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01-19-2014, 08:04 PM   #1
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FA 31 or FA 50 1.7 better in low light?

I have an FA 43 and I know that I need to bump it up from 1.9 to at least 2.8 or more to get a sharper image in low light. I'm wondering if the FA 31 or a fast 50 like the FA 50 1.7 might do a better job inside with low light.



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01-19-2014, 08:50 PM   #2
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I have the 31, 43, and the F50 f1.7 and every one is sharp by f2.2, the 31 is sharp at 1.8. I also have the 77 f1.9 and it too is sharp by f2.2
01-19-2014, 08:52 PM   #3
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I am happy with both FA31 and FA50/1.4 in low light as far as sharpness goes... Haven't used FA50/1.7 but I seem to frequently read how sharp it is, so I'd guess you'd probably be happy with it. The question I would have for you is if you're fine with the FOV of the FA43 for indoors and if so are you fine going narrower with the FA50? I had my FA50/1.4 for years before I had FA31 and it has always felt tight to me indoors. This last Christmas was my first with FA31 and I loved having the extra room in my shots.. It really is a great fit for me indoors FOV wise, and of course I was really impressed with the IQ/colors comparing to previous Christmas's where the FA50 was the go to lens.
01-19-2014, 09:04 PM   #4
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QuoteOriginally posted by Franky2step Quote
I have the 31, 43, and the F50 f1.7 and every one is sharp by f2.2, the 31 is sharp at 1.8. I also have the 77 f1.9 and it too is sharp by f2.2
So you see no appreciable difference between the FA 31 and F50 1.7 in low light? In that case I'll hold off on a fast 50 and just purchase the FA 31.

01-19-2014, 09:31 PM   #5
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QuoteOriginally posted by Driline Quote
So you see no appreciable difference between the FA 31 and F50 1.7 in low light? In that case I'll hold off on a fast 50 and just purchase the FA 31.
Focusing in low light is a function of many things...everything from what kind of light there is to what camera body that you are using. All of the lenses will focus faster (in general) on a K3 than most of the other offerings.

It depends on what you mean specifically as to 'differences'? I don't have the 31 (yet) but I have other fast lenses and I can tell a difference between them. Say like I was able to tell the differences between my 50mm f1.7 and my 50mm f1.4 lens...

A couple of months ago I went to a Renaissance Festival and was shooting in probably the lowest light ever.

https://www.pentaxforums.com/forums/12-post-your-photos/242890-people-renaiss...pic-heavy.html

I use a K5, but I will probably spring for a couple K3 bodies soon enough. The 31mm as well is on my short list.

In very low light your learning how to 'read the light' is vital. And as for how to shoot, you will have a lot easier time with the 31mm merely because the DOF is easier to work with.

The ISO capabilities of your camera body matter as well. I found that in my little 'festival' experiment that manual focusing using live view was much more effective.

In the end I had people literally following me around watching me shoot. I got at least 20-25 very 'oh wow' positive comments about 'my gear'... and 'you didn't use a flash?!'. It was kind of neat to have people line up pretty much to see my shots on the screen... I was able to talk a great deal about 'photography' with several people who really liked what I was into. It was awesome.

When you say 'low light' it just depends on what you are into. From what I hear you will never be disappointed with the 31mm. I have a F28mm and I can tell you that based on that, the focal length there is extremely useful. If I was going back to that Festival again, I would love to get my hands on a 31mm. I would take two lenses. A fast 50 and a 31mm.
01-19-2014, 09:37 PM   #6
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I had the FA50/1.7, F50/1.7, and F50/1.4. None of them have IQ or sharpness as good as the FA43 when shot at the same aperture (I have a fairly early FA43). You should be able to get reasonably good IQ from the FA43 at f/2.2 - though f/2.8 certainly improves IQ on the FA43. While I preferred the FA50/1.7 and the F50/1.4 as being slightly better (similar to what many others have experienced) a direct comparison to the FA43 prompted me to sell them all. If I had kept only one it would have been the F50/1.4, with the FA50/1.7 a close second. But they would both rank about a "6" compared to the FA43, which is an 8 or 9.

QuoteOriginally posted by Driline Quote
So you see no appreciable difference between the FA 31 and F50 1.7 in low light? In that case I'll hold off on a fast 50 and just purchase the FA 31.
I don't know exactly what Frankly2step had in mind, but he did point out the FA31 can be shot wide open, as I also do with mine. So it's not equivalent to the F50/1.7 - it's noticeably better. The F or FA50/1.7 should be stopped down to at least f/2.2 in most cases, so they aren't your solution.


