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05-31-2008, 05:07 PM   #1
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What does the 1:2 Mean?

I have an old ricoh lens with "XR Rikenon 1:2 50mm L written on it. What does the 1:2 mean?

Also- when I look through the lens while it is off of the body, I can't see the appeture blades. Is this bad? the appeture ring still works since it affects the exposure.

05-31-2008, 05:09 PM   #2
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QuoteOriginally posted by columbus Quote
I have an old ricoh lens with "XR Rikenon 1:2 50mm L written on it. What does the 1:2 mean?

Also- when I look through the lens while it is off of the body, I can't see the appeture blades. Is this bad? the appeture ring still works since it affects the exposure.

It means it is an F/2.0 lens.
05-31-2008, 09:28 PM   #3
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1:2 is the same as f/2.0 or f/2. Also commonly referred to a the f-stop. It is the widest aperture your lens is capable of. Smaller numbers denote a faster lens, and generally faster lenses are more versatile because they allow you to take pictures in lower light situations. f/1.4 is faster than f/2, etc.

Faster lenses are not necessarily better, though in many cases they are...
06-01-2008, 04:28 AM   #4
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The 1:2 ratio (=f/2) does also mean the ration between focal lenght and effective inner lens diameter, in this case 50mm/2 = 25mm.

06-01-2008, 01:16 PM   #5
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In other words, it means your lens is pretty "fast" (read as good in low light)
06-01-2008, 04:23 PM   #6
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QuoteOriginally posted by columbus Quote
I have an old ricoh lens with "XR Rikenon 1:2 50mm L written on it. What does the 1:2 mean?

Also- when I look through the lens while it is off of the body, I can't see the appeture blades. Is this bad? the appeture ring still works since it affects the exposure.
The aperture blades stay open until the camera or your finger closes them by pushing on the lever sticking out the back of the lens.
06-01-2008, 08:50 PM   #7
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QuoteOriginally posted by SpecialK Quote
The aperture blades stay open until the camera or your finger closes them by pushing on the lever sticking out the back of the lens.
Just for clarification, older manual style lenses leave the aperture open when the lens is off the camera and while on the camera, will be at the selected apereture setting (unless it has an A setting)

Auto style lenses will keep the diaphragm closed while the lens is off the camera, fully open when on the camera, and when the shutter is pressed (or DoF preview) it goes to the selected aperture.
06-02-2008, 04:52 AM   #8
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QuoteOriginally posted by axl Quote
In other words, it means your lens is pretty "fast" (read as good in low light)
Although f/2 is actually pretty slow in the 50mm non-macro world...

06-02-2008, 05:36 AM   #9
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QuoteOriginally posted by Entropy Quote
Although f/2 is actually pretty slow in the 50mm non-macro world...
If you're a photographer on a budget, an f/2 lens is actually not that shabby.
06-02-2008, 08:47 AM   #10
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Not to be confused with 1:1.2 (we've gone down THAT road before)
06-02-2008, 09:13 AM   #11
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I agree with ftpaddict: f/2 is good, even for a 50mm lens. In terms of light gathering capability, the difference between a 1.7 and 2.0 lens is fairly negligible, and going down to 1.4 is, indeed, more signifcant, but it is still not astoundingly different. In many (or perhaps most) cases, a lens does not look good at wide-open aperture. A half-stop extra may end up having reduced or little significance.
06-02-2008, 09:24 AM   #12
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To add to the confusion...

On macro lenses the reproduction ratio is expressed in the same format, usually 1:n.
This is not the case with your Ricoh 50mm lens. 1:2 means f/2.0, or a relatively fast lens.
BTW most Rikenon lenses are excellent...

Chris
06-02-2008, 10:27 AM   #13
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I think a Pentax-A 50mm F1.7 offers better value...

(unless you got the lens for free)
06-02-2008, 10:54 AM   #14
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QuoteOriginally posted by SpecialK Quote
The aperture blades stay open until the camera or your finger closes them by pushing on the lever sticking out the back of the lens.
Actually it's the opposite; the camera (or your finger) must overcome the spring pressure holding them closed.
If the opening does not change size as you rotate the aperture ring you do have a problem,
either a broken spring or gummed-up blades...

Chris
06-02-2008, 11:22 AM   #15
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Look out for the "Ricoh Pin"

If you haven't yet mounted that lens to a Pentax body, be careful -- look for the infamous "Ricoh pin" first.

Caution regarding Ricoh lenses on Pentax bodies: Pentax SLR Talk Forum: Digital Photography Review

It's not as bad as the original post makes it sound though, if the pin is of the sort that might get caught on the Pentax mount (sharp edges, not rounded), then I would probably just tape it down, and not bother with removing or cutting it.

Personally, I have four Ricoh-mount lenses and all of them have a rounded Ricoh pin that doesn't get stuck, so you might not need to do anything.
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