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09-22-2014, 11:42 PM   #1
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What is this strange symbol?

I noticed it on both my K30 and some of my Magic cards. This obviously has some shared history. Any guesses?

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09-22-2014, 11:45 PM - 1 Like   #2
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That symbol points out the the location of the sensor plane - which is useful for macrophotography.
09-22-2014, 11:52 PM   #3
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QuoteOriginally posted by Digitalis Quote
That symbol points out the the location of the sensor plane - which is useful for macrophotography.
Interesting. I shot this with my 35 Macro, what does this mean for macrophotography?
09-23-2014, 12:29 AM - 1 Like   #4
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QuoteOriginally posted by lithedreamer Quote
I shot this with my 35 Macro, what does this mean for macrophotography?
At infinity focus the optical center of the lens is 35mm away from the sensor - as you focus closer, there will be light loss as the optical center of the lens is shifted further away from the sensor plane. Knowing how many stops you lose from magnification can be useful when calculating correct exposure for your subject as well as flash exposure.

09-23-2014, 12:48 AM   #5
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The greek alphabet phi. Its used to show you where the sensor is.
09-23-2014, 01:02 AM   #6
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QuoteOriginally posted by Anthen Quote
It's used to show you where the sensor is
In the old days it used to be the film plane was.

Anyway you'll be pleased to know it's also nothing to do with crop circles or aliens.

Last edited by Kerrowdown; 09-23-2014 at 01:28 AM.
09-23-2014, 02:01 AM - 1 Like   #7
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In macro photography the extension distances are measured from the film or sensor plane of the camera. These distances are used to calculate magnification and exposure factor.

Basic formula for magnification (M)

extension focal length = M

The basic formula for Exposure Factor (EF):

(1 + M) = EF

To calculate f-stop adjustment (fa)

fa= log(EF) log(2)

Thus a magnification of 1 = 4 EF = a 2 f-stop adjustment
09-23-2014, 02:56 AM   #8
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Look at the distance scales on your lens. Those distances are not from the end of the lens to the focused subject, but from the sensor to the focused subject. This is why that symbol comes in handy.
The distance from the end of the lens to the in-focus subject is called working distance and is not written on lenses.

09-23-2014, 06:17 AM - 1 Like   #9
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Nice to see another MTG player here on PF
09-23-2014, 08:14 AM   #10
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The same symbol is used to designate the diameter of a circle in engineering drawings and mathematical calculations.

You can also see the symbol on almost every interchangeable lens where it is used to designate the diameter of the filter threads.

Last edited by Tako Kichi; 09-23-2014 at 08:21 AM.
09-23-2014, 08:21 AM - 2 Likes   #11
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Its Saturn. On the other side of the camera is Jupiter. On the bottom is Uranus.
09-23-2014, 08:26 AM   #12
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The engineering diameter symbol is different, the line is at a diagonal angle where as the upper case letter Phi and the image plane symbol the line is straight up and down. The lower case phi is often written with the line at an angle but the line does not ascend above the circle which is also open.
09-23-2014, 08:47 AM   #13
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I've been in and and around all sorts of engineering for over 40 years and I've seen the symbol displayed vertically and at an angle many times although strictly speaking you are correct and the symbol for diameter should have the line on a slant. In these days of CAD design you rarely see the vertical symbol but back in the days of hand drawn blueprints it was quite common especially if the draftsman was in a rush.
09-23-2014, 11:28 AM   #14
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Most SLR's have it, I noticed that Pentax's is a little more pronounced. Canon and Nikon have it in relief with no contrast from my quick look on the internet.

In engineering, I've seen it both ways as a diameter symbol, but the slant is more common.
09-23-2014, 11:59 PM   #15
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No, you have it all wrong. This is the ultimate proof that Pentax WR is tops. This is the camera's Load Line when floating Waterline - Wikipedia, the free encyclopedia (ships max draft when floating for the non nautical)

But seriously, good question and well answered. I never knew that symbol significance.

Last edited by KevinR; 09-24-2014 at 12:10 AM.
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