Enlighten us about Lenses.

Unimaxium · Dec 27, 2004

I don't see very many threads about lenses apart from the numerous "what lens is right for me?" or "is this a good lens?" threads. So I'm pretty lost when it comes to knowing much about these things. I've searched around, and haven't found a whole lot that has helped eliminate all the questions I have. I have managed to learn the word bokeh (which I've been dying to throw into a conversation), and a couple more things that have helped me understand lenses a bit, but not much. It would be great if this could turn into something like that "basic photography concepts and vocabulary for newbies" sticky thread, except specifically for lenses. So please, anyone who knows something they can share on this topic, help those of us who are confused here to understand better, by imparting your wisdom unto us :wink:

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I also have a few assorted specific questions: (some may be newb-ish, although I don't like to say that as it makes it sound like I think low of myself for being new to photography)
1) What exactly defines a "prime" lens?
2) I've heard "L" (L-series?) lenses referred to a bit. What exactly are those? Just a brand name for a company's line of prime lenses? Or something?
3) How can I drop "bokeh" into a conversation without sounding dorky?
4) Exactly how great, on a scale of e (2.718) to pi (3.141), is the difference between a bad lens and a good lens? Well, Ok, maybe I don't need it on a scale :lol:

, but can someone help me get a sense of how important/unimportant it is to have a good lens on my camera? I know I'm asking this awfully simplistically, but I wasn't sure how else to ask it.
5) When is it most beneficial to have a well-made lens (what kind of photography)? When might it be least necessary? Or is it maybe equally beneficial for any situation?
6) Similar to #5, what kinds of lenses are good for what kinds of photography? This is another general question I know, but I'm not really expecting a completely comprehensive list of every lense with every branch of photography.
7) Why exactly do lenses in digital cameras have "35mm equivalent" focal lengths? I know that the size of the CCD/CMOS chip is different from a 35mm frame, but wouldn't this simply produce a crop rather than a difference in effective focal length? Is it because the sensor is positioned closer to / farther from the lens than the film normally is?

Thanks to anyone who can help to clarify anything above, or any questions that others might have.

Jeff Canes · Dec 27, 2004

#2: L-series are Canons pro line of lenses

oriecat · Dec 27, 2004

1. A prime lens is a lens that is just one fixed focal length, like a 50mm or a 35mm, as opposed to a zoom, which spans a range of lengths. Prime lenses tend to have larger apertures and better optical quality.

ajmall · Dec 27, 2004

1) a prime lens is a lens with a fixed focal length (ie. doesn't zoom).

2) "L" simply refers to the standard of lens produced by whoever uses that standard. check the manufacturers website or catalogue to learn more about their lenses.

3) still don't know what it means!

4) that's an awkward question really. you need to be specific! but one thing worth mentioning is if u use the same brand lens as camera (canon on a canon as opposed to a sigma), you tend to get better results such as faster auto focusing. photography has reached a point where you don't get "bad" lenses unless there's a speficic fault ofcourse. some lenses are naturally better than others.

5) my first thought would be when it's most important to you and/or the person you might be selling or giving the photo to. if u were thinking of selling your shots either privately or to a publication then good equipment is a must mainly due to the vast array of competition. however thats quite a general question.

6) i haven't got time to write everything but here are a few basic principals. for landscapes, a wide ranging zoom is usually good though prime lenses (around 90mm) are to my knowledge frequentyl used by avid landscape photographers. for action shots such as soccer matches, a fast lens (one with a small F number) usually 200 300 or 400 F2.8. they're common with sports journalists and VERY expensive! for still life/close up, wide angle macro lenses such as 18 to 24mm usually F2.8. for portraits, 105mm 2.8 has been recommended to me numerous times but it all depends on what conditions you're shooting- studio? outdoor? lighting? etc.

7) yes the sensor is at a different distance to a 35mm film camera. most dslrs require u to times the focal length of a film lens by around 1.6x to get the actually focal length. some cameras such as the Kodak 14n has a 35mm sensor though is very expensive.

hope that's cleared a few things and i hope i have made no errors! im sure others will add to what i have written.

