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Old Feb 17, 2008, 11:41 PM   #1
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Hi.... A N O T H E R silly question from a newbie. Thanks in advance.....I've looked and looked for the answer to this, unsuccessfully. I'm sure when I understand photography more it will make sense but in the meantime...a lens has a range of fstops. A camera has a much wider range.Which isletting the light in? I mean, obviously the lens is........but, I don't understand what each is doing. If I set the aperture on my camera at f22 but my lens is a constant 2.8, am I getting a lot of light (2.8) or a little (22). I realize already that I'm getting a lot of light, but what IS it then, that the lens is doing?

I know I'm missing a link here :roll:

Obviouslythey do 2 different things...help me SEETHE LIGHT!! Merci kind ladies and gentlemen
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Old Feb 18, 2008, 2:42 AM   #2
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Most lenses have variable apertures. There are only a few that have constant apertures, and those are usually at f8 or so.

The numbers on the lens refer to the WIDEST possible aperture. So an f2.8 lens can go from a maximum of f2.8 down to a minimum of f22 or f32.

You really need to get yourself a book on basic photography.

Something like "Understanding Exposure" should work.

http://www.amazon.com/Understanding-...531&sr=8-1
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Old Feb 18, 2008, 4:31 AM   #3
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Hi Sketchpad (aka Janet) again,

Peripatetic is right (as usual!) - and often has very good advice. Do pick up a good simple book, perhaps the one recommended by peripatetic.

Maybe I'll add my 2 cents worth (before you can get your hands on that book), as I'm trying to help you understand about f-stops, and maybe pre-empting a further question or two. I remember some years ago when I didn't know so much about f-stops.

1. The first thing I want to say is, f-stop all relates to the LENS, NOT the camera. So when you say a camera has a wider range (of f-stops than a lens) and then you ask: if I set the aperture on my camera at f22 but my lens at constant f2.8, which lets the light in... you are wrong. ONLY the lens lets the light in. In 99% of lenses on digital SLRs you CONTROL the lens' aperture via the camera body (e.g. via the dials, menus, etc). But in effect it is only the lens' aperture you change. Of course if you put a different LENS on the same camera body, then you might get a different possible range of f-stops.

2. Most "non-professional" zoom lenses vary their WIDEST possible aperture, e.g. one of my lenses is the Canon 28-135mm f3.5-5.6 IS USM lens which is the same as you have. This means that at 28mm (widest field of view) the lens wide open will be at f3.5 while at 135mm (it's telephoto / zoomed position) it will only be able to open up to f5.6. Don't ask why. It's technical and mainly got to do with size, cost, etc. (By the way the letters after the lens zoom and apertures are: "IS" meaning: image stabilised. A tip, on your 28-135mm lens, keep the IS switched to ON unless you're really short of battery power.

Then "USM" means "Ultra-sonic motor" on Canon, basically a fast and quiet focussing lens). Both IS and USM aspects are good things. Don't confuse USM on Canon lenses with USM in post processing (meaning Unsharp mask - which actually makes an image SHARPER (not 'less sharp' as one might think from the name!)

I know I'm totally confusing you now..... But basically - all you need to remember is most "cheaper" (but often still very good zoom lenses) will vary their "most wide open" aperture setting. (this is referred to as the "maximum aperture")

3. The "minimum aperture" also varies with these zooms. On my 28-135mm lens it goes from f22 at 28mm to f36 at 135mm. Most of the time you do NOT want to go beyond f11 at any setting. Usually image quality will begin to suffer from f14 or f16 onwards... so don't use it. (again, don't ask why.. it's a technical thing - not worth trying to memorise now! Your brain will explode!)

4. On digital compacts (point and shoots) because the lens is built into the camera (and can't be changed) - it might say "this camera's f-stops range between f2.8 and f5.6 or up to f22", or whatever they want to say... but in reality they are referring to the FIXED lens ON that camera. That's one beauty of digital SLRS (DSLRs) because you can choose lenses for different occasions.

5. Many "non-zoom" lenses (called: "primes") have a wider maximum aperture than most zooms. For example I have a Canon 50mm f1.8 lens and you have the 50mm f1.4 lens, which allows in much more light than our 28-135mm zoom lenses. Usually prime lenses provide higher quality images (sharper, better contrast, less distortion, etc) than zooms, but they lack the versality of zooms. For the majority (maybe 50% to 75%) of DSLR owners having one "normal zoom" lens is enough.

Now I know you have already got other lenses (e.g. your 100mm macro and the Sigma 10-20mm and that 50mm f1.8 lens), but a a general statement, choosing a second lens (or more lenses) is better done when you REALLY know what you want. Don't worry I'm not saying you have chosen the WRONG lenses. Just try to learn one lens at a time. I'd start with the 28-135mm lens. That perhaps covers the most useful zoom range you'd want.

