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01-17-2009, 06:35 PM   #1
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"Auto" Manual Lenses

I know this has ben asked before, but I can't seem to find it. What's the "Auto" function do on the older, manual lenses? How does one take advantage of it?

IIRC it's something to do w/ the apeture ring, but ill be damned if I can't remember exactly how to work it.

01-17-2009, 06:58 PM   #2
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This is one of my pet peeves. The word "Auto" on the barrel or face of a lens has nothing to do with automatic or programmed exposure. It also has nothing to do with auto-focus.

What does it mean? I means that the aperture stays open for focusing and then "automatically" closes just before the shutter opens. When the shutter closes, the aperture "automatically" opens again. Here is the history:
  • In the beginning there were manual aperture lenses. The aperture opening is always the same as what is set on the aperture ring.
  • Then came pre-set aperture lenses. These have two rings, one to set the aperture, and another to open/close the aperture.
  • After that came semi-automatic aperture lenses. With these the aperture closes automatically just prior to exposure, but requires a separate cocking action to open the aperture again.
  • Finally there are auto-aperture lenses as described above.

So what do we call things:
  • If the lens is manual focus, we call it a manual focus lens.
  • If we are referring to the aperture mechanism, we use manual, pre-set, semi-auto, or auto as described above.
  • If the lens has the "A" position on the aperture ring, we call it an "A" setting, K/A, A-type, or A-contact lens.
Steve
01-17-2009, 07:05 PM   #3
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QuoteOriginally posted by Bubbabob Quote
I know this has ben asked before, but I can't seem to find it. What's the "Auto" function do on the older, manual lenses? How does one take advantage of it?

IIRC it's something to do w/ the apeture ring, but ill be damned if I can't remember exactly how to work it.
Steve is right on the mark. To answer your second question: If you use the lens on a bayonet camera (with the appropriate adapter) you can use the auto/manual switch to quickly stop down the lens to the set aperture for taking the picture after you have focused with the lens wide open.

Last edited by Ole; 01-18-2009 at 02:32 PM.
01-17-2009, 07:11 PM   #4
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I forgot one thing...

On most (not all) auto-aperture M-42 screw mount lenses, there is a slider switch labeled "Auto/Manual" or "A/M". When the switch is in the "Auto" position, the lens has an automatic aperture. When the switch is in the "Manual" position, the aperture is fully manual.

On a K-mount body, the switch should always be in the "Manual" position to allow metering.

Steve

Edit: Ole posted (above) while was composing this...oops!


Last edited by stevebrot; 01-17-2009 at 07:17 PM.
01-18-2009, 12:17 PM   #5
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QuoteOriginally posted by Bubbabob Quote
I know this has ben asked before, but I can't seem to find it. What's the "Auto" function do on the older, manual lenses? How does one take advantage of it?
Assuming we're talking about K-mount lenses, I gotta disagree with Steve. In K-mount terms:

"M" lenses (those without an "A" position on the aperture ring) are lenses where you set the aperture on the ring MANUALLY. Whatever you set (ie, f/5.6) is what's used for the shot. The diaphragm remains open until the moment of exposure, closes down briefly while the picture is taken, and then opens back up by itself, no "re-cocking" of the aperture is necessary.

"A" lenses (those WITH an "A" position on the aperture ring) operate identically to the above description if you choose a specific aperture (ie, f/5.6) using the ring. But if you select the "A" position on the ring then the camera chooses the aperture AUTOMATICALLY. In other words, if the camera determines that the exposure should be made at f/8, then it deflects the lens's aperture lever the appropriate amount to close the diaphragm down to that aperture. This lets you shoot pictures in varying lighting conditions without having to touch the aperture ring at all.

BUT - if we're talking about screw-mount lenses then what I just wrote does NOT apply.
01-18-2009, 02:01 PM   #6
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QuoteOriginally posted by Sean Nelson Quote
Assuming we're talking about K-mount lenses, I gotta disagree with Steve. In K-mount terms:

"M" lenses (those without an "A" position on the aperture ring) are lenses where you set the aperture on the ring MANUALLY. Whatever you set (ie, f/5.6) is what's used for the shot. The diaphragm remains open until the moment of exposure, closes down briefly while the picture is taken, and then opens back up by itself, no "re-cocking" of the aperture is necessary.

"A" lenses (those WITH an "A" position on the aperture ring) operate identically to the above description if you choose a specific aperture (ie, f/5.6) using the ring. But if you select the "A" position on the ring then the camera chooses the aperture AUTOMATICALLY. In other words, if the camera determines that the exposure should be made at f/8, then it deflects the lens's aperture lever the appropriate amount to close the diaphragm down to that aperture. This lets you shoot pictures in varying lighting conditions without having to touch the aperture ring at all.

