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07-09-2016, 07:21 PM   #1
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Exposure Value (EV) Compensation Question

I have been mulling this over for quite a while, and searching around the web, essentially coming up with more questions than answers.

Let me take the (M)anual exposure mode as an example. Shutter Speed (say 13 sec), Aperture (f1.8) and ISO (1600) are dialed in and fixed, with an EV bias of 0. Just to make this a bit interesting, let's use a real world example of shooting the Milky Way (no GPS tracking), where the shutter speed really can't be more than about 13 seconds in order to limit star trails (within about 3 pixels), the aperture needs to be essentially wide open to collect as much light as possible, and the ISO needs to be relatively high, but as capped as low as possible to reduce noise.

If an EV bias were to be applied, just how is the camera body going to apply it - given that everything else is fixed?
  • Is it going to boost by an extra bit, the amplification of the signal coming off the sensor - essentially increasing the ISO? or,
  • is it going to be applied in some other way down stream in the image processing chain?



07-09-2016, 07:38 PM   #2
pjv
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I did a quick search on the forums here and found this " older " thread about the same issues. Manual mode and EV compensation. I hope the information in it helps.


https://www.pentaxforums.com/forums/115-pentax-k-5/191057-k5-exposure-compens...nual-mode.html
07-09-2016, 07:50 PM   #3
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There is no EV compensation available in M mode, right? All the EV button does is change what the light meter shows, so if it normally showed +0.5EV, with an exposure compensation of -0.5EV it would be right in the middle. Your settings would be left unchanged.

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07-09-2016, 09:14 PM   #4
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QuoteOriginally posted by pjv Quote
I did a quick search on the forums here and found this " older " thread about the same issues. Manual mode and EV compensation. I hope the information in it helps.

https://www.pentaxforums.com/forums/115-pentax-k-5/191057-k5-exposure-compens...nual-mode.html
I missed that post, and his explanation about the K20 was what I think I was remembering.... Thanks!!
QuoteOriginally posted by Adam Quote
There is no EV compensation available in M mode, right? All the EV button does is change what the light meter shows, so if it normally showed +0.5EV, with an exposure compensation of -0.5EV it would be right in the middle. Your settings would be left unchanged.
Hi Adam, Thanks - I was reading through the manual (K5IIs) and depending on the section, it left the door slightly ajar.
  • On the explanation of exposure mode (pg 88), EV is addresses, but for Manual mode marked neither as "available" nor "not available"
  • On Manual mode explanation (pg 100) it is says its not available, but that is the only place
  • In several other places where EV is not available Manual mode is not addressed, but green and B and X are.
  • In a couple of additional places - it indicates with EV set (other than 0) the EV bar displays the difference between appropriate and current - which ties in with your explanation that it's just a light meter display.
Out on the web, EV is addressed as a control with no view as to how it's implemented. The explanation that it is implemented just changes the presentation of what the light meter displays makes sense.

When bracketing, you can actually see the nodes of the exposure triangle change (e.g., in Av mode the exposure time changes from frame to frame, as EV changes).




Last edited by interested_observer; 07-09-2016 at 09:19 PM.
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