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01-31-2020, 02:18 AM - 1 Like   #16
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Well that was easy and conclusive. I compared a 16-50 and the 55-300, shooting a low contrast, solid colour, curtain (how exciting ;-)) . I set up an LED lighting panel (diffused) on a stand to shine into the viewfinder. Held the exposures to be several seconds. Varied the aperture. FL at 50mm & 55mm. MUP. Remote. etc.

Results: Both were underexposed when the LED panel was on. But, and here's the interesting bit, underexposure susceptibility was worse on the 55-300. I repeated the test and moved the panel a number of times. The camera/lens position stayed the same.

Conclusion: I've become lazy and complacent! I must be more careful to cover the viewfinder properly. I knew it would make a difference but I was surprised by how much, - this was a harsh test. However, what's also clear from this simple test is the 55-300 seems to be more prone to exhibiting the underexposure in this situation. The 16-50 occasionally got fooled by the LED light, but the 55-300 was getting it wrong with the LED light in all positions I tried.

So although I've never knowingly got an underexposure from stray light ingress via the viewfinder, it is a very real problem. However, the issue differs between different lenses. Of course there's a simple fix to this user error ...

01-31-2020, 05:50 AM   #17
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That underexposure was worse on 55-300 probably have a simple explanaition. 16-50 is a faster lens so it lets in more light and is less affected by stray light coming in through the viewfinder.
Stopping down aperture should not matter as metering is done with wide open aperture.

If you also have a slow kit lens like 18-55mm, then the result with it at 55 mm (f/5.6) should be slightly worse than 55-300mm at 55 mm (f/4.5).
01-31-2020, 06:26 AM   #18
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QuoteOriginally posted by Fogel70 Quote
That underexposure was worse on 55-300 probably have a simple explanaition. 16-50 is a faster lens so it lets in more light and is less affected by stray light coming in through the viewfinder.
Stopping down aperture should not matter as metering is done with wide open aperture.

If you also have a slow kit lens like 18-55mm, then the result with it at 55 mm (f/5.6) should be slightly worse than 55-300mm at 55 mm (f/4.5).
That may well be a factor. I've tended to use faster glass so if this is the explanation, then it would perhaps explain what went wrong. Plus user error, of course ...
01-31-2020, 03:40 PM   #19
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It's good that it was user error and not equipment failure. You must have been relieved.

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