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09-15-2013, 03:00 PM   #1
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Fast 50 questions (F50 f1.7)

I have two parts to this thread....

First I have a F50 f1.7 that I really like. This lens is very sharp even wide open. If you nail that focus and it shines! That said I am having to play with the lens quite a bit. I am using the fine adjustment tool on my K-5 to try and get it right into line where it needs to be. That said I am having a tough time dialing the thing in. It seems like under different lighting conditions the lens needs to be offset different amounts. As of right now it sits on -3 and that seems to be the spot I keep going back to. I tried to adjust it under bright broad daylight , then I tried some sample shots and those were off. Then I just played with it more and have been doing so for a while.

Under very low light I don't know if it's the lens or merely the K-5 that is having a time auto focusing. All that said this little gem has a LOT to offer.

Does anyone else have 'experience' with this particular lens that may help me dial it in better? When everything fires right this lens is super sharp in my opinion...

Second part of this thread is to ask why there isn't a side by side comparison of all available Pentax fast 50's on pentax forum? (including the out of production ones)...

Just a few... F50 f1.7, FA50 f1.7, FA 50 f1.4, and on and on... if the current FA 50 f1.4 is just as good as the F50 at similar apertures then I wouldn't hesitate to buy one....The reviews on PF though do not play this out. When I buy lenses I go for the stuff that is tried and true... and the lens database is great. That said it also helps steer me away from getting factory new lenses sometimes because you get better lenses with old lenses sometimes.


If you are going by reviews of actual users the FA50 f1.7 is the best. (Why Pentax doesn't get a clue and produce that one again with all the modern coatings and stuff is beyond me). But anyway I would like to see a full on shootout between all available auto focus fast 50 (sub f2) options... side by side... and have the pros declare a winner in controlled testing....

That way if I decide to get another lens or two or five I can know where to go and what's out there...

09-15-2013, 03:06 PM   #2
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Ive owned the FA 50/1.4 and now have a F50/1.7.

The FA50/1.4 is very soft at 1.4. I like the F50/1.7 more wide open.
09-15-2013, 03:14 PM   #3
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I don't know... maybe I am expecting too much out of the AF of the K5 and the lens... if I stop down at all I don't have a problem... and if I manual focus in live mode then I can nail the shots with a sharp lens... the F50 is fabulous. I am just trying to get that AF tuned in perfectly....
09-15-2013, 03:23 PM   #4
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Its hard to nail down the focus accuately with so shallow depth.

It also depends on if focusing close or far away.

What I do is I fine tune the AF with the distance I usually use for it. I use it for portrait so I'll tune it 3-4 meters from the subject (focus calibration paper).

09-15-2013, 03:31 PM   #5
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QuoteOriginally posted by striker_ Quote
Its hard to nail down the focus accuately with so shallow depth.

It also depends on if focusing close or far away.

What I do is I fine tune the AF with the distance I usually use for it. I use it for portrait so I'll tune it 3-4 meters from the subject (focus calibration paper).
That is one thing I am noticing/learning.... when it's wide open at X distance it can be right on... at Y distance it won't be right on...like I said, maybe I am asking too much for my AF to be able to be 'too perfect'....I am clearly a fan of the lens... but I 'might' just manual focus any wide open shots to save the hassles...

Like I said... stop down even a little and no more problem.
09-15-2013, 03:34 PM   #6
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QuoteOriginally posted by alamo5000 Quote
Second part of this thread is to ask why there isn't a side by side comparison of all available Pentax fast 50's on pentax forum? (including the out of production ones).
There are way too many for a proper test
(at various apertures and various distances).
09-15-2013, 03:36 PM   #7
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Yep. Live view is pretty accurate too.
09-15-2013, 03:40 PM   #8
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QuoteOriginally posted by lytrytyr Quote
There are way too many for a proper test
(at various apertures and various distances).
and various copies too.

09-15-2013, 04:53 PM   #9
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@the OP
  1. The 1.4/50 is softer at F1.4 than the the 1.7/50 is at F1.7. If you stop down the 1.4/50 to F1.7, the difference gets much smaller.
  2. Some of the "softness" maybe caused just by the smaller DOF.
  3. The bigger diameter of the front lens of a 1.4 automatically leads to increased flare. This can be successfully stopped by using a narrower lens hood (adapted to the smaller AoV used with a cropped sensor). Some time ago there was a long thread about this subject, where several members confirmed the use of a step down ring 49mm->46mm would solve most of the softness problems at F1.4 without vignetting. - EDIT: AND inprove contrast visibly!
  4. Shortly after the introduction of the K-5, there were several threads about the inconsistancy of AF with some types of artifical light. Our member Falk Lumo had published some scientific tests he made in his optical laboratory, and linked to them in this forum. The problems seem to be solved with the improved design of sensor lenses/filters of the K-5II.

Last edited by RKKS08; 09-15-2013 at 05:46 PM.
09-15-2013, 06:25 PM   #10
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I've had a F50/1.7 for a while but haven't used it much. Gave it a bit of a workout just yesterday and now wondering why I haven't used it more. Will definitely use it some more. Did have some focus challenges in very low light in a poorly lit and low contrast ship's engine room (and probably at the limit of my K-x's capabilities - it was very dull with just an open door letting in light). Outside in decent light, all seemed fine although I was using F3.2 and smaller out there.
09-16-2013, 05:23 AM   #11
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QuoteOriginally posted by alamo5000 Quote
Second part of this thread is to ask why there isn't a side by side comparison of all available Pentax fast 50's on pentax forum? (including the out of production ones)...
Adam wants to limit reviews to in-production lenses. This I know for a fact, as for the reasons I can only speculate. First, it would be an enormous job to test every lens in history, and if he decided to cover only a few, there would be people whining all over the place requesting this or that lens to be tested. Second, he does offer the site for free and has to turn a profit, linking to B&H and Adorama helps him with that, but it wouldn't help if the tests showed that the F50 f1,7 used was a better purchase than a newer lens.

QuoteOriginally posted by alamo5000 Quote
Does anyone else have 'experience' with this particular lens that may help me dial it in better? When everything fires right this lens is super sharp in my opinion...
I think different lighting conditions mainly mean different light LEVELS. So harder to focus under some conditions AND levels. Plus as light levels drop, your camera is likely to try and use a wider aperture, thus a shallower DOF.
09-16-2013, 10:33 AM   #12
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This has been mentioned, but bears repeating and emphasis:

Autofocus doesn't work well in low light. Low light includes any indoor situation that doesn't have lighting set up specifically for photography.

Autofocus at very wide apertures (wider than f/2.8) will often miss your intended target, because DOF is so shallow.


Don't try to find a setting where your lens will be spot on every time. There is no such setting. If you're getting some keepers, then your lens is fine.

Take lots of shots and delete the ones that miss. This is the only way to use AF under adverse conditions.
09-16-2013, 01:33 PM   #13
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@thornburg

+1
09-16-2013, 06:45 PM   #14
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QuoteOriginally posted by bdery Quote
Adam wants to limit reviews to in-production lenses. This I know for a fact, as for the reasons I can only speculate.
There was the FA 20 review:

Pentax-FA 20mm F2.8 Review - Review - PentaxForums.com

"Review originally published on August 26th, 2011"
09-19-2013, 05:01 AM   #15
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I'll post a photo I took with the F50/1.7 last weekend using my K-x. No sharpness/focus problems here! And no problem tracking the moving subject.



(1980 px image - output sharpened)
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