Possibility of having Nikon AI/AI-S lenses re-engraved for T-stops?

DanielStone · Mar 11, 2013

Hey all,
Has anyone here, reading this post, had 35mm system lenses re-engraved(or a scale made) for T-Stops instead of(or in addition to) F-Stops?

I'm asking because I shoot primarily chrome, and have found some discrepancies in resulting density of exposures in series of DOF tests, (say, 1/60@f8, then 1/30@f11, etc...).

Now, while it isnt "impossible" by any means to work this way, and the discrepancy is hard to see unless really scrutinizing the film on the light box, but its noticeable to me

I know that in the pro cinema industry, t-stops are STANDARD affair, but it seems us 'lowly' stills people get only f-stops!

Guess this same question can also apply to MF and LF shutters/lenses as well. That way each lens is individually tested for transmissive value.

-Dan

Ricardo Miranda · Mar 11, 2013

This may explain why you get discrepancies in exposure:

The FA has a closed-loop exposure system. This means that while displaying the exposure any time the meter is on, the FA measures the actual exposure after the lens stops down to its taking aperture, just an instant before the actual exposure. This way the FA corrects for any errors in the lens' diaphragm mechanism, so I get exposures more consistent from lens to lens than on newer cameras. Some lenses have diaphragms which are calibrated so that they may over or under expose a little, but on an FA, they all expose perfectly.

http://www.kenrockwell.com/nikon/fa.htm

As you are using manual AI/-S lenses, there are tiny differences when the diaphragm closes. The FA is the only Nikon that corrects that difference with manual lenses. Others, like the F4 have a open-loop exposure system.

Chan Tran · Mar 11, 2013

Ricardo Miranda said:
This may explain why you get discrepancies in exposure:

http://www.kenrockwell.com/nikon/fa.htm

As you are using manual AI/-S lenses, there are tiny differences when the diaphragm closes. The FA is the only Nikon that corrects that difference with manual lenses. Others, like the F4 have a open-loop exposure system.

no wonder I hate the FA.

ic-racer · Mar 11, 2013

Most all Nikon cameras since the 1970s have built in meters. Perhaps their intention was that the users would actually use the camera's built in meter?

benveniste · Mar 11, 2013

Ricardo Miranda said:
As you are using manual AI/-S lenses, there are tiny differences when the diaphragm closes. The FA is the only Nikon that corrects that difference with manual lenses. Others, like the F4 have a open-loop exposure system.

I'm not going to comment on Mr. Rockwell as a source in general, but as a long time FA owner, I can tell you that the FA only applies "last look" corrections in S and P modes and not A nor M modes. So for DOF purposes, Mr. Rockwell's claim is a red herring. If you think about how Nikon's aperture lever works, you'll see this has to be the case. (From language in the manual, I think it only applies such corrections when it can't detect an AI-S or Series E lens, but I'm less sure of that.)

You might be able to get a lens re-engraved with T-stops, but unless you also recalibrated the detents you'd still be shooting in f/stops. Since DOF is a subjective "acceptably sharp" criteria to begin with, I suggest you relax, don't worry, and save your money for outings, film, prints, etc.

brucemuir · Mar 11, 2013

How do you know it's not the shutter causing the discrepancy?

Chan Tran · Mar 11, 2013

I have checked my Nikon AI/AIS lenses and found although the T stop is a bit different from the mark f/stop but by the same amount for all stops. The variation between clicks are much less, 1/5 of a stop at most. Depend which camera and condition the shutter speeds generally aren't as accurate as the apertures.
I think the FA does the last look on P and S because the aperture stop down level on the AI lenses is not linear. However the aperture ring is accurate as I have stated above.

ac12 · Mar 11, 2013

I would think the T-stop difference from the F-stop would be a consistent offset, not different for each stop. So if the offset was 1/2 stop, it would be 1/2 stop for all aperture settings. But the only way to really know this is to have a lab do the T-stop testing and calibration for you. $$$

As was mentioned, I think the first suspect in your exposure difference would be the shutter.
Since you are talking about spending $$$ on this endevor...
First I would get all your camera shutters cleaned and adjusted to spec.
Then get the specs of the measurement of the final adjustment and variation for each speed.
Then you know how close it is to marked speed, for each speed.
Example final adjustment could be average of 1/3 stop slower than 1/125 sec (within spec), but with up to a +/- 1/3 stop variation for say 20 shots.
So, with the variation, the shutter could be 2/3 stop slow to dead on.

I think re-engraving would be difficult.
On the cheap, you could put a strip of white tape or label over the aperture ring and relabel it for the T-stops.
I think that is what I did back in the 70s when I was using a hand meter.
Today, with a computer, a color printer and some experimentation to work out the scale and spacing, a label would probably look pretty good.

As for the detents, I would have a tech remove the device making the detent and just use the aperture ring smooth, w/o detents. The detents would be in the wrong place anyway in relation to the recalibrated T-stops.

Someonenameddavid · Mar 12, 2013

I have a Bell and Howell Foton with a 50 mm T2.2 engraved in T stops.... Would trade for an M2 with 35cron....

LJSLATER · Mar 12, 2013

I've tried de-clicking an AIS Nikkor. Removing the click-tab also removes any and all resistance on the aperture ring, so it's free to just turn on its own. In addition to feeling like garbage and occasionally making a fingernails-on-chalkboard noise, the aperture ring moves on its own when attached to the camera since the metering coupler on the camera is spring-loaded. I took some pictures of the lens parts below so you can see how de-clicking/re-clicking the aperture ring would work in theory. I don't know if all Nikkors are built like this, however.