If you photograph lots of field sports, you will often need a fast, telephoto (maybe zoom) lens. A wildlife photographer might need a long telephoto (maybe zoom, maybe not) lens. The landscape photographer might want to get an ultra-zoom lens (like our Sigma 10-20mm lenses). Or if you do a lot of portrait work, maybe a sharp 50mm or 85mm or 100mm prime lens is the answer (your 50mm f1.4 is ideal and sometimes your 100mm f2.8 could also be used for outdoor portraits). It depends a lot on what exactly is photographed and in what conditions (e.g. small birds vs pets, outdoor motor sports vs indoor gymnastics). Studio lighting vs natural outdoor lighting (and is that mostly sunlight or do you live in place where the weather is cloudy most of the year?)

So you see that there are endless possibilities and hence a wide variety of lenses to choose from. And prices from $50 to $5000 and beyond. As you've probably already discovered.

My advice is... Use the 28-135mm lens to begin learning. Photography learning is a life-long exercise, which is fun. Take a photo of a flower at 135mm f5.6 and then take a photo of it at 135mm f16 (just to demonstrate the difference).

Here is a quick googled answer / link, that might also help you in case I've already caused you to go to sleep! http://www.photoxels.com/tutorial_aperture.html Really, try reading a photography book. Experiment. Practise. Learn. Look at the settings (mainly f-stop, shutter speed and ISO). Try making more photos, also thinking about composition, etc.

All the best... Sorry I wrote SO much. My 2 cents worth is obviously not charged by the hour! :-)

Paul
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Old Feb 18, 2008, 12:18 PM   #4
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peripatetic wrote:
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Most lenses have variable apertures. There are only a few that have constant apertures, and those are usually at f8 or so.

The numbers on the lens refer to the WIDEST possible aperture. So an f2.8 lens can go from a maximum of f2.8 down to a minimum of f22 or f32.

You really need to get yourself a book on basic photography.

Something like "Understanding Exposure" should work.

http://www.amazon.com/Understanding-...531&sr=8-1
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I will check into that book.....I do have some basic photography books and am doing a lot of reading, and practicing,but I had not seen what the relationship is between the two or if you set one but not the other, what happens. Thank you for writing.
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Old Feb 18, 2008, 1:44 PM   #5
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Hi Sketchpad (aka Janet) again,

Peripatetic is right (as usual!) - and often has very good advice. Do pick up a good simple book, perhaps the one recommended by peripatetic. Actually, I have quite a few (but not that one....and itsounds like a good one to getwhen I've finishedreading each of these thru...:-). As you have surmised, I tend to go overboard. Apparently this isn't a fieldrewarded byimpatience andI will try to balance my enthusiasm with somedeep breaths...right after I get back from SF.I did actually read every section of each book on the subject of lenses (well, almost each one) but justdidn't get this part.I knowthat it mustgeta tad annoying, on occasions,to see questions that someoneshould already know, or be able to findthe answer to, so thank you BOTH for your patience...The good part though, is that you truly havea gift for making things crystal clear, so I'm sure this post will be of value to other newbies also.Although I had already grasped most of what you've said here, it was said more succinctly and in a manner much easier to understand.

Maybe I'll add my 2 cents worth (before you can get your hands on that book), as I'm trying to help you understand about f-stops, and maybe pre-empting a further question or two. I remember some years ago when I didn't know so much about f-stops.

1. The first thing I want to say is, f-stop all relates to the LENS, NOT the camera. So when you say a camera has a wider range (of f-stops than a lens) and then you ask: if I set the aperture on my camera at f22 but my lens at constant f2.8, which lets the light in... you are wrong. ONLY the lens lets the light in. Yes, I knew it was the lens that let in the light but was confused about what seems like a contradiction when the camera sets one aperture internallybut the numbers on the outside of the actuallens say something else. In 99% of lenses on digital SLRs you CONTROL the lens' aperture via the camera body (e.g. via the dials, menus, etc). Got it. But in effect it is only the lens' aperture you change. Of course if you put a different LENS on the same camera body, then you might get a different possible range of f-stops. And if you are using the manual setting on the lensinstead of the autosetting...?

2. Most "non-professional" zoom lenses vary their WIDEST possible aperture, e.g. one of my lenses is the Canon 28-135mm f3.5-5.6 IS USM lens which is the same as you have. This means that at 28mm (widest field of view) the lens wide open will be at f3.5 while at 135mm (it's telephoto / zoomed position) it will only be able to open up to f5.6.Don't ask why. It's technical and mainly got to do with size, cost, etc. (By the way the letters after the lens zoom and apertures are: "IS" meaning: image stabilised. A tip, on your 28-135mm lens, keep the IS switched to ON unless you're really short of battery power.

