Re-celling the Nikon MN-2 battery pack for the MD-4 motor drive

 

Re-celling the Nikon MN-2 battery pack for the Nikon F3's MD-4 motor drive.

 

 

                The MN-2 battery pack is a nominal 16.2 VDC battery used to supply power to a Nikon F3 equipped with a MD-4 motor drive.  The pack requires the MH-2 charger, which charges the pack in about three hours with its original cells.

                Since these batteries were made in the 1980’s and 1990’s, they are constructed with Nickel Cadmium (NiCd) batteries which had the two-fold disadvantages of having memory and being toxic.  After thirty plus years of service, the NiCd cells in most of these battery packs are now well past their service life, and likely are not holding a charge and a probably leaking within the casing and will need repair.  Fortunately, they are constructed in such a way that the cells can be easily accessed and replaced with superior Nickel-Metal Hydride (NiMH) cells that are readily available.

                One of the changes between the MD-2 for the F2 series and the MD-4 for the F3 cameras is that the power source of the motor drive will alter the performance characteristics of the system.  In the F2, both the disposable battery packs and the NiCd packs supplied approximately 15 VDC to the motor drive.  This allowed for a constant frame rate between the two power sources.  With the MD-4, the alkaline battery insert holds 8-cells, giving the motor drive a nominal 12 VDC of power, and a maximum frame rate of 4 fps with the mirror locked up and 3.8 fps with the mirror down.  This is hardly any better than the Nikon MD-12 of the same era with 3.5 fps with the same battery supply.  Using the MN-2 batteries, with their higher voltages, the frame rate jumps up to 5.5 frames with the mirror down and 6 fps with the mirror up.  One thing to note is that the MN-2 as a small plastic nub that pushes in a switch within the battery chamber of the drive to indicate whether the higher voltage pack or standard AA cell holder is inserted into the chamber.  Because of this feature, using higher voltage cells (e.g. disposable lithiums) in the standard holder will not lead to an increase in frame rate.

                To obtain the boost in voltage and still retain the same battery pack form factor, Nikon had to use more cells, which necessitated that each cell be smaller, and of less capacity.  Since in either case, the battery packs use each cell in series, the overall capacity of the battery pack depends on the capacity of each individual cell.  So with an AA alkaline cell, each battery supplies approximately 2,500 mAH of power.  In the MN-2, the cells are only 2/3 AA cells and supply only 250 mAH of current.  The MD-4 manual estimates at least twice as many film rolls per battery set with Alkalines over the MN-2’s.

                In this re-cell, we will be using NiMH batteries with a 600 mAH capacity, which should give use more rolls per charge.  The other advantages of using NiMH cells is that they have the same 1.2V per cell as the NiCds so we can use the OEM charger.  The final advantage is that NiMH lack the memory of NiCds so recharging mid-discharge will not be an issue.

                The MN-2’s were assembled in Japan from batteries made in the USA (mine was made in Gainesville, FL).   The MN-2’s are assembled with JIS screws which are different than Philip’s head screws.  Using the wrong tool can easily damage the screw heads, so an investment in the correct tools is highly recommended.

                There are four screws that attach the top plate of the pack to the plastic body of the pack.  Once these are removed, the cells are exposed.  On top of the cell bank are two wires stretching between one side of the pack to the other.

                The first task is to carefully desolder the two long wires.  These are the leads that connect the charging socket on the underside of the pack to the pack leads.  The power leads are lead from the bottom of the pack to the contact plates of the pack.  Each cell has a tab that connects it to the next cell in series.  Each cell is inserted in the opposite direction as its neighbor to allow for connecting them in series.  Seven batteries are connected in a row and then the row is shunted to a second row that is soldered in a similar way.

