Posted by Barbara Graham on February 1, 2011 at 12:00 PM
I just can't understand yet anything about mm and lenses and whether you can put a 58-mm UV filter on a 55-250-mm lens and if so why. I also don't understand why a lens says 4.0-5.6 but you can use it at any setting.
Where can I find something to read that really starts from the very, very, very beginning about this? I bought three books at the bookstore this morning, one about the T2i, one about PSE9 and one about DSLR cameras, but I went in to find a book about lenses and there really isn't anything in any book I saw (and I sat down and looked through 10 books at least) about the above types of questions.
To clarify, I'm not a dummy about math. In 1990 at the ripe old age of 43 I got a degree in Computer Science. But I am missing something vital about lenses and the numbers and I can't really grasp it until I can see the foundation that I'm missing.
Can anyone direct me to a place to start with the very, very basics of lenses and the numbers associated with them? I would greatly appreciate it.
The millimeter specification for a given lens is it's focal length; e.g. 55-250. Filter diameter is not related to the focal length. It specifies the size the filter needs to be to fit the particular lens. For example, I have a lens with a 90mm focal length, but it uses a 67mm filter.
I also don't understand why a lens says 4.0-5.6 but you can use it at any setting.
A specification such as this means that the wide open aperture of the lens varies between f 4.0 and f 5.6 as the focal length of the zoom lens is changed. For example, with a 55-200mm lens, the wide open aperture (f 4.0) occurs when the lens is set to 55mm. When the lens is zoomed to 250mm, the wide open aperture is f5.6. Your lens allows you set any aperture between wide open and the minimum (smallest) aperture for the lens, say, f22.
I hope this helps. let us know if you need more clarification.
You are a serious student, and I like that!
--P
Posted by Barbara Graham on February 1, 2011 at 12:44 PM
Thank you so very much, Preston. That helps immensely.
Posted by Luke Ormand on February 1, 2011 at 12:46 PM
I agree with what Preston says.
I must admit I made a similar mistake when I bought my first UV filter - I got a size 55 because the lens was an 18-55mm. Well turns out I needed a 52mm size UV filter - lesson learned!
I don't know of any books that cover just lenses... but any book that covers DSLR's should also mention lenses. I have a book at home that is really helpful for the beginning stuff... maybe I'll do a blog post about that and send you the link.
- Luke
Posted by Barbara Graham on February 1, 2011 at 12:48 PM
Oh, my, there are tutorials there on all the things I need to know, and I can understand them! Thank you!
Posted by Lorna Taylor on February 1, 2011 at 1:52 PM
Keep asking these great questions Barbara, there are answers there every time I read one of your questions, that I did not know at the time that I myself wanted to know more about! Cheers
Posted by David Bostedo on February 1, 2011 at 11:12 PM
Cambridge in Colour is terrific - read everything on there Barbara!!! You also may want to browse the Luminous Landscape articles and tutorials. Lots of good info there too, although not as well organized.
Posted by Kent Staubus on February 2, 2011 at 9:00 AM
The main thing to keep in mind about lenes is they have three different properties directly relating to the photo. One is how long the lens is. Second is how "fast" the lens is, i.e. how much light it let through. Third is how it focuses, such as speed of the autofocus. I guess there are other issues too such as distortion and what the zoom range is (if any,) but for nature photography those might be lesser issues. Not sure why you would choose a UV filter. Modern cameras have a UV filter built in over the sensor. I do often use a polarizer in daytime shots as it removes a lot of glare.
The Luminous Landscape article above is a good one, as is the Cambridge one.
Just to be perfecty clear Barbara, the mm measure for the filters is actually the diameter of the threads on the end of the lens that the filter screws into. That is much different than the focal length.
Posted by Luke Ormand on February 2, 2011 at 11:40 PM
Posted by Barbara Graham on February 3, 2011 at 12:55 AM
Thank you, Luke.
Posted by Paul DeCesare on February 3, 2011 at 1:52 AM
Barbara, once you memorize the aperture numbers it's all easy from there. Aperture number is the same thing as F-Stop, and both of those names tell you absolutely nothing, I understand that. But read those tutorials and you will be "in the know".
