Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
05-29-2015, 09:44 PM   #1
New Member




Join Date: May 2014
Posts: 14
Exposure problems with new K-50

I just upgraded from my Kx to a K-50. I wanted to test out the higher ISO so I started shooting in a dark environment on Av mode (Tripod mounted IR release). My K-50 is exceedingly dark with every shot. I can compensate for this by using exposure compensation but I dont feel I should have to do that (and have to go to +5 to get a properly exposed image). My Kx had adequate exposures but was doing longer shutter speeds (ie at ISO 6400 f3.8 K50 shoots for 1/8s and Kx shoots for 1/5s. The Kx has a shutter speed 1.6X longer for nearly every image). When I set the K-50 manually to settings that match the Kx (i.e. 6400iso; 1/5; f3.8), the K-50s images are still dark. When I turn on the lights, the K-50s images are more properly exposed than the Kxs.
Is there something wrong with my new K-50. I have done the tests using the 18-55 WR kit lens and my Tarmac 28-200 walkabout lens with the same results. Can anyone explain this?

05-29-2015, 10:19 PM   #2
Administrator
Site Webmaster
Adam's Avatar

Join Date: Sep 2006
Location: Arizona
Photos: Gallery | Albums
Posts: 42,840
QuoteOriginally posted by MarkinIL Quote
I just upgraded from my Kx to a K-50. I wanted to test out the higher ISO so I started shooting in a dark environment on Av mode (Tripod mounted IR release). My K-50 is exceedingly dark with every shot. I can compensate for this by using exposure compensation but I dont feel I should have to do that (and have to go to +5 to get a properly exposed image). My Kx had adequate exposures but was doing longer shutter speeds (ie at ISO 6400 f3.8 K50 shoots for 1/8s and Kx shoots for 1/5s. The Kx has a shutter speed 1.6X longer for nearly every image). When I set the K-50 manually to settings that match the Kx (i.e. 6400iso; 1/5; f3.8), the K-50s images are still dark. When I turn on the lights, the K-50s images are more properly exposed than the Kxs.
Is there something wrong with my new K-50. I have done the tests using the 18-55 WR kit lens and my Tarmac 28-200 walkabout lens with the same results. Can anyone explain this?
Are you in matrix metering or something like spot metering?

Adam
PentaxForums.com Webmaster (Site Usage Guide | Site Help | My Photography)



PentaxForums.com's high server and development costs are user-supported. You can help cover those costs by donating. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

05-29-2015, 10:24 PM   #3
New Member




Join Date: May 2014
Posts: 14
Original Poster
Matrix on both cameras
05-30-2015, 12:52 AM   #4
Veteran Member
flaviopetrone's Avatar

Join Date: Aug 2014
Location: Reggio Emilia
Photos: Albums
Posts: 1,147
QuoteOriginally posted by MarkinIL Quote
Matrix on both cameras
I am not sure if this could be the reason, but maybe that matrix exposure settings have been changed in the k50, moving to the left, to keep alive the high lights. Try to compare both cameras with center weighted exposure and spot.
I own a k50 too, but usually I go with center weighted and spot, without any kind of problems. I shot M almost always, so when I know that there is not any highlight in the frame, sometimes I overexpose a little, maybe half stop. But this is my first DSLR, so I don't know if this is something normal or not.

05-30-2015, 07:56 AM   #5
New Member




Join Date: May 2014
Posts: 14
Original Poster
It doesn't matter how I have the AE metering, results are the same. Here are 3 pictures. The first 2 were done inside in room without windows in a dark environment. I can get reasonable exposures if my EC is +3. Outside, metering is fine. My Kx would do 10s, 15s, 30s exposures in dark to get reasonable exposures. In a dark environment the K-50 doesn't want to meter correctly. I don't know if I have a setting incorrect on the camera, if this is just what a K-50 does or if there is a problem with my particular camera. If the EC was the same regardless of lighting I could just set the EC to whatever is needed but in bright light EC (0) is fine, dimly lit rooms EC(+1) is needed and in very dark EC (+3) is needed so its not entirely predictable. When I set the K-50 manually to exposures that are fine with my Kx, I still get very dark pictures with the K-50 so I don't think ISO(Kx) = ISO(K-50) at least in dark environments.
Attached Images
     
05-30-2015, 08:03 AM   #6
Veteran Member
flaviopetrone's Avatar

Join Date: Aug 2014
Location: Reggio Emilia
Photos: Albums
Posts: 1,147
I'm sorry but since some days ago my camera is in for repair, so I can't check it to see if it could be a wrong setting or what. Anyway it's strange that the problem only happens in the dark...
05-30-2015, 08:47 AM   #7
Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 27,291
There are limits to the metering system on your camera. The lower limit for sensor sensitivity is at EV(100) 0* which nominally translates to a 4 second exposure at f/2 and ISO 100 as measured with a hand-held meter. Unfortunately, the light actually reaching the sensor varies with the maximum aperture of the lens mounted and EV(100) 0 comes quickly with slower lenses. As available light approaches the limit, meter linearity drops off resulting in underexposure. Below the limit, the display should blink and all exposures will be dramatically underexposed. Note: The meter sensitivity limits are not affected by ISO or EC settings.

