Lens Education!

Discussion in 'Beyond the Basics' started by Becky, Jul 21, 2005.

  1. Becky

    Becky TPF Noob!

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    Hey again...

    Is anyone able to explain to me the difference between lenses, i.e I know you can have say a 28mm-90mm but how does this differ from another lens and why? How do you know which lens to use for what?

    I know its basic but as an SLR newb I still have loads of questions about stuff like this and its hard to know whats what! I've been researching lots online to try and limit the amount of stupid questions I ask but I can't find a basic easy to understand answer!

    Thankyou :hail:
     
  2. Artemis

    Artemis Just Punked Himself

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    Well, you have aparature and optics mainly...or atleast thats the best I know..

    The lower the number, the higher the aparature, the better the lens because with, for example that 1.8 lens you may get, you will get a very shallow depth of field.
    Optics, just means the lens pictures look nicer I think, and then you have faster focusing, stronger housing and what not.
    Id suggest for you, just go by the aparature for now and dont worry about other things, some lenses that have a f/1.8 up to 3.5 arent bad, but will be more expensive :)
     
  3. SLOShooter

    SLOShooter TPF Noob!

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    Sounds like a basic book in the principles of photography would be a worth while read for you.

    The "mm" on lenses denotes what focal length they are. The higher the number the larger the focal length and the closer you appear to get to the subject. I was tought that 50mm is about what the human eye is so > 50mm makes the subject appear closer than normal and < 50mm makes the subject appear farther away.

    The f number of the lens is the f-stop. It tells you how wide the aperature is. The numbers are fractions so the actual number is inverse to the width of the aperature. The larger the number the smaller the aperature, IE a smaller hole for light to pass through.

    The f-stop determines 2 main things: 1 the amount of light passing through the lens that will eventually hit the sensor or film. Smaller f number means a larger hole and therefore a faster shutter speed will be required for a balanced exposure. 2 it is a major player in setting the DOF. Due to the physics of optics and light a smaller f number, larger hole, results in a shallow DOF. So objects along the focal plane will be in focus while objects in front of and behind the focal plane will quickly become out of focus. A high f number, small hole, results in the whole scene being in focus.

    There are exceptions and further details in the above statements but I think they're generally good rules of thumb.

    What else to know about lenses. hmmm. A prime lens means one with a fixed focal length and a zoom lens means that it has a variable focal length. So in your example a 28-90mm would be a zoom lens covering the focal lengths between 28 and 90mm.

    Hope that helps get your started. You can spend a career, and many have, figuring out everything there is to know about optics.

    Oh yea if any of that info is bogus I'm sure someone will be along to correct me.

    P.S. Read book on basic photography, I'm sure they explain it better than I can plus it will have pictures!
     
  4. Becky

    Becky TPF Noob!

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    :goodvibe:Thanks so much guys
     
  5. pyrgal

    pyrgal TPF Noob!

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    We are traveling to Alaska and Cosamel in the next few months. I am hoping to be using my newly cleaned and working Canon AE-1(I am awaiting its return from the shop). The lens I currently have are a 135mm and the standard Canon 50mm. Any suggestions on lens to buy to get great shots in those landscapes?

    This really has nothing to do with Becky but I couldn't figure out how to do a new post. Sorry
     
  6. wharrison

    wharrison TPF Noob!

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    Becky:

    I posted this response elsewhere and I hope it will just add to the information:

    1. There is a mathematical relationship between the lens aperture (opening) and the focal length of the lens. For example, an 50mm F/2.0 designates that the maximum aperture (lens opening) is 25mm. If you that same lens at an aperture of F/16, it indicates that the lens opening is approximately 3+mm; a 100mm F/4 lens would, therefore, have a maximum lens opening of 25mm;

    2. Depth of field tables are based upon two factors: (1) the aperture of the lens and the ratio of reproduction - which is a ratio between the area of the film, i.e. 1 x 1.5 inches or more precisely 24 X 36mm. Therefore, if you are photographing an area that is 10 times the size of the 35mm negative, it is expressed as a ratio of reproduction of 1:10; if you're film is covering the same area as the film, the ratio of reproduction is 1:1.

    Therefore, all lenses exhibit the same depth of field provided they are used at the same lens opening and at the same ratio of reproduction. Consult some of the older (and still better) books on photography, such as The Pentax Way or The Leica Way - each has depth of field tables in the back of the book.

    Depth of field is based upon the fact that our eyes do always "see" so well. The eye can "see" a circle as a dot if the diameter of that dot is less than 1/100 of an inch in diameter on a 7 X 10 or 8 X 10 print held approximately 10 inches away.