I will be a pest and try to do a quick summary for you, and if you already know this stuff please forgive me: You will hear the word "stop" used all the time. Here's what it means: every time you double or halve your brightness of light, that's a "stop". That's it, that's all it means. So if you shoot at 1/500 of a second and it's too dark, try increasing the amount of light your sensor gets by 1 stop, which means, you guessed it, double the amount of light. How? Just shoot at 1/250. The shutter will be open twice as long, and voila, you get double the light, a.k.a. one stop more light. If that gives you a good exposure, you're done, otherwise you keep going. If you go from 1/500 to 1/125, that's two stops of light, 1/500 to 1/250 is one, and 1/250 to 1/125 is one. Makes sense, right?Your ISO works the same way (ISO is the light sensitivity of your sensor, 100 is noise-free but requires more light, 800 is noisy but needs a lot less light). So, again, going from ISO 200 to ISO 400 is one stop of light increased, because 400 is twice as fast as 200. It's honestly that simple. Application in the field: if you need 1 stop more light and the wind is blowing and you want sharp trees, you have to keep your shutter speed at 1/500, because 1/250 may be too slow. So, change that ISO from 200 to 400 and there's your one stop increase of light to the sensor. Simple! You can't go TOO far, ISO 6400 and higher gets WAY too noisy if your camera even does that high. But that's another subject. And you use the histogram to know if you have the right exposure, again, another topic.
By now you're saying, what on earth does this have to do with a lens and the weird 4.0 and 5.6 stuff? OK, this is where it gets a little tricky and you just need to memorize the numbers I'm about to show you. The lens does offer the same "stop" adjustment, but the numbers are weird. Let me explain:
With ISO it's simple, each number is twice as fast as the previous: 100, 200, 400, 800 (and you can go in-between for half stops of course, but let's keep it whole for right now). Twice as fast means what you think, double sensor speed gives me double the amount of light, hence a one stop increase. OK, shutter speed is the same. As you slow down you get double the light, same principle: 1/2000, 1/1000, 1/500, 1/250, 1/125 1/60 (notice it gets close but not exact there with 1/60), and I could go on, but you get the idea. Double the speed time doubles the light. I know, I know, I've worn that record out down to the grooves, just making sure it sticks, lol!OK, the lens: how do you adjust the "stop" thing? Here are the numbers that we all have memorized for the last 6 decades or longer. Each number CUTS the light in half, so the first number is the brightest. Here are the most common F-Stops you'll see in every DSLR lens, and adjusting this setting is yet one MORE way to double or cut light:
4.0, 5.6, 8.0, 11.0, 16.0, 22.0
That's what those numbers mean! Back to the field example: You're shooting at ISO 200, 1/500 shutter speed, f/5.6. You need one more stop of light, your first shot is too dark. So, you can change your F-Stop (again also known as aperture) from 5.6 to 4.0. You just gained a stop of light. There's a scientific reason for those numbers, but just know that memorizing them is the waty to go. Again, you do have ½-stop options, such as f9.5 which sits between 8 and 11, but I'm using whole stops to keep this simple.BTW, your lens starts at 4.0 as the fastest f-stop at the 55mm end because you get more light at 250mm. When you zoom to 250mm the light decreases and so your fastest F-stop is 5.6 at that point. The pro lenses that cost $700 and up usually have the same f-stop for any focal length in the zoom range.Two final things I KNOW you want answered: One, what about a 50mm 1.8 lens? That's obviously great in low light if it can shoot at a super fast 1.8, but what are the standard "stops" from 1.8 to f4? Here's the range of that lens: f1.8, 2.0, 2.8, 4.0, 5.6, 8.0, 11.0, 16.0, 22.0. Technically 1.7 to 2.0 is a full stop, but close enough. The tutorials will explain that further for you.
OK, the second and final question: If f4 is the fastest aperture on your lens, why not just always shoot at f4? It gets you the most light, right? In fact, that 50mm, why not just shoot at 1.8? That'd be REALLY fast and good in low light. Why even bother with 5.6 or 8 or 11 or whatever else?The answer is a huge one, but here's the first thing you need to know: it's all about the creativity part because the aperture also control how deep your focus will be. Here's why: If you stand at the end of a long row of roses in your garden and you are set at f4 on your lens, the fastest aperture, and you focus on and shoot that first rose, only that first rose will be in focus. The second may be a little, and the 3rd and all the rest will be out of focus which can look very nice if that's the look you ant. OK, set the aperture to f8 which is less light now coming in (you'll need higher ISO or slower shutter speed to compensate, not important right now). Take the same shot. Now you'll see maybe the first 4 roses in focus, THEN the 5th and farther ones start going out of focus. OK, now set that lens at f22. You shoot (given the correct shutter speed to get the right exposure), and what happens? ALL of the roses are in focus! THAT is what Depth of Field is all about, and you control it with your aperture. I will tell you that at f22 the lens is letting in VERY little light, so you probably will end up with a slow shutter speed such as 1 second (or whatever). That means tripod, no hand-holding the camera. But the point is, those weird numbers control your stops of light AND your depth of what is in focus. You may be thinking that f1.8 must be REALLY narrow as to what's in focus. Absolutely, a portrait at close range will have an eye in focus and a nose out! That's how those nifty wedding shots are done. But for landscape, you want deep focus, which requires f11, f14, etc.That means slow shutter speeds which is why so many of us can't function without a tripod, lol.