Nikon 50mm f/1.2 AIS by LJ Slater, on Flickr

Nikon 50mm f/1.2 AIS by LJ Slater, on Flickr

Regarding the exposure discrepancies, I too would be interested to know which camera was used? The F5/F6 are supposed to have shutter monitoring systems that makes corrections as needed. My guess would be that the manufacturing tolerances in Nikkors are not up to your standards, Mr. Stone

There are lots of "T-stopped" cinema lenses for F-mount bodies, but they appear to be upwards of $3K each.

DanielStone · Mar 12, 2013

I use Nikon F4's

Considering the 'hassle' involved with the de-clicking of the AI/AI-S lenses(5 of them total), THEN paying to get them each individually t-stopped, I'm guessing that it'll probably be upwards of ~$1k or so, thats a LOT of film for the freezer !

So, seeing that I'm NOT doing any video work, just stills, I've realized that it's not going to be worth it.

thx,
-Dan

LJSLATER · Mar 12, 2013

Your original findings are interesting though; it makes me want to do DOF tests also. I wonder if making multiple shots with the same exposure would still show discrepancies.

Ricardo Miranda · Mar 12, 2013

benveniste said:
I'm not going to comment on Mr. Rockwell as a source in general, but as a long time FA owner, I can tell you that the FA only applies "last look" corrections in S and P modes and not A nor M modes. So for DOF purposes, Mr. Rockwell's claim is a red herring. If you think about how Nikon's aperture lever works, you'll see this has to be the case. (From language in the manual, I think it only applies such corrections when it can't detect an AI-S or Series E lens, but I'm less sure of that.)

You might be able to get a lens re-engraved with T-stops, but unless you also recalibrated the detents you'd still be shooting in f/stops. Since DOF is a subjective "acceptably sharp" criteria to begin with, I suggest you relax, don't worry, and save your money for outings, film, prints, etc.

Thanks for the clarification and the nice writing!

Jim Jones · Mar 12, 2013

It's easier to calibrate people than to recalibrate lenses to T-stops. Once you've determined the required offset to correct to T-stops, apply it when calculating the desired exposure.

Chan Tran · Mar 12, 2013

LJSLATER said:
I've tried de-clicking an AIS Nikkor. Removing the click-tab also removes any and all resistance on the aperture ring, so it's free to just turn on its own. In addition to feeling like garbage and occasionally making a fingernails-on-chalkboard noise, the aperture ring moves on its own when attached to the camera since the metering coupler on the camera is spring-loaded. I took some pictures of the lens parts below so you can see how de-clicking/re-clicking the aperture ring would work in theory. I don't know if all Nikkors are built like this, however.

Nikon 50mm f/1.2 AIS by LJ Slater, on Flickr

Nikon 50mm f/1.2 AIS by LJ Slater, on Flickr

Regarding the exposure discrepancies, I too would be interested to know which camera was used? The F5/F6 are supposed to have shutter monitoring systems that makes corrections as needed. My guess would be that the manufacturing tolerances in Nikkors are not up to your standards, Mr. Stone

There are lots of "T-stopped" cinema lenses for F-mount bodies, but they appear to be upwards of $3K each.

I found the apertures on Nikkor lenses are very accurate. I have no complain. I found even with the F5 the shutter speed accuracy still not very good.

pen s · Mar 12, 2013

Are you also going to get the shutter speeds checked for accuracy and, more importantly, repeatability?

PhotoJim · Mar 12, 2013

I assume you're not using TTL metering? If you are, T-stops won't help you because the camera is not measuring what the aperture says it is - it's measuring the light that's being transmitted when stopped down to that aperture. An inaccurate shutter or sticky diaphragm can contribute to exposure errors of course (as can a miscalibrated mirror) but getting the camera and lens properly adjusted should eliminate the problem completely.

If you're using a handheld meter, I can see the benefit in T-stops but the light transmission of most lenses for 35mm photography is so good, it isn't likely to make a significant enough difference, even with chrome film. You'd need 15 or 18 elements, I'd think, before it started to make enough of a difference compared to using f/stops.

DanielStone · Mar 13, 2013

Hey Jim,

Not sure if you're talking to the other(F5) guy or me;

If me, I DO use a handheld meter. Hardly ever use the in-camera meter unless I seemingly forgot to put the meter in the bag prior to departure .
A cinema-meter in fact, a Spectra IV digital. Wonderful meter, super accurate, and great for VERY low-light exposures as well(which I'm starting to do more of, @ dusk, etc...)

-Dan

Cybertrash · Mar 14, 2013

I was under the impression that T-Stops hade to be recalibrated every so often... I imagine that'd be fairly pricey in the long run.

skahde · Mar 14, 2013

Hi Dan,

if you really need to be sure, you can always use stop-down metering if your camera provides it. The difference between your measurement off-camera and the value measured via TTL should remain constant with changing f-stops. You will probably never catch the source for the minor variations you describe, though. I'd start with having the shutter checked and - if neccessary - calibrated.

best

Stefan

Chan Tran · Mar 14, 2013

The problem that the OP found is more likely due to shutter speed than aperture.

Possibility of having Nikon AI/AI-S lenses re-engraved for T-stops?

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