Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
03-02-2024, 08:19 AM   #1
Junior Member




Join Date: Mar 2023
Location: UTRECHT
Posts: 37
SMC Pentax-F 1:1.7 50mm overexposes on auto

I recently picked up above lens in a thrift store. It has an aperture ring with 'A' setting. When I set it to 'A' it overexposes consistently, even though the viewfinder shows (I think) a plausible combination of aperture and shutter.
When I set it to a specific aperture, exposure is correct when within the range of shutter speeds. In the menu, I tried both settings for enabling either manual aperture or only 'A'. No difference.
Am I doing something wrong, or is the lens broken?


Last edited by Willem.deboer; 03-02-2024 at 08:29 AM.
03-02-2024, 08:24 AM   #2
Moderator
Loyal Site Supporter




Join Date: Feb 2015
Location: Avalon Peninsula, Newfoundland
Photos: Gallery | Albums
Posts: 1,789
What body? What settings? An example or 2 with exif info would really help here.
03-02-2024, 08:29 AM   #3
Junior Member




Join Date: Mar 2023
Location: UTRECHT
Posts: 37
Original Poster
QuoteOriginally posted by jgnfld Quote
What body? What settings? An example or 2 with exif info would really help here.
It's a K-X on auto.
03-02-2024, 08:36 AM   #4
amateur dirt farmer
Loyal Site Supporter
pepperberry farm's Avatar

Join Date: Dec 2014
Location: probably out in a field somewhere...
Photos: Gallery | Albums
Posts: 41,700
possibly sticky aperture blades are not returning fast enough to prevent the overexposure...

03-02-2024, 08:46 AM   #5
Junior Member




Join Date: Mar 2023
Location: UTRECHT
Posts: 37
Original Poster
I tried the same lens on an iStD2. Same effect but less pronounced.
03-02-2024, 08:48 AM   #6
Junior Member




Join Date: Mar 2023
Location: UTRECHT
Posts: 37
Original Poster
QuoteOriginally posted by jgnfld Quote
What body? What settings? An example or 2 with exif info would really help here.
Attached are images. One on auto, other on manual.

---------- Post added 03-02-24 at 04:50 PM ----------

QuoteOriginally posted by pepperberry farm Quote
possibly sticky aperture blades are not returning fast enough to prevent the overexposure...
Is that en easy fix?
Attached Images
View Picture EXIF
PENTAX K-x  Photo 
View Picture EXIF
PENTAX K-x  Photo 
03-02-2024, 09:01 AM   #7
Site Supporter
Site Supporter




Join Date: Jun 2008
Location: Idaho
Photos: Gallery
Posts: 2,375
Try looking into the lens and take a time exposure (1 - 5 seconds) requiring a small aperture (maybe pointed at the sky over your shoulder). That should give you time to see what is happening with the iris. It is closing at all or making the attempt and not getting there? When you say "manual exposure" are you talking about using the aperture ring on the lens?

Also, it's interesting to note that in your ASIF data, the properly exposed photo was shot at full aperture (like the iris isn't working) and high shutter speed. Was that wide open f-stop specified in your manual setting (second shot) or did you have the f-stop set to another value, and the camera compensated for a stuck iris with a high shutter speed?

Also, you might take the lens off your camera, set it to f22 and move the small lever on the rear of the lens to see if it stops the iris down.

03-02-2024, 09:07 AM   #8
Junior Member




Join Date: Mar 2023
Location: UTRECHT
Posts: 37
Original Poster
QuoteOriginally posted by Bob 256 Quote
Try looking into the lens and take a time exposure (1 - 5 seconds) requiring a small aperture (maybe pointed at the sky over your shoulder). That should give you time to see what is happening with the iris. It is closing at all or making the attempt and not getting there? When you say "manual exposure" are you talking about using the aperture ring on the lens?

Also, it's interesting to note that in your ASIF data, the properly exposed photo was shot at full aperture (like the iris isn't working) and high shutter speed. Was that wide open f-stop specified in your manual setting (second shot) or did you have the f-stop set to another value, and the camera compensated for a stuck iris with a high shutter speed?

Also, you might take the lens off your camera, set it to f22 and move the small lever on the rear of the lens to see if it stops the iris down.
I also noted in the exif info that the overexposed photo says 'manual exposure', whereas the correctly exposed photo says 'auto'.
03-02-2024, 09:19 AM   #9
Site Supporter
Site Supporter




Join Date: May 2023
Location: Northwest Wyoming
Posts: 178
Another thing you might try is to use the camera on "auto" or "green" mode on the dial with the lens on the "A" marking, take the picture, and then look at the settings it selected. Then repeat the picture as quickly as possible (to keep the light on your subject the same) using the aperture priority mode on the dial ("Av") and set the lens aperture ring on the same setting it was on in "auto" mode and see if the shutter speed (and picture) come out the same as the first auto shot.