    In order for that "dot" or "circle of confusion" (its actual name) to be less than 1/100 of an inch on an 8 X 10 print held 10 inches away, that dot or "circle of confusion" has to be less than 1/800 of an inch on the film/negative.

    Therefore, accurate focusing is very important, especially under available light conditions. If you're focus is off, you will be actually enlarging an unsharp image on the negative/film, which will become progressively unsharp the greater the enlargement.

    3. Obviously, a 50mm F/1.0 lens will transmit nearly twice as much light as a 50mm F/2.0 lens (50mm vs 25mm). One of the reasons to purchased high speed lens is to gain greater transmission of light through the lens to your eye so that you can (hopefully) focus more accurately (and more rapidly) under available light conditions.

    4. That factor doesn't make the 50mm F/1.0 lens "better" or "superior" in terms of image quality, because that is dependent upon the type of glass employed in lens construction; the overall design and purpose of the lens, etc. The 50mm F/1.0 M (rangefinder lens) Noctilux by Leica/Leitz is a specially designed lens for available light photography; whereas a 50mm F/1.4 M (rangefinder lens) Summilux or a 50mm M F/2.0 (rangefinder lens) Summicron might be entirely suitable for most of your photographic endeavors.

    A few decades ago, when I attended the week long Honeywell Photographic Technical Seminar, the three lecturers knew that 50mm lenses on SLR camera had to be designed a little differently due to the fact of the greater distance between the lens flange and the film plane - in order to allow for the movement of the mirror. They were also aware of the fact that this "retro-focus" design lead to a slight "barrel" distortation whereby straight lines at the edge of a photograph would be slightly curved.

    So they did a test with several 50mm lens including those made by Leica (rangefinder and SLR) nikon, pentax, canon, olympus, minolta, and a few others. They took photographs of a 20 X 24 test board with several straight lines along the edges; developed them; and enlarged them back up to the same size print (20 X 24 inches) with a Leica/Leitz Focomat IIC enlarger with Leitz enlarging lenses.

    The only lens that reproduced straight lines as straight lines was, of course, the Leica 50mm Summicron (rangefinder), The 50mm Summicron on the Leicaflex SL II (then in current production) exhibited just a slight curve near the center of the outer edges. As the 50mm lenses went downhill in quality, each exhibited more and more barrel distortion (curved, not straight lines).

    Obviously, the type of glass used, the quality of manufacture, the design of the lens, etc. all contribute to the cost of the lens.

    All such lenses worth consideration? That answer depends upon the standards you wish to employ in your photography, the type of photography that you do, i.e. what lens openings you generally use, etc.; and many other aesthetic and real factors, including one of the most important - your budget.

    When I was working at the better camera shop in Peoria, IL - decades ago - our customers would often consider the purchase of a 135mm lens as their next choice of photographic equipment. Although we carried independent lenses, I steered my customers away from them, simply because of the better quality glass and overall construction of the lens.

    Often, I would go to the back of the store and turn off the light in that section of the camera shop; load up two Canon cameras with different 135mm lenses. One would be the independent lens and the other would be the lens made by Canon. Even though the "indie" lens was a F/2.8, which should have, at least, theoretically, transmitted more light, the Canon F/3.5 actually transmitted more light to the viewfinder. And it was so noted by the customer under these "low" light conditions. So with a difference of about $15.00 to $25.00, the Canon lens was the far better buy over the Vivitar.

    5. There is another factor to consider, namely the focusing accuracy of SLR and Rangefinder cameras. In both cases, the accuracy is dependent upon the viewfinder magnification and the base length of the rangefinder. For example, the Leica M3 has a physical rangefinder base of 69.25mm, i.e. the distance that the "range finder" mechanism are separated. Since the M3 has viewfinder image that is almost life size, actually it is 0.92, the measuring base is 63.71mm (The measuring base is determine by multiply the viewfinder image times the rangefinder base or 0.92 X 69.25 = 63.71

    In an SLR camera, the viewfinder image size can usually range from 0.92 to 0.94 - I tried to verify one or two of the older SLR film cameras, but couldn't find the necessary details or confirmation. So, we will settle on 0.92 viewfinder magnification in an SLR for the purposes of our discussion.

    Well, now that we have a viewfinder image size, where do we find the "measuring" or rangefinder base of a SLR (film) camera. Well, the measuring base of an SLR camera is determined by dividing the aperture of the widest lens opening by the focal length of the lens.