Then "USM" means "Ultra-sonic motor" on Canon, basically a fast and quiet focussing lens). Both IS and USM aspects are good things. Don't confuse USM on Canon lenses with USM in post processing (meaning Unsharp mask - which actually makes an image SHARPER (not 'less sharp' as one might think from the name!)

I know I'm totally confusing you now..... But basically - all you need to remember is most "cheaper" (but often still very good zoom lenses) will vary their "most wide open" aperture setting. (this is referred to as the "maximum aperture") No,it's an excellent explanation.

3. The "minimum aperture" also varies with these zooms. On my 28-135mm lens it goes from f22 at 28mm to f36 at 135mm. Most of the time you do NOT want to go beyond f11 at any setting. Usually image quality will begin to suffer from f14 or f16 onwards... so don't use it.Yes,that's interesting. It seems in my practicing that the mid rangeapertures work best in ALL settings, whether day or night. I initiallyassumed I needed the smallest aperture during brightsettings and the largest for night, but it hasn't worked that way (again, don't ask why.. it's a technical thing - not worth trying to memorise now! Your brain will explode!)

4. On digital compacts (point and shoots) because the lens is built into the camera (and can't be changed) - it might say "this camera's f-stops range between f2.8 and f5.6 or up to f22", or whatever they want to say... but in reality they are referring to the FIXED lens ON that camera. That's one beauty of digital SLRS (DSLRs) because you can choose lenses for different occasions.

5. Many "non-zoom" lenses (called: "primes") have a wider maximum aperture than most zooms. For example I have a Canon 50mm f1.8 lens and you have the 50mm f1.4 lens, which allows in much more light than our 28-135mm zoom lenses. And those are fixed so they can stay at 1.4 Usually prime lenses provide higher quality images (sharper, better contrast, less distortion, etc) than zooms, but they lack the versality of zooms. For the majority (maybe 50% to 75%) of DSLR owners having one "normal zoom" lens is enough.

Now I know you have already got other lenses (e.g. your 100mm macro and the Sigma 10-20mm and that 50mm f1.8 lens), but a a general statement, choosing a second lens (or more lenses) is better done when you REALLY know what you want. He he he...ya think? Don't worry I'm not saying you have chosen the WRONG lenses.No, I understand what you're saying and I agree. In hindsight...well, no point going thereJust try to learn one lens at a time. I'd start with the 28-135mm lens. That perhaps covers the most useful zoom range you'd want.

If you photograph lots of field sports, you will often need a fast, telephoto (maybe zoom) lens. A wildlife photographer might need a long telephoto (maybe zoom, maybe not) lens. The landscape photographer might want to get an ultra-zoom lens (like our Sigma 10-20mm lenses). Or if you do a lot of portrait work, maybe a sharp 50mm or 85mm or 100mm prime lens is the answer (your 50mm f1.4 is ideal and sometimes your 100mm f2.8 could also be used for outdoor portraits). It depends a lot on what exactly is photographed and in what conditions (e.g. small birds vs pets, outdoor motor sports vs indoor gymnastics). Studio lighting vs natural outdoor lighting (and is that mostly sunlight or do you live in place where the weather is cloudy most of the year?)

So you see that there are endless possibilities and hence a wide variety of lenses to choose from. And prices from $50 to $5000 and beyond. As you've probably already discovered. Indeed I have

My advice is... Use the 28-135mm lens to begin learning. Photography learning is a life-long exercise, which is fun. Take a photo of a flower at 135mm f5.6 and then take a photo of it at 135mm f16 (just to demonstrate the difference).

Here is a quick googled answer / link, that might also help you in case I've already caused you to go to sleep! http://www.photoxels.com/tutorial_aperture.html Really, try reading a photography book. Experiment. Practise. Learn. Look at the settings (mainly f-stop, shutter speed and ISO). Try making more photos, also thinking about composition, etc.

All the best... Sorry I wrote SO much. My 2 cents worth is obviously not charged by the hour! :-)Paul And I am very grateful that you DID write so much. You are a gem. Thank you Paul
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Old Feb 19, 2008, 1:30 PM   #6
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Hi sketchpad,

a quick reply.. my posts now in blue

I'm glad you appreciated my post... With pleasure.

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Of course if you put a different LENS on the same camera body, then you might get a different possible range of f-stops. And if you are using the manual setting on the lensinstead of the autosetting...?

The Manual setting is something for advanced photographers (I use it very rarely, I'm not at that "stage" yet) or for specific circumstances. If I were you I would begin using AV (aperture priority) mode, where you can set the f-stop of the lens, and the camera will adjust the shutter speed automatically to get what it thinks is the correct exposure... and in most cases that is what you want.


