OK ALL YOU full frame camera fanatics

Started Nov 14, 2012 | Discussions thread
Great Bustard Forum Pro • Posts: 42,222
Re: The question is really about the Pan/Lieca D Summilux f1.4.

dave gaines wrote:

Before anyone starts to argue about lens prices and high ISO equivalence, please don't compare an f/4 or f/5.6 lens to an Olympus SHG f/2 or f/2.8 tele lens. Only compare equivalent focal lengths in the fastest f-stop available for FF, the f/2.8 VR and OIS lenses.

Why do people care about focal length? Answer -- the focal length, in combination with the sensor size, gives us the AOV (angle-of-view).

Why do people care about the f-ratio? Answer -- the f-ratio, in combination with the sensor size for a given perspective and AOV, tells us the DOF, and, in combination with the shutter speed, tells us how much light will fall on the sensor, which, in combination with the sensor efficiency, will tell us the image noise.

In other words, saying "f/2 = f/2" is no more meaningful than saying "50mm = 50mm". When comparing different formats, we must consider the numbers in terms of the effect they have on the visual properties of the final photo.

In short, 50mm f/2 on 4/3 looks nothing like 50mm f/2 on FF, nor does it look much like 100mm f/2 on FF. But it looks very similar to 100mm f/4 on FF.

Of course, 50mm f/2 on 4/3 does not look exactly like 100mm f/4 on FF, but, then again, a photo from an E1 + 50 / 2 macro at f/2 does not look exactly like a photo of the same scene from an E5 + 35-100 / 2 at 50mm f/2.

As for all the other discussion of FF vs 4/3, I have to agree with GB. The 50 mm f/2 lens on 4/3 is equivalent to a 100 mm f/4 on FF in angle of view and physical aperture opening diameter. It offers similar exposures with the conditions he listed.

Actually, 1/4 (two stops less) the exposure, but the same total amount of light falling on the sensor:

Total Light = Exposure x Sensor Area

In other words, total light, not exposure, is the meaningful measure, just like aperture (entrance pupil) diameter, not f-ratio, is the meaningful measure for cross-system comparisons.

(Read those conditions carefully)


But the f/2 lens is faster than f/4, allowing faster shutter speeds.

"Fast" needs a context:


GB says f/4 on FF can be just as fast if you bump up the ISO by two stops. Then you get the same noise as using 4/3 at the native ISO on Olympus' new EM-5 sensor. But given those conditions, those limitations, I would rather use my FF camera at it's native ISO and have more DR and less noise.

GB says that 100mm f/4 1/200 ISO 1600 on FF has the same shutter speed as 50mm f/2 1/200 ISO 400 on 4/3, has the same DOF, and puts the same total amount of light on the sensor, which will result in the same amount of noise if the sensors are equally efficient (less noise for the more efficient sensor, more noise for the less efficient sensor).

I'd want the best fast f/2.8 lenses available for FF. Why pay so much more for FF only to get the same shutter speed and the same noise as 4/3?


So while no two photos from two different systems will ever be equal, Equivalent photos from different systems will be as similar as photos from different systems will get. Clearly, however, the point of choosing one system over another is not simply to get photos as close as possible to other systems (equivalent photos), but to get photos that look "better" (in each photographer's opinion) to what other systems can deliver (non-equivalent photos), or for the differences in operation (AF speed/accuracy, size, weight, frame rate, build, price, etc.).

We can compare systems in many different ways. The five parameters of Equivalence are simply guidelines to comparing systems on the basis of the most similar visual properties of the final photo, and are certainly not a mandate that systems must be compared in such a fashion. Therefore, it is important to specify thepurposeof the comparison, and then not artificially handicap one or the other system with the conditions of the comparison. In addition, it is important to interpret the results of the comparison in the context of the circumstances where the conditions of the comparison are valid.

The point of photography is making photos. As such, one doesn't choose the particular system to get images which are equivalent to another system. A person chooses a particular system for the best balance of the factors that matter to the them, such as price, size, weight, IQ, DOF range, available lenses, and/or operation. By understanding which settings on which system create equivalent images, the difference in their capabilities is more easily understood.

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