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10-31-2007, 05:40 PM   #1
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Need "how to" help - K100d with SMC A lens

Got a Pentax K100d dSLR with the kit lens. Everything working well with that. But I also just bought an older SMC Pentax 'A' 28mm F4 lens.

I mounted it to check it out, but I can't take a picture. The camera turns on but I get these indications:
1. On the top exterior LCD by the on-off switch: Flashes "AV - -" (with the battery icon and number of shots remaining).
2. In the view finder: "F - -" and nothing else.

The lens mounted okay, and I thought I'd have to focus manually, which I can do, but I thought the exposure would function as it does with the kit lens (18-55mm).

So I need some help. I am a rookie if you have not already figured that out.....

10-31-2007, 06:06 PM   #2
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It should expose as you were expecting IF you are using an "A" series lens with the aperture SET TO "A"

Give the electrical contacts on the lens a clean...they might be grubby.

You might want to check the name of the lens again...as far as I know Pentax never made a SMC-A 28mm f4
10-31-2007, 06:08 PM   #3
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Just turn the aperture ring on the lens to the "A" setting and test it again.
11-01-2007, 05:05 AM   #4
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Not sure about the A 28mm, but I know the A 50mm f/1.7 has issues where setting the ring to 'A' doesn't push out the little pin in the mount to tell the body "Hey, I'm set on A", so you could never really use the lens as an A lens. My first 50mm f/1.7 had this problem (so it was basically an "M" lens), my second one worked fine.

Check the mount and see if a little (TINY) pin is engaged when you go from f/22 to A.

11-01-2007, 05:39 AM   #5
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QuoteOriginally posted by pschlute Quote
It should expose as you were expecting IF you are using an "A" series lens with the aperture SET TO "A"
Allow me to pile on and emphasize this point.

Unlike in use with film bodies, where you could set your aperture to one of the numbers or the "A" position, what you want to do with this lens is always leave the aperture in the "A" position. You then set the aperture by using controls on the camera body. In the case of the K100D, you use the thumb wheel on the back of the camera. In Av mode, use the wheel directly. In M mode, the wheel sets the shutter speed and to change aperture you must press and hold the EV button (near the shutter button) while turning the wheel.
11-01-2007, 06:57 AM   #6
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QuoteOriginally posted by Mike Cash Quote
Allow me to pile on and emphasize this point.

Unlike in use with film bodies, where you could set your aperture to one of the numbers or the "A" position, what you want to do with this lens is always leave the aperture in the "A" position. You then set the aperture by using controls on the camera body. In the case of the K100D, you use the thumb wheel on the back of the camera. In Av mode, use the wheel directly. In M mode, the wheel sets the shutter speed and to change aperture you must press and hold the EV button (near the shutter button) while turning the wheel.
How I'd like to use the lens is the easiest way! I had understood with this lens (SMC Pentax-A f1-2.8 28mm is marked on the lens) I'd have to focus manually, but the auto exposure would work just as my DA K100d kit lens.

I am a little confused by your reply due to my inexperience. You say leave the aperture in the 'A' setting, which is where it is, and it is locked. Then you say to use the thumb wheel to set the aperture. With using just the default settings on the K100d, then mounting the 28mm lens set on 'A', I get just the icons I described earlier, even when I rotate that thumb wheel. If I switch from "Auto Pict" to "AV" mode on the left rotary dial on the K100d, then try the thumb wheel, the results are the same.

I suspect there is some setting I need to make in the K100d's menu, I just haven't figured out what that is yet! Someone mentioned to look on page 107 and 188 of the manual, so I'll try that.
11-01-2007, 07:04 AM   #7
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QuoteOriginally posted by egordon99 Quote
Not sure about the A 28mm, but I know the A 50mm f/1.7 has issues where setting the ring to 'A' doesn't push out the little pin in the mount to tell the body "Hey, I'm set on A", so you could never really use the lens as an A lens. My first 50mm f/1.7 had this problem (so it was basically an "M" lens), my second one worked fine.

Check the mount and see if a little (TINY) pin is engaged when you go from f/22 to A.
Where would I look for that? I did try to rotate the 28mm lens from the 'A' position to something else, and it does appear to be locked. At least I cannot rotate it gently from the 'A' to the f22 position. I think I know the pin you mean, but not sure. It's on the lens exterior, when the lens is mounted, and on this lens is just to the left of the green 'A' on the aperture ring?

I have another non-DA lens, a Vivitar 100mm lens in a Pentax-A mount (untried on this camera) that I can try also to see if it works correctly. It is possible the 28mm lens is defective or grubby or whatever, it's just not my first guess on what's happening. I think there is some setting I need to make in the camera's menu.

Thanks for the help to all.
11-01-2007, 07:05 AM   #8
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QuoteOriginally posted by pschlute Quote
......
You might want to check the name of the lens again...as far as I know Pentax never made a SMC-A 28mm f4
My mistake, it's an SMC Pentax A 28mm f2.8 lens.