I know of (and have used) 4 Pentax AF lenses that could work here (the K/A50/1.2 is also very nice if you don't need AF):

Good at f/1.6:
DA*55
FA*85

Good at f/1.8:
FA31
FA77

My experience is the FA77 can also be shot wide open (like the FA31). Nevertheless, I took a chance and sold it to get the FA*85, which was a modest but worthwhile upgrade - just enough better (for my uses at least) that I don't regret or question the move.


But I think the DA*55 best fits your requirements, as long as the focal length works.

Last edited by DSims; 01-19-2014 at 09:42 PM.
01-19-2014, 09:43 PM   #7
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QuoteOriginally posted by DSims Quote
The F or FA50/1.7 should be stopped down to at least f/2.2 in most cases, so they aren't your solution.
I had to fiddle with my F50 f1.7 with the fine focus adjustment more than any other lens, but I shoot it wide open all the time and it mine is pretty darn sharp. I don't have to stop mine down. I do have to manual focus a lot of the time (when wide open) and I also have to be very aware of the super thin DOF produced with that lens and my f1.4 lens even more so.

Like you said though, its more about having a good focal length that is useful and acceptable for the purpose intended.
01-19-2014, 10:02 PM   #8
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QuoteOriginally posted by alamo5000 Quote
In very low light your learning how to 'read the light' is vital. And as for how to shoot, you will have a lot easier time with the 31mm merely because the DOF is easier to work with.
Not to be contrary, but the FA31 is one of two lenses I'd be careful saying this about (the other being the FA*24/2). While it's true that wider lenses give greater DOF at similar apertures, the FA31 has such a smooth transition from in focus to out of focus that missing your focus point at all can just give photos an overall blurry appearance. (The FA*24 has the opposite problem - it has perhaps the most obvious transition to OOF I've ever seen, so you want to make sure you get all important elements within the focus "plane.") And the IQ of the FA31 is good enough that it's tempting to shoot between f/1.8 and f/2.2 much of the time - thus compounding the problem by making the correct focus critical on many of your shots. It's surprising how shallow the DOF can still be on a wider lens around f/2 - especially when the subject is closer to the camera.


Having said that, sometimes I've found the FA31 very good for indoor photos of family, and perhaps my best lens for indoor video as well. But for some reason I use the FA*24 a lot more often these days (and it's good at f/2.2 - which is nice for such a "wide" lens).


QuoteOriginally posted by alamo5000 Quote
I had to fiddle with my F50 f1.7 with the fine focus adjustment more than any other lens, but I shoot it wide open all the time and it mine is pretty darn sharp. I don't have to stop mine down. I do have to manual focus a lot of the time (when wide open) and I also have to be very aware of the super thin DOF produced with that lens and my f1.4 lens even more so.
Interesting - all my AF 50s are long gone, so I can't test this. Perhaps I would have had better results. But in the brief time I used the DA*55 it seemed to focus well and regularly achieve near-optimal sharpness and IQ and f/1.8, and often at f/1.6 (my FA*85 behaves very similarly to this). The only reason I don't own the DA*55 is it's hard to justify when I already have the FA43 and K50/1.2 (the truth is, I'm afraid I'll stop using them - especially the K50/1.2 - yet their good qualities are so nice I don't want to just put them aside).

I still believe the FA43 has better IQ than the AF 50s. But I have trouble believing I could ever get near-optimal IQ out of either AF 50/1.7 wide open, especially considering that both of them, plus the F50/1.4, plus my MF A50/1.7 all needed to be stopped down to at least f/2.0 (and most of them - especially the 1.7s - at least f/2.2) in order to avoid significant loss of IQ, and all behaved very similarly in this regard.

I think all four lenses I suggested are expensive for a reason - their performance is very impressive near wide open, and they produce nice images throughout the faster, lower-light stops.


Last edited by DSims; 01-19-2014 at 10:36 PM.
01-19-2014, 10:16 PM   #9
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I love my FA 31 Limited and it does a magnificent job wide open, just make sure you hit your focus. If you don't then you may believe you have a soft copy. And this is where the problem comes in. It is great in good light, wonderful at landscapes and most cameras have no trouble focusing it. But in low light it becomes a different kettle of fish. Be very, very careful you are getting your focus where you want it. Most Pentax cameras are not terrific low light performers to start with. You are way better off using a tripod and focusing manually.

