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Forum: Pentax SLR Lens Discussion
12-14-2010, 05:42 PM
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Yes, this is true. In my experience though, except in very specific conditions, noise is preferable to such shallow depth of fields.
I find, even in low light, I use my fast 50's at a minimum of f2.4. I very rarely use f2, and never go below that. Everyone is different though... I've seen some rather remarkable f1.2 shots in it's respective thread. The f1.2 shots are good because of their look, though, not because they let more light in.
In my opinion, if you need speed, you should bump the ISO instead of compromising your DOF. Wide-aperture lenses are best used for the shallow depth of field effect, not so much to maximize shutter speed (anymore).
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Forum: Pentax SLR Lens Discussion
12-14-2010, 01:37 PM
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This philosophy is not always true, though.
For example, the FA 50 1.4 is less sharp than the DA 40 2.8 at f 2.8. Obviously, with the DA 40 you are limited to f2.8, but if you really only shoot the FA 50 at 2.8, you should not expect improved image quality at that aperture.
Pentax is doing an odd thing - they are designing lenses for ASP-C digital, which makes it hard to compare their lenses to offerings from their brethren who offer more traditional lens choices. I will not argue that one is better than the other, but rather that the concept of speed is beginning to lose ground to the concept of quality in the Pentax realm.
I think there is no other explanation for the FA limited line, which are really not all that fast, but are quite exceptional when it comes to quality. The DA limited line are an even more extreme example of this, since they are very, very good wide open, but wide open is not extremely fast.
Instead of providing larger, heavier primes which need to be stopped down to f2 or 2.8 to reach really optimal levels, Pentax seems to prefer offering a lens that is quite good from wide open, in a lighter, more compact package.
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Forum: Pentax SLR Lens Discussion
12-11-2010, 03:15 PM
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No, we won't. Thats why it's best to think of "fast" lenses as special effect lenses... unlike the past, where they were considered necessary for fast-enough shutter speeds in a wide range of conditions.
That said, f2 is very functional, and most f1.4 lenses look amazing at f2.
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Forum: Pentax SLR Lens Discussion
12-11-2010, 02:24 PM
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I believe the A/K 50 1.2 is the ultimate for the fast look in pentax land, but the 1.4 is very usable for that soft/fast look (it's not good for shooting test charts), and the old 1.7's are little wonders at f2: for their price, they are absolute steals. It's unfortunate it's so hard to focus with the stock screen with the superfast manual glass.
I've read that a lens that fast (below f1.7) causes issues with the autofocus system. I haven't noticed it too much with my FA 50 1.4, but it sure hunts more than my DA 40 2.8, so maybe that's the issue (and a possible cause for all of the self-destructing FA 50 1.4s :(). It's a shame. I don't think I would have much patients for a 600 dollar lens that is so challenging to manually focus (not that I can afford one anyways).
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Forum: Pentax SLR Lens Discussion
12-11-2010, 08:39 AM
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I think the original term "fast" has become only necessary for creative photography (f1.4 or f1.2). There is no other way to get that look, however. Before it was impossible to get a usable imagine in low light without one of these fast lenses.
Now, fast means between f2 and f2.8, which is a good compromise in my books. I find things such as autofocus tend to work better when the depth of field is a little larger, and the ISO advantage of a modern camera goes well over 2 stops.
However, if a lens moves past f2.8, you will being to run into situations you simply can't photograph ideally. The DOF will be too large for good subject separation, autofocus might have trouble with too little light, and you might have troubles with exposure in low light. Since most lenses must be stopped down a little bit to get the best out of them, I would settle on f2.0 being the new optimal fast aperture, which gives you f2 when you need it, or f2.8 for optimal quality.
This is all, of course, assuming you want that "fast look". Many excellent photographs (before, and now) have been taken at f8, where even lesser lenses will excel nicely.
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