    So with a 50mm F/2.0 lens, the measuring base is 25mm; Using the formula, viewfinder image size times the measuring base the figures are 25mm X 0.92 or 23mm. With a 100 F/2.0 lens, the measuring base increases; again using the formula viewfinder image times the focal length of the lens divided by the maximum aperture or 0.92 X 100/2 or 0.92 X 50mm = 46mm. By the time a 135mm telephoto lens is employed, the focusing measuring base of an SLR will begin to match that of the Leica M-3 rangefinder camera.

    However, with the use of wide angle lenses, the focusing accuracy of an SLR rapidly diminishes. For example, a 35mm F/2.0 lens has a measuring base of 17.5 mm. Multiply that by the viewfinder image size of 0.92 and you'll obtain a measuring base of only 16.1

    Not very accurate!!!

    Of course, we can put it in more simple terms. When you put a wide angle lens on an SLR camera, your lens is including a greater area on the same area of film. In order to accomplish that wider angle, the image size is reduced and looks further away. Consequently, fine detail is made smaller and more difficult to accurately distinguish, especially under low light conditions.

    With a telephoto lens, the angle of view is both narrower - when compared to a wide angle or a "normal" 50mm lens - and the image is magnified in the viewfinder. Therefore, with the use of telephoto lenses - beginning with a 85mm lens - focusing accuracy increases simply because the image details are easier to see and one is better able to determine whether the image is in focus or not.

    Not what does this last discussion have to do with your basic question?

    Well, now that you have a a better idea of the problems of focusing accuracy with SLR cameras, wide angle lenses, and available light conditions, you should opt for the purchase of (good quality) high speed lenses to insure greater focusing accuracy under certain lighting and shooting conditions.

    Well, now you know more than you ever thought possible - thanks to a conscientious, Librarian and photographer! ;>)

    Best wishes in your photographic endeavors.

    Bill
    __________________
    "Great spirits have always found violent opposition from mediocre minds. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence." --- Albert Einstein
     
  7. wharrison

    wharrison TPF Noob!

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    Becky:

    As for some additional and very useful information, I highly recommend the reading of two books.

    The first is "The Eye of Eisenstaedt" by Alfred Eisenstaedt, one of the original photographers for Life magazine. This book is part autobiography, part photographic technical, but mostly it is a discussion of a way of "seeing" photographically. Although the book is a little outdated, etc., and out of print, it is still a very valuable read and should be available through your public library's inter-library loan system or through either abe.com or alibris.com - both of which are excellent sources for used and new books.

    If you wish to explore some of Eisenstaedt's photography, here's an excellent link. Please note his comments on the photograph "Premiere at La Scala, Milan 1933" and then read the last paragraph of the article.

    http://artscenecal.com/ArticlesFile/Archive/Articles1997/Articles0397/AEisenstaedt.html

    The second book is "Better Colour" by Walther Bensor. Again, while it is a little outdated, it is still an excellent read for its discussion of the use of various lenses and the variety of perspective that one can obtain from them. Again, it should be available through your library's inter-library loan system or through either one of the two used book sources mentioned above.

    Again, I hope this discussion is more than useful in your photographic endeavors.

    Bill
     
  8. Becky

    Becky TPF Noob!

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    Wow, thankyou!! I'll check out thoes books and do my reading, excellent thanks again and take care. :)

    I'm still a little confused by the term "high-speed" lens... how do I know which are high speed and which aren't? :???:
     
  9. wharrison

    wharrison TPF Noob!

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    Pyrgal:

    I'd suggest the purchase of a high speed Canon FD wide angle lens, such as the 35mm F/2.0 with lens shade and the purchase of the Canon FD 85mm F/1.8 lens with lens shade as well.

    While a Canon FD 28mm lens might be suitable for some landscape photography, it will make your images that much smaller and also make them look further away. Only by using a projected image, might you and other really appreciate the grandeur of Alaska.

    Decades ago, one of the members of the Peoria Color Camera club used an (now old) Leitz/Leica Prado (single slide) projector with a wide angle projection lens. The couple gave one flat wall of their basement several coats of a nice white paint and used it as a projection screen. The effects of seeing a wide screen display of their slides was breathtaking to say the least.

    The use of a moderate telephoto lens, such as a recommended Canon FD 85mm F/1.8 will give you a nice moderate telephoto lens for both general landscape photography and for portraiture.

    I am certain that there are other lenses which might be equally valuable, such as the Canon 100mm Macro F/4.0 lens or a Canon FD 200mm lens, etc., but I have no idea as to your budget.

