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04-26-2010, 08:10 AM   #1
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Is m42 55mm/2 same as 55mm/1.8?

I'm coming from the digital world and just developed big interest in film cameras, specifically, spotmatics with m42 lenses. I read somewhere that 2/55 is basically the same as 1.8/55 with restriction to aperture openings. Is this true? Any compromise to PQ? I also acquired sigma 28/2.8. Any review on this one? Thanks!!

04-26-2010, 08:35 AM   #2
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Check the lens reviews. I have an Auto-Tak 1.8, SMC Tak 1.8, and a SMC K 1.8 on the way. It's a great lens.

Pentax Lens Review and Specification Database - SMC/Super-/Auto-Takumar 55mm F2

For the Sigma

https://www.pentaxforums.com/userreviews/reviews-Sigma-Lenses-for-Pentax-primes.html
04-26-2010, 08:40 AM   #3
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Yes, the Takumar 55mm f1.8 lenses are identical to the 55mm f2 lenses. The f2 lenses have a part just above the aperture blades that limits the lens to f2. It's the slightly purple-tinted part here.



When the two versions are side by side, this part is visible but not that obvious. If you made the opening in that part a little bigger, the f2 version would work just like the f1.8 version: the aperture blades open wide enough, and the aperture ring's f2 setting opens the blades fully. But the f1.8 version is cheap enough to make the modification more trouble than it's worth.
04-26-2010, 08:42 AM   #4
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QuoteOriginally posted by ragamuffin1171 Quote
I read somewhere that 2/55 is basically the same as 1.8/55 with restriction to aperture openings.
It is true. It is the exact same lens except for 2.0 v 1.8 as largest aperture.

This is perhaps the most authoritative source, though they do not delve into the history. Die Cast Pro - Asahi Optical Super-Takumar 55mm f/2.0

The basic reason for this was that it was sold as a down-market kit lens with a down market body. As stated in the above reference, it was sold as the standard lens for the SP500 which was basically a down market Spotmatic with a 1/500th top speed and no self-timer.

Historically, I believe that the first use of this lens as a down market alternative was as the standard lens on the H1a/S1a. This camera was an SV/H3V without the self timer and without the top shutter speed of 1/1000. (This was almost certainly the precedent for the Spotmatic SP500 that came later.) The SV/H3V came with a 55/1.8. (See also: History of Early Pentax)

This allowed them to eliminate all of the extra tooling that would have been necessary for a wholly different lens and camera, and yet participate in the lower end of the market. Smart.

woof!

04-26-2010, 09:14 AM   #5
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Thank you all for your input. Now I can hold off on buying 1.8/55 and look for some other lens knowing that I have a lens that's just as good as 1.8/55. Perhaps 135mm/3.5?
04-26-2010, 09:26 AM   #6
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"The f2 lenses have a part just above the aperture blades that limits the lens to f2.!.

Can this limit get off and convert the lens in F/1,8?

Rino
04-26-2010, 10:38 AM   #7
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QuoteOriginally posted by estudleon Quote
"The f2 lenses have a part just above the aperture blades that limits the lens to f2.!.

Can this limit get off and convert the lens in F/1,8?

Rino
The same part keeps the aperture blades from falling out, so it must be installed. You could file a larger hole in it and reinstall. The lens would work like an f1.8 lens then. Since both types are very common and inexpensive, it's easier to just find an f1.8 lens.
04-26-2010, 10:44 AM   #8
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Thank you, very much.

You're right, both are cheaper. But I was something curious.

Rino.

04-26-2010, 04:04 PM   #9
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QuoteOriginally posted by woof Quote
As stated in the above reference, it was sold as the standard lens for the SP500 which was basically a down market Spotmatic with a 1/500th top speed and no self-timer.
I'm sure that you know this already, but the SP500 had a top speed of 1/1000. We just weren't supposed to try turning the dial to that setting and discover it was there
04-26-2010, 04:22 PM   #10
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QuoteOriginally posted by little laker Quote
I'm sure that you know this already, but the SP500 had a top speed of 1/1000. We just weren't supposed to try turning the dial to that setting and discover it was there
Thanks.. and guess what? The S1a/H1a is EXACTLY the same. It has a 1/1000th, it just is not marked.

I am certain that the S1a/H1a provided the model for the up/down market duo of the SP and SP500... down to the EXACT feature/defeature set. It was probably a successful attempt, so they replicated it exactly in the later duo.

woof!
04-27-2010, 01:53 PM   #11
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QuoteOriginally posted by Just1MoreDave Quote
Yes, the Takumar 55mm f1.8 lenses are identical to the 55mm f2 lenses. The f2 lenses have a part just above the aperture blades that limits the lens to f2. It's the slightly purple-tinted part here.



When the two versions are side by side, this part is visible but not that obvious. If you made the opening in that part a little bigger, the f2 version would work just like the f1.8 version: the aperture blades open wide enough, and the aperture ring's f2 setting opens the blades fully. But the f1.8 version is cheap enough to make the modification more trouble than it's worth.
I have the super takumar versions of the 55mm f/1.8 and f/2 and I don't believe that they are exactly the same other than the max aperture. Testing with a geiger counter I found that the rear elements of the f/1.8 are radioactive and the f/2 arn't. This means that they use a different type of glass and so if their performance is similar then the optical design must be different. I havent done any serious comparisons of their performance yet though.
05-03-2010, 09:26 AM   #12
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QuoteOriginally posted by MattGunn Quote
Testing with a geiger counter I found that the rear elements of the f/1.8 are radioactive and the f/2 arn't. This means that they use a different type of glass and so if their performance is similar then the optical design must be different. I havent done any serious comparisons of their performance yet though.
It is the f/2 that should be readioactive. If that is not the case, you may have a rare f/1.8. I do not doubt that it could have happened based on the sample variation I have seen.

Notwithstanding the thoriated glass, please note that the optical formulas are the same. Please refer to: Die Cast Pro - Asahi Optical Super-Takumar 55mm f/2.0

However, technically, since the glass **is** different, the performance may vary.

The optical properties attendant upon the use of thorium are high refractivity and low dispersion and these would tend to operate to minimize chromatic aberration. If handled properly to remove any yellowing, we might posit the notion that the f/2 is a ** superior ** lens in this respect.

I doff my hat. You have the last word.

woof!
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