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Thread: SMC Pentax-A 1:4 70-210mm zoom lens

  1. #1

    Question SMC Pentax-A 1:4 70-210mm zoom lens

    Hi Everyone,

    I would like some help in assessing if the manual SMC Pentax-A 1:4 70-210mm zoom lens I just bought at ebay is working properly or not.

    The aperture f-stop increment from 4, 5.6, 8, 11, 16, 22, to 32. As I rotate the aperture ring from 4 to 16, I can see the aperture closing down inside the lens. But from 22 and 32, the aperture does not close down any further and is the same opening size as at 16. Is this normal? If you own this lens, would you be so kind to confirm this operation.

    Any help would be greatly appreciated. Thanks.

    mquon

  2. #2

    Default Re: SMC Pentax-A 1:4 70-210mm zoom lens

    Quote Originally Posted by mquon
    Hi Everyone,

    I would like some help in assessing if the manual SMC Pentax-A 1:4 70-210mm zoom lens I just bought at ebay is working properly or not.

    The aperture f-stop increment from 4, 5.6, 8, 11, 16, 22, to 32. As I rotate the aperture ring from 4 to 16, I can see the aperture closing down inside the lens. But from 22 and 32, the aperture does not close down any further and is the same opening size as at 16. Is this normal? If you own this lens, would you be so kind to confirm this operation.

    Any help would be greatly appreciated. Thanks.

    mquon
    do a metering test to determine if the aperture is stopped down properly. If not there may be stuck apertures.....

  3. #3

    Default Re: SMC Pentax-A 1:4 70-210mm zoom lens

    I think you got some sticky aperture blades there. Saw some similar problems with some other old lenses too, aperture blades can't close down below a certain F stop, and the minimal aperture stuck beyond that.

    If it's cheap, and if it works fine, then just keep it. It's a wonderful lens base on all the reviews. But if you paid a lot for that, I'd suggest you send it back to the Seller for full refund. It'll cost you some big bucks to get this big lens cleaned, might not worth it.

    Just my thoughts.

  4. #4

    Default Re: SMC Pentax-A 1:4 70-210mm zoom lens

    Hi Xdivider and Fengwei,

    Thanks for your infos.

    Surprisingly, if I set the metering at aperature priority, and rotate to f/22 and f/32, the camera sets the shutter speed accordingly. The mystery is the aperture size did not reduce in size.

    There is a mechanical lens aperture lever on the body bottom, as you rotate the aperture ring, this lever slides in a slot accordingly. When f/22 is reached, this lever cannot travel any further as it is against the housing. Could this be the reason why the aperture doesn't step down further?

    mquon

  5. #5

    Default Re: SMC Pentax-A 1:4 70-210mm zoom lens

    could be, or is the diff between f32 and f22 too small to be differentiated....
    Quote Originally Posted by mquon
    Hi Xdivider and Fengwei,

    Thanks for your infos.

    Surprisingly, if I set the metering at aperature priority, and rotate to f/22 and f/32, the camera sets the shutter speed accordingly. The mystery is the aperture size did not reduce in size.

    There is a mechanical lens aperture lever on the body bottom, as you rotate the aperture ring, this lever slides in a slot accordingly. When f/22 is reached, this lever cannot travel any further as it is against the housing. Could this be the reason why the aperture doesn't step down further?

    mquon

  6. #6
    Senior Member fuwen's Avatar
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    Default Re: SMC Pentax-A 1:4 70-210mm zoom lens

    Quote Originally Posted by mquon
    Hi Xdivider and Fengwei,

    Thanks for your infos.

    Surprisingly, if I set the metering at aperature priority, and rotate to f/22 and f/32, the camera sets the shutter speed accordingly. The mystery is the aperture size did not reduce in size.

    There is a mechanical lens aperture lever on the body bottom, as you rotate the aperture ring, this lever slides in a slot accordingly. When f/22 is reached, this lever cannot travel any further as it is against the housing. Could this be the reason why the aperture doesn't step down further?

    mquon
    Hi! When the lens is mounted on the body it is always opened up to f4 to ensure max brightness for focusing and viewing. The body adjust the metering accordingly based on the mechancial aperture linkage and therefore will adjust the speed accordingly. However, the body will not know that the f32 is the same as F22.

