PIX 2015

Panny 25mm 1.4 vs Olympus 25mm 1.8 Reviewed

Started Feb 15, 2014 | Discussions thread
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Junior MemberPosts: 48
Re: T-stops
In reply to Ido S, Feb 16, 2014

Ido S wrote:

The difference in required shutter speeds for any given aperture is caused by the T-stops of the lens. That's the amount of light that actually manages to hit the sensor, whereas F-stops represent the amount of light that goes through the aperture diaphragm. We'll have to wait on a scientific confirmation, from the folks at DxO Labs (who are in charge of the famous, and infamous, DxOMark), as well as SLR Gear, etc.

I have an alternative theory. All lenses change their focal length slightly when focusing. So the 25 mm focal length applies strictly only at infinity. Mr Wong's test shots are portrait shots with fairly short object distance. As he himself noted, Panny has a slightly narrower FOV at that distance, which implies longer focal length. Slightly longer focal length with the same aperture diameter = slightly darker image, as is observed.

This is splitting hairs in any case, the lenses are equally bright at equal f-stops for all practical intents and purposes. The most important selling point of the panny to me is that it has antireflective coating. The night shots look absolutely gorgeous with this lens.

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Disclaimer: Summilux fanboy.

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