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06-20-2011, 12:31 PM   #1
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K-x with Manual lens in Av

Hi.
Recently I purchased a Ricoh 50mm/1.7 manual lens. I use it in Manual mode, metering with the Green button.
When I put the camera in Av mode it automatically adjusts the shutter speed, without using the Green button. But a strange thing though: it seems that changing aperture (with the ring) doesn't affect the shutter speed. I took a picture with a wide open aperture (1.7) and then another one with a closed one (16). In both pics the shutter speed was the same and the brightness was the same also, as though I didn't touch the ring at all.
How come?
Thanks.

06-20-2011, 12:43 PM   #2
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Read the manual. Av mode always shoots wide open because it can't read the lens aperture
06-20-2011, 12:47 PM   #3
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QuoteOriginally posted by Lowell Goudge Quote
Read the manual. Av mode always shoots wide open because it can't read the lens aperture
Maybe I don't understand something...
How can Av shoot wide open, if the shutter is mechanically set to shut?
06-20-2011, 12:55 PM   #4
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With manual lenses in Av mode, the shutter speed is set as if the aperture is wide open. It doesn't change the aperture size but rather uses the biggest aperture to set the shutter speed. That is why the shutter speed doesn't change when you turn the aperture ring. Av mode correctly exposes when wide open. When using Av mode with other aperture values, it will be underexposed.

06-20-2011, 01:04 PM   #5
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QuoteOriginally posted by jellyfish26 Quote
When using Av mode with other aperture values, it will be underexposed.
that's the thing, they aren't.
as I've written
QuoteOriginally posted by MK-x Quote
I took a picture with a wide open aperture (1.7) and then another one with a closed one (16). In both pics the shutter speed was the same and the brightness was the same also, as though I didn't touch the ring at all.
06-20-2011, 01:10 PM   #6
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On manual mode, when you press the green button, does the shutter speed change with the turning of the aperture ring? Are the pictures the same when in M mode with same shutter speed and different aperture?

Do you have any other manual lenses to see whether it is the lens or the body that is not working properly?
06-20-2011, 01:29 PM   #7
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QuoteOriginally posted by jellyfish26 Quote
On manual mode, when you press the green button, does the shutter speed change with the turning of the aperture ring?
yes it does
QuoteOriginally posted by jellyfish26 Quote
Are the pictures the same when in M mode with same shutter speed and different aperture?
pics look different (darker as aperture closes).
QuoteOriginally posted by jellyfish26 Quote
Do you have any other manual lenses to see whether it is the lens or the body that is not working properly?
no, I don't.
06-20-2011, 01:34 PM   #8
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Your lens manual then. I'm used to lenses being A not M. Didn't even consider that as an option. In Av mode, it is all shot wide open no matter what your aperture ring is set to.

06-20-2011, 01:56 PM   #9
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QuoteOriginally posted by MK-x Quote
Maybe I don't understand something...
How can Av shoot wide open, if the shutter is mechanically set to shut?
With this type of lens, the camera can't tell what the aperture ring is set to, which is why it displays "F--". So in in all the modes except M and B, the camera does not move the aperture lever at all. In those modes, the meter is taking its reading wide open for the shuttter speed, and shooting wide open.

In M mode, the camera will stop down the lens, if you permit the use of the aperture ring. It still has no idea of the aperture you've set, it just moves the lens aperture lever as much as it can. The aperture ring allows the blades to open to a particular setting, but this mechanical connection is all in the lens.

You can see the difference if your camera is set up for optical preview by turning the power switch to the right. Set your manual lens to f16, mode to M and engage optical preview while looking into the lens's front element. You'll see the aperture blades stop down. Switch to Av mode and repeat - the blades don't move.

You might think that if the blades move in M mode, it would be simple for Pentax to make them work in all modes. But the camera is missing information about how those lenses work and they don't quite work in the same way as a KA mount lens.
06-20-2011, 02:11 PM   #10
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QuoteOriginally posted by MK-x Quote
Maybe I don't understand something...
How can Av shoot wide open, if the shutter is mechanically set to shut?
if you look at the lens and turn the aperture, there are two bits that move. Since you're using a camera with a "crippled" mount, you lose out on some coupling bits that attach to the bit that's a little reccesed into the bayonet mount. The little metal bit that sticks out at the back of your lens is the only thing pentax dslrs are able to work with on M type lenses, so that means the only metering functionality you get is with that part. The purpose of that little thing is simply to hold the aperture open when stopped down and then the bit is released when you take a shot in M mode, causing it to stop down. For Av mode to work with the aperture ring, you also need the secondary coupling to read what the current aperture on the aperture ring is set to, but since you dont have this, pentax implemented it in such a way that it can only meter at wide open in Av mode.

hope this helped
02-28-2012, 08:26 AM   #11
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You can remove that little thing, if you unscrew the lens. Then it is possible to use the lens in AV mode with the aperture ring. Thats what I do with my M lenses. Just dont forget to put it in again when selling the lens.
02-28-2012, 11:58 AM   #12
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QuoteOriginally posted by Mace Quote
You can remove that little thing, if you unscrew the lens. Then it is possible to use the lens in AV mode with the aperture ring. Thats what I do with my M lenses. Just dont forget to put it in again when selling the lens.
which little thing are you referring to?
02-28-2012, 12:16 PM   #13
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QuoteOriginally posted by MK-x Quote
which little thing are you referring to?
He's referring to the aperture lever. If you remove it the lens acts like a M42 lens set to M, that is the aperture opens and closes when you turn the ring.
03-03-2012, 09:51 AM   #14
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QuoteOriginally posted by boriscleto Quote
He's referring to the aperture lever. If you remove it the lens acts like a M42 lens set to M, that is the aperture opens and closes when you turn the ring.
can you please post a photo or a link to show where it is?
thanks
03-03-2012, 12:48 PM   #15
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look at the back of your lens, see the stick thing that you can move? that's the aperture lever
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