Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
01-22-2018, 08:51 PM   #1
Junior Member




Join Date: Jan 2018
Posts: 36
Sigma 24mm f2.8 Superwide II PKA overexposure

I have the manual focus Sigma 24mm f2.8 on the A mount, and on both my K200D and K100 Super it overexposes quite a bit. The exact exposure seems to be on K100D Super
2.8 0.5 stop Underexposed
4.0 0.5 stop Overexposed
5.6 1.5 stop Overexposed

on the K200D it's about 0.5 overexposed vs the K100D. Is this normal? Need to try on my other Pentaxes, but haven't had the time yet.

It meters ok in stop down mode, but the change in fstop doesn't correlate exactly to what I expect the shutter speed to be.
e.g. f2.8 @ 1/60 should be 1/30 f4.0, but sometimes the camera meters at something faster than 1/30.

I tried to pull the aperture level and it snaps back instantly. Could there be something else wrong with the arm?

Thanks!

01-22-2018, 09:18 PM   #2
Otis Memorial Pentaxian
Loyal Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 31,229
QuoteOriginally posted by keos Quote
I have the manual focus Sigma 24mm f2.8 on the A mount, and on both my K200D and K100 Super it overexposes quite a bit. The exact exposure seems to be on K100D Super
2.8 0.5 stop Underexposed
4.0 0.5 stop Overexposed
5.6 1.5 stop Overexposed

on the K200D it's about 0.5 overexposed vs the K100D. Is this normal? Need to try on my other Pentaxes, but haven't had the time yet.

It meters ok in stop down mode, but the change in fstop doesn't correlate exactly to what I expect the shutter speed to be.
e.g. f2.8 @ 1/60 should be 1/30 f4.0, but sometimes the camera meters at something faster than 1/30.

I tried to pull the aperture level and it snaps back instantly. Could there be something else wrong with the arm?

Thanks!
Welcome to the Pentax Forums!

In M mode, how does manual aperture control using the aperture ring compare to the same setting using body aperture control? Are the exposures comparable?


Steve
01-22-2018, 09:29 PM   #3
Junior Member




Join Date: Jan 2018
Posts: 36
Original Poster
QuoteOriginally posted by stevebrot Quote
Welcome to the Pentax Forums!

In M mode, how does manual aperture control using the aperture ring compare to the same setting using body aperture control? Are the exposures comparable?


Steve
Step down metering in M mode results in an exposure +/- half a stop of what I would expect; the shutter speeds decided by step down metering and the body using A mode are pretty much in line, changes by half a stop here and there, but A mode causes the overexposure when stopped down. I should have added after F5.6 the overexposure stays at 1.5 stops.

---------- Post added 01-22-18 at 09:32 PM ----------

QuoteOriginally posted by keos Quote
Step down metering in M mode results in an exposure +/- half a stop of what I would expect; the shutter speeds decided by step down metering and the body using A mode are pretty much in line, changes by half a stop here and there, but A mode causes the overexposure when stopped down. I should have added after F5.6 the overexposure stays at 1.5 stops.
Ugh, I meant stop down metering. Also to add, stop down metering is close, but if it deviates, it is usually using a faster shutter than the calculated amount.
01-22-2018, 09:43 PM   #4
Otis Memorial Pentaxian
Loyal Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 31,229
QuoteOriginally posted by keos Quote
Step down metering in M mode results in an exposure +/- half a stop of what I would expect; the shutter speeds decided by step down metering and the body using A mode are pretty much in line, changes by half a stop here and there, but A mode causes the overexposure when stopped down. I should have added after F5.6 the overexposure stays at 1.5 stops.
Not a comparison of the metering. I was asking if body control of the aperture has the same affect as using the aperture ring. Steps:
  • M mode, fixed ISO
  • Aperture ring on the "A" position
  • Point the camera at a well-lit blank wall and adjust the exposure using the controls on the camera body. Write down the shutter speed and aperture.
  • Make an exposure
  • Using the aperture ring, set it to the same value you wrote down above
  • Make another exposure
Compare the two exposures. They should be the same brightness. If not, there is a problem with the aperture control by the body. This could be caused by a fault in the body or a fault in the lens actuator mechanism.


