Update on my Photomic FTn CLA (tiny screw thread)

Mission accomplished.

 

The meter has been CLA'd to the best of my ability as a non-camera tech person. The issue I was having was the meter would register low light, but in a bright light situation, the needle would peg all the way to the left. This was with new batteries (PX625A). .I took the meter apart and cleaned up the resistor ring, all the electrical contacts, removing corrosion around the pos battery lead, and finally cleaning and sliding the pot for meter sensitivity and battery test. Put the meter together and still had the same problem.

 

Today I figured that either I had too much voltage (note: the PX625A are 1.55vdc batteries. The meter uses 1.34 volt batteries but they are expensive and hard to come by, even the MR-9 Adapter is expensive) or I had a light leak requiring me to refoam the FTn meter. Well, I decided to check the meter again using as a metric my F2AS (serviced by Sover Wong) and my Canon 5D Classic. Inside the house I metered the white wall in bright sunlight with the Canon and the F2AS and they both agreed to speed, aperture, and ISO. I then setup the FTn to the same setting and it too matched. I was happen, but I was also in a low light room.

 

Next, went outside in the bright sunlight and this time only used the F2AS as my metric. Wow, something changed because the FTn is no longer pegging to the far left. It too matched the F2AS, but not exactly. Looks to be about a stop overexposed. Minor tweak of the meter calibration pot should fix that.

 

So, like I said, mission accomplished. However, I did notice what appeared to be some of the coating on the resistor ring is thinning out. :( might have to look for a broken FTn head and steal some parts. :)

Brian, a popular and cheap replacement for the old mercury batteries that your metered head use are the 675 hearing aid batteries. They are zinc air and put out 1.4v, which is close enough to provide accurate readings. Not only are they close enough, but the also exhibit a virtually identical discharge profile compared to the old mercurys, vastly better than the alkalines so many people try to use. True, zinc air batteries don't last very long, but they're so cheap, who cares? I buy cards of 48 for less than $10 at Costco.

 

The biggest problem with using the 675 size battery in the old F heads is the F head picks up the + voltage from the side of the battery compartment, rather than the cover, the way most other cameras do. This presents a problem with the smaller size 675 batteries. The easiest solution to this problem is to buy rings that are specially machined to fit around 675 batteries, which will provide the proper diameter when fitted, so that your battery will be making good contact with the side of the compartment. Now, I have only one Nikon F with metered head and mine is the very first metered head for the F, so I don't know if Nikon may have changed the + pickup point from the side of the compartment to the cap the way most other cameras operate. So I'm making an assumption here that your camera with its FTn head does the same. If it does, then read on. If it doesn't, and picks up the voltage from the cap, then you don't need the rings. You might could use a cushion for your battery, but even then it's probably not strictly necessary.

 

Anyway, about the rings, I've seen various folks offer them. Jon Goodman of camera light seal kit fame sells them. He doesn't have a website but can be reached at jgood21967@aol.com. And, hey, if your F's light seals are getting a little toasty, it might be time to order a set of those from Jon, too. I have about a half dozen cameras that can use these rings, so I just figure about a half-dozen of 'em is a good amount to have on hand.

Thanks @mwmcbroom for the tip and information. I read about the 675 but have not tried them. I am game to try anything just to see what it does. Well, almost anything that is within a reasonable voltage range for the meter. I was at WalMart today and forgot all about the batteries. I just received a pair of Silver 625 batteries. I understand they last the longest. I'll look for a pair of 675's next time I am out an about.

 

Thanks again.

 

Oh... yes the FTn's positive is a small tab on the side of the battery compartment. The cap does not make contact to the best of my knowledge. Tomorrow I will tape off the tab and see if the cap is making contact.

I have had the best luck using the adapter from CRIS camera. It uses a silver battery and reduces the voltage to 1.3 volts. I use them in all of my older cameras that used mercury batteries. The silver batteries last a long time. I have never had any success with other types of batteries. They all seem to go dead quickly and the meter readings change as they loose their charge. The adapters are not that inexpensive but you only have to buy them once and they do work well.

Good info Robert. I will keep looking for a solution that works for me. I can't justify $75 for adapter rings with a diode in them. Just not cost effective.