3. The "minimum aperture" also varies with these zooms. On my 28-135mm lens it goes from f22 at 28mm to f36 at 135mm. Most of the time you do NOT want to go beyond f11 at any setting. Usually image quality will begin to suffer from f14 or f16 onwards... so don't use it.Yes,that's interesting. It seems in my practicing that the mid rangeapertures work best in ALL settings, whether day or night. I initiallyassumed I needed the smallest aperture during brightsettings and the largest for night, but it hasn't worked that way

Yes, on most lenses, and especially consumer lenses like the 28-135mm, the "mid range" apertures are the sharpest (e.g. around f8 . But you can also often use lenses at their maximum aperture (e.g. f5.6 at 135mm) which is still perfectly acceptable. Pro lenses are often almost just as sharp at max aperture at stopped down....

Many "non-zoom" lenses (called: "primes") have a wider maximum aperture than most zooms. For example I have a Canon 50mm f1.8 lens and you have the 50mm f1.4 lens, which allows in much more light than our 28-135mm zoom lenses. And those are fixed so they can stay at 1.4
Well they are not "fixed" as such, because they can also stop down to e.g. f2, f2.8, f4, f5.6, f8, f11, f14, etc. (and stops in between). I don't know if there are any lenses (apart from maybe REALLY old lenses or very specialist lenses) which can not vary their aperture. Maybe a more knowledgeable person can let us know.... but for all intents and purposes, the apertures of lenses today can be varied.

Maybe you mean of course that because they don't zoom they can have f1.4 at any focus setting (as opposed to FOCAL setting!) On the 28-135mm lens, if you focus on something close at 28mm, the max aperture is f3.5 and if you focus on something far away at 28mm it is still able to do f3.5. Or if you are at 135mm and focus at something close max aperture is f5.6 or if you focus on something distant, you can still have max aperture of f5.6


All the best... Sorry I wrote SO much. My 2 cents worth is obviously not charged by the hour! :-)Paul And I am very grateful that you DID write so much. You are a gem. Thank you Paul

With pleasure.

Paul
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Old Feb 19, 2008, 2:04 PM   #7
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Good advice onthe lens, it will stay on auto unless I've got the leeway to experiment. Yes, that's what I meant aboutthe 1.4 -being able to use thatsame setting atany distance. Maybe "constant" is a better term than fixed.I'm taking just the 10-20 and the 28-135 with tomorrow...I agree that those 2 will give me MORE than enough to practice with. I didn't want to wear out my welcome here so I posted a new question in the newbie section on inclement weather. Just in case you are in that neighborhood...60% chance of rain all thru the week in SF!!
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Old Feb 20, 2008, 6:08 AM   #8
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sketchpad wrote:
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Yes, that's what I meant aboutthe 1.4 -being able to use thatsame setting atany distance. Maybe "constant" is a better term than fixed.
Hi Janet,

Actually, your wording is still flawed (sorry to say!) :roll: "any distance". That lens will always be a 50mm lens. "Focus distance" has nothing to do with "focal distance" in terms of which f-stops are available.

Whereas with the 28-135mm lens for example, it's a 3.5 - 5.6 f-stop lens. f3.5 available at 28mm and f5.6 available at 135mm. The 50mm lens has f1.4 available. At 50mm. Or 50mm or 50mm. (or fifty millimetres).

Hope you get the picture. Enjoy San Fransico. If you want guaranteed warm / sunny weather at this time of year, you need to come here to Australia (or at least Adelaide where I live!) We've had 4 days in a row above 37 degrees (4 days above 100Farenheit)..

Paul
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Old Feb 20, 2008, 3:17 PM   #9
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Actually, your wording is still flawed (sorry to say!) :roll: "any distance". That lens will always be a 50mm lens. "Focus distance" has nothing to do with "focal distance" in terms of which f-stops are available.


...oi vey....yes,at times either the thought process is wrong or the tongue is twisted.Lots of things are falling into place...but somebounce backout...the fact that the 50mm is a fixed lens but is also a telephoto, is interesting (he says, ohmygod, is she EVER getting on the plane???)

We've had 4 days in a row above 37 degrees (4 days above 100Farenheit).

That sounds great! although Ican't complain...there's muchcolder weather going on plus the darkdrizzlies should make the nighttime Alcatraz tour quite authentic! See you when I get back...

:bye:Ciao, Janet

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Old Feb 21, 2008, 7:25 AM   #10
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Janet, here's something that should help you.

Switch you camera to aperture priority mode. Set the aperture to its maximum value at 28mm. Turn the camera around and look into the lens from arm's length.

Now set the aperture to f16. Look into the lens and press the depth-of-field preview button.

Now set it to f8. Press the DOF preview.

Now you can see what changing the aperture is doing.
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