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11-14-2009, 08:59 PM   #1
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Why a Pentax FA50mm f/1.4 ?

I am a noob to DSLR, waiting for my online bought camera to come in to my custody...surely nest week. I am also waiting for my Sigma 17-70 lens to arrive. My questions are, after browsing around:

.1 Why do so many poeple say the everybody should have a 50mm lens?

.2 Is thePentax Fa 50 f/1.4 a good lens, and to what use? (and is it a "limited" or "prime"?)

.3 What would the 50mm 1.4 give me that the Sigma 17-70 won't?


Thanks!

11-14-2009, 09:16 PM   #2
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1. Because in film days or in Full Frame senor, 50mm focal length "generates images that generally look "natural" to a human observer under normal viewing conditions"

2. FA 50mm f1.4 is a good Prime(single focal length) lens, the max aparture of f1.4 allow you to let more light pass through the lens to the sensor, which able you to take shots easier in low light situation. Max Aperture of 1.4 also give you a long range of aperture setting where you can control how narrow or far the depth of view will be; which able you to take more creative shots.

3. 50mm f1.4 is a small lens, so it is lighter to carry around with your camera. And as i said before it has max aperture of f1.4, so you have more control of the depth of view, and able you to use lower ISO/faster shutter speed in low light situation.
11-14-2009, 09:27 PM   #3
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Where else will you find an f/1.4 lens for so cheap?
Why is that so important?
Have a look at what the 50mm lens has captured - it is probably third in line for being the quintessential portrait lens, for a fraction of the price of the first two lenses.
11-14-2009, 10:07 PM   #4
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And just to clear things up, you were asking if it was a limited or a prime. Primes are photo speak for fixed focal length (thought I think at one time they were only certain focal lengths, like 50mm). Limited is a designation of pentax lenses; DA Limiteds are Prime lenses designed for the digital format (which were designed for digital sensors) and FA limiteds are lenses that work both on film and digital cameras. The limiteds (imho) are what sets pentax glass apart from anything else there, and a damn good reason by themselves to be shooting with Pentax gear.

11-14-2009, 10:44 PM   #5
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So the pentax F50 f/1.4 is a prime lens but not a limited.

The Sigma 17-70mm f/2.8-4.5 is a zoom lens.

If I take a picture at 50mm with a zoom lens (lets say a Sigma 17-70), the difference with a picture taken with a Pentax 50 1.4 would be the what?

(I unsderstand that the 50mm lens is better in low light and has a broader apperture sttings range, but does that transcend to IQ?)

Actually, I whant opinions about owning the Sigma 17-70 AND the Pentaf 50mm 1.4...will one remain in the bag because the otherone does it all?

Thanks to everyone for your helpfull input!
11-14-2009, 10:55 PM   #6
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The difference is significant at apertures f/2.8-5.6, thereafter it would be minimal.
Bear in mind, you will want to be shooting a lot at f/2.8-5.6 for portraiture...
Also, don't downplay the usefulness of having f/1.4-f/2.8 - a lot of extra light (speed) can be gathered without having to bump up ISO.
11-14-2009, 10:59 PM   #7
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Zooms vs. Primes

QuoteOriginally posted by mba1971 Quote
So the pentax F50 f/1.4 is a prime lens but not a limited.

The Sigma 17-70mm f/2.8-4.5 is a zoom lens.

If I take a picture at 50mm with a zoom lens (lets say a Sigma 17-70), the difference with a picture taken with a Pentax 50 1.4 would be the what?

(I unsderstand that the 50mm lens is better in low light and has a broader apperture sttings range, but does that transcend to IQ?)

Actually, I whant opinions about owning the Sigma 17-70 AND the Pentaf 50mm 1.4...will one remain in the bag because the otherone does it all?

Thanks to everyone for your helpfull input!
All camera lenses are compromises. Zoom lenses doubly so. In general, it is harder to make a really good quality zoom lens than it is to make a really good prime lens. Prime lenses are simpler. Therefore, in general, prime lenses usually have better image quality than a zoom lens at the same focal length. Back in the sixties, when zoom lenses for still cameras first came to market, it was no contest. Zoom lenses generally were lousy. Today, most zoom lenses have pretty good IQ. Some are excellent. The gap between primes and zooms has narrowed, but a high-quality prime will still usually beat most zooms.

Is it possible to make a zoom lens with better IQ than a prime? Absolutely, but in the case of a really good prime lens, such as most Pentax (or Nikon or Canon, for that matter) lenses, this is usually not the case.

