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06-19-2015, 05:28 AM   #1
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[Asking]SMC Pentax K 50mm f1/4 VS Pentax-M 50mm f1.4 VS Pentax-M 50mm f1.7 ?

Dear Friends,

I am looking for lens for Pentax MX SLR 35mm/film and there's 3 lenses in my choice :

1. SMC Pentax K 50mm f1.4
2. SMC Pentax-M 50mm f1.4
3. SMC Pentax-M 50mm f1.7

Which are from 3 lenses above that have :

- Best sharpness almost in any aperture value
- Low Chromatic Abberations
- Low Distortion
- Good Bokeh
- Good Tonality especially for B/W Photos

Thank you for your help and I looking forward for it.

Best regards,

06-19-2015, 05:43 AM   #3
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Thank you for response. I have read 3 reviews above and these are nearly in capability and performance. For best performance, best vooter here, which are from 3 lense is best choice (have many users)
06-19-2015, 06:01 AM   #4
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All three are OK, very similar in performance, as are all double gauss designs.
The 1.4 designs have (much) more field curvature when used for closeup/macro on extension tubes etc.
The K50/1.4 is probably radioactive (mine are, but other people reported that they have samples which are not), which results in the famous yellowing.
The 1.4 versions will reach their best performance maybe halve a stop earlier than the 1.7. (around f5.6 for the 1.4, and between f5.6..f8 for the 1.7)
Similar for vignetting, the 1.4 versions will have less when comparing against the 1.7 at the same apertures.
The K50/1.4 has the best mechanical construction (brass for the heliocoid, the others have aluminum).

06-19-2015, 06:23 AM   #5
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The 1.7 will likely have a flatter field than either 1.4 (in my experience), but I would prefer a faster 1.4, myself (sharp stopped down a bit, and with great bokeh). Then I would take the K 1.4 over the M 1.4, for the build quality and "feel". [Just my $0.02, YMMV.] (Yes, I've owned far too many MF Pentax 50's "in my day"...]
06-19-2015, 06:29 AM   #6
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Having had all three of these leneses, the M50/1.7 has less distortion (though none has very much) and less CA that either of the f1.4 options. In terms of sharpness, the M50/1.7 gets a slight nod over the K50/1.4, with the M50/1.4 in third. As to bokeh and tonality, I found the K50/1.4 to be the best of the lot by a decent margin.
06-19-2015, 07:13 AM   #7
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Thank you all for info and suggestion
I can make conclusion that for build quality (phisically) K 50/1.4 seems best choice but M 50/1.7 is better in chromatic abberation and sharpness but weak in bokeh of course.

I have 3 quotations :

K 50/1.4 is in mint condition (90%), including 3rd front cap, and original rear cap for USD 76,92
M 50/1.4 is in mint condition (95%) including original front cap but without rear cap for USD 65,38
M 50/1.7 is in mint condition (99% almost like new) including original front and rear cap for USD 76,92

for those quotations, which one must I choose for?

Thank you
06-19-2015, 07:23 AM   #8
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QuoteOriginally posted by liemjerry Quote
- Good Tonality especially for B/W Photos
If you are shooting b&w film these "normal" lens resolution test on FF film may interest you:

http://www.takinami.com/yoshihiko/photo/lens_test/pentax_normal.html

Phil.

06-19-2015, 07:25 AM   #9
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K50/1.4 did NOT use thoriated glass - they are NOT radiocative.
QuoteOriginally posted by glasbak Quote
All three are OK, very similar in performance, as are all double gauss designs.
The 1.4 designs have (much) more field curvature when used for closeup/macro on extension tubes etc.
The K50/1.4 is probably radioactive (mine are, but other people reported that they have samples which are not), which results in the famous yellowing.
The 1.4 versions will reach their best performance maybe halve a stop earlier than the 1.7. (around f5.6 for the 1.4, and between f5.6..f8 for the 1.7)
Similar for vignetting, the 1.4 versions will have less when comparing against the 1.7 at the same apertures.
The K50/1.4 has the best mechanical construction (brass for the heliocoid, the others have aluminum).
06-19-2015, 07:53 AM   #10
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QuoteOriginally posted by monochrome Quote
they are NOT radiocative
Yeah, I always thought the only thoriated glass lenses were all M42 screw mounts, so anything with a bayonet mount isn't going to turn your run-of-the-mill garden lizard into Godzilla.
06-19-2015, 08:09 AM   #11
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QuoteOriginally posted by liemjerry Quote
I am looking for lens for Pentax MX SLR 35mm/film and there's 3 lenses in my choice : 1. SMC Pentax K 50mm f1.4 2. SMC Pentax-M 50mm f1.4 3. SMC Pentax-M 50mm f1.7 Which are from 3 lenses above that have : - Best sharpness almost in any aperture value - Low Chromatic Abberations - Low Distortion - Good Bokeh - Good Tonality especially for B/W Photos
Most of the criteria from your question will hugely depend on the copy of a lens that you end up getting. This is the risk one has to take when buying old second hand lenses. But in case you succeed in getting a nice not battered copy, Any of the three will do all you wanted just fine.
06-19-2015, 08:28 AM   #12
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QuoteOriginally posted by dcshooter Quote
Those are quite good prices for the 1.4s, but the M should be more like $50.
Agreed, very fair prices for the f1.4 lenses, but the M50/1.7 is rather overpriced. Given that there is no differnce in price betewen the K50/1.4 and the M50/1.7, I'd be tempted to get the former.
06-19-2015, 09:45 AM   #13
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QuoteOriginally posted by liemjerry Quote
Thank you all for info and suggestion
I can make conclusion that for build quality (phisically) K 50/1.4 seems best choice but M 50/1.7 is better in chromatic abberation and sharpness but weak in bokeh of course.