The settings for the properly exposed second image indicate a light level well below the meter sensitivity (~ EV(100) -2).

That being said, it might still be good to do a test using manual mode to make sure the shutter and aperture mechanisms are working correctly. You might also want to test the lens aperture off-camera to make sure it opens and closes smoothly.

BTW...you might want to skip the spot metering except for situations where it is actually useful (very seldom). Matrix metering should be your first choice.


Steve

* This is the limit for SPD (Silicon Photo Diode) sensors in general.
05-30-2015, 10:33 AM   #8
New Member




Join Date: May 2014
Posts: 14
Original Poster
Most of my some 200 images were done with matrix metering and spot versus matrix made no difference because the lighting (though low) was fairly uniform and images were centered. I get what you saying, I'm reaching the limits of the sensor but then why did my Kx expose correctly with the same lens. I'd expect it to do worse because it's an older camera. Below is an image with my AF 50/1.8 ISO 6400 Av mode and SS was 1/8s. When I used my Tarmac at f5.6 SS was also 1/8s when it probably should have been 1s due to the higher f-stop. The EC(4) had a SS of 2s and was probably over-lighted. When using the 50/1.8 the exposure is pretty good for the lighting. Maybe it's something with the Tarmac lens in low lighting. It just seems odd that the Kx can expose correctly (by choosing the correct SS) in Av mode with the Tarmac lens but the K-50 can't. I guess even if I'm photographing with a tripod and shutter release, I still need to use my 35/2.4 or 50/1.8 to get a good exposure.

Attached Images
 
05-30-2015, 12:34 PM   #9
Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 27,291
QuoteOriginally posted by MarkinIL Quote
I'm reaching the limits of the sensor but then why did my Kx expose correctly with the same lens. I'd expect it to do worse because it's an older camera.
I can't comment regarding your K-x (which you apparently no longer have to provide comparison), but the exif from your K-50 tells the story in graphic detail. You exceeded the lower limit by several stops. Again, neither exposure compensation nor ISO factor into meter sensitivity or linearity. What happens is that as you approach and exceed the meter's lower range, the response to light becomes increasingly non-linear such that the meter "says" there is much more light than is actually present. The amount of error is exponential as you go down.

If you must shoot in very low light conditions, I would recommend using a high sensitivity (SPD) hand-held meter with range to EV(100) -5 or below. Use M mode and meter once using the same settings until either the subject or lighting changes.


Steve

Last edited by stevebrot; 05-30-2015 at 12:51 PM.
05-30-2015, 02:51 PM   #10
New Member




Join Date: May 2014
Posts: 14
Original Poster
I kept the Kx but basically they looked like the 50/1.8. My night photography consists mostly of cityscapes, fireworks, disney, etc. I'll just have to use the 50/1.8 or 35/2.4 in those settings and maybe do bracketing until I know how the K-50 responds. Thanks for the help.
05-30-2015, 04:41 PM   #11
Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 27,291
QuoteOriginally posted by MarkinIL Quote
My night photography consists mostly of cityscapes, fireworks, disney, etc.
For those subjects, use M mode and estimate the exposure based on available charts. You will get better results than with the camera meter. At least that has been my experience. The meter will attempt to turn night into day and you don't really want that

Here is a link to a great video on the topic:

Thoughts on Exposure Calculators | The Figital Revolution

...and if you don't have the patience to sit through the video, at least consider this reference page on exposure:

http://www.fredparker.com/ultexp1.htm


Steve

Last edited by stevebrot; 05-30-2015 at 04:50 PM.
05-31-2015, 12:12 PM   #12
New Member




Join Date: May 2014
Posts: 14
Original Poster
Thanks again
06-06-2015, 03:18 PM   #13
Forum Member




Join Date: Jul 2011
Location: Texas
Posts: 81
I'd be curious if maybe the newer camera is programmed to try harder to capture the image more like the eye instead of brightening it up to a "neutral" brightness? What happens if shooting night / moon shots? My older K-x would have to be manually set to underexpose several stops to get a more eye-accurate image and not blow out the moon to look like the sun.
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!
difference, exposure, exposure accuracy, f3.8, image, images, iso, k-30, k-50, kx, lens, pentax k30, pentax k50, shutter
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Exposure issue with K-50 nugget247 Pentax K-30 & K-50 4 02-28-2015 05:47 PM
Exposure problems with the K-50 Dewman Pentax DSLR Discussion 6 12-08-2014 01:24 PM
Problems with new k 30. carlosodze Pentax K-30 & K-50 5 07-02-2013 11:08 AM
Problems with K-X exposure Drew Hillier Troubleshooting and Beginner Help 5 05-24-2011 05:14 PM
Need help with exposure problems and snow photography problems, urgent please respond montezuma Photographic Technique 7 02-24-2008 05:43 PM



All times are GMT -7. The time now is 01:08 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