What portrait setup would you suggest?

Started Dec 26, 2008 | Discussions thread
Anthony Cheh
Senior MemberPosts: 2,440
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f/2 is one stop faster than f/2.8 : )
In reply to Alexander Rabtchevich, Dec 27, 2008

f/2 is one stop faster than f/2.8. The f/stop is an expression of lens focal length/aperture ratio and to a large degree, light transmission.

Depth of field is a different phenomena, related to aperture, focal length, subject distance and magnifiction of the final image (circle of confusion size).

The relationship of "crop factor" to differences in depth of field between comparable lenses on different image formats is primarily a result of the differences in focal lengths used to achieve equivalent fields of view, where subject distances are likely to be similar and we are viewing comparable print or screen sizes.

However, a 50mm lens on 4/3s will produce the same depth of field as a 50 mm on APS or "full frame", at the same apertures, assuming other conditions, such as subject distance and the degree of magnification of the final image (not the print or screen size) are the same. By the same token, the depth of field for a subject taken at 20 feet with a 50mm lens at f/2 would be similar to that with a 100mm lens at f/2, IF the degree of magnification of the final image is adjusted to result in the same subject size.

So, instead of saying "I think the idea the 2.0 of 4/3 is a stop faster than 2.8 FF is not fully correct", it would probably be more correct to say that an f/2 lens is one stop fater than an f/2.8, BUT the "real world" depth of field at maximumn apertures would also likely be affected by the format size, among other things, because the differences in focal lengths needed to achieve similar fields of view potentially offsets the greater speed of a lens used on 4/3s, compared with an equivalent field of view lens used on APS format.

The same would be true with APS compared with larger format sizes, such as "full frame" or medium format.

But, there are other considerations too. The high speed Zuiko zooms by Olympus offer generally superior performance at maximum aperture. Even the "professional" f/2.8 zooms from most other manufacturers usually need to be stopped down somewhat to achieve equivalent performance.

Furthermore, for some portraiture, razor thin depth of field is not a desirable phenomena.

Ultimately, there are many factors to consider here. As a user of 4/3s and "full frame" cameras, and a prior user of APS format, each format offers something different. Those differences can be an advantage or disadvantage depending upon our preferences, choice of subjects and style of shooting.

But, for the OP, who uses an E-3 with the very best lenses made by Olympus (they are REALLY good), the positive differences offered by an A700 together with lenses within his budget are not likely to be significant enough to justify spending $3,000, while the Olympus continues to offer advantages in other areas.

Regards,

Tony

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