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FORUMS Photography Talk by Genre General Photography Talk 
Thread started 08 Nov 2017 (Wednesday) 00:47
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about viewfinder!

 
SORENNA
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Post edited 9 months ago by SORENNA.
     
Nov 08, 2017 00:47 |  #1

hello
please read this paragraph:

"Satisfied with your composition, you back away from the
tripod to make sure your body doesn’t wiggle the camera during the exposure. While
your eye blocked the viewfinder, your backing away now allows ambient light to enter
the viewfinder. The additional light added to the ambient light entering the lens and the
camera responds to increased light by reducing the exposure. You are perplexed by the
butterfly being so dreadfully underexposed."


can someone paraphrase that.. is it reaaly saying by vewing through viewfinder you practically decreases the light and exposure by blocking the stary light entering from visor?

thank you




  
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Wilt
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Post edited 9 months ago by Wilt. (2 edits in all)
     
Nov 08, 2017 00:56 |  #2

  • When your eye is at the viewfinder, it limits the amount of stray light which MIGHT enter the eyepiece. So the meter's photosensors read only the amount of light which is coming through the lens itself.
  • When your eye is NOT at the viewfinder, the stray light which enters the eyepiece MIGHT fool the photosensors of the meter to think that the scene is brighter than it truly is...resulting in possible underexposure.

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SORENNA
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Nov 08, 2017 01:06 as a reply to  @ Wilt's post |  #3

thank you so much ..
i get the point there now




  
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nardes
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Nov 08, 2017 01:06 |  #4

I think that this is saying there are two ways in which light can affect the camera’s built in exposure meter.

  • The desired light arriving at the exposure meter via the lens, based on the subject matter you are trying to record.
  • The undesired, stray light that enters the system via the rear optical viewfinder for long exposures.


For long exposure photographs, my Canon DSLRs come with a small, clip-on rubber cover for the rear optical viewfinder, so that you can fit the cover to the viewfinder which should then prevent any unwanted light from entering the viewfinder.

For daylight shots, your head is generally shielding the rear optical viewfinder so stray light will not be an issue for the normal range of daylight exposures.

For long exposures, stray light may enter the open rear optical viewfinder and therefore skew your exposure. The brighter the stray light and the longer the exposure, then the more your desired subject exposure will be affected.

Cheers

Dennis



  
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Wilt
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Post edited 9 months ago by Wilt.
     
Nov 08, 2017 10:58 |  #5

nardes wrote in post #18491521 (external link)
For long exposures, stray light may enter the open rear optical viewfinder and therefore skew your exposure. The brighter the stray light and the longer the exposure, then the more your desired subject exposure will be affected.

The duration of the exposure has no bearing on the degree to which the exposure is wrongly biased by stray light entering the viewfinder -- once the shutter button has been depressed, the exposure duration is unalterable during the exposure itself, as it is already 'locked in' ...changes to light DURING the exposure have no effect on the exposure duration in the Canon dSLR.
So an exposure of 1 sec. f/2 is no different than an exposure of 64 seconds f/16, in terms of stray light entering the eyepiece.

(As an aside, in the past there WERE cameras like the Olympus OM-4 which did measure light striking the film during the exposure and it would indeed alter exposure duration to suit any changes to light falling upon the scene during the open shutter time!)


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about viewfinder!
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