So that's it, Photography 101 and what aperture numbers mean. There's a LOT more to it such as balancing that trio of ISO, shutter and aperture, but now you know the mechanics. BTW, the FILTER size is totally separate, that just means how wide you lens barrel is where the filter threads are.
Isn't this a great hobby??
Posted by Katja Rosvall on February 3, 2011 at 3:07 AM
Speaking of filters, it's pretty much vital to have one permanently installed on each lens you own (the so called 'protective filter'). It protects the outermost glass surface (well, lens) of the lens; it's much cheaper to replace the filter than to repair damage to the lens itself. My filters are labelled 'skylight' (except the one that claims to be a 'skyligt' ), but there must be other kinds of filters suitable for the job. It's a good idea to make sure the filter has threads on both sides, so that if you want, you can add another filter on top of it.
Each lens should have its own protective filter, so that it's always there whenever you need the lens, and all your lenses may have different thread sizes anyway. Needless to say, a bad-quality filter may affect your photos, so investing in good quality will pay off.
Posted by David Bostedo on February 3, 2011 at 9:44 AM
... it's pretty much vital to have one permanently installed on each lens you own (the so called 'protective filter'). It protects the outermost glass surface (well, lens) of the lens; it's much cheaper to replace the filter than to repair.
Hey Katja - That's certainly a valid viewpoint, but I'd prefer not to put any more glass between my subject and the sensor. The possible drawbacks to image quality aren't worth it to me, and I'm much more likely to damage the lens barrel than the front element. I think if you search you'll find some threads discussing both sides of things, and I'd guess - and it's just a guess - that the majority (i.e. more than 50%) of people don't put "protective" filters on their lenses.
Discussion
15 repliesWhere can I find something to read that really starts from the very, very, very beginning about this? I bought three books at the bookstore this morning, one about the T2i, one about PSE9 and one about DSLR cameras, but I went in to find a book about lenses and there really isn't anything in any book I saw (and I sat down and looked through 10 books at least) about the above types of questions.
To clarify, I'm not a dummy about math. In 1990 at the ripe old age of 43 I got a degree in Computer Science. But I am missing something vital about lenses and the numbers and I can't really grasp it until I can see the foundation that I'm missing.
Can anyone direct me to a place to start with the very, very basics of lenses and the numbers associated with them? I would greatly appreciate it.
The millimeter specification for a given lens is it's focal length; e.g. 55-250. Filter diameter is not related to the focal length. It specifies the size the filter needs to be to fit the particular lens. For example, I have a lens with a 90mm focal length, but it uses a 67mm filter.
A specification such as this means that the wide open aperture of the lens varies between f 4.0 and f 5.6 as the focal length of the zoom lens is changed. For example, with a 55-200mm lens, the wide open aperture (f 4.0) occurs when the lens is set to 55mm. When the lens is zoomed to 250mm, the wide open aperture is f5.6. Your lens allows you set any aperture between wide open and the minimum (smallest) aperture for the lens, say, f22.
I hope this helps. let us know if you need more clarification.
You are a serious student, and I like that!
--P
I must admit I made a similar mistake when I bought my first UV filter - I got a size 55 because the lens was an 18-55mm. Well turns out I needed a 52mm size UV filter - lesson learned!
I don't know of any books that cover just lenses... but any book that covers DSLR's should also mention lenses. I have a book at home that is really helpful for the beginning stuff... maybe I'll do a blog post about that and send you the link.
- Luke
Here is a nicely written and illustrated tutorial that should be helpful...
Understanding Camera Lenses .
--P
The Luminous Landscape article above is a good one, as is the Cambridge one.
Kent in SD
I will be a pest and try to do a quick summary for you, and if you already know this stuff please forgive me: You will hear the word "stop" used all the time. Here's what it means: every time you double or halve your brightness of light, that's a "stop". That's it, that's all it means. So if you shoot at 1/500 of a second and it's too dark, try increasing the amount of light your sensor gets by 1 stop, which means, you guessed it, double the amount of light. How? Just shoot at 1/250. The shutter will be open twice as long, and voila, you get double the light, a.k.a. one stop more light. If that gives you a good exposure, you're done, otherwise you keep going. If you go from 1/500 to 1/125, that's two stops of light, 1/500 to 1/250 is one, and 1/250 to 1/125 is one. Makes sense, right?Your ISO works the same way (ISO is the light sensitivity of your sensor, 100 is noise-free but requires more light, 800 is noisy but needs a lot less light). So, again, going from ISO 200 to ISO 400 is one stop of light increased, because 400 is twice as fast as 200. It's honestly that simple. Application in the field: if you need 1 stop more light and the wind is blowing and you want sharp trees, you have to keep your shutter speed at 1/500, because 1/250 may be too slow. So, change that ISO from 200 to 400 and there's your one stop increase of light to the sensor. Simple! You can't go TOO far, ISO 6400 and higher gets WAY too noisy if your camera even does that high. But that's another subject. And you use the histogram to know if you have the right exposure, again, another topic.