    For inspiration, I'd rent the DVD version of "Never Cry Wolf" and enjoy and learn from it; this movie is extraordinary in its storying telling, but especially so in its photography. And even though the movie is excellent, the book of the same title by Canadian author Farley Mowat is far better.

    For additional inspirational photography, you might also take a look at the DVD version of "Winged Migration".

    I would also recommend the rental or borrowing of some films on Alaska, etc, from your local public or college library. I am certain that a conscientious Librarian will be most helpful in finding a number of films and/or books for you to read.

    Finally, I would also recommend the reading of the two books previously mentioned by me in this post. The latter, "Better Colour" by Walther Bensor will be most helpful.

    Hope this is also helpful in your forth coming trip!

    Bill
     
  10. hobbes28

    hobbes28 Incredible Supporting Member

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    I'll chip in here too. I love John Hedgecoe's New Manual of Photography to learn some more of the basics of photography all the way up to the more advanced.
     
  11. wharrison

    wharrison TPF Noob!

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    Becky:

    Remember the specific reference to high speed lenses was made to wide angle lenses; therefore, if you have a choice between a 35mm F/2.8; a 35mm F/2.0 or a 35mm F/1.4; the later two - the 35mm F/2.0 and the 35mm F/1.4 lenses would be considered "high speed" lenses when compared to the 35mm F/2.8.

    Think in terms of the fact that wider aperture wide angle lenses - F/2.0 or F/1.4 - would transmit more light into the viewfinder to permit more or better accurate focusing under low light conditions and the fact that they would also better enable you to take available light photographs as well.

    However, the quality of the wider aperture lenses is dependent upon the design of the lens; the glass used; and the quality of manufacture at all points. Therefore, a 35mm F/1.4 lens may not be "better" quality wise when compared to a 35mm F/2.0 lens - even though the F/1.4 lens was a "higher speed lens than the F/2.0

    For this reason, I recommend that you stick with the lenses made by the manufacturer of your camera - something I noted in my previous discussion.

    By way of example, I found two 28mm wide angle lenses - both have aspherical lens elements and one is, ever so slightly "faster" than the other F/1.8 is ever so slightly faster than the Leica F/2.0, but look at the difference in price!!!!!!


    Sigma 28mm F1.8 EX DG Aspherical Macro AutoFocus Wide Angle Lens with Hood for Minolta Maxxum $229.00

    Leica 28mm f/2 SUMMICRON-M Aspherical Black Lens (E 46mm Filter) $2,795.00

    Is there a difference between the two lenses that one could normally see in a 4 X 6 inch print; perhaps to probably yes. But as a Leica user of several decades, I have been to many photographic seminars, including two 2-day Leica Photographic Seminars in which they projected 35mm slides on to a 8 X 12 FOOT screen and one could still easily see incredible detail, fine color definition and separation, etc. at a 96 times magnification!!!! So yes, there is a definitive difference between Leica equipment and other 35mm cameras/lenses.

    Now I am almost certain that this will statement will begin "heated" discussion, but it is not intended to do so. I should remind you and other readers that it is the photographer who takes the photograph, not the camera and that we should consistently work to obtain the best possible results from the camera equipment on hand.

    Even though I am a long standing Canon, Pentax, and Leica user, the $2,795.00 price tag for a new 28mm is currently way beyond my present and perhaps, future, budget considerations, but since there are other, older Leica 28mm lenses of years past, I might well consider their purchase should I have need of one. Currently, my range of Leica rangefinder lenses go from 35mm to 200mm - a range more than adequate for my photographic needs.

    Accordingly, I try to "practice what I preach" and I have all Pentax lenses for my K2 body, which I recently gave to my daughter, Heather, and have all Canon FD lenses for my wife's AE-1 and my A-1 camera. There is also a difference between lenses made by the manufacturer of the camera and those made by independent lens manufacturers.

    Remember to do your "homework" and then make the best or wisest choice possible.

    Again, I hope that this information is useful!

    Best wishes in your photographic endeavors!

    Bill






     
  12. Becky

    Becky TPF Noob!

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    So summing up a little, with the choice of taking the camera alone with a 28mm-90mm lens and buying another lens separately... or...

    taking the camera with both the 28mm-90mm and the 90mm-300mm...

    what would one do!?

    And if I take the single lens, what other reasonably priced lens would be recommended? To begin with I'll be trying my hand at a bit of everything and I want to make sure I have the right kit assist at least some experimentation in different techiniques...landscape/closeup/portrait etc?

    Thoughts anyone? I just don't want to make a bad choice and regret it later :|
     

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