Prime vs. Zoom lenses

Discussion in 'Photographic Discussions' started by mallard, Aug 1, 2008.

  1. mallard

    mallard TPF Noob!

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    now that I am thinking about getting a DSLR, the subject of which lenses to get comes into play.

    im planning on a Pentax K20d. I have a few pentax bodies (Me Super, K1000, MX) and some lenses and would like to be able to use them but also, I will probably get a couple lenses for the native digital format (in this case, the CCD is smaller than a 35mm film frame).

    When I was doing photography for fun 10 years ago, I had: 28mm/2.8, 50mm/1.4, 100mm/2.8 and a 200mm/2.5 and I carried them all around with me to use as situation demanded. The quality was just fine with them. I never really tried zoom lenses. In this day and age, are the zooms for digital SLRs of sufficient quality that I can just get by with a couple of them? I notice they still make a lot of primes (and some are application specific like a portrait lens).

    Also, does anyone have a link or a chart showing me the values of focal length between digital and 35mm formats? if say a lens is 18mm digital, would that be like a 28mm on film?
     
  2. nynfortoo

    nynfortoo TPF Noob!

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    Zoom lenses can rival the image quality of primes, but it really depends which lenses you're comparing; some are obviously of better quality than others.

    You can easily get by with just a few zoom lenses, but the downfall here is that fast zooms are more expensive and much bulkier than their slower zoom counterparts.

    Primes will beat zooms in term of physical size and price, generally. But obviously you don't have the versatility in focal length. It's a decision you have to weigh up.

    Someone will no doubt give more specific, more-accurate information on this.

    It depends on the size of the sensor compared to a 35mm one. I think Pentax DSLRs have a crop factor of 1.5 (correct me if I'm wrong, but the maths is the same), so you just multiply the focal length by the crop factor to get the effective focal length for that lens on that sensor.

    18mm * 1.5 = 27mm in 35mm terms.

    You lose out on the wide end, but gain on the telephoto end with cropped sensors.
     
  3. NateS

    NateS TPF Noob!

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    I agree with above. Zooms can rival Prime quality but there's two factors...... Price vs. Convenience. You could pick up two primes to cover a range of an equal quality zoom for probably half the price. But, you have to switch lenses more often. Also the primes come in really handy in lower light situations with their larger max aperture.
     
  4. prodigy2k7

    prodigy2k7 No longer a newbie, moving up!

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    Some cameras have full size sensors (full frame; more expensive) or some have smaller sensors (like Canon Rebels with 1.6x crop)
    http://en.wikipedia.org/wiki/Crop_factor

    BTW, with a cropped body, you dont actual get the higher focal length. It is just the same FoV (Field of view) as the 1.6 times focal length of the lens.
     
  5. usayit

    usayit No longer a newbie, moving up!

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    I don't agree that it is a matter of Price versus Convenience. There are many examples of prime lenses that are far more expensive than zooms. Buying a set of primes to cover some of the wide range of focal lengths covered by a single zoom can be much much more expensive.

    IMO, it is matter of Image quality/performance versus Convenience. I don't think that zooms can rival the performance of a prime in the same price range. Zooms are a compromise in image quality for convenience and Primes are not. It is as simple as that.

    If image quality is going to enable you to create the photo you want, then shoot primes.
    If convenience and flexibility is going to enable you to create the photo yo seek (sports for example), then shoot with zooms.


    Also remember... focal length is not just to bring things closer or to fit more in a frame. It is a change in perspective and composition much like a choice of a paint brush to a painter. Its more difficult to realize this with a zoom.. the tendancy is to twist not walk.
     
    Last edited: Aug 1, 2008
  6. Overread

    Overread has a hat around here somewhere Staff Member Supporting Member

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    I think these are the key factors: Price, convenience, versatility and quality.
    (all for a given price range)
    For a given price range a zoom will be beaten by a prime at a single (the primes) focal length - that is clear. If you were to use only that focal length most of the time then a prime would be your best bet
    For a given price range though a zoom can give you a wider array of focal lengths than the same cost in primes - and in cases where you would need many primes - the zoom would also have a good chance at beating quality of the primes as well (remember you are getting the range of primes for the same cost as a single zoom)
    Convenience is another factor - if you are only getting a range of lenses for small time use - say holiday snaps and such. You might be tempted towards a zoom over a prime for the range offered and the convenience of only having one lens and not having to change for each shot - this also makes a zoom more Versatile than a prime as its able to adapt for more ranges quicker and easier than a prime (you can walk, but sometimes you just don't have the option or the time inorder to get the shot).

