Pentax 18-55 DA lens

Discussion in 'Camera Building, Repairs & Modification' started by David Lyga, Nov 6, 2013.

  1. David Lyga

    David Lyga Subscriber

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    I bought this lens for next to nothing recently as part of a deal and was sufficiently distracted with the other items so that I did not notice that this lens has no aperture ring. Obviously, it is for digital and its 35mm equivalent is about 28mm-85mm. Still, its glass is pristine and, when mounted on my K1000, its image quality is stupendous. Of course, it always stops down to about f22 when the shutter is pressed.

    What to do? The amount of money paid was about $3, so I cry not here. But, I do get to thinking of how to wring blood out of this stone. There really is a workaround, but the method is, perhaps, an exercise is taxing one's credibility: one can actually create a tiny shaft of metal or plastic that can fit snugly into the slot that the aperture lever runs through, preventing stopdown from closing past, say, about f8. One could do this quite effectively with mere eye evaluation but tests would define this precision more effectively, In effect, the full aperture for mounting and viewing would be preserved (as the aperture lever would be free to move within the range of f4 to f8), but, when firing the shutter, the smallest aperture would be the f8 that I had set it at. Of course, for changing to a different aperture, one would have to reposition this tiny shaft's location in the slot and that obviously requires removing the lens from its mount.

    Some sane ones out there will venture to say that this is, indeed, an exercise in futility. Actually, I partially agree, but it would be a fun thing to do (giving one the feeling that this matter had been 'conquered'), and one that is really not too difficult to implement. It is a thought concerning how to deal with lenses that do have an aperture lever but place reliance for aperture information through electronics. - David Lyga
     
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  2. L Gebhardt

    L Gebhardt Subscriber

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    Does it even cover the full frame with sharp corners? I doubt it. Probably best to sell it and buy a few rolls of film. But it might be fun if you want to experiment.
     
  3. David Lyga

    David Lyga Subscriber

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    It seems to. I have not given it a definitive test yet, but scrutinizing it though the viewfinder, carefully, focusing at the far corners even, it seems excellent. - David Lyga
     
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  4. Mustafa Umut Sarac

    Mustafa Umut Sarac Member

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    David,

    18mm is an excellent view. Use with tripod and slow shutter speeds. I dont know if you are an photographer who is running and shooting but if you are slow pacer , it does work. I was an member of German Goethe Institute and reading not reading looking to german tests of lenses at a german magazine and pentax was number one in whole 100 cameras. Its still in my mind. May be its a full frame dslr lens and it covers the whole.
    3 dollars is a steal , if you want to steal a lens , gas , food makes it more expensive.
    If I would have money, I would not bother to pay it 200 dollars or more. Good catch and wishing happy use.

    Take care ,

    Umut
     
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  5. wombat2go

    wombat2go Subscriber

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    Hi, David,
    I have used this 18 ~ 55 mm lens on M43 in unmodified form by holding the aperture lever at about f/8 with heatshrink tubing slid over the lever. This does not hurt the lens.

    On a Pentax film slr, the lens vignettes slightly below 20mm or so.
    http://www.flickr.com/photos/fluffyrazor/sets/72157630944498102/
    Here is a link to a disassembly procedure. I have not tried, but if you are handy, it might be possible to lock the aperture ring at about f/8 for example by replacing the spring with a solid wire. For the camera metering to work, you would also have to fix the aperture position lever at the same level as the aperture is locked at. Tricky, but it might be possible with some research and fiddling,
     
  6. redrockcoulee

    redrockcoulee Member

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    Some Pentax film bodies will allow you to adjust the aperature from the camera body. I bought a MZ7 and two lenses just for the ability to use some of our DA lenses on film as well as digital. I would guess that this lens will not cover FF below about 22mm based on my wife's 16-45 4.0 which starts at 21mm. Your lens is only the kit lens so not much resale value anyways so play around
     
  7. David Lyga

    David Lyga Subscriber

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    Interesting, red rock.

    wombat2go: the lever still has to be able to move freely so that it can register full aperture for focusing. The lever in the K mount camera FORCES it to be at full aperture. Thus, the impediment has to be separate from that lever in the lens.

    Mustafa, at first I was truly thrilled to have, finally, an '18', but as I said the '18' is really a '28' when used on full format 35mm cameras. Still, it was a steal. Some people are sick and tired of looking at their accumulations (I wonder when I will) so I am ready to buy if, and ONLY if, it is priced at a level that I know I could get if I wanted to sell back. Again, I am lucky to be in the Philadelphia-New York area for this, as I do not think that there is a place on Earth where so many cameras and lenses were bought. - David Lyga
     
  8. Ricardo Miranda

    Ricardo Miranda Member

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    You are confusing formats and concepts there. A 18mm is a 18mm in whatever format. The angle of view will change according to the format used. A 18mm angle of view on the 35mm format is a ultra-wide angle, but when employed in a smaller format as in the Pentax D-thingies, is equivalent to the angle of view that a 28mm would give you on 35mm.
    Your sentence would be correct if it reads this: "but as I said the '18' is really a '28' when used on APS format cameras."
     
  9. David Lyga

    David Lyga Subscriber

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    Yes, perhaps I meant, " is LIKE the view gotten from a 28mm lens made for full format 35mm film". Thank you for the correction Ricardo.

    Here are two photos of the lens, as well as a photo that the lens took out of my window at the smallest aperture (by default), which I would estimate at f32. The fire escape window in my efficiency provides three uses: 1) an escape from fire, 2) a portal to feed the pack of chickadees who park there, on cue, each morning, to be fed bits of whole wheat bread, and 3) an ideal 'infinity focus view' that I use when I need to check focus.

    The print is razor sharp, no matter what the distance. Diffraction did not seem to be an issue here, despite using a tiny aperture at full wide angle. (Thus, would it be yet sharper at f8?) Perhaps my digital Canon "S2 IS" did not do justice to the 5X7 B&W print. But... is there a bit of barrel distortion? Very dreary weather.

    NOTE BENE: You know, the reason I guess I posted this in the 'repairs' section is because I had removed the front part of this lens to fix the focus: it was smooth until about 10 feet, then it was stiff from 10 feet to infinity. Turns out that it was only a piece of broken plastic near the helicoid that was providing a barrier and was easy to remove. - David Lyga
     

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  10. wombat2go

    wombat2go Subscriber

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    Min aperture is actually f/22 on 18mm rising to f/38 at 55mm.
    On dslr, with a 22 inch monitor size, diffraction is a little bit apparent at 18 mm f/22, and quite apparent beyond about f/30 or so
    In my tests here, the lens is best at f/8 ~f/11, as usual.
     
  11. John Koehrer

    John Koehrer Subscriber

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    Just use a flat plate on the back of the lens. A small rectangle or square with a screw through it.
    double purpose it one side for f8 the other for f16 or whatever. It would just be different lengths on each side.
    There will be plenty of clearance using a flat head, countersunk screw. Hey, if you have a scrap lens make the stop from an old stop down lever.
     
  12. David Lyga

    David Lyga Subscriber

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    John, you cannot use the aperture placement as you suggested because it is not INSIDE the lens. I was under the impression that the planar location of the aperture is VERY important. - David Lyga
     
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