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Filters: how reliable is what you see in the viewfinder?


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#1 Karel Bata

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Posted 03 May 2009 - 04:19 AM

Over the years I've heard and read a number of cinematographers say that when using a filter or net over the lens you can't trust what you see in the viewfinder - the final result is often noticeably different. This has always puzzled me.

Is it true? Why?

And while we're here - what other ways might the viewfinder image be misleading?
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#2 David Mullen ASC

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Posted 03 May 2009 - 10:46 AM

Over the years I've heard and read a number of cinematographers say that when using a filter or net over the lens you can't trust what you see in the viewfinder - the final result is often noticeably different. This has always puzzled me.

Is it true? Why?

And while we're here - what other ways might the viewfinder image be misleading?


The strength of a diffusion filter has to be judged by looking at the image at the likely display size. That's why for a small magazine ad photo, they often have to show you a heavy strength like a ProMist #1 just to show the effect. A viewfinder image is too small to judge whether the diffusion is too much or not.

Also, the viewfinder image is an optical projection onto a groundglass, which is a form of very mild diffusion and contrast loss, so you want to factor that into your thinking. But the main problem is the size of the image; you respond to certain things differently when they are on a much bigger screen.
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#3 Tom Hall

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Posted 03 May 2009 - 02:18 PM

It's the same reason trying to get exact focus through a viewfinder is a bad idea when it's headed to the big screen.
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#4 Karel Bata

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Posted 03 May 2009 - 04:42 PM

Thanks. Your answers are a little surprising. I thought it would be something more technical. After all, looking down a viewfinder the image is as big on your retina, if not bigger, than you would see projected in a cinema. The brain refuses to be fooled eh?

" ...an optical projection onto a groundglass, which is a form of very mild diffusion and contrast loss, so you want to factor that into your thinking"
That makes sense. ;)
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#5 Kenny N Suleimanagich

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Posted 04 May 2009 - 03:41 AM

Also, not every viewfinder is the same. For example the viewfinder image of an old Eclair won't be the same as one on an Arricam. The technology has progressed that to blanket-question every viewfinder wouldn't make sense.
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