Steve

01-22-2018, 09:50 PM   #5
Junior Member




Join Date: Jan 2018
Posts: 36
Original Poster
QuoteOriginally posted by stevebrot Quote
Not a comparison of the metering. I was asking if body control of the aperture has the same affect as using the aperture ring. Steps:
  • M mode, fixed ISO
  • Aperture ring on the "A" position
  • Point the camera at a well-lit blank wall and adjust the exposure using the controls on the camera body. Write down the shutter speed and aperture.
  • Make an exposure
  • Using the aperture ring, set it to the same value you wrote down above
  • Make another exposure
Compare the two exposures. They should be the same brightness. If not, there is a problem with the aperture control by the body. This could be caused by a fault in the body or a fault in the lens actuator mechanism.


Steve
Sorry, misunderstood you.
Yes, if for example Av meters at F8 0.5s and I manually set the ring to F8 and shutter to 0.5s there is about a 1.5 stop difference between the two.
01-22-2018, 09:50 PM   #6
Otis Memorial Pentaxian
Loyal Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 31,229
QuoteOriginally posted by keos Quote
Ugh, I meant stop down metering.
I was hoping to avoid open-aperture vs. stop-down metering for now. There will likely be inconsistent stop-down metering with your cameras as with the K10D and K20D that is not related to problems with the lens.


Steve
01-22-2018, 10:12 PM   #7
Pentaxian
johnyates's Avatar

Join Date: Aug 2011
Location: Saskatoon, SK
Photos: Albums
Posts: 1,252
Mine does that too. I just live with it as otherwise it's an excellent lens.
01-22-2018, 10:32 PM   #8
Pentaxian
Just1MoreDave's Avatar

Join Date: Feb 2007
Location: Aurora, CO
Photos: Gallery | Albums
Posts: 5,233
If I remember right, I had the same problem with another Sigma of the same vintage. I could never figure it out. I took it apart several times to look at the aperture arm mechanism. I checked the contacts inside and out. Eventually I sold it with that problem. My Superwide works fine. Sorry I can't be more help. If you can think of any tests I can run on mine, I'll give it a shot.

01-22-2018, 10:58 PM   #9
Marketplace Reseller




Join Date: Nov 2008
Location: Canada
Posts: 6,078
I had bought one once that arrived with this issue, I contacted Gentec (Sigma's service in Canada) and due to the lack of any chance for getting new parts I sent it back to the person I bought it from. I think mine was either exposing correctly at F2.8 and horribly over exposing as you stop down or it was the other way around, horrible over exposure at F2.8 and better as you stop down... it was years ago so I just don't recall the exact issue.
01-27-2018, 10:11 AM   #10
Junior Member




Join Date: Jan 2018
Posts: 36
Original Poster
looks like I have found the problem. Using the optical preview, the aperture doesn't actually stop down until around f5.6; meaning it's about 2 stops before the aperture on the Av control actually does anything. Would explain why the overexposure maxes out after f5.6. Is this a loose aperture arm?
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!
24mm, 24mm f2.8 superwide, aperture, body, camera, f2.8, f2.8 superwide ii, f5.6, half, k100d, k200d, meters, mode, overexposure, pentax help, photography, shutter, sigma, sigma 24mm f2.8, step, stop, superwide ii pka, troubleshooting
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Is the Vivitar 24mm f2 PKA as good as the Vivitar 28mm f2 PKA (Close-focus by Komine) Pepe Guitarra Pentax SLR Lens Discussion 13 03-25-2016 06:50 AM
Sigma 24mm. f2.8 Superwide 2 not sharp. robert Pentax SLR Lens Discussion 8 01-30-2016 10:42 PM
Sigma 24mm f/2.8 Superwide II Autofocus - $126 BGN condition at KEH seventysixersfan Pentax Price Watch 9 10-01-2013 06:42 PM
For Sale - Sold: Sigma 24mm f2.8 SuperWide II (manual focus "A" lens) w/Perfect Hood cheekygeek Sold Items 8 10-03-2012 08:36 AM
For Sale - Sold: Sigma SuperWide II 24mm f2.8 Macro Manual Focus w/ A Setting EdwardConde Sold Items 4 05-30-2012 10:50 PM



All times are GMT -7. The time now is 06:24 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