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04-27-2011, 11:55 AM   #1
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Basic Lens Question form a New User

I got a K-X kit back in December with the 18x55 and 55x300 lenses. Shortly after I got a Sigma 24-70 F2.8 ex lens for better low light shots and action shots at kids volleyball and basketball games and it works great. I have a few hundred dollars in my paypal account and was looking at the Pentax Smc 50mm f1.4 lens. The reviews of this lens are almost hard to believe "best lens ever" "if I only had 1 lens this is the one 1 would pick" etc etc. I do take alot of portrait shots.

Here is my ? Everyone says that the Pentax 50mm 1.4 is soft wide open and at f2.8 nice and sharp. Isn't the main reason to get this lens the large f1.4 am I missing something, why would I get a expensive f1.4 lense and stop it down to say f2.8 so it's sharp I paid for the f1.4 to let in lots of light, my Sigma can shoot f2.8 at 50mm and the images look great. Would the Pentax f1.4 lens be WOW thats a better photo. Am i missing something. I do understand Boken and how aperture afects it.

Thanks.

04-27-2011, 12:03 PM   #2
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It's just how lenses work- some are softer than others wide-open, but they will all be sharper stopped-down.

Adam
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04-27-2011, 12:22 PM   #3
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QuoteOriginally posted by stonecreek Quote
I got a K-X kit back in December with the 18x55 and 55x300 lenses. Shortly after I got a Sigma 24-70 F2.8 ex lens for better low light shots and action shots at kids volleyball and basketball games and it works great. I have a few hundred dollars in my paypal account and was looking at the Pentax Smc 50mm f1.4 lens. The reviews of this lens are almost hard to believe "best lens ever" "if I only had 1 lens this is the one 1 would pick" etc etc. I do take alot of portrait shots.

Here is my ? Everyone says that the Pentax 50mm 1.4 is soft wide open and at f2.8 nice and sharp. Isn't the main reason to get this lens the large f1.4 am I missing something, why would I get a expensive f1.4 lense and stop it down to say f2.8 so it's sharp I paid for the f1.4 to let in lots of light, my Sigma can shoot f2.8 at 50mm and the images look great. Would the Pentax f1.4 lens be WOW thats a better photo. Am i missing something. I do understand Boken and how aperture afects it.

Thanks.
note that with any large aperture lens, and lenses that do not have aspherical elements specifically, as the lens gets larger (faster) spherical aberration begins to cause loss of sharpness. Note spherical aberration is the fact that with a spherical profile on the lens (which is easy to make) as you move further away from the center of the lens the lens focus point shifts inward. This makes the lens less sharp. stopping down excludes the light from the edges resulting in increased sharpness.

while part of the idea or use of an F1.4 lens is to have it soft wide open, this I think, is an afterthought.

I want lenses that are fast because of either low light, or because I want shallow depth of field. Shallow depth of field is not the same as being soft. Shallow depth of field means just that, but when an object is on the plane of focus I want it sharp.
04-27-2011, 12:26 PM   #4
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Would the pentax at f2.8 be noticeably better that the sigma at 50mm f2.8?. Also some people say they like soft portrait shots and thats fine but I can use photo shop to do that if needed.

04-27-2011, 12:55 PM   #5
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The main reasons you might want to consider the 50 f1.4

-if you often find yourself needing an extra stop of light when shooting with the Sigma
-if you find your shots with the Sigma are not as sharp as you'd like
-you think the Sigma is just too big sometimes.
-you have a severe case of LBA

I have the FA50 1.4 and although I love the lens, I'm about to sell it.
I wanted to consolidate my lenses as much as possible, and the DA* 16-50 seems like it's going to cover most of the shooting I want to do right now.

I might miss the FA50 at some point, but the images I'm getting from the DA* are equal to the FA50 90% of the time, and it's much easier to use indoors where the FA50 is a bit too long.
04-27-2011, 12:57 PM   #6
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A good copy of the 50 1.4 *is* sharp wide open, but in such a small sliver of space that your image is very likely to come out looking soft. The lens is also much sharper at f2.

I would not buy the lens for low light... the f-stop advantage would be better served by high-iso. Buy the lens for a nice rendering (soft backgrounds and sharp in-focus images). It's a great portrait lens.

