View Full Version : stop down metering /that little green button

01-06-2011, 5:26pm
Hi all.......I was wondering if anyone had a good link or explanation of stop down metering. I have bought some extension tubes for the K5....the Pentax ones with the single contact pin........struggle struggle :o

01-06-2011, 6:04pm
I've Never even heard that term I'm sorry

01-06-2011, 6:10pm
:confused013 Sorry Jan, Same as Ving/Darren, But , Had a Google http://www.kallepahajoki.net/2009/07/28/stop-down-metering-for-manual-pentax-lenses/ Maybe this will help - Bill :)

01-06-2011, 8:15pm
Copied this from an article I had on file:

"On film cameras, the "A" setting on the aperture ring of Pentax lenses permits shutter-preferred autoexposure and program autoexposure. With Pentax's digital SLR's, lenses that lack the "A" setting require that the photographer use stop-down metering.

Pentax provides quasi-automation of this with the "Green Button" feature: Pressing the Green Button (or AF button on some models) momentarily stops down the lens diaphragm and automatically sets the correct shutter speed using the Program autoexposure line and center-weighted metering. This requires that you change the default settings of your camera (through the custom menu) to allow the shutter to fire with a lens off its "A" setting. (See your owner's manual for details.)

Spot metering and multi-segment metering are not available when using lenses that lack the "A" setting."

Because your extension tubes only have the 1 pin any lens you use need to be treated as a non "A" lens - that us to use the aperture ring manually.

The green button will simply work out the best shutter speed for the light available.

Hope this helps.

01-06-2011, 9:52pm
Yes that does help thanks Kevin.......I also googled and have worked out that the pin is just a locking pin...so that changes my A lenses to non A lenses......but what happens when I want to do something that the camera doesn't......if I want to change the amount of light......I am restricted to changing the aperture by the aperture ring and/or iso? In M mode can I change the shutter speed as well ?
So if I cant see thru the view finder at f22 but that is the f stop I want to use ( I dunno for some reason or other ) I focus at say f2 and then change the fstop back to 22? and pray I haven't jiggled the focus?

01-06-2011, 10:27pm
Further to Kevin's post, once upon a time to use through the lens exposure metering you had to push a button to stop the lens down to the chosen aperture and adjust the shutter speed until the needles matched or the needle was in the circle or whatever system the camera used. Sometime in the late 70's I think along with aperture priority metering, the camera sensed what aperture was being used and adjusted the shutter speed with the lens remaining wide open. Although if I remember correctly many cameras still allowed you to stop the lens down to get a depth of field preview.

04-06-2011, 1:37pm
spot on Wazza999, that's how my spotmatic operates

05-06-2011, 8:36am
Thanks guys
I think I have it worked out. It works way better on a Penatx zoom A 35-135........:confused013 dont care....... I am having all sorts of fun with it. One day I may even have one to show! I do need rails I think :(

07-06-2011, 5:18pm
1 Just a quick reply if you use an "A" lens you use it the same as an AF lens but have to manual focus it.

2 If you use an "M"or manual lens you must set the apture ring to the "F" stop, ie 1.8 or what you want for depth of field. then press the green button which will give you the correct shutter speed,but you will probable need to adjust or fine tune it.

PS, If you have extention tubes without electrical contacts you will have to set up as in 2.


10-06-2011, 9:21am
as an added bonus, if you are using this setup in manual mode you don't get the exposure meter thingie in the bottom of your viewfinder .... Until you use the Optical DOF preview (on/off switch to the right) (at least it is on the *ist and the k10d

23-06-2011, 9:47am
Hi All,

I use a Tamron 90mm f2.5 adaptall and a Vivitar 105mm f2.8 on my K20D with manual extension tubes, ie., K mount. With these I just have to run the camera on full manual and chose the length of the lens for the camera, which it asks for as soon as I turn it on.
For perfect focusing on macro you will find that you will need a Manfrotto 454 focusing rail or similiar and mount it on a good, sturdy tripod. I looked at cheaper brands but when you locked them down, they still had movement.
I have obtained a set of electronic extension tubes for when I get a full electronic macro lens.