4V.  The schematic shows that this pack, and this pack alone, supply power to the motor in the rewind direction.  The drive works perfectly well, sans power rewind, with only three power packs.  The other three packs are wired in series with a common ground/earth.  A tap is taken from the one pack through a separate pin to supply 7.5 volts to the drive’s circuitry.  This battery is the lower left in the MB-100.  The top two packs are wired in series and, along with the circuit pack, supply 22.5V to the motor in advance mode.  Even at the full 8.0V from each pack, the drive uses 24V, not 30V as often stated.

The MN-1 battery pack is fitted with a stack of button Ni-Cd cells.  Since these are wired in series, the voltage is increased with each cells, but the current rating remains the same.  These cells provide only a nominal 280 mA current.  MS-1’s can use higher current cells, but with slightly lower voltage as the cells deplete.  The unfortunate choice is high frame rate with very few rolls per charge, or slower frame rate with longer shooting time.  A solution to this would be an external power supply via the accessory port but with only a 30V (via resistor) input along with the remote release, some functionality (power rewind) would be lost.  The best option would be supply power via the bottom plug, but this would require a custom mount.   AC power is not available via standard Nikon AC/DC converters due to the extra voltage required.

The final flaw in the F2H power system is that the voltage required to power the circuit as well as the motor are in parallel.  When the drive is in operation, the loaded motor reduces the circuit voltage as the cells deplete and the drive will stop working.  Using a pack for the circuit alone and then tap the three other stacks for rewind would probably have worked much better.  While there is not scientific data, at about 80% of full charge and lower, the drive ceases to work. 

The four MN-1’s required are charged by a “special” charger called the MH-100 which is effectively a pair of MH-1’s screwed onto a plate with an extension cord to plug them both into a common cord.  Charge time is approximately 2-3 hours, so you might need spare change outs for any longer shooting.

The F2H system works as advertised, but not as well as it might.  While the frame rate is an impressive 10 fps, the size, bulk, weight, and poor battery performance limit its use.  Also, since the MF-1 cannot be used, a firing time of 3.6 seconds between roll change outs do not help the case for use.  Unfortunately due to the poor power supply, use of 250- exposure backs would not only add to the bulk, but also would require battery change outs as often as film roll exchanges for a standard F2H.  Ideally the system would be similar to the F250 by combining a 24V-250 exposure back with the high speed drive, and larger capacity external batter pack to supply the high voltage and current required for the load.  Sadly this was not pursued. 

Most F2H’s remain on collector’s shelves and probably rarely, if ever get a roll of film through them.  Given the cost of even partial systems in the used market, this is likely to remain the case.  It is too bad, as the camera, even without the drive, is a different shooting experience than a standard SLR, and with the drive, can be used to capture fast action on film.  This need has been largely eclipsed by high speed digital cameras which allow for even faster frame rates and the much higher capacity (with no bulk) digital media cards. 

 Here is a video of the F2H in operation with three MN-1 battery packs.  Here is a second video of the shutter in action in slow motion at 1/250th of a second and 10fps.