The sigma 50mm 1.4 is the better buy if you want extreme low light performance.
04-27-2011, 01:13 PM   #7
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When you need light, there's no way around it. You will need to accept that a lens wide open is not the sharpest, but a f1,4 lens will give you 4 times more light than a f2,8 lens. Is that worth a little softness? You're the judge.

for the record, the older F and FA 50 f1,7 are sharper wide open than the F and FA 50 f1,4. If you can find one used, it can be a great solution.
04-27-2011, 02:20 PM   #8
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Usually lenses are not the sharpest when wide open. They are better when they are stopped down. The Sigma wide open at 2.8 maybe sharp in your opinion but if stopped down it will be even better. It is typically how all lens work. With that said I own a Pentax-M f1.4 and I find it sharp wide open on what I focused on. However, I would not always shoot wide open on it due to the shallow dof. A fast lens can only get you so far. Eventually you will have to bump that ISO.

04-27-2011, 03:18 PM   #9
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QuoteOriginally posted by epqwerty Quote
Eventually you will have to bump that ISO.
Exactly. Don't expect miracles at f1.4.
04-27-2011, 11:45 PM   #10
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A few of points here:

The 50/1.4 just happens to have a maximum aperture of f1.4. You might want to choose it for this reason alone, but there are other attributes to this lens: for instance, it's extremely sharp at all other apertures - just check here:

Nifty 50 Shootout on Pentax K-7 (updated 1/22) ERPhotoReview

In fact, according to these measurements, it's significantly sharper than anything else (including perhaps its main rival, the 50/1.7) from f2 to f4 (unless you're looking at the 50/4 macro lens). And, as the author says, even wide open, you can restore sharpness by boosting contrast in PP (because it's a contrast problem rather than resolution).

In addition to this, it's been shown in the past (on this forum) to have very acceptable bokeh.

In short, it's a great all-round lens, if you're happy with this focal length.

On the subject of portrait photography, it's important to have sufficient DOF, and f1.4 will usually result in too shallow a DOF: it's less than 1 inch at 3 feet distance from subject (which is about right for a head and shoulders shot), and that is way too little. You'd need to stop down to at least f4 for this type of shot. (However, for a whole-body shot, you're probably OK at f1.4.)
04-28-2011, 03:52 AM   #11
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With regard to lens reviews, a lot depends on what those are reviewing the lens are comparing it to. If people are used to shooting the FA limiteds and then pick up the FA 50, I don't know that they will actually be that impressed. The FA 43 is probably sharper at f2 than the FA 50 is. The other thing is that at one time the FA 50 was the cheapest Pentax prime lens out there (now the DA 35 is quite a bit cheaper). With that in mind, it was sort of the entry point to the world of primes for those beginning in photography.

Currently, the FA 43 is a couple hundred more and the DA *55 is about three hundred more at B and H. Both of these lenses are considerably better in my opinion, than the FA 50. Both are more usable wide open, more resistant flare, and have better builds. The issue currently is that I feel that FA 50 is over priced by about 50 dollars.
04-28-2011, 05:08 AM   #12
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QuoteOriginally posted by m42man Quote
n fact, according to these measurements, it's significantly sharper than anything else (including perhaps its main rival, the 50/1.7) from f2 to f4 (unless you're looking at the 50/4 macro lens). And, as the author says, even wide open, you can restore sharpness by boosting contrast in PP (because it's a contrast problem rather than resolution).
My expreience with the A50 f1,4, F50f1,7 and FA50 macro show that the FA macro is ludicrously sharper. the f1,7 is sharper from f1,7 to f2,8, then it and the f1,4 even out. The bokeh is a bit smoother with the f1,4, and the f1,7 has a cooler cast.
04-28-2011, 06:20 AM   #13
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QuoteOriginally posted by stonecreek Quote
I got a K-X kit back in December with the 18x55 and 55x300 lenses. Shortly after I got a Sigma 24-70 F2.8 ex lens for better low light shots and action shots at kids volleyball and basketball games and it works great.
[ ... stopping down from f1.4 discussion snipped ...]
In selecting an exposure (ISO, aperture, shutter), you weigh four problems against each other. I've listed them below in their order of significance FOR INDOOR SPORTS PHOTOGRAPHY:

1. motion blur
2. missed focus
3. noise
4. lens softness

If you already get great results at f2.8 (as you say you do), you won't get better indoor sports shots with f2.0 or f1.4. Quite the contrary, you might get more out-of-focus shots.

But if you often discard shots because of motion blur, you might get more keepers at f2.0 or f1.4. At the expense of more out-of-focus shots. That's the tradeoff.

For indoor sports, don't worry about lens sharpness.

Sincerely,
--Anders.
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