Comparing Olympus 4/3lenses to FX "Full Frame" offerings

Started Jan 25, 2014 | Discussions thread
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Re: Take photos....
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citizenlouie wrote:

DoF equivalency has little to do with actual photography. When I got a new camera, I learn its differences and adopt the different shooting style.

It has as much to do with "actual photography" as DOF and noise have to do with "actual photography". If neither DOF nor noise are issues for you, then, for sure, I agree.

If you must insist on knowing why (for example) a 75mm @ f/1.8 is the same across the platform...

If, by "the platform", you mean the same sensor size, then, sure...

...consider this: It's not the focal length, nor aperture that give a 75mm f/1.8 lens a greater DoF on a 4/3 per se. It's the fact on a 4/3 (or m4/3) camera, you simply have to stand twice as far to get the same field of view.

For the times you can standing twice as far away, this will change the perspective, which will result in a different photo.

Therefore the depth of field is lessened due to subject-to-focal-plane distance.

There are many factors for DOF. In terms of format independent terms, they are:

• Perspective (subject-camera distance)
• Framing
• Aperture Diameter
• Display Diagonal
• Viewing Distance
• Visual Acuity

This is further complicated by the fact 4/3 lenses are designed for a squarer format sensor. I have no idea how some of you guys can be so sure that a f/1.8 on a 4/3 sensor is exactly f/3.6 equivalent on a FF sensor, not to mention 4/3 sensor is squarish, so the angle of view calculation would be different so will be the lens design (and I have a feeling telecentric lens design will give a greater DoF, just a hunch, not proven though), so the DoF is a lot more complicated than simply double the number.... But does any of these calculations meaningful in actual photo taking?

If a 4/3 lens is exactly 75mm f/1.8, then a photo of the same scene from the same position at exactly 150mm f/3.6 on FF, displayed with the same diagonal size and viewed from the same position, will have exactly the same DOF.

If you want to compare apple to apple, go use a Nikon D800 on a tripod at a fixed distance, use a FX prime lens (for example, a Nikkor 35mm f/1.8G), and shoot one photo in FX mode and one photo in DX crop mode and everything else remains constant (e.g., 35mm @ f/1.8 @ ISO 200 @ 2 meters from subject). I assure you both photos will have the same DoF.

But now they have different framing. Why would we compare such photos? Sounds rather unnatural, in a photographic sense, to me.

It has nothing to do with whether it's FX (FF), DX (APS-C) or 4/3. If D800 could take a 4/3 lens, and do the exact same experiment, the DoF will be similar also at the given FL.

You might find this illuminating:

http://www.josephjamesphotography.com/equivalence/index.htm#crop

Given four cameras, one with...

• ...an mFT (4/3) sensor,
• ...another with a 1.6x sensor,
• ...another with a 1.5x sensor,
• ...and another with a FF sensor...

...and...

• ...a photo of a scene from the same position with the same focal point and the same settings (e.g. 25mm f/1.4 1/200 ISO 400) with all cameras,
• ...the photos cropped to the same framing as the photo from the mFT (4/3) camera,
• ...and the photos are displayed at the same size...

...then the resulting photos will be . In addition, if...

• ...all the sensors are equally efficient, then all the photos will also have the same noise,
• ...the pixels are all the same size, the AA filter the same strength, and the lens is the same sharpness, then all the photos will also have the same detail,
• ...the exact same lens is used and the sensors are of the exact same design with the exact same size pixels, AA filter, CFA, and processing...

...then the photos will not merely be Equivalent, but be identical.

You may also find this illuminating as well:

http://www.josephjamesphotography.com/equivalence/index.htm#tc

Given...

• ...a 25 / 1.4 lens on an mFT (4/3) camera,
• ...the same lens and a perfect (aberration free) 1.25x TC (teleconverter) on a 1.6x camera,
• ...the same lens and a perfect 1.33x TC on a 1.5x camera,
• ...the same lens and a perfect 2x TC on a FF camera...

...and a photo of the same scene taken from the same position with the same focal point at...

• ...f/1.4 1/200 ISO 100 on the mFT (4/3) camera,
• ...f/1.8, 1/200, ISO 160 on the 1.6x camera,
• ...f/1.9, 1/200, ISO 180 on the 1.5x camera,
• ...and f/2.8, 1/200, ISO 400 on the FF camera...

...then the resulting photos will not merely be Equivalent, but be identical.

Alternatively, given...

• ...a 50 / 1.4 lens on a FF camera,
• ...the same lens and a perfect (aberration free) 0.67x FR (focal reducer) on a 1.5x camera,
• ...the same lens and a perfect 0.625x FR on a 1.6x camera,
• ...the same lens and a perfect 0.5x FR on an mFT (4/3) camera...

...and a photo of the same scene taken from the same position with the same focal point at...

• ...f/1.4 1/200 ISO 400 on the FF camera,
• ...f/0.9, 1/200, ISO 180 on the 1.5x camera,
• ...f/0.9, 1/200, ISO 160 on the 1.6x camera,
• ...and f/0.7, 1/200, ISO 100 on the mFT (4/3) camera...

...then the resulting photos will not merely be Equivalent, but be identical.

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