Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
10-15-2011, 11:28 PM   #1
Loyal Site Supporter




Join Date: Jan 2008
Location: Virginia, USA
Photos: Albums
Posts: 232
Vivitar 70-210 Series 1 Exposure Issue

On most of my K and M lenses I usually have to dial in some level of EV compensation depending on the F-stop, and I'm used to that, but my A lenses have almost always been spot on.

I have two copies of the Vivitar Series 1 70-210 (Version 3 Komine) (probably due to LBA). Both have the 'A' setting, one is a "P/K-A" mount the other is a "P/K-A R-P/K" with the Ricoh pin which is rounded and has never been an issue on either my K10 or K20. I noticed the other day that when shooting in Av mode the P/K-A version needs no exposure compensation other than when shooting at 210mm where I have to dial in -.7 to -1 Ev due to the lens being F4 while the camera still thinks it's F2.8, but the one with the Ricoh pin needs anywhere from -1 to -2 Ev at anytime other than when the lens is at max aperture where it needs no Ev compensation, almost like an M lens. I can shoot the same scene with both lenses one right after the other with the F-stop set at say F8 and the camera will set the shutter speed the same on both lenses, but when you look at the pictures and the histogram the one with the Pentax/Ricoh mount is clearly overexposed, usually by a whole stop, almost like the lens isn't setting the aperture to the same F stop that it's telling the camera that it is when I take the picture. I don't remember having this issue with film, but that seems so long ago.

My first question is this a normal variation in the run of a lens since other than the mount the lenses are nearly identical, and could it be the mount itself causing the problem?

Second if it is the mount would it be possible to switch the entire mount / aperture assembly from one lens to the other. The P/K-A version is the older of the two, it was CLA'd about a year ago, needed a new focus ring and had a old bout with some fungus from years ago that unfortunately left the glass a little scarred in a couple of spots around the edges which don't seem to impair the images on the reduced sensor digital cameras. The P/K-A R-P/K version is in excellent condition and I would prefer to use this one due to the old fungus issue with the other one.

Steve

10-16-2011, 12:23 AM   #2
Senior Member




Join Date: May 2009
Location: Edmonton, AB
Posts: 245
My guess would be your lens has sticky aperture.
10-16-2011, 06:21 AM   #3
Loyal Site Supporter




Join Date: Jan 2008
Location: Virginia, USA
Photos: Albums
Posts: 232
Original Poster
I just took a look at the lens. The aperture is very quick and snappy, at least while manipulating it with my hand. Perhaps something binds when it is mounted to the camera?
10-16-2011, 07:08 AM   #4
Loyal Site Supporter




Join Date: Jan 2008
Location: Virginia, USA
Photos: Albums
Posts: 232
Original Poster
Okay, I just did another test. Setting the camera in 'M' mode I manually set the aperture on both lenses rather than using the 'A' position and keeping the shutter speed and aperture consistent on both lenses the exposure comes out identical on both so it seems that the "A" setting on these mounts are not working the same.

10-16-2011, 10:05 AM   #5
Pentaxian
Just1MoreDave's Avatar

Join Date: Feb 2007
Location: Aurora, CO
Photos: Gallery | Albums
Posts: 4,814
QuoteOriginally posted by Odinz Quote
...Second if it is the mount would it be possible to switch the entire mount / aperture assembly from one lens to the other. The P/K-A version is the older of the two, it was CLA'd about a year ago, needed a new focus ring and had a old bout with some fungus from years ago that unfortunately left the glass a little scarred in a couple of spots around the edges which don't seem to impair the images on the reduced sensor digital cameras. The P/K-A R-P/K version is in excellent condition and I would prefer to use this one due to the old fungus issue with the other one.
Because the original design was produced in multiple mounts, it should be possible. On some lenses it's even easy and trivial. Your biggest obstacle will be some sort of production change, but you won't know until you try.
10-16-2011, 04:20 PM   #6
Pentaxian




Join Date: Oct 2011
Location: Savannah, GA
Posts: 4,989
I hate to mention it, but it could also be that your camera is only intermittently setting the aperture. (Which wouldn't happen in M lens mode since it is already stopped down.) I have a K10D that does this about half the time, with any lens or even testing with no lens at all. Try this -- set the lens in A mode. Set the camera in M mode with the custom option so that the green button sets the exposure by adjusting shutter speed. On the K10D this option is set on custom setting menu page 4, the last option called "green button in Tav & M" -- set it to #2 Tv Shift. Now if you set the lens to a small aperture and hit the green button, face the camera towards you and should be able to see the blades close as the camera tests the exposure. (This will even work with no lens at all and you can see if the little shuttle thing moves up and down.) So try that and hit the green button 20 times or so -- you should see the blades close every time. On my camera, at least some of the time the aperture doesn't close. (You'll be able to hear the difference as well.)

So far it is unclear whether this is a purely mechanical problem, or something to do with the electronics or control chip. I am debating whether to have it serviced since I've already got a K-7 and in either case it is going to cost almost as much or more than the total worth of the body.

Good luck.
10-16-2011, 04:28 PM   #7
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,314
You need to consider thatthe K10/20 are the worst metering cameras pentax ever made. When they first came out the was a big discussion on metering errors when using teleconverters and legacy lenses.

For fast lenses F2.8 and faster they will under expose by about a stop. If your lens is really F3.5 but reporting F2.8 there will be an error because the camera applies an aperture correction factor abased upon reported max aperture
10-16-2011, 06:14 PM   #8
dms
Site Supporter




Join Date: Aug 2011
Location: New York, NY
Photos: Gallery
Posts: 1,552
Believe it was Mark Roberts in his discussion on VS1 70-210 (ver 3) where he mentions intermittent problems on A mode--also said this can occur with non Pentax glass. I had a used (that I returned) 28-90 VS1 that had the problem on A also. But was fine in M mode.

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, camera, compensation, ev, issue, k-mount, lens, lenses, mount, p/k-a, pentax lens, slr lens, version
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
For Sale - Sold: Vivitar Series 1 70-210 F2.8-4.0 PKA Mount ecwoj Sold Items 2 08-15-2011 05:32 PM
K7: Focus problem at infinity (Vivitar Series 1 70-210 F3.5) peter.antonius Pentax SLR Lens Discussion 3 05-27-2010 02:34 PM
For Sale - Sold: Vivitar Series 1 P/KA 70~210 1:2.8~4.0 VMC Macro Focusing Zoom (Komine) monochrome Sold Items 2 01-03-2010 03:01 PM
Vivitar Vivitar Series 1 70-210 (62mm) or Pentax 50-200? DMH Pentax SLR Lens Discussion 23 10-25-2007 08:04 AM



All times are GMT -7. The time now is 09:56 AM. | See also: NikonForums.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