    So u can still happily use the lens. However metering is only correct up to f22. At f32 u will get 1 stop over exposure as the body thinks the aperture used is f32 but actual aperture is f22.
    Rolleiflex 3003 - SL66 - Sony Alpha 7R1/2 - ZF - Batis - ZM - Otus - HFT - T* My website

  7. #7

    Default Re: SMC Pentax-A 1:4 70-210mm zoom lens

    Hi All,

    Thanks to your infos, I was able to compare the operation against my 35-105mm zoom lens.

    When the 70-210 is set on aperture priority or fully automatic mode, the aperture automatically set (or stuck) to f16 opening. (On the 35-105, aperture is at the maximum opening). Aperture does not move at all, doesn't matter what is the shutter setting set by me or the camera. (On the 35-105, aperture only closes when shutter release button or preview lever is pressed).

    IT SEEMS DEFECTIVE and hopefully I can get a refund without too much hassle. Paid $100US for it.

    mquon

  8. #8

    Default Re: SMC Pentax-A 1:4 70-210mm zoom lens

    Quote Originally Posted by mquon
    Hi All,

    Thanks to your infos, I was able to compare the operation against my 35-105mm zoom lens.

    When the 70-210 is set on aperture priority or fully automatic mode, the aperture automatically set (or stuck) to f16 opening. (On the 35-105, aperture is at the maximum opening). Aperture does not move at all, doesn't matter what is the shutter setting set by me or the camera. (On the 35-105, aperture only closes when shutter release button or preview lever is pressed).

    IT SEEMS DEFECTIVE and hopefully I can get a refund without too much hassle. Paid $100US for it.

    mquon
    does it work in M mode, as in set aperture ring to F22, press Ael, 1/30, then set aperture ring to F32, ael, 1/15? I had a M-135mm which meter the same for any apertures smaller than F8 and sent it for servicing.

  9. #9

    Default Re: SMC Pentax-A 1:4 70-210mm zoom lens

    Quote Originally Posted by mquon
    Hi All,

    Thanks to your infos, I was able to compare the operation against my 35-105mm zoom lens.

    When the 70-210 is set on aperture priority or fully automatic mode, the aperture automatically set (or stuck) to f16 opening. (On the 35-105, aperture is at the maximum opening). Aperture does not move at all, doesn't matter what is the shutter setting set by me or the camera. (On the 35-105, aperture only closes when shutter release button or preview lever is pressed).

    IT SEEMS DEFECTIVE and hopefully I can get a refund without too much hassle. Paid $100US for it.

    mquon
    In that case, better send back to the seller for refund. Don't worth spending extra $$ to get it fix imo.

    Good luck.

  10. #10
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    Default Re: SMC Pentax-A 1:4 70-210mm zoom lens

    Quote Originally Posted by mquon
    Hi All,

    Thanks to your infos, I was able to compare the operation against my 35-105mm zoom lens.

    When the 70-210 is set on aperture priority or fully automatic mode, the aperture automatically set (or stuck) to f16 opening. (On the 35-105, aperture is at the maximum opening). Aperture does not move at all, doesn't matter what is the shutter setting set by me or the camera. (On the 35-105, aperture only closes when shutter release button or preview lever is pressed).

    IT SEEMS DEFECTIVE and hopefully I can get a refund without too much hassle. Paid $100US for it.

    mquon
    Is your camera a Pentax? I ask because I know there are some Pentax M42-mount lenses which doesn't work well on non-Pentax M42-mount cameras, and although I've not heard of a similar case for K-mount, well it might exist in odd ball cases for all we know.

  11. #11

    Default Re: SMC Pentax-A 1:4 70-210mm zoom lens

    Hi All,

    I have invested a little time in understanding how the lens work with my Pentax Super Program body.