BUT - if we're talking about screw-mount lenses then what I just wrote does NOT apply.
Sorry Sean, but I must disagree. The mount type has nothing to with the "auto" designation when talking about a lens. It refers to the aperture mechanism. There are "auto" K-mount lenses and accessories that lack the A contacts. A good example might be this lens in the third-party database:

PentaxForums.com Third-Party Pentax Lens Review Database - 135mm f2.8 Auto Multicoated

or this Pentax brand K-mount extension tube set:

Pentax | Auto Extension Tube Set (B) | 30535 | B&H Photo Video

Both of these items are "auto", but neither has the A contacts. It is a fine point of photo jargon, but can cause some confusion with noobies who expect that the word "Auto" on a lens will allow them full automated exposure on their dSLR. They are also disappointed when the "Auto" lens they bought on eBay is found to lack the "A" setting on the aperture ring. The automatic aperture is an intrinsic feature of the lens that functions on a supporting body. Automated exposure, on the other hand, is a body feature that functions when mated with a supporting lens. An "auto" body may refer to automatic or programmed exposure. An "auto" lens always refers to the diaphragm mechanism.

Steve

Last edited by stevebrot; 01-18-2009 at 02:15 PM.
01-18-2009, 02:22 PM   #7
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QuoteOriginally posted by stevebrot Quote
Sorry Sean, but I must disagree. The mount type has nothing to with the "auto" designation when talking about a lens. It refers to the aperture mechanism. There are "auto" K-mount lenses and accessories that lack the A contacts.
This is quite true, and I was glossing over this when I mentioned K-mount vs. screw mount, for pointing this out.

I think the original poster's question was ambiguous, and it's unclear exactly what he's referring to when he uses the word "auto". This is why in my post I specifically defined my reference to "auto" as being a lens with an "A" position on the aperture ring. Any lens with an "A" position on the aperture ring should work as I described.

It's clear that there are different understandings of the term "automatic lens", and I hope this helps the OP realize this.
01-18-2009, 04:22 PM   #8
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QuoteOriginally posted by Sean Nelson Quote
Assuming we're talking about K-mount lenses, I gotta disagree with Steve. In K-mount terms:

"M" lenses (those without an "A" position on the aperture ring) are lenses where you set the aperture on the ring MANUALLY. Whatever you set (ie, f/5.6) is what's used for the shot. The diaphragm remains open until the moment of exposure, closes down briefly while the picture is taken, and then opens back up by itself, no "re-cocking" of the aperture is necessary.

"A" lenses (those WITH an "A" position on the aperture ring) operate identically to the above description if you choose a specific aperture (ie, f/5.6) using the ring. But if you select the "A" position on the ring then the camera chooses the aperture AUTOMATICALLY. In other words, if the camera determines that the exposure should be made at f/8, then it deflects the lens's aperture lever the appropriate amount to close the diaphragm down to that aperture. This lets you shoot pictures in varying lighting conditions without having to touch the aperture ring at all.

BUT - if we're talking about screw-mount lenses then what I just wrote does NOT apply.
Yes, there's a manual focus lens with an A designation on the aperture lens, and thus the lens aperture can be controlled in-camera.

But in older lenses..

Auto refers to an auto diaphragm lens, not necessarily an auto-aperture lens. As Stevebrot described. The auto-diaphragm lenses, once mounted on your SLR, the lens "stays" open via a lever which allows you to view and compose and focus, then when you press the shutter button, the lever releases and the lens diaphragm returns to the selected aperture setting to take the photo. In a (seems like) not too long ago period of time, this wasn't the case.... it's taken for granted now, but there was a time that this was a new novelty, and these new lenses were labeled as "auto" This designation also appears on some of the older Taks and m39 and m42 screwmount lenses. The auto-aperture lenses (designated as the A series) didn't appear until the early 80's.

take your lens off your camera and select a small closed down aperture, say f16, then flip the little lever and see the diaphram open up to max size. That's your auto-diaphragm and that's why when mounted on your camera body you can get as much light in to your viewfinder as your lens is fast.

Your SLR Camera's Automatic Diaphragm - The Facts You Need to Know

Early Pentax Takumar Lenses


That's what the Depth of Field lever did on some film bodies was for (bypassed the auto lever and let you see with the lens stopped down, for checking DOF, etc. but the image would be darker)

On the K20D if you select "optical preview" as your preview button choice, that's also what you get. (you can also manually meter in this mode as well for older, more finicky lenses and it works quite well, also focusing a fast lens that suffers from a focus shift error)

01-18-2009, 04:27 PM   #9
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If move the lever and you see the word AUTO does that mean it's in the auto position or the manual
01-18-2009, 05:20 PM   #10
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QuoteOriginally posted by augustmoon Quote
Auto refers to an auto diaphragm lens, not necessarily an auto-aperture lens.
Yes, and this is exactly where the original poster's question is (IMHO) ambiguous. Until he comes back to say which type he's referring to we don't really know which answer applies to him. I just wanted to be sure that IF he was referring to a lens with an "A" position on the aperture ring, the first replies might not apply.
01-19-2009, 12:16 AM   #11
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QuoteOriginally posted by Fl_Gulfer Quote
If move the lever and you see the word AUTO does that mean it's in the auto position or the manual
Yes.

the word that is visible shows you what mode you are in. you can see this for yourself by looking at the lens and watching the aperture blades. when set to auto the blades don't move. when set to manual the blades move.
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