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02-11-2015, 01:30 AM   #1
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Noob Question: What is stop-down metering?

Can someone please educate me about Stop-Down metering? I recently bought K3 and am looking at buying some legacy lenses. Some of the old M lenses seem to have amazing optical quality but need Stop-Down metering.

What I understand is:

Step 1. Set the aperture value on the lens.

Step 2. Set the shutter speed (manual mode) or half press the shutter release button so that the camera will decide the shutter speed (aperture priority)

3. Fully press the shutter to take the picture.

So, what is the difference between a stop-down metering and Aperture priority mode. I follow the above steps for every lens in Aperture priority mode. I can't really figure out the difference between a lens which requires stop down metering and a lens which does not.

Am I understanding this correctly? Also, I have read some articles mentioning that K3 is not good for stop-down metering. What is that about? Isin't the metering system/technology remain the same irrespective of how we choose to meter?

Any info is highly appreciated. Thank you.

02-11-2015, 01:56 AM   #2
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the mount on all modern DSLR's from pentax are crippled, that means they cannot measure exposure on K and M optics correctly as is but need to actually "look through the lens" to see amount of light coming through. Step down metering is in other words the camera moving the aperture lever on the lens so that it will close down to the set value, and then reads the amount of light and sets the appropriate shutterspeed to get a correct exposure.

---------- Post added 02-11-15 at 10:05 AM ----------

On my camera I can only use step down metering in manual mode, I am unable to do so in Aperture priority mode. If I use AV mode I will always shoot wide open.
02-11-2015, 02:16 AM   #3
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QuoteOriginally posted by uday029 Quote
Can someone please educate me about Stop-Down metering? I recently bought K3 and am looking at buying some legacy lenses. Some of the old M lenses seem to have amazing optical quality but need Stop-Down metering.

What I understand is:

Step 1. Set the aperture value on the lens.

Step 2. Set the shutter speed (manual mode) or half press the shutter release button so that the camera will decide the shutter speed (aperture priority)

3. Fully press the shutter to take the picture.

So, what is the difference between a stop-down metering and Aperture priority mode. I follow the above steps for every lens in Aperture priority mode. I can't really figure out the difference between a lens which requires stop down metering and a lens which does not.

Am I understanding this correctly? Also, I have read some articles mentioning that K3 is not good for stop-down metering. What is that about? Isin't the metering system/technology remain the same irrespective of how we choose to meter?

Any info is highly appreciated. Thank you.
It just means that the aperture diaphragm needs to be closed before the camera can evaluate the exposure and give you a recommended shutter speed (as opposed to open-aperture metering, which is the norm these days).

Adam
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02-11-2015, 03:38 AM   #4
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02-11-2015, 04:34 AM   #5
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QuoteOriginally posted by EJMzagsfan Quote
Using Manual Lenses (M42 Screwmount, M , K) on Pentax DSLRs F--
It may seem a bit daunting on first reading but the process is pretty straightforward and once you've had a couple of goes it comes naturally.
02-11-2015, 07:05 AM   #6
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QuoteOriginally posted by uday029 Quote
Can someone please educate me about Stop-Down metering? I recently bought K3 and am looking at buying some legacy lenses. Some of the old M lenses seem to have amazing optical quality but need Stop-Down metering.

What I understand is:

Step 1. Set the aperture value on the lens.

Step 2. Set the shutter speed (manual mode) or half press the shutter release button so that the camera will decide the shutter speed (aperture priority)

3. Fully press the shutter to take the picture.

So, what is the difference between a stop-down metering and Aperture priority mode. I follow the above steps for every lens in Aperture priority mode. I can't really figure out the difference between a lens which requires stop down metering and a lens which does not.

Am I understanding this correctly? Also, I have read some articles mentioning that K3 is not good for stop-down metering. What is that about? Isin't the metering system/technology remain the same irrespective of how we choose to meter?

Any info is highly appreciated. Thank you.
I have a K-3 and an M (manual focus, manual aperture) lens. To me, in practice, it works like this:

(1) Put the camera in M (all-manual) mode.

(2) Set the aperture using the aperture ring on the lens.

