[jimby]

Well after more research I've only reinforced what I initially thought -- which is that the f/1.7 lens is sharper than the f/1.4 lens.

I'm not sure how so many people in this thread find the FA/1.4 to be better than the FA/1.7, but would urge posters to speak objectively rather than defensively and subjectively. Given the comparisons I found in the thread I linked above, and given the reviews I've found of the optics of the FA/1.4, I don't see how it would be possible that the FA/1.4 is "sharper." The photo posted above only reinforces this -- I see a failed attempt to compensate for very poor sharpness with software and terrible purple fringing. Also, lens hoods may increase contrast (which if post-processed is a non-issue), but certainly not sharpness.

You are reducing everything down to sharpness. What some people are telling you is that sharpness is not the only quality to consider. If I want super sharp, I have lenses that will deliver that. I can shoot with my FA 50mm F2.8 Macro, or my M 50mm F1.7, or half a dozen other lenses I have in that range. The FA 50mm F1.4 has its own look, and that includes variable edge sharpness based on aperture, great bokeh, fantastic low light capability, and great depth of the field control. ALL of these attributes are unique and important if you know how to use them.

The FA 50mm F1.4 has fine center sharpness even wide open. The control of edge sharpness based on aperture is a nice aspect of the lens.

[oeriies]

I own the F 50mm 1.7 and the FA 50mm 1.4. I've tested them for sharpness under identical conditions through the aperture range from wide open to f/8.0: My testing conditions were shots of a $20 bill from about 3 feet away using a tripod-mounted K-5, setting ISO to 100, letting shutter speed vary, using autofocus, and a remote shutter release with a 3 sec delay. I cropped each image to the size of the $20 bill and pixel peeped. I found that the FA 1.4 was quite soft wide-open, sharpening up nicely by f/2.8, whereas the F 1.7 was sharp wide-open and very sharp stopped down to f/2.8, where it held a slight edge on the FA 1.4. After f/2.8 the lenses were very close but I thought the FA 1.4 had more contrast.

While I was at it I tested the zooms I own that have a 50mm focal length, including the DA* 16-50, the DA* 50-135, the F 35-70, and the A 24-50. None was as sharp at 50mm as either the F 1.7 or the FA 1.4. The DA* 50-135 was the best of the zooms, and to my surprise was followed closely by the F 35-70 and then the DA* 16-50. All were acceptably sharp whereas the A 24-50 was soft. My comparison of the zooms was only done systematically at f/5.6. Obviously these zooms might perform differently at other focal lengths and f stops and all of this pertains only to my copies of these lenses and is only about their sharpness at 50mm. As has already been commented on in this exchange, there is more to a lens that its resolution.

As to the choice between the F (or FA) 1.7 and the FA 1.4, based on my copies and tests I would prefer the 1.7 because it is sharper than the FA 1.4 at the fastest apertures, which is where I expect most people want to use a fast lens. And although it is slower than the FA 1.4, unless you want a "dreamy" rendering the 1.4 needs to be stopped down to be acceptably sharp. The 1.7 is also less expensive.

Russ

[msatlas]

I went for the FA 50/1.4 because I mostly use a 50mm lens on APS-C as a portrait lens. It has much smoother bokeh than the 50/1.7 versions, even if the 1.7 is sharper wide open. Really the DOF from either lens is so shallow wide open that for portraits I'm stopping down anyway. Usually somewhere from f/2.2 to f/4 depending on the situation. Just use a hood on the 1.4 and it's fine.

[Docrwm]

Well after more research I've only reinforced what I initially thought -- which is that the f/1.7 lens is sharper than the f/1.4 lens.

I'm not sure how so many people in this thread find the FA/1.4 to be better than the FA/1.7, but would urge posters to speak objectively rather than defensively and subjectively. Given the comparisons I found in the thread I linked above, and given the reviews I've found of the optics of the FA/1.4, I don't see how it would be possible that the FA/1.4 is "sharper." The photo posted above only reinforces this -- I see a failed attempt to compensate for very poor sharpness with software and terrible purple fringing. Also, lens hoods may increase contrast (which if post-processed is a non-issue), but certainly not sharpness.

And here are the reviews I found:
Pentax SMC-FA 50mm f/1.4 - Review / Lab Test Report - Analysis & Verdict
Pentax smc FA 50mm 1:1.4 review: Digital Photography Review

You'll notice that the reviews are perfectly consistent with each other. I know some people are going to have a problem with this, but I find it hard to believe after thousands of lens reviews that either dpreview or photozone are fundamentally screwing up their sharpness tests.

