stop down metering

[abhishek_rai]

<p>Recently i've posted asking about adapting different lens on to the fd system and people have mentioned stop down metering. From what i under stand it mean i have to stop down the lens and meter it then shoot. This mean the viewfinder is considerable darker. </p>

<p>This led me to a different problem, on the ae-1 program when i stop down my lens the aperture blades don't move so, they stay at maximum aperture does this mean i have to take into account the stops of light i'm going to lose at f4 as oppose to it maximum aperture and the change in dof. From my assumption it does matter however dop increases so focusing is not much of a problem.</p>

<p>And finally since there is no mechanical link between lens like the m42 mount and the fd system when using an adapter, how will i stop down and meter? does the aperture decrease as i turn the ring or does it stay at maximum like fd lens then become smaller when i shoot. The second I think is impossible cause there is no link with the camera?</p>

<p>I think i'm confusing myself.</p>

<p>Comments Please!</p>

<p>Thanks for looking</p>

<p>Abz~</p>

[SCL]

<p>The FD lenses have a auto-diaphragm linkage to the AE-1 body, so unless you move the lens to manual mode, you focus and meter in wide open mode and at the moment of exposure the aperture stops down in advance of the shutter opening and closing. When you use another lens on the body which isn't linked to the body, you choose your aperture by moving the ring on the lens and it stops down immediately, rather than at the moment of exposure; the camera meters with whatever aperture you have selected. The FD line of bodies was so popular that many manufacturers produced lenses in an FD mount which operated just like the FD lenses. In addition to the FD lenses on my Canon T90 and A1 (now sold) I used lenses in an FD mount by Vivitar, Kiron, Tamron and a department store brand which I think was made by Cosina.</p>

[philip_wilson]

<p>To use other lenses on the FD system than do not have an FD mount you have to use them in stop down mode. Sometimes this means that the adaptor has a ring that activates the stop down lever on the lens when the lens is mounted (the adaptor I use to put FD lenses on M4/3 works this way) sometimes the lens stops down when you turn the aperture ring (this means it has no automatic diaphragm).<br>

On your FD body you can use the stop down lever on the body to manually stop the lens down to the taking aperture. With TTL metering manually stopping down the lens does not confuse the meter as it measures the light it receives.<br>

The taking sequence is:<br>

Focus, stop down the lens to the desired aperture, check focus and DOF, meter (assuming TTL - otherwise just use the handheld meter readings) adjust the lens / shutter speed for correct exposure then shoot. It is slow but works fine - cameras used to work this way!<br>

On some modern bodies - especially M4/3 and similar the stopping down of the lens is not a big issue as the electronic viewfinder automatically adjusts brightness.</p>

[mwmcbroom]

<blockquote>

<p>This led me to a different problem, on the ae-1 program when i stop down my lens the aperture blades don't move so, they stay at maximum aperture does this mean i have to take into account the stops of light i'm going to lose at f4 as oppose to it maximum aperture and the change in dof.</p>

</blockquote>

<p>This statement is what caught my eye. If your lens's aperture blades are not moving to the aperture set on the lens when you push in the stop down lever, then you have a problem. That is, unless you forgot to take the lens off the "A" setting. If you didn't, then most likely your lens's aperture blades are fouled with oil. I'd favor this explanation over any sort of problem with the linkage, although I have had situations before occasionally where I've mounted an FD lens to an FD camera and, for whatever reason, the linkage wasn't synced right and the lens wouldn't stop down. Dismounting and then carefully remounting the lens took care of the problem. It's worth noting that this has only happened with breechlock lenses, and never with New FD mount lenses.</p>

<p>Canon retained stop-down metering as a hold-over from their earlier cameras, such as the FT, which used FL lenses, and which could only be metered in stop-down mode. They retained it so that all the FL lenses they'd produced over the years could still be used with FD cameras. THAT is the reason for the existence of stop down metering on Canon FD cameras.</p>

<p>It's worth noting as well that Canon claims that if you are going to manually stop down the aperture on your lens, you have to use the stop down metering mode to insure correct exposure -- so sez Canon's manuals.</p>

<p>Now, with a preset lens, or just a plain old manual aperture lens, where there is no linkage at all between the camera and the lens, you still must use stop down metering. Preset lenses have two aperture dials -- and so do FL lenses, sorta -- so you can focus at wide open aperture, and then quickly stop down to taking aperture. If you're using another type of lens, like just a plain old manual aperture lens, then just focus with the lens set to wide open, crank the aperture down to the right amount and fire away, just putting up with the dim viewfinder. </p>