I hope this thread can be useful for anyone experiencing a similar situation, especially for Nikon photographers using D5200, D5300, D5500 and D5600 cameras.
Some time ago, I saw a small hawk over a palm leaf and decided to take a photo of it. The bird was a little far away, it was in the shade and the light condition was unfavourable, but I wanted to test my Nikon D5300 and register the presence of the bird. The settings of my camera were shutter priority, AF-S (single-servo autofocus), single point autofocus (in the center), exposure spot metering (because of the light condition) and auto ISO (*).
The result was this dark disappointing photo.
#1- The disappointing picture I took.
I didn't expect a great picture, but a photo with more light (like the following one).
#2- That was roughly what I expected.
Trying to understand what happened, I verifyed the settings of my camera using the softwares Capture NX-D and Irfan View.
#3- According to Capture NX-D software, the focus point position was the center of the photo.
#4- The Irfan View software confirmed that the exposure metering method used was "spot point" (I drew two diagonals to confirm the center of the photo).
Everything was ok (but not the photo)!
I had already read both manuals of my camera when I bought it (in 2014), but I did a search in the D5300 Reference Manual (the most complete) to find out what area was covered by the spot metering and I found the following explanation: "Spot metering: choose this mode to ensure that subject will be correctly exposed, even when background is much brighter or darker. Camera meters current focus point; use to meter off-center subjects". That was my case and this statement was exactly the reason of my choice of spot metering! But I didn't find any information about the area covered by the spot metering. This way, I continued without to know why my photo was so dark!
I asked Nikon (in Brazil), but I couldn't get a useful answer (I prefer to comment this subject in other thread).
Continuing my search for a proper explanation, I reread the other manual (the D5300 User's Manual). In the Specifications part I found this much more objective information: "Spot metering: Meters 3.5 mm circle (about 2.5% of frame) centered on selected focus point". That was the information I needed! (Later I discovered that the same information was available in the specification part of the D5300 Reference Manual).
The dimensions of the D5300 sensor are 23.5 x 15.6 mm, then 3.5 mm corresponds to 14.9% of the width and 22.4% of the height of the sensor. I drew (in the center of the original picture) a circle with a diameter of 22,4% of the height of the photo. This showed me that there was dark and light areas within the spot metering area, what probably misled the exposure metering system. That was the reason why my picture was so dark!
#5- The area covered by the spot measurement (a circle with a diameter of 22,4% of the height of the photo).
Extra infos:
A- This is about the center-weighted metering.
"Center-weighted metering: Weight of 75% given to 8 mm circle in center of the frame". This corresponds to 34,0% of the width and 51,3% of the height of the sensor. Only for comparison, I drew (in the center of the original picture) a circle with a diameter of 51,3% of the height of the photo.
#6- The areas covered by the spot metering and center-weighted metering (circles with diameters of 22,4% and 51,4% of photo height).
B- To help Nikon D5200/D5300/D5500/D5600 users, I plotted the positions of focus sensors and the areas covered by spot and center-weighted meterings.
#7- D5300 viewfinder (the positions of focus sensors and the areas covered by spot and center-weighted meterings).
(*) The information I used automatic ISO was written after seeing Peter's question.
Comments and opinions are welcome.
Cheers,
Antonio.