11-01-2007, 07:11 AM   #9
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No, it's on the MOUNT of the lens. You won't see it if the lens is mounted (I'm not talking about the little "button" you press to go from f/22 to A). Take your Vivitar and move the ring from f/22 to A, and you should see a little pin "emerge" from the mount. This pin engages an electrical connection to the body's mount that says "I'm in A". Like I said, the 50mm f/1.7s were notorious for this pin to get funked up (like in my first copy). I had a 28mm A f/2.8 that worked fine (since sold it to a friend)

Other than the lens being on A (and of course the pin working), you DO NOT NEED TO DO ANYTHING FOR THE LENS TO WORK! If the pin is fine and the electrical contacts on the lens with info on the f-stop range are clean, the camera will pick up the f-stop for (and allow you control the f-stop via the thumb wheel)

So my guess is either the pin is funky or the contacts on the lens are dirty.
11-01-2007, 07:44 AM   #10
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QuoteOriginally posted by Papersniper Quote
How I'd like to use the lens is the easiest way! I had understood with this lens (SMC Pentax-A f1-2.8 28mm is marked on the lens) I'd have to focus manually, but the auto exposure would work just as my DA K100d kit lens.

I am a little confused by your reply due to my inexperience. You say leave the aperture in the 'A' setting, which is where it is, and it is locked. Then you say to use the thumb wheel to set the aperture. With using just the default settings on the K100d, then mounting the 28mm lens set on 'A', I get just the icons I described earlier, even when I rotate that thumb wheel. If I switch from "Auto Pict" to "AV" mode on the left rotary dial on the K100d, then try the thumb wheel, the results are the same.

I suspect there is some setting I need to make in the K100d's menu, I just haven't figured out what that is yet! Someone mentioned to look on page 107 and 188 of the manual, so I'll try that.

You have to change something in the custom menu. On one of the options says "allow the aperture ring work" (or something like that).
11-01-2007, 07:46 AM   #11
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That's ONLY for M-lenses (or earlier) or using an A lens off of A. The OP's problem is that when the lens if on "A", the body is not picking up the f-stop. Nothing to do with that Custom Menu option.

I suspect his lens is broken

QuoteOriginally posted by Gruoso Quote
You have to change something in the custom menu. On one of the options says "allow the aperture ring work" (or something like that).
11-01-2007, 07:47 AM   #12
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QuoteOriginally posted by egordon99 Quote
....Take your Vivitar and move the ring from f/22 to A, and you should see a little pin "emerge" from the mount. This pin engages an electrical connection to the body's mount that says "I'm in A"......."
I just dismounted the Pentax 28mm and checked. That pin you mention is there, but it's more like a little piece of metal, maybe 1/16th inch wide and it sticks out about a quarter inch from the lens unit. That pin is there both the 'A' or f22 or other aperture settings.

So, the lens seems to be working (I noted the aperture does seem to move as I went from 'A' to f22 to other f settings). Maybe the electrical contacts are dirty, but they don't look that way. I will clean them with a little alcohol and see what that does.


QuoteOriginally posted by egordon99 Quote
Other than the lens being on 'A' (and of course the pin working), you DO NOT NEED TO DO ANYTHING FOR THE LENS TO WORK! If the pin is fine and the electrical contacts on the lens with info on the f-stop range are clean, the camera will pick up the f-stop for (and allow you control the f-stop via the thumb wheel)

So my guess is either the pin is funky or the contacts on the lens are dirty.
I borrowed another lens, an "SMC Pentax-A Zoom 1:3.5-4.5 35-70mm". This one will work on the camera, at least the info in the viewfinder and top LCD screen look okay to me. However, I can't trip the shutter unless the camera thinks it's focused. On the K100d I get a little green icon in the view finder when it's focused. Without that, the camera will not trip the shutter. I had a heck of a time focusing (and getting the icon), but I suppose that will come with practice.

So, I hope cleaning the contacts with the original 28mm lens works, otherwise it's back to B&H. I thought they enjoyed a good reputation with photographers, but with this lens I am certainly NOT impressed.
11-01-2007, 07:51 AM   #13
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Put the camera body in Manual Focus, and you will be able to trip the shutter whenever you press the shutter button

Good luck with the lens!
11-01-2007, 08:44 AM   #14
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QuoteOriginally posted by egordon99 Quote
That's ONLY for M-lenses (or earlier) or using an A lens off of A. The OP's problem is that when the lens if on "A", the body is not picking up the f-stop. Nothing to do with that Custom Menu option.

I suspect his lens is broken
Ooops! my bad
11-01-2007, 12:39 PM   #15
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QuoteOriginally posted by egordon99 Quote
Put the camera body in Manual Focus, and you will be able to trip the shutter whenever you press the shutter button

Good luck with the lens!
Duh! Well, I am so very embarrassed, but also very thankful for the help I'm receiving. With the second lens, the 35-70mm, that was indeed the problem. I knew I needed to manually focus, I just forgot to flip the camera's switch from Auto to Manual. <g> Once I did that things are working very well.

Also, the original lens is now working!! It's a miracle! I took it off and re-installed in 2-3 times, that didn't do anything, so then I took a clean pencil eraser and went over the contacts on the lens. The next time I mounted the lens, voila, it works. So I suppose it was dirty contacts, at least partially.

I just knew it would end up being something simple, but the apparent dirty contacts threw me for a loop. They did not look dirty or corroded at all. Now to take some pictures and see how good that glass is......I've heard some good things about he Pentax SMC-A 28mm f2.8. That's now my fastest lens, and since I mainly shoot landscapes, it should work very nicely for that. I'm expecting that the sharpness and color will be better with the 28mm prime lens that with the 18-55mm kit lens even though the latter is a little more of a wide angle/landscape lens.

Again, thank you for the help.
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