I had thought the F versions were the same optically as the FA; this is incorrect?

Yep, I've read the reviews of the Sigma 50mm. However for me, one of the biggest points of having a prime lens, aside from being fast and sharp, is that it should be small!

Interesting how others have opinions but you have facts. Thanks for your thoughts on this subject.

[DSims]

I had thought the F versions were the same optically as the FA; this is incorrect?

On paper they're optically identical, but in practice they never are. I think it's because the glass elements were manufactured slightly differently in each generation. In my experience, each generation has a distinct character of it's own - in other words, K glass looks different from M glass, which looks different from A glass, which looks different from FA glass, ...

I find the character of the F and A glass are the most similar to each other - F glass looks almost like A glass with AF added. And occasionally a particular F lens model may look like FA glass (or visa versa). Perhaps this is mostly with later model F lenses or early FA lenses, where they "crossover" somewhat. But in general each generation yields a distinctive appearance. If you're a discerning viewer, you can often identify the generation of the glass just by looking at the images it produces (if you study the http://www.pentaxphotogallery.com/photos/gallery/query?camera=&lens=820 long enough you'll start to notice the differences, and then as you build your own lens collection you'll see they follow the same trends). On the surface you might describe the "look" as differences in attributes like color, contrast, or CAs, While these differences are subtle, they're identifiable, and in my opinion subtle differences can make the difference between an image people stop to admire and one they pass right over.

I never tried the FA50/1.4 (there was no point for me, since the F version was rated better, and I usually favor F glass anyway), but I owned the other 3. I'd already viewed enough images to know I didn't want the FA50/1.4. However, I thought my F50/1.4 was rather nice - that is, until I compared it to the FA43. To put them in perspective, the scale (from 1 to 10) from the perspective of a discerning, near-perfectionist would go something like this:

10 - none (this is reserved for lenses like the Sony Zeiss 135/1.8)
9 - DA*55 (nearly 10 for sharpness, but backgrounds are a mixed bag)
9 - K50/1.2 (OK sharpness, but excellent backgrounds)
8 - FA43 (perhaps the best color of any Pentax lens)

5.5 - F50/1.4 (nice, rich color)
5 - FA50/1.7 (overall pleasing images)
4.5 - F50/1.7
4 - FA50/1.4 (rating based on comparing many images online and comparing to lenses I owned)

2.5 to 3.5 - Excellent kit zooms like the F35-70/3.5-4.5, F70-210/4-5.6, or F24-50/4
2 - DA18-55 kit zoom
1 - Canon ~18-55 kit zooms (sorry Canon, your L glass is great, but not your kit lenses!)

So a "3" is a nice lens I still enjoy using, even though there's better glass out there. As you can see, while the AF 50's are good, they're not outstanding. So while you may still want to take the time to find the particular model you like better, keep in mind that the differences become mostly irrelevant when you compare them to the more expensive models.

[It should be noted that most of my shots, with any lens, are taken within 1 stop (or sometimes 2) of wide open, so my assessments should be viewed in that light]

[snake]

Also, don't forget that the coatings are not the same, either. While they all might carry "SMC" as a name, the formulations and processes were different.

Additionally, over time, coatings do change when exposed to air and light. May not be significant in most cases, but it does exist and why labs and observatories have lenses on their instruments refinished and recoated in certain applications.

[lytrytyr]

On paper they're optically identical, but in practice they never are. I think it's because the glass elements were manufactured slightly differently in each generation. In my experience, each generation has a distinct character of it's own - in other words, K glass looks different from M glass, which looks different from A glass, which looks different from FA glass, ...

I find the character of the F and A glass are the most similar to each other - F glass looks almost like A glass with AF added. And occasionally a particular F lens model may look like FA glass (or visa versa).

Interesting observation.

If you look at the optical diagrams for the 50/1.4 lenses on Boz Dimitrov's K-mount site,
you can see changes (for example in the curvature of the cemented join)
from K to M and from M to A, but no more change from there through the FA 50/1.4.

[lytrytyr]

I own the F 50mm 1.7 and the FA 50mm 1.4. I've tested them for sharpness under identical conditions through the aperture range from wide open to f/8.0: My testing conditions were . . . using autofocus . . . . I found that the FA 1.4 was quite soft wide-open

As to the choice between the F (or FA) 1.7 and the FA 1.4, based on my copies and tests I would prefer the 1.7 because it is sharper than the FA 1.4 at the fastest apertures

In the test, how did you deal with the vagaries of autofocus?
That could conceivably be a significant factor in the negative assessment of the fully open f/1.4 lens.

