Nikon EM and fast lenses?

[Patrologia]

I just picked up a Nikon EM for one of the lenses being sold with it, but have been messing around a bit with camera itself just to be familiar. I noticed that when I mount the 50mm Series E 1.8 lens open to 1.8, it doesn't move the aperture follower (right term?) at all--it just meets it in its resting position. Does this mean that the EM isn't able to recognize wider apertures than 1.8? I realize, of course, that anyone who owned a 1.4 or a 1.2 lens wouldn't really have been in the market for an EM, but this still seems like a curious design decision. It is also possible that I really just don't understand how the whole system works, so feel free to enlighten me, and satisfy my curiosity.
I don't own anything faster than 1.8 myself, so I can't experiment. The best I could do for that was to mount a 1.8 lens onto another Nikon and see that it did move it's follower a little bit.

 

[shutterfinger]

The instruction manual http://www.cameramanuals.org/nikon_pdf/nikon_em.pdf makes no reference to fast lens but some AI lens will not work.

 

[jimjm]

The Nikon EM manual does refer to 1.4 and 1.2 lenses as being compatible.
The maximum aperture of the lens is not set by the lever around the outside of the bayonet mount, it's set by a pin (tab) on the back of the lens that engages a lever inside the lens mount, at the bottom, seen here.

 

[Chan Tran]

You can use lenses with any aperture with the EM (f/1.4, f/1.2). When you mount the lens on the EM (just like most Nikon cameras) the lens would open to its widest opening. Only when you actually takes a picture the aperture will close down to the value set on the aperture ring.

 

[Patrologia]

But would it be able to meter accurately?
I promise I'm not trying to be obtuse--I'm told it just comes naturally. If I'm understanding how the coupling ridge works, a 1.4 or 1.2 would not come around enough to make contact with the follower when fully open, and I assume would just touch it when set to 1.8, leading the camera to think 1.8 for all three. The lens wouldn't let it close the aperture down to 1.8, but if the meter calculates shutter speed for 1.8 and then actually gets 1.2, would the picture be over exposed? Or if it works differently, then if I set the lens at 1.8 but haven't moved the follower the meter thinks I'm shooting fully open, and when the picture is taken the aperture closes down to 1.8, underexposing the picture. I think.
Somewhere in that meandering though process I probably reveal where I'm confused about how it works!

 

[Dan Fromm]

RTFM! To get TFM, go to https://www.butkus.org/chinon/nikon/nikon_em/nikon_em.htm and download it. Then see the list of usable lenses on p. 30.

 

[Patrologia]

I have seen the manual, and know that you can use them (so I guess I phrased that poorly). I'm trying to understand how the camera/meter is able to distinguish between lenses that would leave the aperture indicator ring in exactly the same place. That information is not in the manual, which is reasonable since it has more to do with how the Ai system works than with how to use the camera. If it irks people, I can keep poking around the web instead of asking on a forum.

 

[ic-racer]

I'd like to get an EM some day; let us know if you find out.

 

[Patrologia]

I'd like to get an EM some day; let us know if you find out.

I think I've figured it out. As far as I can tell, every lens will just nudge the follower slightly. I had misunderstood, thinking that the feeler communicated an absolute aperture value to the camera, but it doesn't; it communicates a value relative to the starting point, the maximum value. So when you turn the ring, the camera doesn't know (and doesn't need to know) that you're going to close down to 4 from 1.8, it just knows that you're closing down roughly 2.3 stops. What changes from lens to lens appears to be the position of the aperture ring relative to the mount. I'm probably not phrasing that well, but if you look at different lenses with different maximum apertures you can see that a different f number sits directly above the flange edge when fully open, but the ridge starts at the same point relative to the flange. Pics are of my slowest and fastest to make the difference more visible.

 

[shutterfinger]

I'm trying to understand how the camera/meter is able to distinguish between lenses that would leave the aperture indicator ring in exactly the same place

The camera only knows if the lens is wide open or not. It does not matter how fast the lens is. The aperture numbers are for operator confidence so the operator can control the depth of field. The camera meters light and sets a shutter speed to give a preprogrammed correct exposure. All that matters is how much light is reaching the sensor. As you turn the aperture ring from wide open toward fully stopped down the follower changes the voltage/current to the meter.
4 variables are involved, light intensity, lens aperture, shutter speed, and film sensitivity.
Note that as you turn the aperture ring on the lens that the aperture stays wide open and does not close down until the lever is operated then only moves as far as the aperture ring will allow.

 

[Theo Sulphate]

Actually, the EM, FA, F4, and a few others do need to know the speed of the lens, hence the need for the "speed post" on AI lenses.

Description in detail here:

http://www.throughthefmount.com/articles_back_difference_aid_ai.html


I agree with the original poster that there should be some discernible mechanical difference when an f/1.2 is mounted vs. an f/1.8 lens -- although that difference might not be apparent just by mounting the lens: perhaps the shutter needs to be tripped to observe the interaction of the body with the lens components. If I had an EM, I would be able to experiment with this.

 

[shutterfinger]

Apertures are logarithmic, not linear. The aperture ring in the camera is a rheostat or variable resistor whose resistance matches the logarithmic progression of an aperture therefore the mechanical change between f1.2 and f2 is very minor and one may need a caliper to measure it.

 

[Chan Tran]

But would it be able to meter accurately?
I promise I'm not trying to be obtuse--I'm told it just comes naturally. If I'm understanding how the coupling ridge works, a 1.4 or 1.2 would not come around enough to make contact with the follower when fully open, and I assume would just touch it when set to 1.8, leading the camera to think 1.8 for all three. The lens wouldn't let it close the aperture down to 1.8, but if the meter calculates shutter speed for 1.8 and then actually gets 1.2, would the picture be over exposed? Or if it works differently, then if I set the lens at 1.8 but haven't moved the follower the meter thinks I'm shooting fully open, and when the picture is taken the aperture closes down to 1.8, underexposing the picture. I think.
Somewhere in that meandering though process I probably reveal where I'm confused about how it works!

All Nikon AI are the same. The coupling ridge is at exactly the same position on all lens when it's set at maximum aperture regardless of what the maximum aperture is. The camera has no idea which aperture it is. The only thing it knows is how many stops the lens will stop down from the maximum aperture.

 

[Chan Tran]

Apertures are logarithmic, not linear. The aperture ring in the camera is a rheostat or variable resistor whose resistance matches the logarithmic progression of an aperture therefore the mechanical change between f1.2 and f2 is very minor and one may need a caliper to measure it.

The resistance is linear with the number of stops. For every stop it changes the same amount of resistance.

 

[Chan Tran]

Actually, the EM, FA, F4, and a few others do need to know the speed of the lens, hence the need for the "speed post" on AI lenses.

Description in detail here:

http://www.throughthefmount.com/articles_back_difference_aid_ai.html


I agree with the original poster that there should be some discernible mechanical difference when an f/1.2 is mounted vs. an f/1.8 lens -- although that difference might not be apparent just by mounting the lens: perhaps the shutter needs to be tripped to observe the interaction of the body with the lens components. If I had an EM, I would be able to experiment with this.

There is absolutely no difference. The camera only knows that the the lens is set at maximum aperture. It doesn't know whether it's f/1.2 or f/4. For this reason the Nikon F5 matrix metering doesn't work with non CPU lenses because it doesn't know the maximum aperture of the lens. Newer cameras can but you have to enter the maximum aperture with every non CPU lens you use.