                After the leads are de-soldered, the next step is to unscrew and remove two small brass tabs that hold the batteries down.  Be sure not to lose either the tabs or the screws.  Next, work each row of cells out of the plastic holder and dispose of them per local regulations.  NiCd batteries cannot be disposed of in regular household waste.  If the batteries have leaked, there will be a whitish-blue powder that may be green on the wires if they came in contact with copper.  This powder is toxic and should not be handled.  Once the cells are removed, any residual powder can be neutralized by vinegar and then the case is rinsed with water and thoroughly dried.  Any metal contacts displaying corrosion should also be treated the same way with vinegar.

                Using solder, connect each cell in series in the same configuration as the original cells.  I did have one tab be a bit short on the last cell in the line and used a bit of tinned desoldering braid to make a jumper.  I tested each row of cells with a voltmeter.  Each row should be approximately 8.5-9.0 volts if the cells are charged.

                Before inserting each row of cells, solder the lead from the battery pack to the leading cell in the first row, with the red wire to the positive terminal, and the black wire to the negative terminal of the second row.  Carefully insert each row of cells into the plastic holder, taking care not to damage the lead wires.  Once each row is inserted, you can then solder the final shunt between the two rows.  At this point, test the voltage on the battery pack.  The voltage on my pack read 17.7 V, although if the cells are not charged as much, it may be as low as 16.8 volts.  Zero voltage indicates an open in the circuit somewhere and a lower voltage may indicate a cell that was installed the wrong way.  Any issue must be corrected before the next step.

                Once the voltage is determined to be correct, re-insert the tabs and their respective screws to keep the cells in place.  You can then resolder the charging leads to their terminals.  These wires were initially taped down and small squares of electrical tape can be used to keep the charging wires in place.

                Before re-installing the top plate, make a label with the date of the re-cell and install it on the bottom of the plate.  Fit the plate on top of the cells, If there is a bit of play, a small bit of foam can be installed on top of the cells.  Just be sure no to cover any of the four screw holes. Carefully install the screws, retest the voltage at the terminals for a final time and then you should be ready to test the camera with the refurbished battery pack.

                The best way to test the battery pack is to first insert it and hit the battery test button on the back of the drive.  Two red LED’s should illuminate.  Next set the shutter speed to 1/500^th , lock up the mirror and set the MD-4 to “C.”  Fire off a series of frames.  You should be able to hear a noticeable increase in the speed over the AA-cell battery insert.  If you care to, you can also set the frame limiter to a set number and measure the time it takes to run through that number of frames.

                The MH-2 charger is designed for NiCd cells but has no auto switch off when the charge cycle is complete.  The manual states it takes 3 hours to charge NiCd MN-2’s at 250 mAh cells.  Since we are using 600 mAH cells, it may take up to 7 hours 15 minutes to charge the new pack.  Lesser discharging will require less time on the charger, but knowing how much time will be difficult to determine.  A bit of experimentation will be in order to dial in the process.

                Re-celling these battery packs is well worth the effort since it is relatively easy if you have some rudimentary soldering skills.

               

               

               

 

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 21^st 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 1/2000^th of a second.  The shutter range is 1 second to 1/1000^th with a flash synch of 1/80^th of a second.  The elimination of the slower speeds goes along with the elimination of the self-timer but the loss of 1/2000^th 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 1/2000^th 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 1/250^th and 1/1000^th 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 1/250^th +

M3: 7.5fps 1/125^th +

M2: 6 fps 1/60^th +

M1: 3.5 fps 1/60^th +

L: 3.0 fps 1/30^th +

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. 

 

 

Macro Nikkor 12cm f6.3

So I got myself a new lens.  It is the Macro-Nikkor 12cm f6.3,  This is a pretty rare lens and is actually closer to an industrial lens than a camera lens.  It was designed for low magnifications on the Multiphot system that Nikon made and is one of four lenses for the system.  This is the longest of the four and has the greatest working distance and least magnification.

So lets see what the lens is and what it does.

