Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
11-15-2010, 08:17 PM   #1
Site Supporter
jonhock's Avatar

Join Date: Oct 2009
Location: NorthEast Pennsylvania, USA
Photos: Gallery | Albums
Posts: 377
aperture wide open?

I was poking around in the camera reviews and came across something in Ole's "K7, K20D, and K10D comparison chart" that he posted back in May 24, 2009, which I am not sure of.

I was good with the comparison chart until I got to this phrase, "Exposure modes with M and K lenses restricted to Av (with aperture always wide open) and M, but I don't quite get the "aperture wide open" thing in Av mode. I tried it and I don't see the difference between the lens being wide open or at f8 or so. As usual, any and all help, is welcome. Shoot, I might even learn something

11-15-2010, 09:48 PM   #2
Veteran Member
sterretje's Avatar

Join Date: Dec 2008
Location: Roodepoort, South Africa
Photos: Gallery | Albums
Posts: 3,534
Next time, please post the link so we don't have to search

I think what is meant is that the camera has no means to control the aperture (but I've never seen a M or K lens). So on these lenses you have to set your aperture manually.


PS
Sorry, I have to correct that; somebody just dropped a M 50/1.7 in my lap for approx. US$25
11-15-2010, 10:56 PM   #3
Veteran Member




Join Date: Nov 2010
Location: San Diego, CA
Posts: 360
QuoteOriginally posted by sterretje Quote
Next time, please post the link so we don't have to search

I think what is meant is that the camera has no means to control the aperture (but I've never seen a M or K lens). So on these lenses you have to set your aperture manually.


PS
Sorry, I have to correct that; somebody just dropped a M 50/1.7 in my lap for approx. US$25
you are kidding me lol, cheapest I've found is like 50...
11-15-2010, 11:11 PM   #4
Veteran Member
sterretje's Avatar

Join Date: Dec 2008
Location: Roodepoort, South Africa
Photos: Gallery | Albums
Posts: 3,534
I showed the guy (colleague at work) the average price here in the lens database and told him what I was prepared to pay and the next moment there was the handshake to sign the deal.



11-16-2010, 12:31 AM   #5
Senior Member
pontusadefjord's Avatar

Join Date: Apr 2009
Location: Uppsala
Photos: Gallery
Posts: 111
In Av it doesn't matter what the aperture is set to on the lens, the camera will always shoot wide open (at least my K200D does that). That's why you can't see any difference between wide open and f/8, because even though it was set to f/8 it was in fact wide open. I hope I haven't made you more confused...

sterretje, congratulations on that M 50/1.7 - it's a lovely lens!
11-16-2010, 02:11 AM   #6
Veteran Member
sterretje's Avatar

Join Date: Dec 2008
Location: Roodepoort, South Africa
Photos: Gallery | Albums
Posts: 3,534
pontus, you definitely made me more confused. Turning the aperture ring on the lens does change the aperture (when it's not mounted on the camera); need to test tonight to see what you mean.

PS thanks for the congrats.
11-16-2010, 02:29 AM   #7
Site Supporter
pschlute's Avatar

Join Date: Mar 2007
Location: Surrey, UK
Photos: Gallery
Posts: 1,248
The M and "K" series lenses have an aperture ring on the lens that you have to turn by hand.

If you use theses lenses in Av mode the camera will NOT use the selected aperture but will capture always at wide open.

To get the camera to use the selected aperture you must use the camera in M (manual) mode, and use the stop-down metering method. The camera will then use the selected aperture.

The modern digital camera bodies do not have a physical coupling that can "read" the aperture set on a manual lens, so Av mode will not work properly as the camera has no idea what the aperture is set to. When you use the stop-down metering method the camera still has no idea what the aperture is, but will correctly expose as it takes an actual light meter reading while the lens is stopped down.

Having said all that there are exposure errors when using stop-down metering with these lenses, but that is for another thread.
11-16-2010, 03:47 AM   #8
Ash
Community Manager
Loyal Site Supporter
Ash's Avatar

Join Date: Mar 2007
Location: Toowoomba, Queensland
Photos: Gallery | Albums
Posts: 22,695
You will need to read up on the function of the green button when M and K lenses are being used on Pentax dSLRs. This will explain all you need to know about the aperture being wide open until the camera meters with the stopping down feature of the green button and enables you to take shots at the aperture of your choosing.

11-16-2010, 06:32 AM   #9
Veteran Member
sterretje's Avatar

Join Date: Dec 2008
Location: Roodepoort, South Africa
Photos: Gallery | Albums
Posts: 3,534
Got home and tried it in Av on a K100D. Coming from manual M42 lenses (where the aperture actually changes when the aperture ring is turned), the experience is disappointing Got in M mode and it worked as expected (using DOF preview).
11-16-2010, 06:44 AM   #10
Senior Member
pontusadefjord's Avatar

Join Date: Apr 2009
Location: Uppsala
Photos: Gallery
Posts: 111
QuoteOriginally posted by sterretje Quote
pontus, you definitely made me more confused. Turning the aperture ring on the lens does change the aperture (when it's not mounted on the camera); need to test tonight to see what you mean.

PS thanks for the congrats.
Yes, when it's not mounted on the camera. When it's mounted the camera keeps it open.

It's hard to explain, pschlute sure did a better job.
11-16-2010, 08:35 AM   #11
Veteran Member
Docrwm's Avatar

Join Date: Sep 2010
Location: Somewhere in the Southern US
Photos: Gallery | Albums
Posts: 11,275
Treat your M42 mount lenses as completely manual, just like with a K1000. Set everything yourself. You can get guidance, in M mode, from the green button but it can be off (for a variety of reasons explained in a variety of posts) so I do some adjusting based on each shot. If you need to shoot 1 shot without time or the chance to adjust and reshoot then you will need to learn the camera with that lens and make your best guess. Takes practice in my experience to produce nice photos but it can be worth it using older glass too. Good luck.
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!
aperture, av, camera, comparison, pentax help, photography
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Nature Some wide open Tulips JeffJS Post Your Photos! 6 04-18-2010 07:37 AM
77/1.8 wide open... igor Post Your Photos! 14 08-17-2009 05:36 AM
Spotmatic F - open aperture metering filmamigo Pentax Film SLR Discussion 12 03-19-2009 06:47 AM
Which 50/1.4 is best wide open? Big I Pentax SLR Lens Discussion 5 08-05-2008 09:23 AM
DA 18-55 wide open Ash Pentax SLR Lens Discussion 16 01-03-2008 08:30 PM



All times are GMT -7. The time now is 09:24 PM. | 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