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Viewfinder Magnification
Is there a way to make an APS sensor-sized camera have a viewfinder with the size and brightness of a full-frame camera? This is really a major concern for me, as I'm trying to choose between the 40D and the 5D...

Comments (6)

You have magnification, brightness and precision. Increase one and you will have to take from one of the others. It all depends on the size of the focus screen..

Shoot...

Comment #1

Size and brightness? No. The smaller image circle would give you a much dimmer image if it was enlarged further..

Refrigerator wrote:.

Is there a way to make an APS sensor-sized camera have a viewfinderwith the size and brightness of a full-frame camera? This is really amajor concern for me, as I'm trying to choose between the 40D and the5D...

Comment #2

...unless the camera with the 36x24mm sensor is handicapped with a very inefficient optical path or a very slow lens..

A 36x24mm sensor has ~2.322x the area of a 23.7x15.7mm DX sensor. If you hold the viewfinder size and coverage equal, the DX system needs to bring in correspondingly *more* light per unit area to maintain identical brightness over a larger magnification..

There are two ways to make up that gap..

1- Bring in more light with a wider maximum aperture; for instance, a half-stop advantage lets in ~41.4% more light per unit area covered..

2- Sending more of that light to the eyeball either through minimizing mundane transmission losses as the light goes via mirror and prism, or by losing less light to other subsystems like AF. There are focusing screens meant to be brighter with the same light, but they're not necessarily known for focusing snap...

Comment #3

You need a HUGE pentaprism in an APS or similar sensor size to approximate the view size and brightness of a FF. The only cropped sensor camera to do so is the Oly E-3, which has a huge bulge on top of the body from the enlarged pentaprism - but it offers a viewfinder nearly as large and bright as a FF, with a magnification of over 100%..

But then again, the 40D allows you to compose with LiveView, which the 5D does not. Depending upon your shooting style, this may overcome the limited VF in some instances, especially when composing set scenes.RobertOlympus E-3 & E-500, 7-14mm, 14-54mm, 40-150mm, 30mmOlympus 1030SW P&SYashica Lynx-1000..

Comment #4

Robert999 wrote:.

You need a HUGE pentaprism in an APS or similar sensor size toapproximate the view size and brightness of a FF..

A pentaprism can't amplify light. As long as it's big enough to cover the focusing screen, the only thing making it larger will do is increase the eyepoint by allowing more room for the eye to move and still maintain a view of the entire screen..

A certain amount of light illuminates the focusing screen. All modern cameras at the intermediate and high end have about the same screen, a 5 degree scattering ruled 60 degree microprism. They all let about the same amount of light through. So the quantity of light is proportional to the area of the screen. Enlarge the screen more (more powerful "telescope" in the viewfinder lenses) and you cut the brightness down. That's the trade off..

The only croppedsensor camera to do so is the Oly E-3, which has a huge bulge on topof the body from the enlarged pentaprism - but it offers a viewfindernearly as large and bright as a FF, with a magnification of over 100%..

Although the magnification is 1.15x, it is still far too low to give the E3 a viewfinder "nearly as large" as FF..

The 1Ds III has a magnification of 0.76x, which puts them at 30.6x20.7 degrees of visual field, or an area of 633 square degrees..

E-3, even at 1.15x, is 22.5x17.0 degrees, an area of 383 square degrees..

The full frame is 65% larger..

Both cameras have 5 degree ruled cut screens typical of modern DSLRs. So, the ratio of brightness is the inverse square of the ratio of magnifications, 1/(1.15/0.76)^2 = 2.29. The 1Ds III is log(2.29)/log(2) = 1.2 stops brighter than the E-3..

So, E-3 is not "nearly as large and bright as a FF", at all..

Canon 40D, by comparison, at 0.95x magnification on a 1.6x crop camera, is 23.5x15.8 degrees of visual field, or an area of 372 degrees squared, only 3% less than E-3. It's essentially the same size..

But 40D is a half stop brighter..

E-3 is as large as, but not quite as bright as, 1.6x crop APS..

But then again, the 40D allows you to compose with LiveView, whichthe 5D does not. Depending upon your shooting style, this mayovercome the limited VF in some instances, especially when composingset scenes..

I can't see that making much difference, except for very special cases, such as high magnification macro..

Rahon Klavanian 1912-2008..

Armenian genocide survivor, amazing cook, scrabble master, and loving grandmother. You will be missed..

Ciao! Joseph.

Http://www.swissarmyfork.com..

Comment #5

Leejay Wu wrote:.

...unless the camera with the 36x24mm sensor is handicapped with avery inefficient optical path or a very slow lens..

A 36x24mm sensor has ~2.322x the area of a 23.7x15.7mm DX sensor. Ifyou hold the viewfinder size and coverage equal, the DX system needsto bring in correspondingly *more* light per unit area to maintainidentical brightness over a larger magnification..

There are two ways to make up that gap..

1- Bring in more light with a wider maximum aperture; for instance, ahalf-stop advantage lets in ~41.4% more light per unit area covered..

Unfortunately, pretty much all cameras these days have converged at a 5% scattering ruled screen. That means that an f1.4 lens is no brighter on the screen than an f2.8. Jay Tuirberville, a regular on the Oly forums, shot images through the viewfinder of an Oly, stopping down to different apertures. Basically, anything from f1.4 to f4.0 had the same brightness, corresponding to that of an aerial image..

2- Sending more of that light to the eyeball either throughminimizing mundane transmission losses as the light goes via mirrorand prism, or by losing less light to other subsystems like AF..

Now, that would help. Most SLR mirrors are partially silvered around 65% transmission to accommodate the AF system..

There are focusing screens meant to be brighter with the same light,but they're not necessarily known for focusing snap..

You can't get much brighter than these current ruled screens. As I mentioned earlier, they approach aerial image (no screen at all) brightness for apertures above f4. Which is also why there's no "focusing snap"..

Until the dawn of the large, bright, fast, high resolution electronic viewfinder, we're stuck with physics that says the only way to get more brightness is to go to larger formats..

Rahon Klavanian 1912-2008..

Armenian genocide survivor, amazing cook, scrabble master, and loving grandmother. You will be missed..

Ciao! Joseph.

Http://www.swissarmyfork.com..

Comment #6

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