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04-08-2016, 03:59 PM   #16
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Out of curiosity I did some testing today. Using a Hoya NDX400, nominally 9 stops. I noticed that there was a difference in metering of between 3 and 4 stops depending on whether the viewfinder was covered or not. If you metered with the viewfinder covered it did not seem to make any difference to the actual exposure if it was covered during the shot or not, just during metering. This is in 'M' mode so no change to the settings after you uncover the viewfinder however the meter definitely changed. And this varied by how much light was getting through the viewfinder. I tried the same shot from inside in a dark room to the outside and in this case there was no noticeable difference in the metering.

To me this seems to prove that light going through the viewfinder affects metering, which might be part (or all) of the OP's issue. With light shining through the viewfinder the camera consistently underexposed by close to 4 stops.

04-08-2016, 04:04 PM   #17
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There was also a noticeable red flare and color tint to the images. I have seen this before and had it ruin images. I know, you folks that do this regularly are laughing and saying "well, duh".

Anyway see below:
Image 1: viewfinder is not covered and I am standing behind the camera, light hitting me and reflecting into the viewfinder.
Image 2: viewfinder is covered
Image 3: viewfinder is not covered and I held my hand 6 inches away from the viewfinder and reflected the light with my hand into the viewfinder

Guess I need to dig out that little finder cover.........
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04-08-2016, 04:09 PM   #18
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And here are two showing the metering:
Image 1: metered with the viewfinder uncovered
Image 2: metered with the viewfinder covered
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04-08-2016, 04:20 PM   #19
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QuoteOriginally posted by jatrax Quote
And here are two showing the metering:
Image 1: metered with the viewfinder uncovered
Image 2: metered with the viewfinder covered
WOW! That is some huge difference. Thank you for doing the experiment and posting the photos. Do you know if I can buy the view finder cover? I am sure I misplaced/lost mine.

04-08-2016, 04:30 PM   #20
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And two more, this time using Liveview:
Image 1: In liveview but with the viewfinder uncovered - red tint not as pronounced but still there
Image 2: In liveview but with the viewfinder covered - no red tint

Not much difference in the exposure, I did not change the metering for these two so the only difference would be the slight increase in exposure in image #1 due to the light from the viewfinder

---------- Post added 04-08-16 at 04:34 PM ----------

QuoteOriginally posted by uday029 Quote
Do you know if I can buy the view finder cover? I am sure I misplaced/lost mine.
A quick search finds nothing, but I suspect something could be found on ebay. I might be tempted to just use a cloth or a strip of gaffers tape. But this has convinced me 100% that on any long exposures the viewfinder has to be covered.
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04-08-2016, 04:48 PM   #21
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In the K-3 specs it lists the "finder cap ME" as the viewfinder cap that is in the box. The closest thing I found to it which has the same name is at the following link. If you want to verify it is compatible with the K-3 with Adorama, which I think it almost definitely is since it has the "ME" specification in its title, you could contact their customer service.

Pentax Finder Cap for K2000, K200D, K20D and ME Cameras 31011

Last edited by C_Jones; 04-08-2016 at 05:15 PM.
04-09-2016, 12:17 AM   #22
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Nice test series, John - thanks!

So what we learn from this, Ricoh/Pentax should develop a small manual buildin viewfinder shutter for their DSLRs. Would be a nice little improvement for their cameras.

Last edited by acoufap; 04-09-2016 at 02:35 AM. Reason: I forgot the most important word ...... viewfinder ...
04-09-2016, 06:56 AM   #23
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QuoteOriginally posted by jatrax Quote
A quick search finds nothing, but I suspect something could be found on ebay. I might be tempted to just use a cloth or a strip of gaffers tape. But this has convinced me 100% that on any long exposures the viewfinder has to be covered.
This problem has been around since the invention of through the lense metering. If you lost or don't have your View Finder cap use your lens cleaning cloth(double triple)
Also when the view finder is open to strong lighting in any situation not just ND shots e.g. Direct Sunlight , Spot lighting your meter reading will be affected. Tripod shooting leaves it exposed always to possible stronger backlight than scene light.

04-09-2016, 08:33 AM   #24
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QuoteOriginally posted by acoufap Quote
Ricoh/Pentax should develop a small manual buildin viewfinder shutter for their DSLRs. Would be a nice little improvement for their cameras.
+! I agree 100% and I have found that some high end cameras of other brands provide a viewfinder shutter, apparently the Nikon D800 and D5 have this anyway.
QuoteOriginally posted by honey bo bo Quote
This problem has been around since the invention of through the lense metering.
Yep, I'm sure it has and I can only say I am embarrassed to be at this point in my career and not have known this. Like I said above all the experienced photographers are reading this and saying "well duh??" Part of the problem of being self taught is these little things that you don't know but were probably taught on the second day of school if you were trained.

There are two separate issues here: stray light causing metering inaccuracies and stray light showing up in the image itself.
The metering problem is present on all exposure lengths when the view finder is uncovered and might be the cause of random poor exposures I see reported occasionally.

The stray light in the image problem is also always present (when the viewfinder is uncovered) but at most shutter times is such a small percentage of the total light that it is not noticeable. However, at very long shutter times (>2 seconds and up) it starts to be a noticeable percentage of the light shown in the image.

A third issue is the red streaks and tint seen in the images above. I do not know why they are red, maybe someone else can jump in and explain that. I used this ND filter on the coast last summer and got images with the red streaks in it, I blamed the filter and have not used it since. I can see now it was not the filter but my technique.
04-28-2016, 08:21 AM   #25
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As a follow up on this I did some research on viewfinder covers and found this article: DIY eyepiece cover / viewfinder cover - Sensorgraphy.net

I made a couple of these and they work very well. I had a problem finding the material mentioned, it has to be plastic, I tried several things but any kind of fiber material was not stiff enough. I finally found a spiral bound notebook at the grocery store with a plastic back cover of precisely the correct thickness and cut it up to size. I made two, one for a spare and kept the notebook cover in case I need more.

Material thickness is .0195 inch or .50mm. Dimensions are: .92in wide (23.25mm) and about 1.6 inch long (42mm) . Length is not critical but width is, to have a snug friction fit. I made several paper test copies first to get the dimensions correct.
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04-28-2016, 12:04 PM   #26
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Looks like sort of a handy idea. It would replace the having to remove the eyepiece and sliding the normally used cover into place step (as long as it does not harm anything).
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