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03-08-2008, 08:11 AM   #1
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A Step-by-Step Guide to Using M and A Lenses

I just bought a couple old lenses (an M and an A lens). They are now "in the mail"!

Maybe this should go in the new "Newbie" thread, but can someone "verify"/state the steps to use a Pentax M and Pentas A lens?

Per finding a piece here and there, I assume it is something like the following:


FOR A M LENS (in Manual Mode)
0. Go into the custom settings, and set to "permit" use of the aperture ring. I assume you can leave this setting on permanently, even if you switch back to a newer lens?
1. Set the aperture ring to the desired setting
2. Set the camera body for manual focus (not sure if this is required since there is no interaction between the lens and the camera at this level)
3. Focus manually.
4. Hit the green button to set the shutter speed. Could you press the shutter release button half way and accomplish the same thing?
5. Use the appropriate dial (based on camera type) to adjust the shutter speed as desired to tweak the exposure
6. Shoot the pic
7. View the pic, histogram, etc. and repeat with adjustments as required/inclined

FOR AN A LENS???
I assume you can use an A lens in Tv or Av mode and just do a manual focus and that is it?


Last edited by krs; 03-10-2008 at 07:39 PM. Reason: Cleaning up title
03-08-2008, 08:23 AM   #2
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0. No problems by leaving it on.
2. Not required, but you must have focus before taking a picture.
(The camera switches to center focus automatically, and the focus indicator still works.)
4. You have to use the green/AE-L button, but you can use the DOF preview in M-mode and then adjust the shutter speed by looking at the light meter in the viewfinder

Also, steps 1 and 4 refer to the manual mode. In Av mode, you can basically ignore the mentioned steps, but you are only able to take pictures with the aperture wide open.
03-08-2008, 08:56 AM   #3
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QuoteOriginally posted by krs Quote
I just bought a couple old lenses (an M and an A lens). They are now "in the mail"!

Maybe this should go in the new "Newbie" thread, but can someone "verify"/state the steps to use a Pentax M and Pentas A lens?

Per finding a piece here and there, I assume it is something like the following:


FOR A M LENS (in Manual Mode)
0. Go into the custom settings, and set to "permit" use of the aperture ring. I assume you can leave this setting on permanently, even if you switch back to a newer lens?
1. Set the aperture ring to the desired setting
2. Set the camera body for manual focus (not sure if this is required since there is no interaction between the lens and the camera at this level)
3. Focus manually.
4. Hit the green button to set the shutter speed. Could you press the shutter release button half way and accomplish the same thing?
5. Use the appropriate dial (based on camera type) to adjust the shutter speed as desired to tweak the exposure
6. Shoot the pic
7. View the pic, histogram, etc. and repeat with adjustments as required/inclined

FOR AN A LENS???
I assume you can use an A lens in Tv or Av mode and just do a manual focus and that is it?

Pretty good,

Note however you can also use the lenses in Av mode, it's just that they only will shoot wide open, but the camera does correct with shutter speed for wide open apature.

You should also add one additional thing with M and K lenses. This is with respect to flash photography.

Only the *istD and DS have TTL flash capability with an external flash. As a result, these are the only bodies that can really use an K or M lens effectively for flash photography. On all other bodies, to use P-TTL flash, youo must have an A lens or newer.

You can use K and M lenses with flashes that support autop mode
03-08-2008, 09:44 AM   #4
krs
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QuoteOriginally posted by Lowell Goudge Quote

Note however you can also use the lenses in Av mode, it's just that they only will shoot wide open, but the camera does correct with shutter speed for wide open apature.
Can you clarify what this means? If I am in Av mode with the aperture ring set at 11 as an example, what will happen, and how would this be different than in manual mode with the aperture set at 11?

03-08-2008, 10:00 AM   #5
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In Av, it will shoot at the widest setting, regardless what you set the aperture ring to. The difference is quite obvious.
03-08-2008, 10:44 AM   #6
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Sorry - I am still not getting it. Just to clarify the context, we are talking about a Pentax M lens in Av mode with the aperature ring set to F11....

Wide open to me means the widest the aperture will go. If a 50mm F1.7 lens that would be 1.7. So is what you are saying is that in Av mode it will open the aperture to F1.7 in this case regardless of what the ring is set on?
03-08-2008, 10:51 AM   #7
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QuoteOriginally posted by krs Quote
Sorry - I am still not getting it. Just to clarify the context, we are talking about a Pentax M lens in Av mode with the aperature ring set to F11....

Wide open to me means the widest the aperture will go. If a 50mm F1.7 lens that would be 1.7. So is what you are saying is that in Av mode it will open the aperture to F1.7 in this case regardless of what the ring is set on?
Yes. To be able to take advantage of all F stops, you need to put the camera in "M" mode
03-08-2008, 10:54 AM   #8
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That's right. At least, it's what I've found with my K100D and M 135mm. Note that (at least for me) the aperture will stop down for a moment after exposure is complete.

03-08-2008, 11:03 AM   #9
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Seems to me that for a "manual" lens, the aperture ring setting should override any other setting, but given the lens was designed and built way before the camera maybe it is just a case of documenting the way it behaves with the newer body rather than they way it "should" operate...

Certainly good to know! Thanks everyone for your patience with me!
03-08-2008, 11:07 AM   #10
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Oh, and don't forget to set the focal length for SR!
03-08-2008, 11:15 AM   #11
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Thanks for the reminder - I remember reading that, but forgot about it!

For a prime lens - set it once when you put on the lens, and you are in business. I assume with a zoom lens (is there such thing as a manual zoom lens?) it is a bit more challenging!
03-08-2008, 12:23 PM   #12
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My experience with M lenses and using the green button is that the picture becomes slightly overexposed. I usually expose a bit shorter then it tells me after using the green button.
03-08-2008, 12:30 PM   #13
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QuoteOriginally posted by krs Quote
Can you clarify what this means? If I am in Av mode with the aperture ring set at 11 as an example, what will happen, and how would this be different than in manual mode with the aperture set at 11?
In Av mode, it does not matter where the apature ring is set, the lens will remain wide open and the camera meter for the wide open shot.

in M when you press the green button the camera will stop the lens down momentairly, read the light, and set the shutter to that apature.


(both points assuming you have selected use apature ring)
03-08-2008, 12:39 PM   #14
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QuoteOriginally posted by Lensvision Quote
My experience with M lenses and using the green button is that the picture becomes slightly overexposed. I usually expose a bit shorter then it tells me after using the green button.
I have noticed on my K10, that the green button will underxpose F2.8 and lower, expose pretty well from F4 to F5.6, and overexpose F8 and higher with fully manual lenses
03-08-2008, 12:50 PM   #15
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QuoteOriginally posted by Stratman Quote
I have noticed on my K10, that the green button will underxpose F2.8 and lower, expose pretty well from F4 to F5.6, and overexpose F8 and higher with fully manual lenses
I have written the following so many times I don't need to even look at the curves any more.

at F1.4 it under exposes by about 1 stop, by F8 it over exposes by 1 to 1 1/2 stops and seems to max at +2 stops at F11, then drop back to 1 1/2 stops at f22-f32.

I have checked this with lthe following lenses
50mm F1.4
100mm F4 Macro
105 mm f2.8,
135mm f2.5
300mm F4
400mm F5.6
70-210 F3.5 (series 1)
and a new tamron 28-75 F2.8 when using the apature ring.

It seems to be a K10D thing, my *istD meters very consistently on all lenses
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