Why do telephotos produce a sharper image when used for extreme close ups?

Discussion in 'Beyond the Basics' started by subtleRIPPLE, Mar 31, 2007.

  1. subtleRIPPLE

    subtleRIPPLE TPF Noob!

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    Hello all,

    So, I keep reading that faster lenses are more crispy??? (make sharper pictures) Why?

    And why do people taking images of flowers and bugs and birds use telephotos, what are they able to do with their fstops and zooms that they cannot do with a normal or wide mm lense?

    What seems might be the reason, is that they can open a really nice telephoto lense up to say f2 and be able to zoom way in, making the subject large in their composition, with the ability to fill the frame with their subjects...but why does this also allow for a sharper image?

    Thanks for your thoughts.

    Angeline
     
  2. Ken_D

    Ken_D TPF Noob!

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    1. The faster the lens, the wider the aperture. (f/1.4 is wider than f/3.5) The wider the aperture, the more light, the more light, the sharper the image. As a rule. the faster the lens the more it costs.

    2. They are not just telephoto, they are macro lenses, they are able to focus much closer than regular lenses. Most macro shots (close-ups) are not shot wide open, they are more likely f/8-f/11 or more for greater depth of field. If they tried to shoot wide open, the DOF would be so shallow 98% or more of the photo would be out of focus. It's like shooting with a built in magnifying glass. The longer the lens, the greater the magnification. Hope this helps.
     
  3. fmw

    fmw No longer a newbie, moving up!

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    Faster lenses are not sharper. I think the confusion comes from the fact that the manufacturers normally put their best designs into faster lenses. When we talk about sharpness, understand, we are talking about the performance of the lens around the edges of the frame. They are all sharp in the center.

    Lenses are at their worst wide open. That's just a reality of lens design. It might be more accurate to say that slower lenses are sharper. Theoretically it is true but in practice, the manufacturers use their best designs for fast lenses as mentioned above. So the answer to your first question is that faster lenses are not more crispy because they are faster. If they are crispier it is for some other reason.

    Telephoto lenses are not inherently sharper than shorter lenses. They are easier to design and correct simply because there is less light refraction going on inside so you will find fewer poor designs in telephotos than in shorter lenses.

    The trick to making good closeups is not necessarily the use of long lenses. It is the use of close focusing lenses. The macro lens I use for flowers and bugs is a normal lens, not a telephoto lens, as an example. Some macro lenses are telephoto and some are zooms. But the issue is close focusing, not focal length.

    Telephoto lenses do magnify the subject just like a binocular would. That provides more detail. It isn't the sharpness of the lens that does that. It is the focal length of the lens.

    Your readings have caused some confusion. I hope my short reponse helps put things into perspective a little bit.
     
  4. fmw

    fmw No longer a newbie, moving up!

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    Point 1 is just plain dead wrong. Sorry, but I don't want to add any more to Angeline's confusion. The faster the lens, the more it costs. Yes, but not because it is sharper. It costs more because it is more expensive to manufacture. Faster is not sharper. In fact, slower is sharper given the same basic design.
     
  5. Garbz

    Garbz No longer a newbie, moving up!

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    /edit: took to long to respond nothing new been said

    /edit: I did just think of something. The perspective change when you focus something with a longer lens causes a shallower depth of field. If I shoot a flower at 50mm f2.8, the background would be sharper than say if I used a 100mm from further away at the same aperature.
     
  6. Ken_D

    Ken_D TPF Noob!

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    "Point 1 is just plain dead wrong."

    I just can't think of anything to say that isn't sarcastic so I'll bow out and leave this and other threads to your vastly superior knowledge of all things photographic.
     
  7. Alex_B

    Alex_B No longer a newbie, moving up!

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    Ken, I think fmw was referring to "the more light, the sharper the image" which is wrong.
     
  8. Alex_B

    Alex_B No longer a newbie, moving up!

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    So I will mess a bit with this thread as well ;)

    This has been answered ... apart from playing with depth of field you need some magnification which you either get by a longer lens, or by getting closer to the subject.

    Getting closer to the subject is often limited by the minimum focussing distance of lenses, and with telephoto lenses you might even have a much larger minimum focussing distance. Therefore most people use Macro lenses which are specifically designed for shorter distances. Or you can use a close up lens with your telephoto lens which allows for shorter focussing distances.

