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01-09-2009, 03:25 PM   #1
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AV Mode - Screwy?

Hi,

Recently i've been using an old Pentax-M 40mm 1:2.8 lens on my Pentax K110D, and today I put my Pentax DA 18-55mm lens on, and most of the time I shoot AV mode, so like usual, I put it to AV mode, but when I go to change the aperture, it changes the shutter speed at the same time, and then I go take a photo, and if I raise the aperture the the highest (22), it still is just as bright as if I took a photo at 3.5 aperture.

Could someone please help me? It's quite annoying..

Thanks,

-Isaac

01-09-2009, 03:31 PM   #2
Ed in GA
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QuoteOriginally posted by IsaacSteiner Quote
Hi,

Recently i've been using an old Pentax-M 40mm 1:2.8 lens on my Pentax K110D, and today I put my Pentax DA 18-55mm lens on, and most of the time I shoot AV mode, so like usual, I put it to AV mode, but when I go to change the aperture, it changes the shutter speed at the same time, and then I go take a photo, and if I raise the aperture the the highest (22), it still is just as bright as if I took a photo at 3.5 aperture.

Could someone please help me? It's quite annoying..

Thanks,

-Isaac
Yes. that's exactly the way it's supposed to work. If you make the aperture smaller, the shutter must stay open longer and vice-versa.

You knew this though? Right?
01-09-2009, 04:04 PM   #3
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Yes, I did. But the photo should get darker as you raise the aperture, no?

Because it's not for me..

-Isaac
01-09-2009, 04:15 PM   #4
Ed in GA
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QuoteOriginally posted by IsaacSteiner Quote
Yes, I did. But the photo should get darker as you raise the aperture, no?

Because it's not for me..

-Isaac
Rasing the aperture (which I think means making it smaller) will increase the length of time the shutter is open. If the change proportionately, the exposure should remain the same.

A properly exposed picture is a properly exposed picture regardless of the combination used.

You change aperature to change DOF.

You change Shutter to freeze action or blur the action.

If you go into manual mode and set the shutter speed to, let's say 500/sec and the properly exposed photo will be at f/11. Then, yes, if you increase (higher number) the aperture, the photo will get darker if you don't change the shutter speed.

Maybe someone else can jump in and explain it better.

01-09-2009, 04:24 PM   #5
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QuoteOriginally posted by IsaacSteiner Quote
Hi,

Recently i've been using an old Pentax-M 40mm 1:2.8 lens on my Pentax K110D, and today I put my Pentax DA 18-55mm lens on, and most of the time I shoot AV mode, so like usual, I put it to AV mode, but when I go to change the aperture, it changes the shutter speed at the same time, and then I go take a photo, and if I raise the aperture the the highest (22), it still is just as bright as if I took a photo at 3.5 aperture.

Could someone please help me? It's quite annoying..

Thanks,

-Isaac

I believe you're expecting M(anual) mode. That will behave like you're expecting. Av and Tv still keep the same exposure by adjusting one value to counteract the affect on exposure of the other value you changed.
01-09-2009, 05:37 PM   #6
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The preceding posts are correct. Av and Tv modes are essentially semi-automatic in that the camera adjusts the non-user-defined parameters to achieve what it meters as correct exposure. If you find that the metering is too dark or too bright (it sounds like you were attempting to solve a problem like this) then you should adjust the EV compensation. I'm not sure if it is the same for the K20D, but on the K200D it is done by holding the EV button down and rotating the thumb dial.
01-09-2009, 05:52 PM   #7
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QuoteOriginally posted by IsaacSteiner Quote
Recently i've been using an old Pentax-M 40mm 1:2.8 lens on my Pentax K110D, and today I put my Pentax DA 18-55mm lens on, and most of the time I shoot AV mode, so like usual, I put it to AV mode
Ahh, I think I see what the problem is. You've been using the M 40mm in Av mode, haven't you?

When using lenses from before the A series (e.g. M and K series), the camera cannot tell which aperture you have set with the lenses aperture ring.

What you will see when you do this is that the camera will meter with the lens wide open (f2.8), and then when it goes to take the picture, it will stop the lens down to the aperture you have selected with the lenses aperture ring.

So, say, if you had the aperture ring on the lens at f5.6, then the photo will be underexposed (darker) by two stops. This is because the camera metered for f2.8, but with the lens actually set at f5.6, you've lost two stops of light.

With more modern lenses (e.g. DA series, FA series, F series, A series), the camera can sense the aperture the lens is set to and thus meter correctly.

So, what you're seeing is not anything wrong with your kit lens, it's actually a reverse expectation caused by using an old manual lens in the wrong mode. The only mode which works properly for older manual lenses is Manual mode, or Av mode, provided the lens is set to maximum aperture (f2.8 in this case).

There are some instructions on how to use an older manual lens here:
https://www.pentaxforums.com/forums/pentax-photography-knowledge-base/3800-ca...unt-d-slr.html
Ignore step 3, as that is specific to screwmount lenses. Aside from that, the process is the same.
01-09-2009, 06:33 PM   #8
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There is no mechanical aperture coupling on DSLR's, so M lenses are always wide open if set to Av. You have to use stop-down metering in M mode.

01-09-2009, 07:04 PM   #9
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QuoteOriginally posted by IsaacSteiner Quote
Recently i've been using an old Pentax-M 40mm 1:2.8 lens on my Pentax K110D, and today I put my Pentax DA 18-55mm lens on, and most of the time I shoot AV mode
If you've been using your M lens on Av mode, you've been shooting at nothing but f/2.8 even if you've been using the aperture ring to select other apertures. The aperture ring is ignored in Av mode. You need to use M mode if you want to shoot an M lens at aperture other than wide open.

QuoteQuote:
like usual, I put it to AV mode, but when I go to change the aperture, it changes the shutter speed at the same time, and then I go take a photo, and if I raise the aperture the the highest (22), it still is just as bright as if I took a photo at 3.5 aperture.
As others have said, that's the whole point of Av mode - the camera chooses an appropriate shutter speed for you, so no matter what aperture you choose, the exposure is the same. If you want to change aperture *without* changing shutter speed, that's what M mode is for. Decreasing aperture *without* a corresponding decrease in shutter speed - that's how to make your pictures darker.
01-10-2009, 08:34 AM   #10
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QuoteOriginally posted by Marc Sabatella Quote
If you've been using your M lens on Av mode, you've been shooting at nothing but f/2.8 even if you've been using the aperture ring to select other apertures. The aperture ring is ignored in Av mode. You need to use M mode if you want to shoot an M lens at aperture other than wide open.



As others have said, that's the whole point of Av mode - the camera chooses an appropriate shutter speed for you, so no matter what aperture you choose, the exposure is the same. If you want to change aperture *without* changing shutter speed, that's what M mode is for. Decreasing aperture *without* a corresponding decrease in shutter speed - that's how to make your pictures darker.

With the M lens, i've been shooting in M mode. Like I know how to use it in M.

But when I went back to AV mode with the auto focus lens, it was weird. Because it felt like I was missing a step or something. But thanks for the help everyone, I get it now.

-Isaac
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