It is a 120mm f6.3 lens constructed with 5 elements in 4 groups.  The lens is fairly old so has the older coatings.  This should not be much of an issue for macro work, but doesn't seem to flare in my work and has nice contrast.  The lens is small, with a 38mm front thread and a M39 rear thread.  There is no focal helicoid and will require bellows or other extension means to focus at various distances.  The iris is 6 blades and is operated similarly to the 105 mm f4 Bellows Nikkor.  That is, there are two rings. The first ring has 1 stop detents on it that will allow you to set a minimum closure and then a second ring that will allow continuous change of the diaphragm from fully open to the setting of the first ring.  In a departure from photographic lenses, the stops are marked from 1-7 where 1 is 6.3 and each number denotes a 1-stop reduction in iris side.

What does this lens give you that a standard micro lens does not?  First is image circle. This lens is designed to cover 4x5 inch film so will allow as much swing and tilt as your bellows will normally allow.  Don't expect any vignetting from movements like you can see with standard or even PC-E micro lenses.  Second is a flat field.  There is no appreciable field curvature which is critical in macro photography (greater than life size) where depth of focus is in fractions of a millimeter.

This lens requires substantial extension and I am often testing the limits of my PB-6 Bellows.  Bellows extension will allow for more magnification but the lens is optimized for about 1:2 to 4:1 so you will see some degradation in performance outside of these ranges on 35mm/FX images.  Working distance is much better than what I am used to with other lenses (e.g. a reversed 50mm) which makes lighting substantially easier.

To fit this lens to the bellows, a method to convert the Leica M39 screw thread to Nikon F bayonet is required.  This adapter (nikon's is BR-15) is pretty rare, but off brand adapters can be had on the internet if you are looking.

During my experimentation, the exposure difference between settings 1 and 2 on the lens barrel were actually 1.3 stops at the same extension.  This means that setting 2 is f10.  The remaining settings are close to 1 stop each, so 2 is f14 and 3 is f2.  I would not suggest going beyond setting 3 (f20) as diffraction starts to get the better of you, especially if you are using high-MP cameras.  Better to keep a wider aperture and use focus stacking techniques than trying to stop down the lens that much.  Also remember that the effective aperture as it relates to exposure also has to take into account the large extension you are using (usually over 100mm) so exposure times, and the noise inherent in those settings increase dramatically.

In the end this is a fine lens for bellows offering a small package to get into the macro range of photography with a lens specifically designed for this application.

For the best write-up on this lens (and the source for this entry) visit Enrico Savazzi's website here

My First Lens Repair

It was a sunny day in May of 1993.  I was heavily into photography as the photo editor to the school yearbook and a staff photographer on the paper.  Not to mention my senior photography class and independent study photography project. I tended to always have a camera or two with me when I went to high school.

Back then we shot film.  I remember reading about the first digital cameras in magazines, but for mere mortals, we were still using the analog stuff.  My photo equipment at the time would be considered meager in the 21st century, but it was all that I had and I really didn't know any better.  I had a Nikon F with a broken meter head.  This was my flash camera which was typically mounted next to a Sunpak 544 "potato masher" flash.  My other camera was a Nikkormat FTN which was similar to the F but with a working meter.  For lenses, I had a 28mm f2.8 Vivitar lens, a 50mm f1.4 S Nikkor, a 43-86 f3.5 zoom, and a 135mm f3.5 Q lens.  All but the Vivitar were from the 1960's.  This kit had served me fairly well in those days, but I often wished that I had a slightly faster lens in the telephoto department.  I really didn't wish for anything longer most of the time, which is strange thinking to me these days.

That fateful day in May,  I was sitting in the passenger seat of the 1978 Buick LaSabre that served as the main mode of transportation for my brother and myself, and the Nikkormat with the 50mm f1.4 S was mounted on it was on the floorboard along with my book bag.  Well as fate would have it, I grabbed the book bag and it somehow caught the camera in one of the straps and it fell, lens first, onto the pavement.  The drop was perhaps six inches, but that was all it took.  Despite the Nikon legend of durability, this little drop did both camera and lens in.  The glass was okay, but the iris in the lens would no longer respond, and the focus ring did not move.  On the camera side, the shutter speed dial (located near the aperture ring on that model) would not turn and the camera shutter was not doing well either. 

