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01-19-2010, 09:18 AM   #1
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Different rings in 1,4/50

See please :

Images Photo Gallery by Sean Carpenter at pbase.com

There you can note that in the S.T. 1,4/50, the aperture ring has the 1,4 setting to close to the point that main F/2. It seems to be a F/1,8 setting more than the 1,4 (but it's 1,4 one, ins't it?). I read posts where the ST owners said that their lens not so luminous than others 1,4 lenses. In facts one of them said that his planar 1,7 let pass more light than his takumar 1,4.

Beside it, the S-M-C 1,4. The last has the F/1,4 setting so near to the F/2 one like the F/2 is close to the F/2,8 and so.

Is the last element of the hot ST more hot than the S-M-C ones and let, in the 1,8 setting, pass the light like a common 1,4 lens?

I donīt think so.

But then why that difference?

Rino.

01-19-2010, 09:45 AM   #2
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QuoteOriginally posted by estudleon Quote
See please :

Images Photo Gallery by Sean Carpenter at pbase.com

There you can note that in the S.T. 1,4/50, the aperture ring has the 1,4 setting to close to the point that main F/2. It seems to be a F/1,8 setting more than the 1,4 (but it's 1,4 one, ins't it?). I read posts where the ST owners said that their lens not so luminous than others 1,4 lenses. In facts one of them said that his planar 1,7 let pass more light than his takumar 1,4.

Beside it, the S-M-C 1,4. The last has the F/1,4 setting so near to the F/2 one like the F/2 is close to the F/2,8 and so.

Is the last element of the hot ST more hot than the S-M-C ones and let, in the 1,8 setting, pass the light like a common 1,4 lens?

I donīt think so.

But then why that difference?

Rino.
I am not sure what you are asking here but my Super Tak and my SMC Pentax 50mm F1.4 lenses have no detents between 1.4 and F2.

Note also that when it comes to light transmission, the issue of transmission and coatings changed the transmission by about 2% therefore you would never nitice it. a stop is double or half the light.
01-19-2010, 10:07 AM   #3
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QuoteOriginally posted by estudleon Quote
But then why that difference?

Rino.
The difference is purely in the spacing between stops on the aperture ring.

The SMC lens has a diaphragm setting coupler lever in the lens mount, requiring that the aperture stops be evenly spaced. The super-tak does not.

See Screwmounts for lens mount details.
01-19-2010, 10:33 AM   #4
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I have just checked my Super Takumar 50mm f/1.4 and it clicks precisely on 1.4 and 2 ... nothing inbetween.

I get a click between 2 and 2.8 though.

01-19-2010, 02:46 PM   #5
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QuoteOriginally posted by troyz Quote
The difference is purely in the spacing between stops on the aperture ring......
First- Thanks to all the guys.

Second- I was thinking about that the difference is only in the space between stops.

Yes, you are right.

But how can the mechanism close/open the aperture in one stop from 1,4 to 2 and viceversa while the way that crosses the aperture ring is equal to only half aperture ?

The space between F/1,4 and F/2 in the S.T. is only half of the rest of the spaces between all apertures.

It's rare to my eyes, I don't remember any other lens with similar characteristic.

Rino.
01-19-2010, 02:51 PM   #6
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QuoteOriginally posted by estudleon Quote
First- Thanks to all the guys.

Second- I was thinking about that the difference is only in the space between stops.

Yes, you are right.

But how can the mechanism close/open the aperture in one stop from 1,4 to 2 and viceversa while the way that crosses the aperture ring is equal to only half aperture ?

The space between F/1,4 and F/2 in the S.T. is only half of the rest of the spaces between all apertures.

It's rare to my eyes, I don't remember any other lens with similar characteristic.

Rino.
Without taking all the lenses apart, and looking at the shape of the aperture blades, and the shape of the linkages that move them, it is enrirely possible that the movement is not linear.

I have seen cams shaped like sine waves controlling the aperture of kiron lenses, which produce just this type of effect, also if the blades are curved as opposed to streight (or nearly so) it will also impact the relitive motion.

there may also be some impact on number of blades, my ST is 6 blades, my SMC Pentax is 8, and the curvature of the blades is different. But on my two lenses the approximate spacing between each full stop detent is about the same
01-20-2010, 06:18 AM   #7
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Thanks Lowell.

It seems that you have the answer.

Rino.
01-20-2010, 12:54 PM   #8
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This is not going to solve your mystery, but I had my S-M-C Takumar 50mm f1.4 all apart already, so here's a photo of the mechanism within the mount.



The fork at the bottom center connects to a pin that moves the aperture blades. The fork is at the end of a brass-colored C-chaped arm. When the auto/manual switch is in Manual (shown here), this arm is spring loaded to press toward the center of the lens. In Auto, it is spring loaded to press outward. There's a black ring underneath it with a pin that follows the inner edge of the C arm in Manual mode. The black ring is connected to the aperture ring, so moving the aperture ring moves the C arm according to the shape of the inside curve, then the fork moves the blades.

Tthe stop-down pin is at the top, just right of center. In Auto mode, pushing the pin in moves the end of the C arm, so it travels until it touches the pin on the black ring like in Manual mode.

The tiny pin that locks the auto/manual switch in Auto when the lens is off-camera is at the bottom, right of the fork. On the black ring, there's a tab you can't see below the follower pin that tells the camera where the aperture ring is set.

01-22-2010, 09:13 AM   #9
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The SMC rear element is 1 mm bigger than the S.T. ones.

Are they the same lens? It seems that not.

Rino.
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