7)

Jeff Canes · Dec 27, 2004

3: Englishlized Japanese out of focus
Japenese "boke" fuzziness or dizziness

Dude after we bunted a few last night I was bokeh

mrsid99 · Dec 27, 2004

#3 - Sneeze first.
#4 - You're going to have to figure it out yourself.
#6 - Better lenses usually have some or all of the following attributes: Lower "F" numbers (larger aperture) for a given magnification, Better (more) light transmission, Lower tendency to produce chromatic aberration (color fringing), sharper focussing (sharper detail), All of the above attributes across the whole lens (no light fall off at lens edges or magnification differences across the lens etc.) and probably some more I haven't thought of.
Lower "F" number apertures are useful in low light situations because they allow faster shutter speeds thereby reducing blurring due to camera or subject movement. They're also useful for limiting the DOF (depth of field) for instance when you only want say a portraits head in focus.
All the other attributes simply help produce a more accurate picture without introducing distortion.
#7 - You're correct in that it is a crop but when the crop is then used as the picture size it's effectively a magnification.
If I've made any errors please anyone jump in and correct me.
HTH.

motcon · Dec 27, 2004

Jeff Canes said:
3: Englishlized Japanese – out of focus
Japenese "boke" fuzziness or dizziness

Dude after we bunted a few last night I was bokeh

thanks. i just shot wine through my nose onto my keyboard in laughter.

it hurt.

crap, no my double u key on't ork.

wait, too much wine in me, not the keyboard.

k.

bokeh.

how do you fit it into a conversation? easily. observe the dof of a photograph and if it is a shallow dof, the 'blurry' part of the photo (generally background, though could include fore (especially in macro shots)); make note of how it is patterned. is it mush? are there specular effects?

work it in by starting with 'dof', then comment on the bokeh.

motcon · Dec 27, 2004

Unimaxium said:
4) Exactly how great, on a scale of e (2.718) to pi (3.141), is the difference between a bad lens and a good lens? Well, Ok, maybe I don't need it on a scale , but can someone help me get a sense of how important/unimportant it is to have a good lens on my camera? I know I'm asking this awfully simplistically, but I wasn't sure how else to ask it.

oops, forgot to comment on this one. it all depends on what you consider to be a 'good' lens. to me a good lens is one that, first and foremost, has a high mtf rating. i could have a 1.4 super duper macro lens that takes three people to steady, but if it has a low mtf, the product will be c_r_a_p.

i'd be happy to do a mtf curve for you, but they've already been done. check it out.

a site on mtf

Jeff Canes · Dec 27, 2004

boken

I think but am not sure, it may have more to do with out of focus or over exploded background lighting? This site has some examples
http://www.luminous-landscape.com/columns/sm-04-04-04.shtml

But IMO DOF would all so be boken.

motcon · Dec 27, 2004

bokeh has to do with the 'quality' of out of focus dof.

http://www.kenrockwell.com/tech/bokeh.htm

If the film is not exactly where that cone of light reaches it's smallest point, then that point of the image is not in focus. Then that point is rendered on film as a disk of light, instead of as a point. This disc is also called the "blur circle," or "circle of confusion" by people calculating depth-of-field charts. In a lens with no spherical aberration this blur circle is an evenly illuminated disc. Out of focus points all look like perfect discs with sharp edges.

**another edit. technically speaking, there is a 'circle of confusion' that is inherent in lenses. 'tis true that it will have an effect on the overall image, but not glaringly apparent. for that reason dof/aperture shooters (such as myself) utilize 'bokeh' in terms of dof.

Jeff Canes · Dec 27, 2004

For 7: So far I do not think any of the answers are right for that Unimaxium is asking.

You see this type of equivalent rating with fixed lens digital cameras. Because, The lens is designed to match up with the sensor. If a camera has a 7-15mm lens that is equivalent to a 21-43mm 35mm lens then the sensor is 3 times smaller that 35mm film frame of 24x36mm. This type of rating is a marketing tool to let buyer know what to expect out of the lens

DSLR use 35mm lenses that are not designed to match up with the sensor. This is what has be addressed in pervious answers

Unimaxium · Dec 27, 2004

Wow, thanks everyone so far for having such quick responses! Keep the knowledge comin'...