It is now twenty-years later, and this lens has been sitting on my shelf for many years now;  mounted on it's original body, the Nikon F that my father has since given to me.  The F is in little better shape than the lens at this point, as the shutter has holes in the curtain.  Recently I was looking on YouTube and decided that there might be a video that could guide me into the lens repair.

Unfortunately for me, the videos on YouTube don't include this particular model of Nikkor, but a quick email to a Flickr friend gave me a clue on how to get started.  The focus ring is actually two rings threaded together.  The forward, beveled ring can be twisted off which reveals three screws that can then be removed so that the focus ring can be pulled off.  My focus issue was that the ring had landed on a rock and had dented the focus collar so that it was impinging on the underlying ring, causing the ring to not allow the helicoid to turn.

Digging deeper into the lens, I found that there is a copper retaining spring/ring deep in the lens that keeps an internal ring locked into the aperture ring screw.  This retaining spring had come loose so that the internal ring was not mating with the pin.  A bit of fiddling with a screw driver, and then careful re-assembly had the iris working correctly again. 

Fixing the focusing ring is not easy.  I do not have the correct tools, but I was able to bend the focus ring enough so that it will turn once more, but not as smoothly as any would like.

I would love to mount this on one of my digital cameras, but it is a Non-AI lens so can only be used on certain bodies, and even then only with stop down metering.  So I will probably never again use this lens in the field, but it was a nice feeling to be able to get this lens back into working condition.

An Open Letter To The US Congress on Gun Violence

Dear Congress,

Please pass legislation to offer block grants to state and local governments to harden our schools against gun violence. I think that as a start, we need police presence at all schools as well as hardened doors and bulletproof glass on the 1st floor. I don't know why schools can't be at least as well protected as airports. While you're at it, provide money to increase law enforcement budgets so that all illegal weapons charges are properly investigated and prosecuted. This will get both guns and criminals off of the streets.

If you need more money, tax weapons and ammo like you do cigarettes. Please remember to have DHS et al to remit their taxes to this program for the 1.6 billion rounds they bought last year for whatever reason.

 

  Sincerely...

 

Tax Day: Form 1040EZ-LIB

IRS Form 1040EZ-LIB

(an easy Income Tax form for Progressives who want to pay their fair share)

1) Enter your W-2 Wage income:

2) Enter your 1099 Interest/Dividend income:

3) Enter your capital gains income:

4) Enter any other income (see note A):

5) Sum lines 1-4, this is your total income:

6) See Table A and enter multiplication factor:

7) Multiply Line 5 by line 6, this is your tax due:

8) Enter total taxes witheld by employer:

9) Enter total quarterly tax payments made:

10) Sum Lines 8 and 9, this is the tax you paid:

11) Subtract line 10 from line 7:

12) If Line 11 is negative, see note B; if positive, see note C; if zero, see note D

Table 1: Factor Single Married/Joint

0.1: $ 1-$8,700 $1-$17,400

0.15 $8,701-$35,350 $17,401-$70,700

0.25 $35,351-$85,650 $70,701-$142,700

0.28 $85,651-$178,650 $142,701-$217,450

0.33 $178,651-$388,350 $217,451-$388,350

0.35 over $388,350 over $388,350

Note A: Be honest! Hungry children are depending on you.

Note B: You have over paid your taxes and are a noble citizen! Thank your for your kind donation to your government. Rest assured that these funds will be put the best possible use.

Note C: You should be ashamed! Underpayment of your taxes most likely caused some poor child go go hungry last night. Write a check to the US Treasury immediately! To help cope with the guilt you should feel, add a bit extra to the check.