Brian, I am not sure I can find the link now (will look and repost if I do) but the FTn meter is not hard to recalibrate for higher voltage batterries, either alkalines or silver oxides. The original size silver oxides are not easily gotten now, but it is possible with a conductive ring to use smaller SO batteries. Because the contact is on the side, you can't just use an O-ring as you can in some other cameras. I have in a pinch bodgedit with aluminum foil, but a metal ring works better. One possibility is to disassemble a correct sized battery and use that as a case, but of course you should never do that with a mercury battery! Alkalines get a bad rap because of their inconsistent voltage, but they work pretty well, and since you can also recalibrate the battery test, you can keep track.

 

OK, here is a copy of the page I used some years ago on mine: http://ss-it.de/data/finder/F%20Photomic%20FTN%20Adjustmment.pdf

 

Note that to do this best you will have to adjust the two pots a couple of times, as they influence each other a little. You can use a gray card, or other standard. What I used for mine was a Minolta X-370, because I always found its meter to be surprisingly accurate. I set the Minolta on a tripod with a 50 mm. lens, aimed at a blank off-white wall, and took the meter reading, and then put the Nikon on the same tripod with a 50 mm. lens of the same aperture, and duplicated the reading. I did this a couple of times alternately. Later I compared the meter reading with that of a Nikon F100 with the same lens, and it compared well too. The meters I did this on got Velvia slides right, so I figure that's likely as good as they ever were.

 

There is some question about the linearity of the meter, and one can get a bit fanatical about it, but I figured if you start somewhere close to where you expect to be using it, it will ge good enough. I set my cameras to ASA 100 and a shutter speed of 100, and worked from there.

 

By the way, I've mentioned it elsewhere, but will again - for the leatherette covering the best thing I've found to stick it back on is Aleene's Tacky Glue, available at craft stores. It's nice and sticky but allows a little realignment unlike contact cement, and though it stays on well, it's relatively easy to remove again without leaving residue.

Hi Matthew,

 

I use that very document to study the FTn meter function. That, and making measurements with 2x PX625A batteries I have concluded that the Meter Sensitivity (MS) pot does not have enough resistance to support anything above 3v. Right now my MS pot is to the far clockwise rotation meaning it is at its maximum resistance and I still cannot achieve center swing. The require voltage (according to the document) for center swing is .134v at the resistor with .109 voltage drop and .025v at the meter. I am getting .035v at the meter side of the MS pot. So there are a couple of options.

 

1. Change out the MS pot with a higher resistance pot allowing the use of higher voltage batteries.
    
   
2. Get the rings that Robert mentioned @ $36/ea to use different batteries and bring down the voltage.
   
3. Get some rings from PX625 Battery Adapter <battery.adapter@online.nl> @ 16eur/ea ($19.56) if paid by Paypal.
   
4. Make my own rings using BAT43 Diodes to achieve a voltage drop.
   
5. Install in the meter a voltage dropping device such as a BAT41 Diode.
   

 

At this moment, I have ordered BAT41 Diodes and will go with that option. Two diodes in series should (according to documents I have read) result in the correct voltage for the meter to function correctly. Just so you know, the meter is indeed working. I am just a stop too high. That is fine for me but if someone else uses the camera they will not know this.

 

Appreciate the comments and recommendations. Even though I am sure I own the solution for this, it is good to have a record for anyone else who is considering doing their own CLA or even trying to repair their FTn meter,

I can't remember now where I read it, but I seem to recall reading that some FTn finders have less adjustment range than others - perhaps a matter of whether they're early or late. It's too bad. I have three and all of them had plenty of range. But if they did not, I'd be more inclined to find a battery solution or fudge the ISO setting than to fuss with the components much.

No, you are 100% Matt. It is much better to have a battery solution than a hardware solution. However, I feel that if the solution I have in mind works then I do not have to worry about this anymore. Nor will the person who gets the camera next. All they need do is insert two S625PX batteries and be done with it. I still have the ring option on the table. And lastly, a minor modification to the MS pot can also solve issues, but that is so far from now that I am not even thinking on that level.

 

The diodes should be here tomorrow afternoon. I should have them in by Tuesday and I will post an update.

Brian, just another quick note about the 675 hearing aid batteries. You mentioned that you'll look for a pair of 675s next time you're out. Well, because they're hearing aid batteries, and because they don't last a long time (a few months, typically), they are typically sold in bundles of six. As I mentioned above, I buy mine from Costco. You can buy a card of 48 for less than $10 at Costco. That's so cheap that I will typically just drop in a fresh one when I'm ready to take out for a shoot one of my cameras that used the old PX625 mercury batteries.

Thanks, mwmcbroom.