My K100D is now carrying a M42-to-K-mount adapter and is home to my old film-era lenses. Several of those lenses do not expose correctly for whatever unexplainable reason, severely under-exposing shots when taken either full-manual/metered, or in aperture-priority ("Av") mode. The simple solution for mine (no green button on a K100D) is to simply bump the exposure compensation by 2.0 full stops, which works well enough on my 135mm/f2.5 lens. I just found a mint-condition 200mm/f4.0 in a local pawn shop for $25 and it requires the exact same compensation, so there's something about those two lenses and my K100D that just ain't right...but can be easily fixed.

Best of luck.
03-02-2024, 09:31 AM   #10
Junior Member




Join Date: Mar 2023
Location: UTRECHT
Posts: 37
Original Poster
QuoteOriginally posted by Bob 256 Quote
Try looking into the lens and take a time exposure (1 - 5 seconds) requiring a small aperture (maybe pointed at the sky over your shoulder). That should give you time to see what is happening with the iris. It is closing at all or making the attempt and not getting there? When you say "manual exposure" are you talking about using the aperture ring on the lens?

Also, it's interesting to note that in your ASIF data, the properly exposed photo was shot at full aperture (like the iris isn't working) and high shutter speed. Was that wide open f-stop specified in your manual setting (second shot) or did you have the f-stop set to another value, and the camera compensated for a stuck iris with a high shutter speed?

Also, you might take the lens off your camera, set it to f22 and move the small lever on the rear of the lens to see if it stops the iris down.
Yep, I can see the aperture close and open. But don't know if it reacts quick enough.
03-02-2024, 10:15 AM   #11
Site Supporter
Site Supporter
JensE's Avatar

Join Date: Dec 2015
Location: Leipzig
Photos: Gallery | Albums
Posts: 1,970
One way to check this is using the 2s timer: The aperture is closed when the timer starts, so it has ample time. If two exposures, one without and one with the timer are the same, it's likely something else. The aperture could still get stuck somewhere, but this is normally obvious when manually closing it off-camera. Taking it off in the A-Setting (or f/22), opening it slowly using the lever at the back and slowly closing it back, one can normally feel some "hesitation" if there that is a problem.
03-02-2024, 10:17 AM   #12
Site Supporter
Site Supporter




Join Date: Nov 2012
Location: North Wales
Photos: Gallery | Albums
Posts: 2,869
Have you set "use aperture ring" in the menu?

Set the camera on jpg - low (just for convenience). Point it at eg a whitewashed wall. Run through the f stops in both manual M using the aperture ring and changing the shutter speed to match, and aperture priority Av with the aperture ring set to "A", f stop set using the dial on the camera. What do you get?
03-02-2024, 10:31 AM   #13
Junior Member




Join Date: Mar 2023
Location: UTRECHT
Posts: 37
Original Poster
I have compared the aperture lever on the back of the lense. It definitely moves heavier, compared to the other Pentax FA lenses. I think that is where the problem may be.

---------- Post added 03-02-24 at 06:32 PM ----------

QuoteOriginally posted by marcusBMG Quote
Have you set "use aperture ring" in the menu?
Yep, I have.
03-02-2024, 12:15 PM   #14
Pentaxian




Join Date: Sep 2020
Posts: 655
I wonder if the double image in the first shot points towards sticky shutter, not aperture.
03-02-2024, 02:46 PM   #15
New Member




Join Date: Mar 2019
Location: Bavel
Posts: 21
QuoteOriginally posted by Willem.deboer Quote
I recently picked up above lens in a thrift store. It has an aperture ring with 'A' setting. When I set it to 'A' it overexposes consistently, even though the viewfinder shows (I think) a plausible combination of aperture and shutter.
When I set it to a specific aperture, exposure is correct when within the range of shutter speeds. In the menu, I tried both settings for enabling either manual aperture or only 'A'. No difference.
Am I doing something wrong, or is the lens broken?
Dear Willem,

I think you first want to compare the recordings you made.
You should look carefully at the settings and it may also be that you have the
contacts should be cleaned thoroughly.

The attached shows that the HDR setting is on, which may give you a distorted image of aperture, time and possibly ISO value.


Greetings Hans,
Attached Images
 
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!
50mm overexposes, aperture, aperture lever, k-mount, lens, overexposes, pentax lens, pentax-f 1:1.7 50mm, shutter, slr lens, smc pentax-f
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Pentax K1 + Asahi SMC Pentax 24mm 2.8 Manual : Overexposes matroxication Pentax K-1 & K-1 II 41 07-23-2018 01:37 PM
Camera overexposes every few pics? Elisha Pentax K-r 5 09-20-2011 06:44 AM
K-7 Overexposes dhulsmeyer Pentax DSLR Discussion 28 08-05-2010 11:55 AM
flash overexposes at < F2.8 ??? larryroohr Pentax DSLR Discussion 9 05-17-2010 08:32 AM
K100D overexposes with dedicated flash Hennie Pentax DSLR Discussion 4 08-02-2009 06:16 AM



All times are GMT -7. The time now is 07:32 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