birdpix Loc: South East Pennsylvania

I'm wondering if the florescent lights weren't the problem. They flicker at the same rate as the 60 hertz current here in the US. Theoretically, shooting at 1/60th should include the entire cycle of the lights but, if the shutter is not exactly 1/60th this might explain the exposure differences.

Florescent flicker is a well known phenomenon and causes exposure and color balance problems. The problem is worse at shutter speeds higher than 1/60. If you shutter is well worn then it may be off enough to allow the flicker to affect exposure.

In Europe the electric is 50 Hz.

Zone-System-Grandpa Loc: Springfield, Ohio

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Jerry, when it comes to making multiple or bracketed exposures for HDR, ~ as you already know, you should always set your camera whereas, only if needed, it will change the shutter speed, but you never want to set your camera whereas the aperture changes, however; if your camera [without your permission :)] had changed its aperture setting not more than 1 stop, such is probably the reason why you were able to get away with the change or the changes the camera had made on its own for the aperture size.

Should you set your camera whereas you've programmed the camera to lock in a particular aperture setting, any subsequent shots made by your camera are at liberty to change shutter speeds which should give you results having no blur even if your light source had changed and the camera had opted to change it's shutter speed setting..

My thoughts listed above are predicated upon the usage of my Nikon D810..

Best Regards, Jerry..
~Doug~

Coker Loc: Havana, IL

Did you cover the eye piece? Tripod pic allow light to come in through the eye piece. Maybe....? You asked a very good question. I'd love to see the histogram.

pithydoug Loc: Catskill Mountains, NY

Jerry you are a bit confused. The exif data says, as we expected from what was changing, you were in SHUTTER priority. Why your ap changed had to be something with the light.

I don't know why the second shot was shot fired at 5.6 but it did, and that is why it is darker. 4.0 to 5.6 is a stop less light..go to f/8 and even darker. Working as designed. :)

Still not sure what you were trying to do.

Jim-Pops Loc: Granbury, Texas

Jerry, I think as others said you were in Shutter priority. I understand you were sure it was in A position for aperture priory. One time while shooting my D600 I found that I was not locked into the A slot on the camera. Still took pictures but not as I was hoping for. This might have happened.
If you have Photoshop, open the picture, under File you will see File Info. At that point look under Camera Info and in the Exposure area you will see how the camera was set on both pictures. Aperture or Shutter.
Having said that the reason I think the camera changed between shots is the light coming in from the window. Something changed the amount coming through. On the first picture look at the drapes. Looks good. On second picture the drapes are more blown out. More light. I think quite a bit of additional light because as you said the aperture changed to f/5.6 allowing less light to enter the camera. If less light is entering the camera and the drapes are now blown out it indicates to me light coming in through the window is changing. At f/5.6 if light was not changing the drapes would have even more detail.
This is my view of the problem.

I am new to The Hedgehog and was wondering how others say they got information of all you setting. I got some but not the Aperture or Sutter setting on the camera. Am I downloading pictures incorrectly? I have a Mac.

Jim

pithydoug Loc: Catskill Mountains, NY

Simple to get to the EXIF data. Just download the picture(the original not the stub) and use whatever photo browser that allows you to get to the properties. I'm on a PC so don't know what that mac Offers.