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06-11-2019, 04:11 PM - 1 Like   #1
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Difference between K mount and M42 mount 15mm/F3.5 (with aspherical element)

Is there a difference between these 2 versions of the same lens, other than mount type? the ratings on the reviews are vastly different.

thanks in advance.
PS first post. go easy on me.

06-11-2019, 04:29 PM   #2
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Generally I don't think so, except in the way the mount changes lens behavior (always stopped down on M42 vs. default open on K). M42 lenses may be older or more worn, and I'd say the experience of attaching them to the camera is inferior.

Do you have a specific pair in mind?
06-11-2019, 04:41 PM   #3
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QuoteOriginally posted by BugsDogsAndSunsets Quote
Do you have a specific pair in mind?
It's in the title, the 15mm f 3.5

QuoteOriginally posted by borneo1910 Quote
PS first post. go easy on me.
welcome!

My guess is that it's small sample variation, of opinion and not lens to lens variation. If you look at the K version, only one review has the various rating criteria filled in (sharpness, aberrations, etc), and that particular user didn't like the lens as much as the 12 for the m42 version. And even comparing the overall score, 7 vs 12 answers are quite few.
06-11-2019, 04:52 PM   #4
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it may depend upon which mount is more convenient for you to use...

06-11-2019, 04:59 PM   #5
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If you are talking about the reviews in the lens review section you must take into consideration the ratings are totally subjective. One reviewers 5 might be another reviewers 8. Even reviews by the poster are subjective and may reflect unconscious bias.
06-11-2019, 05:11 PM - 1 Like   #6
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When Pentax transitioned from M42 to K-mount some lenses were identical optically, they just changed the mount. Over time the older designs were replaced with new ones. So it is possible that both are the same in this case. Both are 13 elements in 12 groups and since this was a rare and slow selling lens I would suspect they are identical. Of course there were also a lot of changes in coatings going on, so that most likely would have changed over time.

And welcome! Also why is it most new posters say "first post, take it easy"? This is an exceptionally friendly place if you stay out of the "rumors" section, so don't be afraid to ask anything Pentax related. Most likely someone here will have an answer.
06-11-2019, 05:44 PM - 1 Like   #7
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Welcome to the Pentax Forums!

There are six variants of the 15mm f/3.5 (SMC Takumar (2), Pentax-K (3), and Pentax-A), only two of which is have an aspheric element. The story of the AL versions and their relationship to each other and the non-AL lenses is summarized on the K 15/3.5 AL article on the K-Mount Page Website...

The K-Mount Page | Pentax-K 15/3.5 AL

As for differences in reviews...paying a steep price may bias a review two ways. The more common is to inflate the rating to match the price. The second is down-rate the lens based on the realization of poor investment. The best reviews are complete and provide a detailed rational for both positive and negative evaluation.


Steve

Last edited by stevebrot; 06-11-2019 at 05:45 PM. Reason: Typo
06-11-2019, 09:23 PM   #8
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Thank you all for your help.

Here's a follow-up question. Is there a way to take the hood off or rotate the mount? I'm adapting the lens (via Pentax K to EOS then EOS to E) to my Sony a7iii. In this configuration, the lens hood is at a 45 deg rotation causing vignetting in the corners (Tope Left, Bottom Right).

There seem to be some slots for a spanner to remove the ring just around the lens, but it doesn't seem to want to come loose. I can't find any diagrams or videos on how to tear down the lens, which might help.

Is this even a possibility? I've seen it used in video and there was no vignetting, I'm wanting to believe that it wasn't with a sensor crop.

Let me know what you think.
Thanks

---------- Post added 06-11-19 at 09:37 PM ----------

QuoteQuote:
And welcome! Also why is it most new posters say "first post, take it easy"? This is an exceptionally friendly place if you stay out of the "rumors" section, so don't be afraid to ask anything Pentax related. Most likely someone here will have an answer.
A lot of times when newcomers post to forums with people who have been here for years, they can get aggressive or hostile if the newcomers ask questions that have already been asked or basic questions that most people know. It's not something I noticed on this forum, but something I'm aware of and don't like.

06-12-2019, 12:42 AM   #9
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A factor to consider when comparing lenses like this, which would have been fairly esoteric in their day, is that there were quite possibly very few 15mm M42-fit lenses ever produced and sold. Take into account the proportion of those that will have been retained by the original purchaser, as it would have been a significant investment, and what you've got left are those that have been passed on or rejected for any reason, a relatively high proportion of which may well be imperfect to one degree or another.


Of course, you could get lucky


YMMV!
06-12-2019, 02:52 AM   #10
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QuoteOriginally posted by borneo1910 Quote

A lot of times when newcomers post to forums with people who have been here for years, they can get aggressive or hostile if the newcomers ask questions that have already been asked or basic questions that most people know. It's not something I noticed on this forum, but something I'm aware of and don't like.

early on, for me, there were several photography forums that I joined and then left because of this same attitude - this rarely happens here at PF (thankfully)..

there may be a list of regularly-asked questions that are regularly-answered, usually quickly and politely...

welcome aboard!
06-12-2019, 07:54 AM   #11
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I had the A15/3.5 and now have the K15/3.5AL and did not see any difference optically. (Though I did not test them side by side at the same time.)

I don't think you want to mess with the built in lens hood, as the protruding front element is just waiting to be scratched. Also no one really wants to deface a classic Pentax lens, do they?

Phil.
06-12-2019, 08:34 AM - 1 Like   #12
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QuoteOriginally posted by borneo1910 Quote
Here's a follow-up question. Is there a way to take the hood off or rotate the mount? I'm adapting the lens (via Pentax K to EOS then EOS to E) to my Sony a7iii. In this configuration, the lens hood is at a 45 deg rotation causing vignetting in the corners (Tope Left, Bottom Right).
If yours is the K-mount version, I would try a direct K-to-E adapter. If you have the M42 version, that is a little more problematic in that M42 lenses seldom line up exactly with the index mark at 12:00.* That being said, 45 degrees off is extreme. Again, an adapter proper to the mount might be a quick fix. Given that two of the reviews on this site describe the hood performance as "weak", using a different adapter might be enough to get the lens closer to the more typical 5 degrees or so "off".


Steve

* I have a fair selection of M42 lenses and bodies and none line up with any lens, but no combination is more than 5-8 degrees and most are much closer.
5 Days Ago   #13
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QuoteOriginally posted by stevebrot Quote
If yours is the K-mount version, I would try a direct K-to-E adapter. If you have the M42 version, that is a little more problematic in that M42 lenses seldom line up exactly with the index mark at 12:00.* That being said, 45 degrees off is extreme. Again, an adapter proper to the mount might be a quick fix. Given that two of the reviews on this site describe the hood performance as "weak", using a different adapter might be enough to get the lens closer to the more typical 5 degrees or so "off".
You're Brillant!!!! Why didn't I think of that adapter. It's coming today. I'll let you know how it fares.

Thank you!!!

Mike
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