[DSims]

Also, don't forget that the coatings are not the same, either. While they all might carry "SMC" as a name, the formulations and processes were different.

Additionally, over time, coatings do change when exposed to air and light. May not be significant in most cases, but it does exist and why labs and observatories have lenses on their instruments refinished and recoated in certain applications.

Good point. Perhaps this is the sole reason for the differences. I never tried to determine the scientific cause - I was more interested in determining the effect from a qualitative standpoint.

If you look at the optical diagrams for the 50/1.4 lenses on Boz Dimitrov's K-mount site,
you can see changes (for example in the curvature of the cemented join)
from K to M and from M to A, but no more change from there through the FA 50/1.4.

I've never looked at this - interesting. So there's something else making the difference between not only the 50's but also many other "optically identical" F and FA series lenses.

[lukelbd]

Great post DSims, thank you for your thoughts.

9 - DA*55 (nearly 10 for sharpness, but backgrounds are a mixed bag)

However this confuses me. I had thought its IQ was pretty similar to the FA 50mm f/1.4, and the reviews on photozone and dpreview seem to reinforce this. Just very, very slightly better sharpness, and slightly improved bokeh/fringing compared to the FA/1.4.

[EarlVonTapia]

I'm currently participating in the "Single in December" monthly challenge, where for the month you have to take at least one picture with a single lens of your choice. The lens I chose for this month is the Pentax F 50 1.7.

My submission today has particularly pleased me, as I feel it is a good example of just how amazing the F 50 1.7 is.

https://www.pentaxforums.com/forums/groups/102-monthly-photo-challenges/2241-...#gmessage26606

Keep in mind, that picture was at f 2.8. I did take a shot at F 1.7, but there is some loss of detail, as well as some purple fringing. Nevertheless, I feel this is an excellent example of what the F 50 1.7 can do.

[DSims]

However this confuses me. I had thought its IQ was pretty similar to the FA 50mm f/1.4, and the reviews on photozone and dpreview seem to reinforce this. Just very, very slightly better sharpness, and slightly improved bokeh/fringing compared to the FA/1.4.

This might be true at f/2.8 and narrower. But IMO almost no one does lens reviews properly, at least in this regard.

Lenses should be tested at 1/3 stop increments for the first 2 stops. Most reviews only test every full stop, at best. In fact, a lens' performance near wide-open is the best measure of its quality I've found. For example, some Sigma lenses are so weak throughout the first stop that you'd be better off with a lens from the camera manufacturer that's one stop slower.


For a 50mm f/1.4 lens, the entire story takes place between f/1.4 and f/2.8 (non-inclusive). Almost every lens is weak at f/1.4 and strong by f/2.8, so those test shots are nearly worthless. But there can be huge differences in lens performance at f/1.6 or f/1.8. Quite frankly, that's where I plan on often using it - otherwise I'd get a slower lens. And what you'll find is that at these apertures the AF 50's are unusable, while the DA*55 is excellent. Simply put, It's the fastest K-mount Pentax lens you can buy (well, my K50/1.2 and FA*85/1.4 are almost equal to it, but they're only available on the used market).


If you only have $200-300 to spend, any of the Pentax F/FA 50's can be very useful. But they (any of them) need to be thought of as simply a reasonable quality 50mm f/2 lens. Not to worry - I doubt anyone else's cheap 50 is much good below f/2 either.

[oeriies]

In the test, how did you deal with the vagaries of autofocus?
That could conceivably be a significant factor in the negative assessment of the fully open f/1.4 lens.

Initially I went through several rounds of autofocus with the intent of taking the best result but in practice these lenses were spot on everytime with a $20 bill on a flat surface. In other words, no whirring screwdrive after the first focus. Also, I'm more confident in autofocus for this sort of test than the vagaries of manual focus -- at least I'm out of the equation. So I'm convinced by my test that my 1.4 is quite soft wide open. That was my impression based on everyday use.

[lytrytyr]

Initially I went through several rounds of autofocus with the intent of taking the best result but in practice these lenses were spot on everytime with a $20 bill on a flat surface. In other words, no whirring screwdrive after the first focus.

Thanks for the reply.

Did you use the usual phase-detect autofocus,
or the contrast-detect autofocus from live view?

[oeriies]

Thanks for the reply.

Did you use the usual phase-detect autofocus,
or the contrast-detect autofocus from live view?

phase detect