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Old Dec 1, 2008, 2:48 PM   #1
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Hi. I know its been months since I last posted but I thought I had everything pretty much under control. Silly me. :?

Here's the problem. I bought this beautiful 40-80 mm Pentax-M lens that goes down to 2.8 so I have something to use for low light. The problem is that for anyone that uses the older lenses- you have to manually turn the f-dial for the aperture, and it doesnt send the f-stop to the camera.

I'm trying to use my flash unit with it to see if I can boost up shadow. It looks like however that I can't seem to do any exposure comp with it. And obviously- TTL is out. Yes, it will match the light to the f-stop on the camera if and only if the camera is at max synch speed. (1/180) but if I lower the flash output using AUTO mode then everything comes out underexposed. And if I match the flash output in AUTO with the f-stop on the lens then almost everything comes out overexposed. I'd need to lower the flash output by three stops to have it balance. If I'm going pure manual then I'd have to go all the way down to 1/16 or 1/32 power.

I know that I matched the ISO with both the cam and the flash so that shouldnt be a problem. The flash comp function on the camera in setup is 0.0. Is it just that the newer flashes can't work well with fully manual lenses? With my DA lenses they work fine and with my 50mm-A lens its perfect too. I'm figuring the flash is pretty much guessing how much to put out. I know also that its not sending out full pwer each time because the recharge time is very quick, not like when it sends out light at full power.

I hope someone can help. This post is kinda lengthy I know but I'm trying to put in as much info as I can.

Thanks.

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Old Dec 1, 2008, 5:04 PM   #2
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To make a manual (M- andK-lenses) stop down you have to

a) choose "allow aperture ring" in the menu (what camera model do you have?, it might be found under different places in the menu for different models)

b) choose the aperture with the ring on the lens.

c) put the camera in manual mode M with the exposure mode wheel

d) use the DOF preview (turn the on/off button past "on" to DOF) and check in the viewfinder if the exposure time will give you a correct exposure with the chosen aperture

When you use a flash TTL doesn't work with manual lenses, you have to see the guide (usually written at the back of the flash) what aperture to use at different distances.

Hope this helps a bit or that someone else chimes in, otherwise ask again.

Kjell
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Old Dec 1, 2008, 5:55 PM   #3
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Hi BillyBianca. Thank you for your help. Yes, I've done all of those steps on my k100. but what I've noticed is that no matter what aperture I turn to on the lens its always going to meter and shoot at f2.8 (max aperture). I can set it to f/11 or 22 but itll still meter at 2.8 when I press the AE-L button. Even though its in M mode. And I'm allowing the aperture ring. If you don't, then the cam just flashes Av and does nothing.

It makies sense now why everything was washed out when i used the on cam or external flash. The lens stays wide open no matter what! With the external flash I had to set it at 2.8 for it to be acceptable. With the cam flash it'll always pop full force once you take the lens off "A" or use a fully manual lens.

Now the question is, why wont the lens stop down to meter and shoot?
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Old Dec 1, 2008, 6:58 PM   #4
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JBoyde wrote:
Quote:
I've noticed is that no matter what aperture I turn to on the lens its always going to meter and shoot at f2.8 (max aperture). I can set it to f/11 or 22 but itll still meter at 2.8 when I press the AE-L button. Even though its in M mode. And I'm allowing the aperture ring. If you don't, then the cam just flashes Av and does nothing.

It makies sense now why everything was washed out when i used the on cam or external flash. The lens stays wide open no matter what! With the external flash I had to set it at 2.8 for it to be acceptable. With the cam flash it'll always pop full force once you take the lens off "A" or use a fully manual lens.

Now the question is, why wont the lens stop down to meter and shoot?
Hi JB,

I have absolutely no experience with M lenses and flash (I'm an "A" or newer lens user), but if your lens isn't stopping down to meter with the AEL button or to take the exposure, then it sounds like the aperture blades might be stuck or sticky. Have you tried moving the lever on the back of the lens and seeing if the blades easily snap open and closed? If it takes any real effort to actuate them manually, or the blades don't immediately react, then the camera will have a problem closing them down in the split second it takes to do so before the exposure. If this is the case, then you will probably have to find a good lens tech to clean and lubricate it.

Another possibility is that the aperture lever in the lens is bent, taking it out of the path of the matching actuating lever in the camera.

Just an idea since it's a new (to you) lens. . .

Scott
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Old Dec 1, 2008, 9:54 PM   #5
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I would second what Scott and Kjell have posted. If you have set the custom menu to allow M lenses then the symptoms you describe would seem to indicate a oily/stuck aperture blades.

Tim
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Old Dec 1, 2008, 11:23 PM   #6
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The only time I've tried my 540 flash with a "manual" lens was when I was using a K extension tube with the FA77 - the extension tube has no contacts on it so the lens became a manual one. I found that using the guide on the back of the flash in A mode gave me an over-exposed picture (I was shooting macros so I wasn't surprised), so I usually adjusted either the ISO or the shutter speed to get the exposure right. It was definitely stopping down the lens as I had a pretty good DOF, which I wouldn't have using f1.8, 77mm and an extension tube.
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Old Dec 2, 2008, 1:04 PM   #7
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Actually, all the blades snap open and closed very well. I'm glad to say that its a well-made and kept lens. I was reading up on this situation and I think what's going on is that one of the contacts on the camera is keeping the lens open. This is probably why I can open and close the aperture when the lens is off the camera but opens wide once I mount it. When I put the lens on my older K1000 the meter needle reacts as it should with the change in aperture. I guess it isnt too bad a problem since I use this lens in low-light situations only. I just have to get used to the fact that, technically, its a 40-800 mm 2.8 fixed aperture lens when put on a digital camera.


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Old Dec 2, 2008, 3:53 PM   #8
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There must be something wrong somewhere, it should work just fine. I don't have this lens, but my M 100 mm Macro works and off-brand lenses (Tokina, Makinon, Vivitar) also worked as they should. What happens if you try the DOF preview instead of the AE-L button?

Kjell
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Old Dec 2, 2008, 10:42 PM   #9
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You aren't trying to shoot in Av mode are you? An M lens in Av mode will stay wide open, no matter what you have the aperture set to.

Tim
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Old Dec 3, 2008, 4:08 PM   #10
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Nope, its in M mode. Ironically, the top display still says Av even though the knob is at M.
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