    Well, every lens has got f-stops, and some lenses are zooms, and other's aren't, both terms are not restricted to telephoto lenses. There are also wide lenses which are zooms and which have a large maximum aperture (small number in the minimum f-stop).

    it does not necessarily.

    Often, as already mentioned, faster lense are also generally high end lenses which are sharper anyway, in particular if you close their aperture by one or two stops.

    Also, having a faster lens allows for shorter exposure times for given ISO, so therefore motion blur of the subject is reduced. And camera shake is reduced if you do not work with a good tripod.
     
  9. fmw

    fmw No longer a newbie, moving up!

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    I think that is a good idea. We want to try to avoid misinformation. By the way, you were sarcastic anyway.
     
  10. fmw

    fmw No longer a newbie, moving up!

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    Alex, you make good points. I guess I view the term sharpness differently. What I mean by sharpness is resolution and a lack of softness at the edges of the image circle. While it is possible to cause motion blur and it is possible to control depth of field, these things are the same with any lens of the same focal length used at the same aperture. Yes, it is easier to cause motion blur with a slower lens using a slower shutter speed but it is also possible bo eliminate motion blur.

    It would be true to say that the faster lens has the capacity to produce shallower depth of field but we're talking about lens sharpness, not depth of field - or at least I am.

    These things have nothing really to do with whether a lens is fast or slow. They have more to do with the focal length of the lens.
     
  11. Alex_B

    Alex_B No longer a newbie, moving up!

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    Actually we see this the same way, I did not use the term sharpness referring to motion blur and DOF, i just wrote of the latter two since some of the confusion the original poster tries to get rid of might also be related to these terms.
    ;)
     
  12. subtleRIPPLE

    subtleRIPPLE TPF Noob!

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    I apoligize for a poorly versed question - it was not all that clear. Now that I've read your posts, I see I am confused by two things. One has been answered:

    Thank you, on my research I kept reading faster = sharper. Now I understand. All glass is better able to produce sharpness of image in the center and become less sharp as you radiate away from center. Manufacturer's put the money in the faster lenses, so, that includes the glass, so the light clarity is better, as a matter of business. Does not mean that my cheap lense opened to f4 will not be clear (especially in the center)...yes?

    2. Here I'm not quite there...For a sharp image of a small item which fills the frame, one needs to reduce min.focal distance and use the right part of the glass. From what I understand from your posts, Either a close up lense on a longer lense or a macro lense is required to accopmlish this. But (as long as you're outside min. focal distance) the sharpness of the image is not dependant on which type of lense you use. yes? (consequentially a longer lense will also produce a shallower depth of feild, which one must be aware of, especially at lower aperatures) (which also happens with my wide angle lense, semmingly...)

    So, thanks to you all, I have a much better Understanding lenses and of course the hard part is puttng it into practice. (any books you would reccomend?)

    If possible, I'd love your thoughts on how to solve my problem:

    I have minimal equiptment and am still on a HUGE learnng curve. But I do have a small project taking some product pictures for a friend's kayaking business. The project: A map and compass. (and some other objects) I was going to post my attempts but guess it needs to be online somewhre else in order to do so? )

    now, alot is wrong with my sitation. I still need to learn how to use my SB800 as an off camera light source (currently using 250 watt light bulbs, so, I am hoping to complete this with daylight natrual light and my strobe, also the images below were accidentlay dialed in at 500 ISO - no good.. BUT, the issue is that I find there is a remarable difference in sharpness of the images using my normal nikon (28 - 80 mm) kit lense than by using my fancy wide angle 12 -24mm nikon lense dialed to 24 and positioned at the min focal distance. (a lense I bought to do wacky environmental protraiture and interior shots with)...I'm guessing it's not the right lense to use for this products stuff? stick with my 28 - 80mm?

    Simply in terrms of my lenses, which would you use and what aperature would you not use to get a the details of compass and the map (lots of text, as well as full map? Since I'm shooting in Raw, I know that there is post production work to do with sharpness, but my question here is about the lenses - which to use and why.

    (I feebly ask for constructive critisim on how I have posted this question - I want to use the forum correctly...thank you all)



    Angeline
     

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