Edit in: PS: I'm sorry that some of the questions are kind of akward, but it was kind of hard to know how to word some of them so they weren't to general. I wasn't expecting a whole lot in terms of answers to those, but I've got quite a bit so far! Maybe a better way to word the one about the importance of good lenses is: at what point(s) in my photographic "career" (notice it's in quotes) is it worth the money to upgrade or expand my lens collection? Like if I am a hobbyist, would it be enough of a difference in your opinion to invest in a nicer lens than the one that came with my camera (pretending what I currently have is medium-to-low quality for SLR lenses)? Or should I not worry about that until I get into selling photos? Maybe I'm just asking for too much knowledge in a small answer with this question, in which case I guess I should just wait and gain experience in time.

PPS: That sentence for bokeh was funny! I'm still laughing (especially at motcon's reaction). I should say that to my photo teacher. Although he probably wouldn't find it as funny as I did. I don't know if he even knows about bokeh or not. He prolly just calls it "out-of-focus-space" or something. :\

Unimaxium · Dec 27, 2004

Jeff Canes said:
For 7: So far I do not think any of the answers are right for that Unimaxium is asking.

You see this type of equivalent rating with fixed lens digital cameras. Because, The lens is designed to match up with the sensor. If a camera has a 7-15mm lens that is equivalent to a 21-43mm 35mm lens then the sensor is 3 times smaller that 35mm film frame of 24x36mm. This type of rating is a marketing tool to let buyer know what to expect out of the lens

DSLR use 35mm lenses that are not designed to match up with the sensor. This is what has be addressed in pervious answers

It seems I've gotten 2 contradictory answers from other people, and I'm not sure what to make from this. The other 2 answers, from ajmall and mrsid99, did kind of get at what I was asking, as did you too. I was wondering why there is a purpose for having a 35mm equivalent. ajmall supported my hunch that it is because the sensor is a different distance from the lens than a plane of 35mm film would be. This is what I have been thinking, but was unsure about. mrsid99 said that it is a different focal length with digital because it is a crop, but then a magnification causes the equivalent of a different focal length. But it would seem to me that ajmall is more correct, considering the way that the focal length is measured. But then again, considering the effect of changing the focal length, it seems like there's some validity in what mrsid said, since if you increase the focal length then you are essentially making the FOV smaller; the same as if you were to crop the image. So maybe it's a combination of both.

But actually thinking about what you said, Jeff, I forgot to wonder whether there is even such a thing as 35mm equivalents on DSLRs. When you put a 35mm lens on a DSLR, does it change the effective focal length, or is the DSLR made with the sensor closer than a 35mm frame so that it compensates for the smaller chip size? Or am I making any sense?

markc · Dec 27, 2004

"Hey babe, that's some nice bokeh."

The Holga uses a one-piece plastic lens that's the epitimy of cheap that a lot of artists like the look of, but a National Geographic photographer is going to used the top-of-the-line pro lenses. It depends on your experience as to how well you can tell the difference. Who's your audience? Many people can spot the Holga flaws, which it's users are counting on, but the average person won't notice the difference between modern consumer and pro lenses, especially at 4x6. Though there is a quality you can pick up on subconsciously. Shot's from a Leica can illustrate this, even if you can't say why.

Jeff Canes · Dec 27, 2004

Not contradictory answer, I should had said that other answers fell short because they only addressed DSLR and not fixed lens camera where this rating is more significant IMO

Unimaxium said:
------When you put a 35mm lens on a DSLR, does it change the effective focal length, or is the DSLR made with the sensor closer than a 35mm frame so that it compensates for the smaller chip size? Or am I making any sense?

I believe it in the same location as 35mm, but with DSLR the light rays land on empty space outside of the sensor area. This is not a true 35mm equivalent as it's with fixed lens cameras.