MFT 25mm f/1.4 fails to blur background like Full Frame 50mm lens @ f/2.8

Started 9 months ago | Discussions thread
assaft
Contributing MemberPosts: 923Gear list
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Re: Look at the shutter speeds
In reply to Ido S, 9 months ago

Ido S wrote:

This may not be relevant to the subject matter, but I'll type and publish it anyway.

To my eyes, the blur is similar enough. It's not so different. But I noticed something really cool. With the Nikon D700, you used ISO 3200 and a shutter speed of 1/80 sec., at f2.8. With the Olympus OM-D E-M1, you used ISO 200 (base ISO, if I'm not mistaken), and a shutter speed of 1/20 sec. at f1.4.

Sometimes, 50mm at f1.4 gives a depth of field that's too shallow for a lot of uses. Using that aperture value on a 25mm lens, gives more depth of field, yet on a µ4/3 camera, it gives a very similar -- if not identical -- field of view. Yet it still is f1.4 in light gathering (though T-stops vary between one lens to another), letting you use a lower ISO for better image quality, and the OM-D's 5-axis in-body image stabilization lets you use very slow shutter speeds, so even if the light drops, you can shoot at base ISO with the aperture set to f1.4, and get a sharp photo with the exposure time close to a full second!

That's one of the advantages of µ4/3 to me: more depth of field for the same field of view and aperture. I don't shoot a lot of portraits (if at all), focusing (pun-intended) more on landscape imagery. And being able to shoot at 12mm, while not including too much in the frame, is very nice. It lets me fight diffraction, and sometimes even allows me to leave my trusty Manfrotto at home.

Generally, to maintain the same dof and shutter speed on a FF sensor, you'd need to set the ISO two EVs higher. In this scenario, DxO measures show that the state-of-the-art m4/3 (E-M1) has an advantage over the state-of-the-art FF sensor (D800E) in the shadows (DR measure): 0.7 EV at base ISO and about 1-1.3 EV at higher ISOs. In the highlights (SNR 18% / Tonal range measures) it's a tie. There are no diffraction / hand shake considerations that favor one format over the other. On a FF camera you use smaller apertures, but diffraction kicks in later. As for the shutter speed with the 12mm, you'd need 1/24th according to the rule of thumb to avoid hand-shake issues, just as little as you need at 24mm on a FF camera.

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