    I would love all primes, but then again I can see many times when a prime would be a pain to have - a need to switch rapidly beating me there.
     
  7. Bifurcator

    Bifurcator TPF Noob!

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    I agree with this.

    With exceptions of course primes always produce better image quality than zooms! And side by side it's quite noticeable too. On the other hand the image quality difference from different sensor size and density may be just as or more dramatic than prime vrs. zoom and... if you're not looking at a side by side comparison or haven't trained yourself to know the difference you probably won't notice the differences between a average to good zoom and an average to good prime respectively.
     
  8. astrostu

    astrostu Guest

    I agree with the above. I would add that I view primes more for "specialty" applications vs. zooms more as a "walking-around / travel" application.

    For example, if I had all the lenses that are currently on my wish list, I would probably still only bring a 24-70 mm f/2.8L and 70-200 mm f/2.8L on a field trip to Yellowstone that I'm going on in the Fall. Even though I'd also have 14 mm, 35 mm, 50 mm, 105 mm, and 300 mm primes. This is because I would want to travel relatively light but still have a large range of focal lengths.

    On the other hand, if I were going to a friend's birthday party, I would probably bring a 14 mm and 35 mm or 50 mm. The reason being that I would need the larger apertures and it would be a situation where I'd need shorter focal lengths.

    Or if I were going birding, I may bring a 300 mm prime along with a 70-200 mm IS.

    I think it really depends on the photography you're going to do and the situations you find yourself in, and if you're only going to get a very few lenses, then zoom's the way to go because it offers a better range of applications.
     
  9. ksmattfish

    ksmattfish Now 100% DC - not as cool as I once was, but still

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    Primes are often smaller, lighter, faster, sharper, and cheaper.

    Zooms cover an entire range of focal lengths. May be more convenient than changing lenses, although larger size may make it less convenient.

    Focal length is magnification. Focal length combined with format size creates angle of view. Perspective is controlled by where the camera lens is in relation to the subject and sensor/film. Unless you are using a tilt/shift lens or a view camera the lens is always going to be in the same position compared to the sensor/film, so all you have to worry about is where the lens is in relation to the subject.

    The shooting situation and preferences of the photographer will dictate which is more important: magnification, angle of view, or perspective. If I were photographing tigers or killer bees magnification might be a priority. If I were stuck in a small area angle of view could be pretty important. Of course every shot is a combination of all of these aspects, but most of the time I'm mainly concerned with perspective, which is controlled by where I've got the camera placed. Perspective would be the same whether I was using APS or 4x5, and whether either had a 50mm or a 150mm lens on it. The 150mm would be more magnified than 50mm, and 4x5 would have a wider angle of view than APS, but perspective stays the same.

    To me the necessity of variable focal length depends on how efficiently I need to crop the photo in-camera. With 4x5 or medium format it's no big deal cropping to the angle of view I want post exposure. With APS and 35mm cropping in-camera makes better use of the small format. So I control perspective with my feet, and use the zoom lens to adjust the angle of view/in-camera crop.

    Sharper is always nicer, and many lens tests show 2 figure primes to be better at resolving fine details than 4 figure zooms, but today's zooms are pretty sharp. They aren't the zooms of 20 years ago. 9 times out of 10 if there are softness issues it's going to be my fault and not the lens. I do love the small size and big apertures of primes, and although there are some very expensive primes, most are quite affordable. $80 primes rock! $80 zooms I'm more leery of.

    Whatever you choose it's a compromise. If you can't efficiently crop in-camera and get the perspective you need, then you'll have to crop after the exposure, and the additional enlargement ratio may eliminate any prime lens advantage in sharpness or resolution. The best lens would be a razor sharp, no distortion, no CA, 10mm to 1000mm zoom, f/1, that's small and light. Anything less is a compromise. ;)
     
  10. deudeu

    deudeu TPF Noob!

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    Personnally I would like f0.9 better!

    But to get back to the OP's question, you should also consider the fact that the new sensor ofthe K20D outresolves some of the cheaper zooms. Of course, this is only relevant for very large prints, but it is something I would consider when purchasing a lens on this system. I mean, why would you spend over $1000 on a camera to have the quality of your images altered because of the $70 piece of glass that is mounted on it.

    Now, the camera that will outresolve your prime line up is not going to be in the shop before a WHILE!
     

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