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Old Nov 27, 2010, 10:34 PM   #1
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Default why prime?

The difference I see between the prime lenses and the zoom lenses is a little self explanatory. Obviously the prime doesn't zoom, so my question is is if you have a 18 - 55mm lens and then a 50 - 300mm lens than what benefit would a prime have? And if there is a substantial benefit, what prime lens would be best for me and my Pentax K-x for an all around use between portrait and in the city and maybe some other applications?
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Old Nov 28, 2010, 4:25 AM   #2
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Prime lenses tend to be better, optically, than zoom lenses, and they usually have larger apertures and/or can focus closer than zoom lenses.

Zoom lenses are usually fine for most purposes. If you don't know why you might need a prime, then you probably don't need one.
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Old Nov 28, 2010, 4:27 AM   #3
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for the pentax the FA 50 1.4 will give you a very good prime lens, big aperture, so it will make the k-x a better low light camera, and you really can get creative with shallow dof shooting at 1.4-2.8 giving you very nice bokeh indoors where you do not have as much working space for good separation of subject and background.
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Old Nov 28, 2010, 10:23 AM   #4
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Quote:
Originally Posted by shoturtle View Post
for the pentax the FA 50 1.4 will give you a very good prime lens, big aperture, so it will make the k-x a better low light camera, and you really can get creative with shallow dof shooting at 1.4-2.8 giving you very nice bokeh indoors where you do not have as much working space for good separation of subject and background.
Large apertures do not necessarily mean you will get good bokeh. There is much more to bokeh than just the out of focus background (which is easier to do with a large aperture lens). Also lenses with smaller max apertures can have good bokeh, sometimes better than some larger aperture lenses. And of course bokeh is purely subjective anyway.

The main advantages to primes are:
1. Better in low light without flash...if you use flash regularly than this is a moot point.
2. They are usually optically better and have less complex distortion
3. They are smaller and lighter in weight
4. It is easier to achieve the out of focus background with larger apertures.


Disadvantages to primes
1. less flexible, you have to zoom or widen with your feet which isn't always possible.
2. you have to carry more lenses to cover large focal ranges
3. more lens changes

For me primes are pretty specialized..so if you find you spend a lot of time at one or two focal lengths and need the benefits...especially existing light shooting (no flash) then primes are likely a good fit. Some say it's nice to have one or two primes in the bag just in case. For me, my primes just stayed in the bag. Your mileage may vary.
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Old Nov 28, 2010, 11:09 AM   #5
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But the FA 50 1.4 does produce nice bokeh. It is a very nice lens for the pentax. The OP ask for the pentax, and the FA 50 1.4 works really well.
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Old Nov 28, 2010, 12:36 PM   #6
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Personally i love my pentax 50mm 1.4 the best out of all my lens's. I thought that when i first bought it, i might not like it due to the fact that you cant zoom, but i didnt miss it at all. I love it for low light shots. I never use flash.
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Old Nov 28, 2010, 1:34 PM   #7
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Pentax also bring with it access to a very large population of older lenses, both in the M42 mount, as well as the more recent K mount. Although the older lenses have gone up in price, you can still easily find an "SMC" (or K model), "A" model or "M" model, along with the "F" model 50/f1.4 and A 50/f1.7 for very reasonable prices. Depending on the model and speed the prices start at around $50 and go up. There are even f1.2 lenses available, however the prices on these lenses are very expensive.

The M42 (or screw mounted) lenses also offer excellent images and bokeh, although they need a M42 to K adapter (about $30) to work. I would suggest taking a closer look at some the lenses that Canon photographers have mounted on their camera bodies, and you will find a number using the older Pentax M42 Takumaras or SMC Takuamars (Super Taks).

One reason why these older lenses are so prized is the wonderful construction/build, excellent glass and exceptional bokeh.
These lenses are manual focus and depending on the lens manual aperture (although the body will indicate in the viewfinder when focus is achieved), they may not be for everyone.


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Old Nov 29, 2010, 12:50 PM   #8
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So what length would be closest to how the human eye sees for the K-x?
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Old Nov 29, 2010, 12:52 PM   #9
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it would be a 35mm with the 1.5 crop factor, as 50mm is the closest to the human eye
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Old Nov 29, 2010, 1:17 PM   #10
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closest to human eye.. relative to distortion, or field of view?
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