Another difference in your scenario would be the aperture. Few, if any, zoom lenses have a maximum aperture of f/1.4. I'm not sure about the Sigma you mentioned, but most have a maximum or f/3.5 or f/4. A few are f/2.8, but that is still two full stops slower than f/1.4. This would have a noticeable effect on depth of field.

Lenses are surprisingly complicated and zoom lenses are even more so. Zooms are often sharper at some focal lengths than at others. IOW, it might be sharper at the wide angle end of its range than at it telephoto range. The same thing is true of aperture. Any lens will vary in sharpness as its aperture is changed. Most get a little bit softer at their maximum aperture. At their smallest aperture, diffraction may begin to affect the IQ. Most lenses have a sweet spot, usually in the middle aperture range (say f/8 or so) at which they are their sharpest.

As with anything, there are always exceptions. I've heard that some Leica lenses are sharpest wide open. This sort of thing is one of the many compromises that lens designers must make.
11-14-2009, 11:05 PM   #8
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For me, sharpness matters

QuoteOriginally posted by mba1971 Quote
So the pentax F50 f/1.4 is a prime lens but not a limited.

The Sigma 17-70mm f/2.8-4.5 is a zoom lens.

If I take a picture at 50mm with a zoom lens (lets say a Sigma 17-70), the difference with a picture taken with a Pentax 50 1.4 would be the what?

(I unsderstand that the 50mm lens is better in low light and has a broader apperture sttings range, but does that transcend to IQ?)

Actually, I whant opinions about owning the Sigma 17-70 AND the Pentaf 50mm 1.4...will one remain in the bag because the otherone does it all?

Thanks to everyone for your helpfull input!
Well, for me the difference is image "sharpness." I recently sold the Tamron 28-75 f/2.8 although it is very highly regarded on this forum and others because comparable prime lenses (the Pentax 35 and 50s) are sharper at those apertures than any zoom can be.

Keep in mind "sharpness" is all a bit abstract because it's made up of both resolution (the detail of the stuff in the image) and the acutance (the perceived contrast between the detail in the stuff). Or something like that. Notice the word "perceived," because sometimes it gets pretty subjective.

In any case, I set sharpness as the highest image quality; others set the color or tone; others care a great deal about the wide aperture out-of-focus blur. It depends on what you like and how you like it,
Brian

11-15-2009, 05:55 AM   #9
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QuoteOriginally posted by mba1971 Quote
So the pentax F50 f/1.4 is a prime lens but not a limited.

The Sigma 17-70mm f/2.8-4.5 is a zoom lens.

If I take a picture at 50mm with a zoom lens (lets say a Sigma 17-70), the difference with a picture taken with a Pentax 50 1.4 would be the what?

(I unsderstand that the 50mm lens is better in low light and has a broader apperture sttings range, but does that transcend to IQ?)

Actually, I whant opinions about owning the Sigma 17-70 AND the Pentaf 50mm 1.4...will one remain in the bag because the otherone does it all?

Thanks to everyone for your helpfull input!

What he said! (I mean virtually everyone above).
However, I am a fan of the Sigma 17-70. When I first bought my K10D, I started using an old Vivitar Series 1 28-105 from my Super Program days. I loved that lens (still do), but wanted autofocus and to adjust the focal lengths to the 1.5 crop of the APS C size. As I checked around I found the Sigma 17-70 which is roughly the equivalent focal lengths to my old Viv. I also picked up a 1.4X TC to aviod buying lots of lenses right away, but to give me added reach when needed for a three week vacation trip to Greece and Italy. Thousands of shots later, I still found no need for a 50mm. I've since added a 21Ltd prime, a DA*50-135, and a Sigma 135-400, which completes my main "kit".
Out of curiosity, I pulled out an old 50mm F2 M lens that I've had forever. I found working with the green buttom not to my liking, so it got put away. I've since picked up an "A" 50mm 1.7 and just recently did some shooting with it (Its still on my camera, BTW). I never owned one of these with my Super Program even though it was the "perfect" mate fot it. It does live up to the 50mm reputation for sharpness and light grabbing ability, but I find the 50mm focal length too limiting on the APS C format. It is the equivalent of a 75mm lens on 35mm format which does put it in the "perfect" range for formal head and sholder portraits. I just don't take many (or really any) formal portraits like that. This lens does have a home in my main "kit" bag, but its tucked away in the bottom.
I prefer landscape, general tourist type, environmental, and detail photography. The 17-70 gives a great range for me. The Sigma is quite sharp with very little abberation and virtually no color fringing. It includes the range I need for the type of portraits I generally take which includes the local environment. It also close focuses so I can take those really close, face only shots and the detail pictures I generally take for work.
My suggestion would be to live with your Sigma for a while and see how it serves you. Unless you really need the light gathering ability of the 1.4 (or 1.7, 1.2) or the ability to make the depth of field really narrow, you probably won't need the 50mm. If you feel the need for the "normal" perspective that the 50mm gave to film cameras, then you need to pick up something in the 30mm range. The 31mm Ltd comes to mind for the best qualities of Pentax glass or Sigma makes a 30mm F1.4 that is supposed to be very good as well.
Enjoy what you've got on its way to you first, then grow from there.
Regards,
Brian