(3) Hit the green button. This stops down the aperture blades and meters through the lens.

(4) Make adjustments to the exposure/ISO as I see fit, repeating (3) if necessary.

(5) Fully press the shutter button to take the shot.

It's a bit slow, but the lens I have is a macro lens, and I only use it on a tripod taking pictures of inanimate objects, so it's not a problem for me.
02-11-2015, 08:51 AM   #7
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QuoteOriginally posted by Outis Quote
I have a K-3 and an M (manual focus, manual aperture) lens. To me, in practice, it works like this:

(1) Put the camera in M (all-manual) mode.

(2) Set the aperture using the aperture ring on the lens.

(3) Hit the green button. This stops down the aperture blades and meters through the lens.

(4) Make adjustments to the exposure/ISO as I see fit, repeating (3) if necessary.

(5) Fully press the shutter button to take the shot.

It's a bit slow, but the lens I have is a macro lens, and I only use it on a tripod taking pictures of inanimate objects, so it's not a problem for me.
An alternative to using the green button ( to set the shutter speed ) is to use DOF preview to stop down the lens, and use the camera's meter to check your exposure settings.

The nice thing about this method is that you can point your camera at something like your palm, or snow, or something that is NOT gray, and as long as you know what exposure
that target should meter at ( eg. 1 stop over neutral, 2 stops over neutral or whatever ), you can set your aperture/shutter speed accordingly.

This doesn't work on camera bodies that lack the DOF preview position on the on/off switch ( eg. K30 ). With those cameras, the metering is disabled during DOF preview.

So there's two options: Green button if you're pointing the camera at something you want to come out as neutral, or DOF preview if you want to use the meter and set the exposure yourself.

( I don't know if exposure compensation works with green button exposure setting - but if you're going to second guess the green button exposure, you might as well just set the exposure manually based on a meter reading )
02-11-2015, 09:46 AM   #8
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QuoteOriginally posted by uday029 Quote
Can someone please educate me about Stop-Down metering? I recently bought K3 and am looking at buying some legacy lenses. Some of the old M lenses seem to have amazing optical quality but need Stop-Down metering.
The following applies to all cameras, including those before new fangled gadgetry like depth-of-field-preview and auto-exposure:
  1. Adjust the aperture diaphragm to wide open, compose the scene, and focus the lens
  2. Stop down the lens (i.e., adjust the f-stop down to the desired aperture size)
  3. Meter the light
  4. Based on the meter reading, adjust f-stop or shutter speed or both if necessary to achieve the desired exposure, depth of field, and motion freeze
  5. Trip the shutter

On a Pentax DSLR:
  1. The diaphragm is already wide open, so compose and focus
  2. Meter the light while stopping down the lens to the desired aperture size, i.e., depress the Green Button or hold On/off switch in the depth-of-field-preview position while looking at the exposure guide in the viewfinder (see your owner's manual section on Manual Exposure Mode)
  3. Based on the meter reading, adjust shutter speed and/or ISO and/or f-stop if necessary to achieve the desired exposure, etc., i.e., see your owner's manual section on Manual Exposure Mode; NB: this is already done if you used the Green Button!
  4. Trip the shutter



Last edited by pete-tarmigan; 02-11-2015 at 09:56 AM.
02-11-2015, 10:27 AM   #9
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Sometimes stop-down metering is no problem at all, sometimes really frustrating. The lenses will all be manual focus, so you need time to focus and measure the light somehow. If the light isn't changing, it's almost no trouble at all. At first, you don't want to try photos of kids playing in the yard, running from a shaded area to full sun. The changing light and focus together will be frustrating. But if you plan ahead a little, you can set exposure for the sun and wait for the kids to run over there.

So when you're looking at buying a lens, if you think you'll have a little planning time for the shots, the metering step is a small issue. Focusing skill helps too; if you are really quick at focusing, you have more time to think about light.

QuoteOriginally posted by arkav Quote
( I don't know if exposure compensation works with green button exposure setting - but if you're going to second guess the green button exposure, you might as well just set the exposure manually based on a meter reading )
Exposure compensation in M mode does work on some Pentax DSLRs but not all. It works on my K-5 IIs.
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