I have pretty good luck on film with the PZ1p, but my digital cameras have all struggled. The only way I was able to get consistent low light keepers with my K7 was to manual focus with the Katzeye screen. I just picked up a K5iis around Xmas and haven't really tried it yet so I am not sure how that one will do with it.

My F50/1.7 is fairly reliable in low light with auto focus and I seem to get a higher percentage of keepers with it. However, it still is not terribly fast and will hunt sometimes.
01-19-2014, 10:30 PM   #10
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If I know I am shooting in low to "no" light, I grab the 43, set it to 1.9 and shoot away. Myself, I prefer it's wide open renditions better than the 31 and my M50.

Plus I accept the fact that cranking the ISO is going to eat away at any "sharpness" anyhow, so choosing a focal length becomes more important than the oft over emphasised "sharpness."
01-19-2014, 11:01 PM   #11
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I have the FA31 f1.8 and the FA50 f1.7. I use them with my K-7, which is not the ideal camera for high ISO.

The difference between f1.8 and f1.7 is very small. But the difference between a normal FA (FA50mm) and a FA Limited (FA31 Ltd) is huge in terms of IQ. In my case, and with my gears, the FA31mm f1.8 will give much better pictures in low light.

Off course the comparison between the two lenses is not that simple since the focal length difference is huge.

If you need a fast fifty with great IQ, I would recommend the DA*55mm f1.4 (that I do not have) and the Voigtlander Nokton 58mm f1.4 (that I own). With my camera, the VL58mm is on par with the FA331mm Ltd in terms of IQ (see https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/209251-fa31...mm-f1-4-a.html), minus the AF and price tag.

Hope that the comment may help.
01-19-2014, 11:43 PM   #12
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Try DA*55

I've had a few different 50's (FA 50/1.4, F50/1.7, M50/1.7), and now, for that "approximate" focal range being discussed, I have the FA 31, DA 35 Ltd, FA 43, and DA*55. These are used on a K5ii. Before that, I was using a K20D, and the low light / high ISO capability of the K5ii is amazing. The FA 31 can be good wide open, but as was mentioned, your focus accuracy had better be right on. I did have to do an in-camera AF adjust for the 31; before that one could mistake it for being a little soft wide open. The FA 43 used to be my go-to lens, but has fallen out of favor. I never felt very confident using it at 1.9, but bumping slightly to f2.0 does seem better. The problem with the 43, which I've heard from a few others, is that it can miss focus, sometimes quite noticeably. In comparison, the DA 35 Ltd is always dead-on, and sharp as hell wide open (of course at f2.8, so is the FA 31/FA43/DA*55 !)

For my money, the DA*55 rules, if you're OK with that focal length. I recently got a nice deal on a used model and the AF accuracy is perfect, hasn't missed yet, even at f1.4, and like Dave said it's already good and sharp at f1.6. Bokeh is amazing. The DA*55 blows away any other 50-ish lens I've ever used. I initially had bought it thinking it would be a "just a nice portrait lens", but once I got to playing around with it, wow! The FA 31, 35 Ltd and DA*55 are all about a three-way tie as to sharpness, but the the DA*55 takes the checkered flag in my book, being faster and having weather-sealing and quick-shift focusing as well. A little larger physically but nothing unmanageable. I'm sure that the improved low light capabilities of the K5ii help tremendously, but also, which ever lens you do choose, (or even with your current FA 43), check to see if you in-camera AF needs any adjustment as well. Good luck with your choice!
01-20-2014, 02:01 AM   #13
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In my experience my M 50 f/1.7 is better wide open in low light than my 31mm Limited.

Sorry. But after trying and trying with the 31 thing wide open in low light all I found was the thing was very trying. Whereas the f/1.7 thing gives good results.

Add to this the M f/1.7 thing was less than a twentieth of the price of the 'special' Limited thing.

Try the cheap lens first. If it doesn't do what you want flog it and try the expensive thing if you must.
01-20-2014, 11:02 AM   #14
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Why not the DA 50 1.8 instead of the M/F/FA 50 1.7? It's basically the same lens but with improved coatings, revised rounded blades, etc. And lighter plastic

I love my M 50 1.7 (and my Rikenon 50 1.4, which renders very similarly and is just as sharp from f2 on). But I'm looking forward to substituting it with the DA 50 1.8, with its improved contrast, colors, flare resistance and bokeh. I expect sharpness to be roughly the same - excellent, that is.

I can't comment at all on the FA 31...
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