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Last edited by calicojack; 11-15-2009 at 10:17 AM.
11-15-2009, 08:21 AM   #10
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What I would say is that if you want to try a 50mm then look for a Pentax-A 50mm f1.7, or the older M version. The A will work exactly like current lenses but with manual focus, the M is manual focus but also requires you to set the aperture manually on the lens. Both will cost a lot less than an F or FA (auto focus) 50mm, so you can try the focal length and see how useful it is to you before spending big money on an auto focus version. Prices are steady, so in the event of deciding to buy a later lens you'd be able to recoup your investment in the manual focus one.
11-15-2009, 08:28 AM   #11
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As a new DSLR photographer, the 17-70 you are getting with your kit will do a fine job. Most of us who are a little older learned photography and how to use our film SLR's with 50mm lenses as that was the kit lens of the day. Most of the good points about these lenses are already mentioned. For someone new however, don't go out and buy one just because someone else thinks you should, or you read a magazine article that mentioned that every photographer should have one of these in his/her bag. I don't use mine often as my 18-55 is my walkaround lens and to be quite honest, if I didn't already own one I probably wouldn't buy one. Pentax has an excellent lineup of primes from 14mm on up to 300mm. I would suggest using that zoom for a while and then purchasing the lenses you know you will use.
11-15-2009, 09:41 AM   #12
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No one's mentioned that the 50 1.4 is just sweet, too, for image quality, this will beat about any zoom out there. And it's small.

The field of view, (and thus the distance you will be at to have a given framing) will be the same as 50mm on your zoom:

(This is a little tight on a cropped sensor for most people's general photography, but it's suited to a lot of portraiture and, it happens to be right in my very favorite range of focal lengths, (in full-frame 35mm film, which is sort of the standard, a 75mm would give you the same field of view as a 50mm does on your camera: this is what it means when we say 'crop factor.') My favorite lenses in various formats equate to between 67 and 85mm ones, so it was the first thing I picked up when I got my Pentax digital. No-brainer there for me, but you may wish to choose another focal length if you decide to buy a prime lens.)

You can use the zoom lens you have to 'shop' for focal lengths, simply by watching where that zoom ring ends up for most of your photos, or the ones you like best, or by whatever other criteria you like.

Many people will like something more like a 35mm, a 30mm or even wider.

...obviously a 50mm, it'll be a lot lighter and smaller, especially for the speed. Because it was once the 'standard' lens for film cameras, just about every manufacturer knows how to make them well, (Pentax was always famous in particular for em.) and they're plentiful. Hence the popularity.

You don't really need to hurry: I believe that lens you have is considered pretty nice. But you're with Pentax people. Prime lenses are the thing for very many of us.
11-15-2009, 09:51 AM   #13
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To add to and clarify some of the good information provided already:

- 50mm used to be a popular focal length on film for reasons already stated. It's less usefull in general for digital because the filed of view is a lot narrower, but it's not bad for portraits.

- 50mm lenses are still the cheapest way to get a lens with a large maximum aperture (eg, f/1.4 instead of f/4), so they are still very popular.

- The 17-70 will be limited to f/4 or so when set to 50mm. In situations where there is enough light to get a good picture at f/4, there might be *some* difference in image quaity, but it probably wouldn't be enough to jutsify getting and using the 50. The main advantage of the 50 is that it offers larger apertures, giving you faster shutter speeds in low light.
11-16-2009, 07:49 PM   #14
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So, If I'm plannign a vacation this winter, and plan to take evening and night pictures, would you recommend keeping the 17-70 lens or putting on a 50mm 1.4, or something else for that matter, that would be a better performer?
11-16-2009, 09:22 PM   #15
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I'd say you want both lenses - the 17-70 for most shots, but something with a larger maximum aperture ("faster") for use in low light.
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