Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
01-20-2011, 02:47 PM   #1
Forum Member




Join Date: Jan 2011
Photos: Gallery
Posts: 50
M series Primes on K200D -Exposure metering

Ok, so I can shoot in manual mode (M) and get a meter reading by pushing the Green button. The camera stops the lens down momentarily to get the meter reading. Then I shoot. No problem. OR I can also use the depth of field preview to stop down the lens to wherever I have it set and adjust the shutter speed for the desired exposure. No problem.

I can also shoot in Aperture Priority mode (Av) with full Auto metering but ONLY with the lens wide open. No problem.

Ok, here is my question.
Drum roll please...

If the camera is capable of stopping down the lens to get a meter reading by pushing the Green Button in Manual mode then why can it NOT stop down the lens in Av mode for full auto exposure convenience ?

Am I missing something ?
I like shooting in manual but it seems to me that all the bits and pieces are present here for full auto exposure metering in Av mode. Could anyone enlighten me ?
Oh yeah, lens in question is a 50mm M series f/1.7 prime. I love the combination just wondering if I am getting full use of it.
TIA for any and all replies.


Last edited by uptheriver; 01-20-2011 at 02:48 PM. Reason: Added TIA line
01-20-2011, 03:27 PM   #2
Senior Member




Join Date: Jan 2009
Posts: 173
Basic idea behind this problem is that the camera has no idea of knowing to which aperture you've stopped down the lens. When you use green button, the camera closes the diaphragm to the desired setting and measures the light coming in, but in AV mode the lens never gets stopped down, it stays open no matter what diaphragm setting your lens is set. A series lenses have A contact which tells the camera what is the aperture setting, and I believe the older bodies had an extra lever which would move according to the aperture setting. The new digital bodies do not have this lever.
01-20-2011, 08:13 PM   #3
Ole
Administrator
Ole's Avatar

Join Date: Sep 2006
Location: Copenhagen, Denmark
Photos: Gallery | Albums
Posts: 3,853
The camera doesn't need to know what aperture is set on the lens so I see no technical reason that the camera can't stop down, meter, set the shutter speed and then fire in Av mode with M/K lenses. It would probably require more shutter lag so that the camera would feel slower - perhaps that's why Pentax hasn't implemented it?
01-20-2011, 11:24 PM   #4
Senior Member




Join Date: Jan 2009
Posts: 173
What would be the point of Av mode then if the camera would have to stop down the lens every time before taking a pic, that's pretty much what you are doing with the green button.

01-21-2011, 09:51 AM   #5
Forum Member




Join Date: Jan 2011
Photos: Gallery
Posts: 50
Original Poster
I guess what I was trying to ask is this..
With an manual lens why can I not just press the shutter release (assuming I have focused) and have the camera take the picture. All the doohickeys are present here. Its just that the software(firmware) to perform the task is absent.
Oles' explanation of extra shutter lag seems to make sense here but there is a lot more lag of one has to jump on the green button and then wander over to the shutter release. :-)
Still shooting on full manual is good for the soul of a photographer.
01-21-2011, 10:09 AM   #6
Site Supporter




Join Date: Nov 2008
Location: Minneapolis
Photos: Albums
Posts: 588
QuoteOriginally posted by uptheriver Quote
Am I missing something ?
I like shooting in manual but it seems to me that all the bits and pieces are present here for full auto exposure metering in Av mode. Could anyone enlighten me ?
Yes, you are missing something. More importantly, the camera and lens are missing something.

All pentax DSLR's since I think the *ist are 'crippled' in that they can't tell what the aperture setting on the lens is. That is why you get the 'F--' in the LCD.

Older manual lenses in the 'A' series have an 'A' setting on the aperture ring. You can set them to 'A' and then shoot in Av mode with the camera dictating aperture to the lens (but not vice versa).

With an 'M' lens, the camera has no idea what the aperture is set to, so the only way for it to meter the exposure is by stopping down momentarily (via the green button). As far as stopping down and whatnot, your brain is probably faster than the camera. Get to know your F/stops and shutter speeds, and if you change your aperture, compensate with the shutter.

