Expert: David Silver - 7/18/2005

Question
       Ok, so if I zoom back to 30mm and physically walk towards my subject so that it is framed in the viewfinder the same as it was when the lense was zooomed all the way set to 80mm would it produce the same picture?  And if not would it still be the same porportion, just slightly different detail due to the difference is f-stops and shutter speed.
     Another question, with my zoom lense I can zoom/set it to 50mm, is that the most realalistic lense length, like for portraits-or am I not really getting it?
    Thanks for spending time to explain this stuff,  I'm learning more and more about cameras and photograpgy and then I take a look at lenses see that its more complicated than just the ashethics (sp).

ps:  So if zoom lenses are so great and versitle why doesn't everyone use them?
Answer -
Hi again,

Yes, if you zoom back to 30mm on that lens, and then physically walk towards your subject so that it is framed in the viewfinder as it was when you were zoomed up to 80mm, it will produce the same image!  That is the whole purpose of using telephoto lenses...to make the subject appear closer.  When you can NOT get close to your subject, you choose a telephoto lens.  On the other hand, if you are already up close to a subject that is very big, and the telephoto or normal lens is incapable of seeing the entire thing, and there's no way for you to back up (for example, you're standing in a room), then you choose a wide angle lens because this will give the illusion that you are standing farther away!

As for that 50mm setting, it is the conventionally accepted "normal" focal length on a 35mm camera because it seems to give the most natural looking perspective for all subjects.  MANY professional photographers (me included) prefer to keep a wide angle lens on their camera most of the time (I always have a 28mm mounted on mine) because the reality is that you will need a wide angle far more often than a telephoto, and it's frankly much better to err on the side of captuirng an image that has too much stuff in it rather than one with too little.  However, the 50mm is the best for all the standard applications in between, and truthfully the typical family photographer could go years without needing anything more than that.  As for portrait work in particular, experience has taught us that there is some flattering benefits to shooting faces with 80mm to 110mm lenses.  It flattens the features a little, and you can shoot from a comfortable distance of about 10 feet rather than having to be right on top of people to fill the frame.  I use a superb 105mm lens on my camera for portraits, but the 80mm setting on your zoom would definitely do the trick.

Yes, zoom lenses are versatile, but not "so great" as you might think.  There is a major optical compromise made to allow these lenses to cover a range of focal lengths, and they simply do not make images as sharp as fixed focal length lenses.  As a professional, although I do own a couple of exotic zoom lenses, my typical working bag of lenses contains a 28mm, 45mm, 55mm macro (it has the ability to focus extremely close), 105mm, and 180mm.  I have MANY other lenses for special purposes, but I use my zooms much less than the rest.  Usually only for sports events (I have a massive 100-300mm model), and occasionally for fast moving "street" shooting (a 28-85mm).  I also think zooms are a fun alternative for family photographers and people who only want a single lens to cover a lot of situations and they aren't that concerned about extreme image quality.

Best wishes,

David Silver

         FOLLOWUP:
     This is my last question, I'm sorry it didn't occur to me before and I could have saved you some time, but- All this stuff about lenses you are explaining does it refer to both film AND digital?

Answer
Hi yet again,

Yes, all of this information is standard optical theory that applies to ALL forms of photography, including digital.  The specific focal length examples we used, in particular the 50mm "normal" focal length lens, was for 35mm cameras, and different sorts of cameras that use different size films or digital imaging receptors will have different ideal "normal" lenses (bigger cameras, like those that use #120 roll film for "medium format" pictures, usually have normal lenses of about 80mm, while smaller cameras, like the majority of digital cameras, tend to favor about 38mm as the normal lens focal length), but the theory is absolutely the same.

Have fun!

Best wishes,

David Silver