    As you rotate the lens aperture ring, two things happens:

    First, there is this mechancial aperture linkage at the bottom of the lens that travels in a slot according to the aperture setting. When the lens is mated to the body, this linkage connects to another lever on the body which holds it at f4 opening irregardless of the chosen aperture setting. As Fuwen pointed out, this is to ensure max brightness. As you release the shutter button, the linkage is then allow to travel to the chosen aperture setting. One of my reported problem before was that when the lens is mated to the camera, the aperture is not at f4 max opening. That's because the linkages on lens and body is not touching. With a little careful help from a plier, I readjusted/straighten the linkage on the lens and is now working fine.

    The second thing is as you rotate the lens aperture ring, it rotates another inside ring with a notch on it. The camera uses this to calculate shutter speed.

    It seems like a manufacturer defect that the aperture opening stops at f22, f32 as the linkage hits the lens housing. Aperture definitely did not change in size.

    Took a couple of rolls of films yesterday with different camera setting combinations, paying special attention to f22, f32. Surprising I was expecting over-exposure at these two f-stops but that did not happen. Depth of field is the same as f16 though. Overall results were acceptable.

    Based upon the above, I have decided to keep the lens. It doesn't seem to be the seller's fault about the linkage adjustment (it is used!) and the manufacturer defect. I actually benefited by getting more intimate with my camera.

    Thought I owe all of you a complete explanation since you were all so helpful. Thanks again.

    mquon

  12. #12
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    Default Re: SMC Pentax-A 1:4 70-210mm zoom lens

    Quote Originally Posted by mquon
    Hi All,

    I have invested a little time in understanding how the lens work with my Pentax Super Program body.

    As you rotate the lens aperture ring, two things happens:

    First, there is this mechancial aperture linkage at the bottom of the lens that travels in a slot according to the aperture setting. When the lens is mated to the body, this linkage connects to another lever on the body which holds it at f4 opening irregardless of the chosen aperture setting. As Fuwen pointed out, this is to ensure max brightness. As you release the shutter button, the linkage is then allow to travel to the chosen aperture setting. One of my reported problem before was that when the lens is mated to the camera, the aperture is not at f4 max opening. That's because the linkages on lens and body is not touching. With a little careful help from a plier, I readjusted/straighten the linkage on the lens and is now working fine.

    The second thing is as you rotate the lens aperture ring, it rotates another inside ring with a notch on it. The camera uses this to calculate shutter speed.

    It seems like a manufacturer defect that the aperture opening stops at f22, f32 as the linkage hits the lens housing. Aperture definitely did not change in size.

    Took a couple of rolls of films yesterday with different camera setting combinations, paying special attention to f22, f32. Surprising I was expecting over-exposure at these two f-stops but that did not happen. Depth of field is the same as f16 though. Overall results were acceptable.

    Based upon the above, I have decided to keep the lens. It doesn't seem to be the seller's fault about the linkage adjustment (it is used!) and the manufacturer defect. I actually benefited by getting more intimate with my camera.

    Thought I owe all of you a complete explanation since you were all so helpful. Thanks again.

    mquon
    mquon:

    It is possible that this lens works perfectly fine on the seller's camera body, so he might not be in the know of this problem. Another similar problem could be the "stuck" mirror syndrome, where an old mechanical camera like the Pentax MX may have its mirror stuck in the up position after exposure with some lenses, and not others. A minor plier tweak will solve that problem as well.

    There might be an exposure difference as you had expected in the f/22 and f/32 setting, but assuming you shoot negative film, then that difference is negligible since the image will be corrected in the printing process. I wouldn't worry too much about it however. That lens will probably perform best at f/8 and f/11, and anything near the two extreme ends of the aperture range should be avoided as a general rule of thumb to avoid aberration and diffraction problems anyway.

    If you find that you really like the lens, it might be worth it to send it for a fix-up, just to make sure that when you set the aperture ring to f/8, it is really f/8 and not f/9.5 or f/6.3. That happens when the aperture blades become sticky from aging lubricant, or just a case of mis-calibration of the aperture ring due to wear and tear.

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