Last edited by grainbelt; 01-21-2011 at 10:23 AM.
01-21-2011, 10:26 AM   #7
Veteran Member
sewebster's Avatar

Join Date: Jun 2008
Location: Vancouver, BC
Photos: Gallery
Posts: 533
Not sure if this helps, but:

The way the aperture motion works on the M lenses is there is a lever that the camera pushes to stop down the aperture. Turning the aperture ring on the lens changes the "stop" of this lever... it changes how far the aperture stops down when you push it. When you take the picture with the M lens the camera just pushes the lever "all the way" and where it stops is dictated by the aperture ring setting.

So when you green button meter with an M lens the camera still has no idea what the aperture is, it just pushes the lever all the way and takes a reading.

Personally I'd not want to have any shutter lag.
01-21-2011, 06:27 PM   #8
Ole
Administrator
Ole's Avatar

Join Date: Sep 2006
Location: Copenhagen, Denmark
Photos: Gallery | Albums
Posts: 3,853
QuoteOriginally posted by grainbelt Quote
Yes, you are missing something. More importantly, the camera and lens are missing something.

All pentax DSLR's since I think the *ist are 'crippled' in that they can't tell what the aperture setting on the lens is. That is why you get the 'F--' in the LCD.

Older manual lenses in the 'A' series have an 'A' setting on the aperture ring. You can set them to 'A' and then shoot in Av mode with the camera dictating aperture to the lens (but not vice versa).

With an 'M' lens, the camera has no idea what the aperture is set to, so the only way for it to meter the exposure is by stopping down momentarily (via the green button). As far as stopping down and whatnot, your brain is probably faster than the camera. Get to know your F/stops and shutter speeds, and if you change your aperture, compensate with the shutter.
The camera doesn't need to "know" which aperture is set in Av mode. Think Takumar lenses. If you mount a screwmount lens and manually stop it down, Av mode works just fine: shooting at the stopped down aperture. So with an M/K lens the camera might as well stop the lens down for you, then meter, then shoot.

Since it will meter at the stopped down aperture it doesn't need to "know" what that aperture is.

01-21-2011, 06:36 PM   #9
Site Supporter




Join Date: Nov 2008
Location: Minneapolis
Photos: Albums
Posts: 588
QuoteOriginally posted by Ole Quote
So with an M/K lens the camera might as well stop the lens down for you, then meter, then shoot.

Since it will meter at the stopped down aperture it doesn't need to "know" what that aperture is.
I don't see the advantage... either the lens is stopped down while you're composing and focusing, making that difficult, or you get a mystery shutter speed and some wicked shutter lag.
01-21-2011, 06:45 PM   #10
Ole
Administrator
Ole's Avatar

Join Date: Sep 2006
Location: Copenhagen, Denmark
Photos: Gallery | Albums
Posts: 3,853
The lens would not be stopped down when you focus. As compared to the green button methos you save a button press at the cost of some shutter lag.

I'm not arguing that it is an advantage. I'm just saying that it would be doable to implement in firmware as per the OP's question.
01-21-2011, 07:47 PM   #11
Forum Member




Join Date: Jan 2011
Photos: Gallery
Posts: 50
Original Poster
Yes Ole- thank you- that answers my question.
A little shutter lag would still be faster than manual.
:-)
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
auto, av, camera, dslr, exposure, lens, meter, mode, photography, question
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
km exposure metering newf6401 Troubleshooting and Beginner Help 2 10-13-2010 05:33 AM
exposure metering TakeshiKovacs Pentax DSLR Discussion 4 09-06-2009 10:12 AM
Exposure Metering Timer samiam Pentax DSLR Discussion 11 08-13-2009 10:19 AM
For Sale - Sold: smc Pentax M Primes, S-M-C Primes, THE Series 1 70~210 Zoom, Viv MFTC and more monochrome Sold Items 33 02-13-2009 01:29 PM
Exposure metering with K10D Workingdog Pentax DSLR Discussion 22 03-08-2008 04:19 PM



All times are GMT -7. The time now is 10:11 AM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top