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03-24-2011, 06:45 PM   #1
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Aperture/shutter speed problem with 50mm f/2

I have been using my K110d for about 1.5 years with the kit lens and I just purchased a used Pentax-A 50 mm f/2 lens to broaden my skills. I've read (it seems like) 1000 posts on aperture and shutter speed and I can not figure out what's going on with this lens. Please forgive my ignorance.

From what I understand, the larger the f stop (f/2) the faster your shutter speed can be, and vice versa. Aperture and shutter speed relate inversely, so if I decrease the aperture, I have to slow the shutter speed down. However, with the 50 mm lens that I purchased, I can not seem to get a faster shutter speed than 1/45s inside my house regardless of the aperture. I can get great results out doors, but everyone says that the 50 mm takes great low light photos and I can not get it to work indoors. I have the ISO set to auto.

Could someone please help me figure this out? I would GREATLY appreciate any help or examples of setting combinations. I know practice makes perfect and i won't stop practicing, but there is an abundance of knowledge on this website that I can learn from. Thanks in advance.

03-24-2011, 06:58 PM   #2
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I would start by not using auto ISO. I recommend 200. With the ISO fixed, you will see the relationship better between shutter speed and aperture.
Are you using manual mode? Aperture priority mode? (Av) Shutter speed priority (Tv)?
I personally prefer Av. I select the aperture and the camera determines the correct shutter speed. For this you need to set the lens to A.
Hope this helps!

03-25-2011, 05:48 AM   #3
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Thanks for your response. I've been shooting in M mode. I really want to learn to control everything myself.

But, I took your suggestion and switched to AV mode, which is what I shoot in with my fully automatic lens. And now I have another question:

So far, with this Pentax-A 50mm lens, I've been turning the aperture ring everytime to try different shots. What does the "A" on the aperture ring do?

Which is better, using the "A" setting on the aperture ring or turning the ring to get the desired aperture?
03-25-2011, 06:35 AM   #4
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When you set the lens to A-position, the lens becomes an automatic aperture lens. Only then you can shot in Av mode. Aperture adjustment is now in-camera.

The Av mode is simpler, but you still have full control of the parameters. f2 gives you more blur in out-of-focus areas (bokeh, or thin DOF). f8 or f11 gives you sharp all the way out. Aperture opening and distance is a few way to isolate the object in the photo. Closer the subject more bokeh.

When I use Av mode, I set the camera to center weight metering or spot metering. When I point to a dark or light object, I use EV compensation to control the metering. In M-mode, you have to deal with everything, but sometimes it is needed that way.

03-25-2011, 06:43 AM   #5
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Okay, so I have my camera set to "A" on the aperture ring and manual mode. I'm starting to see the relationships b/w aperture, shutter speed and ISO.

Now, I've read a lot about the mysterious green button. Is it correct that you can only use this button in manual mode? If so, since my cameral doesn't literally have a green button on it, is this the same as the AE-L button? When I press this button, it changes the shutter speed.

Is this stop down metering?

Again, thanks for accepting me and my ignorance. I'm really trying to learn.
03-25-2011, 07:02 AM   #6
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We're here to help.

Green button is useful when you need to 'reset' the camera to correct setting according to a scene. I don't use K110, so you need to find out. In my K20, I can set the behaviour of the green button to change only the speed, not aperture. One of my dial is linked to EV compensation permanently - it's only my style to use the camera for the quickest.

Yes it is stop down metering, because the camera does a quick switch on the lens at the aperture you set to measure the light. It also works fine for manual lenses without the A-switch.

My case, I use to stick with one iso setting, depends on the condition. It's one parameter less to worry.

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