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Old Dec 26, 2010, 6:37 PM   #1
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Default Before there was AF .... ?

According to Wikipedia, cameras with AF were first mass produced in the mid seventies. In the very late 60's or early 70's I remember trying a relative's film camera. As I recall, the focus indicator involved two halves of a square or triangle which came together as one when focus was achieved. At that moment I think the subject was also in focus through the viewfinder.

How's my memory ?
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Old Dec 26, 2010, 6:53 PM   #2
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My SRT-101 and SRT-202 had a ground glass focusing screen. In the center was a circle that was split in half. As you adjusted the focus, the images in the two halves would shift, and when they were together, the image was in focus. It was called a "split-image rangefinder". Surrounding the circle was a ring of microprisms that, again, would accurately display the image when the focus was correct. Otherwise, that ring would seem to just display random triangles.
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Old Dec 27, 2010, 6:22 AM   #3
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Default Focusing a Crown Graphic

This weekend, I posted about my father's old Crown Graphic here: http://forums.steves-digicams.com/ot...ic-camera.html There were three bog-standard ways that that one camera was focused. First, the ground glass image was large enough (4x5 inches) that you could just look and see when the image was in focus (the referenced slide show includes a photo of an image through the ground glass). Second, the RangeFinder had two views of the same scene (there were little periscope windows on top and bottom of the long box on the side of the camera). When you looked through the peephole, you would see two images separated vertically. As you adjusted the focus, the two views would merge into one when the image was in focus. The third method, which was the standard one for photojournalists, was that the track had a distance scale. The photographer would eyeball the distance and set the scale to the desired focus that way.
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Old Dec 27, 2010, 11:49 AM   #4
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My old (all manual) Minolta 35mm SLR has the split circle surrounded
by the microprisms... I really miss that and I'm thinking of getting the
same style focusing screen for the D7000 I'm planning to buy when I
get my tax return...

This is the one here that I've heard good things about...

http://www.katzeyeoptics.com/item--N...rod_D7000.html

They have them for many different cameras...

Here's my Minolta SRT SC-II with the standard "Nifty-Fifty"...


Last edited by Wizzard0003; Dec 27, 2010 at 11:57 AM.
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Old Dec 27, 2010, 12:58 PM   #5
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Hmm, the problem is that you will probably mess up the AF system.

Not permanently, just as long as you have the split screen installed. So you can have either/or, but not both at the same time.

Most people, under most scenarios, cannot focus nearly as accurately or quickly as the camera's AF system.
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Old Dec 27, 2010, 1:17 PM   #6
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Quote:
Originally Posted by peripatetic View Post
Hmm, the problem is that you will probably mess up the AF system.

Not permanently, just as long as you have the split screen installed. So you can have either/or, but not both at the same time.

Most people, under most scenarios, cannot focus nearly as accurately or quickly as the camera's AF system.
Nope...

Direct replacement for the stock screen, does not effect AF...

From the site at that link:
(I added the bold highlight)
Quote:
The KatzEye™ focusing screen for the Nikon D7000 is a laser matte with
a split prism circle and a microprism collar, very similar to the one you’d
find in many classic SLRs. It is a direct replacement for the original, with
no modifications required to the camera at all. The split prism with microprism
ring is a great combination for focusing in a variety of situations. The
screen will have NO effect on the functioning of the autofocus sensors of
the camera and the on-demand grid lines will continue to function as intended.
I learned about it from a poster at another site that got one for his new
D7000 and has used them on several other cameras... The AF does not
use the focusing screen, it's a separate thing altogether... The most you
would have to do is (possibly) make a slight adjustment (allen set screw)
to the focusing screen alignment to fine tune "Manual" focus but that does
not effect AF in the least...

Edit:

Just to be clear, the "Optical" viewfinder in the D7000 gets it image from
the main mirror that redirects the image coming from the lense up to a prism
that bends the light to the eyepiece... The AF sensors get their image from a
second smaller sub mirror on the backside of the main mirror that directs the
image from the lense downward to the AF sensors... The focus screen is mounted
between the main mirror and the eyepiece prism and does not effect the AF
sensors in any way...

Here's a diagram of how a typical DSLR focus system works...

In this image they call the focus screen the "Finder Screen"...


Image source: http://knol.google.com/k/vijainder-k...o54fmdhy2mq/78#

You will notice also in that diagram, right by the eyepiece, is a "Photo Sensor for
exposure control"... This adjust exposure and "May" be effected buy a change
in brightness because of the new focus screen... This can be compensated by
setting a perminent + or - EV offset value in the camera menu...

Last edited by Wizzard0003; Dec 27, 2010 at 2:02 PM.
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Old Dec 27, 2010, 3:18 PM   #7
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Quote:
Originally Posted by Wizzard0003 View Post
You will notice also in that diagram, right by the eyepiece, is a "Photo Sensor for
exposure control"... This adjust exposure and "May" be effected buy a change
in brightness because of the new focus screen... This can be compensated by
setting a perminent + or - EV offset value in the camera menu...
Not quite. The KatzEye site explains that the exposure value has no effect on matrix or center-weighted imaging, but affects spot metering in a manner that varies with maximum aperture of the lens. In that case, your perminent EV offset would simply not work unless you always used the same metering method (and possibly the same lens). I think that KatzEye is an interesting option, but it is not without issues, however slight. If you use manual exposure frequently and cannot make do with the rangefinder option or the live imaging view, it may be a good choice. But I am ambivalent enough about the screen that I have put off adding it until I am confident that its value would exceed its aggrevation. I haven't reached that conclusion yet...
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Old Dec 28, 2010, 10:16 PM   #8
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Quote:
Originally Posted by tclune View Post
Not quite. The KatzEye site explains that the exposure value has no effect on matrix or center-weighted imaging, but affects spot metering in a manner that varies with maximum aperture of the lens. In that case, your perminent EV offset would simply not work unless you always used the same metering method (and possibly the same lens). I think that KatzEye is an interesting option, but it is not without issues, however slight. If you use manual exposure frequently and cannot make do with the rangefinder option or the live imaging view, it may be a good choice. But I am ambivalent enough about the screen that I have put off adding it until I am confident that its value would exceed its aggrevation. I haven't reached that conclusion yet...
You could be right (that's why I said "May") but they could be talking
about manual lenses that stop down manualy rather than those that
stop down only when the shutter fires... Unless you use DOF preview
most modern lenses are wide open until you take the shot and I 'believe"
that's where they are metering, wide open...

It's worth more reaserch for sure and that's a good question you bring
up... I'm planning to use the camera for a bit before deciding... I may find
I'm happy enough without it but if not this is an option...

Edit:

In mulling this over for a bit, what you're saying is true but would also
be the case with the stock focus screen as well... If you use any lens
that the aperture is not controled by the camera, such as when using
a "dumb" teleconverter (a TC that does not electrically or mechanically
alter the aperture) then when stopping down the aperture will also close
down and reduce the light getting to the eyepiece exposure sensor...

But you are right that setting a perminant EV offset is probably not the
answer as that would change exposure across the board for all metering
modes...

Good things to think about and thanks for pointing out the flaw in my
reasoning...

Last edited by Wizzard0003; Dec 29, 2010 at 2:51 AM.
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