Note D: You nailed it, but we are watching you!

Nikkor 7.5mm f5.6 Circular Fisheye Lens

The 7.5mm f5.6 is a hemispheric fisheye lens that provides a full 180 degrees of view in a circular image that is 23mm in diameter on the film. This lens will see everything in front and next to the lens. The effects are dramatic, but of limited utility.

This is not your typical Nikkor however. It is not a retro-focus design, and therefore the rear elements are very close to the film plane of the camera. In order for this lens to even be mounted on the camera, you need to lock the mirror up. The official Nikon line is that this camera is only to be mounted on the F and F2. I will add that if you have a Photomic finder on a Nikon F, you will have to remove it as it will get in the way. It will work with the Photomic finders of the F2 however. I can see no reason that the lens will not mount on the F3 or F4 which have full time, mechanical mirror lock up. Besides having limited compatibility, the camera design also precludes the use of TTL metering.

To use this lens, you need to use an external meter or the Sunny 16 rule. When I use this lens, I use a hand-held meter. The MLU also precludes the use of a view finder, so Nikon thoughtfully included one with the lens. The viewfinder is not exact however, giving a 120 degree angle of view. I find it nearly useless. If it will capture everything in front and on the side of you, you just need to align the camera and level it and try and avoid getting your fingers or feet in the frame. The finder fits over the rewind crank of the F and F2 but some have been modified to fit in the standard hot shoe.

This lens is also of a fixed focus design so all elements are fixed. Fortunately with such a short focal length, even wide open at f5.6, pretty much everything will be in focus. The front element of this lens, and the viewfinder for that matter, is very bulbous and sticks out. There is no ability to filter the lens and no lens shade in made. This makes the lens very susceptible to damage. You need to put the screw-on lens cap on as soon as you are done shooting to avoid damage. I do the same with the viewfinder lens cap. Since there is no ability to filter the front element of this lens, Nikon installed a filter turret inside of the lens that is selected via a wheel on the lens barrel. Sadly for us, this lens was made in the later 1960's so most of the filters are really use useful when using black and white films. The filters include a L1A for normal shooting, Yellow 48, Yellow 52, Orange 57, Red 60, and XO.

Construction of this lens is first rate, as was the norm with Nikkors of that era. The lens barrel is metal with a small rubber ring near the lens cap threads. There are six aperture blades that are not rounded and if you get a point light in the view, which is pretty easy when you see half of the world through it, you get a rather ugly flare. The lens coatings are older so the lens does lose some contrast if it flares. The aperture is selected by a lever on the side of the lens and it can be difficult to adjust when it's on the camera. The aperture range is from 5.6 to f22. I like to shoot it from f8 to f11.

  I am not a huge fan of writing about image quality. Still, I will write what I have found, but keep in mind that I don't do scientific tests, or even under controlled conditions. Also note that I have only used this lens on film cameras, so the high density pixel DSLRs might display more flaws than I see when I shoot film. The lens is sharp enough for my film use. While it isn't tack sharp, it will pass at proper viewing distances for film under most enlargements. Contrast is moderate, but it can suffer from flare which reduces contrast. There is some vignetting which appears as a ring around the edge of the image circle. This can be reduced slightly by stopping down, but since the angle of incidence of the light rays is so small, there will be some light loss no matter what. There is little CA that I can observe. There is major barrel distortion but that is normal for fisheyes.

While the lens works fairly well, it is more of a collectors piece than a working lens, especially these days. The going rate for these lenses is about $1,000, and it's very limited utility and shortcomings such as no TTL viewfinding or metering make 3rd party fisheye lenses that have retrofocus designs a more cost effective option. The newer optics are much easier to use, and will probably offer image quality as good, or better than this lens.

  I have also included a link to a YouTube video I made for operating the lens, and also some photos I shot of, and with, the lens itself.

7.5mm Nikkor mounting video