I have 3 quotations :

K 50/1.4 is in mint condition (90%), including 3rd front cap, and original rear cap for USD 76,92
M 50/1.4 is in mint condition (95%) including original front cap but without rear cap for USD 65,38
M 50/1.7 is in mint condition (99% almost like new) including original front and rear cap for USD 76,92

for those quotations, which one must I choose for?

Thank you
Like what others mentioned.. I would say your choice of lenses K/M 1.4 are pretty much identical. Actually even 1.4 gives a bit more pleasing bokah, but the nature of 1.4, it makes wide open aperture sharpness way lower than 1.7 even the 1.4 lens is set to be 1.7~1.8ish. Between 1.4 and 1.7, you won't get too much of the boost during the night either.

From your situation, I would say, rather debating on 1.4 vs 1.7, I would.. indeed pick up a even cheaper 50mm 1.8 or 2.0 as alternative options for 1.7, and keep a cheaper 1.4.

My personal opinion is, none of those 3 are my liking really.

for compactness, price, image quality, performance, for large aperture I would go for :
Pentax-A 50/1.2
Pentax-A 50/1.4
Pentax SMC Takumar 50/1.4

Small aperture, but even more compact I would go for :
Pentax-A 50/2.0
Pentax-FA 43/1.9
Pentax SMC Takumar 55/1.8


I currently have Pentax-M 50/2.0, Be honest with you, it's way lower performer than other fifties I have owned. I would personally stay away from M version and early K versions. Early K is just K mount of SMC Takumar version with less of yellow glass element. But it would be bigger, heavier, and more expensive compare to SMC Takumar.

If you want to have nice bokeh, then the choice could be 50/1.2, 50/1.4, or 55/1.8. I found that 55/1.8 has the best bokeh even compare to any version of 50/1.4. As for Pentax-A 50/1.2, it's an unique lens. You simply will never get sharpness till your aperture goes down to F4 or beyond. But it is what it is.. It's a 1.2!! It works best on crazy smooth bokeh and when you absolutely don't need sharpness on the subject. The painting quality of 1.2 is probably strictly to artists (maybe).

Let you have the taste of 55/1.8 (which is a cheap lens BTW.. my had tiny bit trace of fungus and it's still super sharp! I picked up around $30 I believe) Using fairly wide but not widest 50 range, but makes it a 55 (even more telephoto).. It brings up the characteristic similar to medium format. There is a reason why on 645 a 80mm F2.8 although it's F2.8 it gives much better bokeh than a 135 50mm F1.4 but subject is WAY SHARPER!! Because you are in theory at F2.8 compare to F1.4!!! That's why I would say, if you want great bokeh, 50mm F1.4 vs 55mm F1.8.. I would personally pick up 55/1.8 any given day!



06-19-2015, 01:41 PM   #14
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QuoteOriginally posted by monochrome Quote
K50/1.4 did NOT use thoriated glass - they are NOT radiocative.
We have had this discussion before, and you never indicated what your source is for claiming that it is not radioactive.

06-19-2015, 02:24 PM   #15
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QuoteOriginally posted by dcshooter Quote
Well, the lens elements are interchangeable between the SMC Tak equivalent and the SMC Pentax, so it's conceivable that 1) the SMC Pentax is radioactive across the board, 2) some SMC Pentaxes are radioactive, while others are not, or 3) The affected SMC Pentaxes have been repaired at some point and had the second from rear element swapped out with one from a Tak.

Coming to a firm conclusion would require a large sample size across the serial number range and a geiger counter. Any volunteers?

FWIW, of the SMC Pentaxes I've owned, none have yellowed, while all of the SMC Taks have. On the other hand, I've owned a couple of 8 element Supers that have had significant yellowing, and that caused some REAL gnashing of teeth around here when I shared that little tidbit, since conventional wisdom has that that particular model does not yellow.
This is normally how it breaks down..

Takumar - yellow
Super Takumar - yellow
S-M-C Takumar - yellow
S-M-C Super Takumar -yellow
SMC Takumar - yellow

SMC K - not yellow

You can swap out elements just means they are design identically and glasses are identical shape. the only difference is after discovering the radioative issue, Pentax "REPLACED" the rare element to glass. No harm no foul.. Only people mentioned without the radioactive, the sharpness goes softer a tiny bit. true or not? who knows?

The truth is they were also saying even your cellphone emits more radioactive reading than your lens.. so I am sure as long as you don't hug your lenses to sleep, you'll be fine.
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