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jmiguez Silver Member Nikonian since 17th Oct 2010Fri 19-Nov-10 09:41 PM
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"Exposure questions and file size question"


Lafayette, US
          

In south Louisiana it is sugarcane harvesting time. While driving I noticed some harvesting off the road and stopped. I took out the D7000 with the 18-105 kit lens mounted, then proceeded to shoot eighty something pictures of the process.

I just got through reviewing the pictures and noticed that some images were light and some darker. After reviewing the camera data of the RAW (14 bit)files I have a couple questions.

I was shooting in Aperture Priority with the lens set at F8. Focus was set to AF-A, Auto, Matrix and AF Fine tune OFF. ISO was set to 3200 (From last night and I forgot to change it).

All of the shots were similar, in that it was an overcast day and I was following the progress of the combine and loading tractor as they slowly crossed in front of me. The shutter speed changes, which I would expect. However, it is the EV which puzzles me. It is all over the place. It varies from 0 to -2.0EV, which I assume explains the dark and light shots. My question is why? Why would the EV change? I thought the camera just changes the shutter speed? The shutter speed did go all the way to 1/8000 with a low of 1/2500. However, some of the -2.0 EV shots were at the lower range. I would have thought that at 1/8000 the EV would be in the negative range if the light was too bright? Yet, some of the 1/8000 and -2.0 EV shots are the darker ones? wouldn't they be lighter?

My other question is the file size. It ranges from 20.6 MB to 24 MB. Why does this change?

I can see I have a lot to learn with this camera.

John

My Pictures may be seen here: http://jmiguez.smugmug.com/

  

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Replies to this topic
Subject Author Message Date ID
Reply message RE: Exposure questions and file size question
JosephK Silver Member
20th Nov 2010
1
Reply message RE: Exposure questions and file size question
wwt67 Silver Member
20th Nov 2010
2
Reply message RE: Exposure questions and file size question
blw Moderator
20th Nov 2010
3
Reply message RE: Exposure questions and file size question
jmiguez Silver Member
20th Nov 2010
4
     Reply message RE: Exposure questions and file size question
Mike Buckley
20th Nov 2010
5

JosephK Silver Member Nikonian since 17th Apr 2006Sat 20-Nov-10 12:24 AM
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#1. "RE: Exposure questions and file size question"
In response to Reply # 0


Seattle, WA, US
          

The first possibility for the wide EV is that you have exposure bracketing turned on by mistake.

Without seeing any of the pictures, my real guess is that the overcast sky was messing with your matrix metering. As the combine moved, you got more or less sky in the picture. If you go back and look at the shots, you will probably see that the too dark pics were the ones with lots of overcast sky. (All cameras have this problem.)

Changing to center-weighted or spot metering allows you to help tell the camera what is important for the "correct" exposure as one of many possible work-arounds.

If the file size is changing, you probably have file compression turned on. The amount of compression depends on the details of the picture, which changes from shot to shot.

---------+---------+---------+---------+
Joseph K
Seattle, WA, USA

D200, 17-55mm f/2.8 DX, 70-200mm f/2.8 VR, 50mm f/1.4 D
18-70mm f/3.5-4.5 DX, 70-300mm f/4-5.6 ED, D70S

  

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wwt67 Silver Member Nikonian since 07th Apr 2010Sat 20-Nov-10 12:24 AM
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#2. "RE: Exposure questions and file size question"
In response to Reply # 0


Warsaw, US
          

Did you change the EV setting or are you saying the camera changed it automatically?
If you change the EV to something negative, while in aperture priority, the shutter speed will increase to make the image darker.

Visit my Nikonians gallery.

  

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blw Moderator Awarded for his high level of expertise in various areas Nikonian since 18th Jun 2004Sat 20-Nov-10 01:07 AM
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#3. "RE: Exposure questions and file size question"
In response to Reply # 0


Richmond, US
          

> Why would the EV change?

A good bet you'll find that you have bracketing enabled.

> file size... ranges from 20.6 MB to 24 MB. Why does this change?

I assume you're not using TIFF format? All of the other formats do compression of one sort or another, and compression is dependent upon the image contents. A picture of a smooth, evenly lit wall takes up a lot less space after compression than a picture of random noise on an old TV screen. If you're using TIFF, that simply saves every pixel's full data no matter what, and those will all be the same size. (Note that there are optional ways of writing TIFF files that also use compression, and in that case they're like raw or jpeg files and they vary in size depending on their content.)

_____
Brian... a bicoastal Nikonian and Team Member

My gallery is online. Comments and critique welcomed any time!

  

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jmiguez Silver Member Nikonian since 17th Oct 2010Sat 20-Nov-10 02:45 AM
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#4. "RE: Exposure questions and file size question"
In response to Reply # 3


Lafayette, US
          

Joseph, wwt67, and Brian (blw) thank you for taking the time to answer my questions.

Joseph, You were correct, I had somehow turned on bracketing. I am going to set the camera just the way I normally shoot and set that as U1. It is either that or use a checklist, like I did in my flying days.

wwt67 and Brian, I was shooting (RAW compressed). I wasn't aware that RAW files could be difference sizes. I am used to my D40 where it was always the same size.

There is a lot to learn about this camera. You guys are a big help.

John

My Pictures may be seen here: http://jmiguez.smugmug.com/

  

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Mike Buckley Registered since 22nd Aug 2010Sat 20-Nov-10 02:47 PM
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#5. "RE: Exposure questions and file size question"
In response to Reply # 4
Sat 20-Nov-10 02:49 PM by Mike Buckley

US
          

>I am going to set the camera just the way I normally shoot and
>set that as U1. It is either that or use a checklist

You have another alternative that preserves the use of U1 and U2 for other settings. Check out page 244 of the manual. You can write all of your settings to a settings file that is stored on the memory card in Slot #1. Each time you begin a shoot, you can upload that settings file to your camera. I'm told that both writing and uploading are instantaneous.

I don't have the camera yet, but I plan on inserting a 128 MB card in Slot #1 that otherwise is so small that it is of no use to me. I'll download the settings file to that card and I'll lock the card. I'll put a normal memory card in Slot #2 and configure it for overload. Using that configuration, all of my images will be written to Slot #2 and my settings file will always be available for upload to the camera. There will be no possibility of wiping out my settings file by accidentally formatting the wrong card.

Also, if I ever have a need to reset the camera to the default settings as happened to me recently with my D80, I'll be able to quickly upload my own settings using that memory card in Slot #1.

Author of "IDimager Version 5 Workbook"

Visit my Nikonians gallery.

  

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