By now you're saying, what on earth does this have to do with a lens and the weird 4.0 and 5.6 stuff? OK, this is where it gets a little tricky and you just need to memorize the numbers I'm about to show you. The lens does offer the same "stop" adjustment, but the numbers are weird. Let me explain:
With ISO it's simple, each number is twice as fast as the previous: 100, 200, 400, 800 (and you can go in-between for half stops of course, but let's keep it whole for right now). Twice as fast means what you think, double sensor speed gives me double the amount of light, hence a one stop increase. OK, shutter speed is the same. As you slow down you get double the light, same principle: 1/2000, 1/1000, 1/500, 1/250, 1/125 1/60 (notice it gets close but not exact there with 1/60), and I could go on, but you get the idea. Double the speed time doubles the light. I know, I know, I've worn that record out down to the grooves, just making sure it sticks, lol!OK, the lens: how do you adjust the "stop" thing? Here are the numbers that we all have memorized for the last 6 decades or longer. Each number CUTS the light in half, so the first number is the brightest. Here are the most common F-Stops you'll see in every DSLR lens, and adjusting this setting is yet one MORE way to double or cut light:
4.0, 5.6, 8.0, 11.0, 16.0, 22.0
That's what those numbers mean! Back to the field example: You're shooting at ISO 200, 1/500 shutter speed, f/5.6. You need one more stop of light, your first shot is too dark. So, you can change your F-Stop (again also known as aperture) from 5.6 to 4.0. You just gained a stop of light. There's a scientific reason for those numbers, but just know that memorizing them is the waty to go. Again, you do have ½-stop options, such as f9.5 which sits between 8 and 11, but I'm using whole stops to keep this simple.BTW, your lens starts at 4.0 as the fastest f-stop at the 55mm end because you get more light at 250mm. When you zoom to 250mm the light decreases and so your fastest F-stop is 5.6 at that point. The pro lenses that cost $700 and up usually have the same f-stop for any focal length in the zoom range.Two final things I KNOW you want answered: One, what about a 50mm 1.8 lens? That's obviously great in low light if it can shoot at a super fast 1.8, but what are the standard "stops" from 1.8 to f4? Here's the range of that lens: f1.8, 2.0, 2.8, 4.0, 5.6, 8.0, 11.0, 16.0, 22.0. Technically 1.7 to 2.0 is a full stop, but close enough. The tutorials will explain that further for you.
OK, the second and final question: If f4 is the fastest aperture on your lens, why not just always shoot at f4? It gets you the most light, right? In fact, that 50mm, why not just shoot at 1.8? That'd be REALLY fast and good in low light. Why even bother with 5.6 or 8 or 11 or whatever else?The answer is a huge one, but here's the first thing you need to know: it's all about the creativity part because the aperture also control how deep your focus will be. Here's why: If you stand at the end of a long row of roses in your garden and you are set at f4 on your lens, the fastest aperture, and you focus on and shoot that first rose, only that first rose will be in focus. The second may be a little, and the 3rd and all the rest will be out of focus which can look very nice if that's the look you ant. OK, set the aperture to f8 which is less light now coming in (you'll need higher ISO or slower shutter speed to compensate, not important right now). Take the same shot. Now you'll see maybe the first 4 roses in focus, THEN the 5th and farther ones start going out of focus. OK, now set that lens at f22. You shoot (given the correct shutter speed to get the right exposure), and what happens? ALL of the roses are in focus! THAT is what Depth of Field is all about, and you control it with your aperture. I will tell you that at f22 the lens is letting in VERY little light, so you probably will end up with a slow shutter speed such as 1 second (or whatever). That means tripod, no hand-holding the camera. But the point is, those weird numbers control your stops of light AND your depth of what is in focus. You may be thinking that f1.8 must be REALLY narrow as to what's in focus. Absolutely, a portrait at close range will have an eye in focus and a nose out! That's how those nifty wedding shots are done. But for landscape, you want deep focus, which requires f11, f14, etc.That means slow shutter speeds which is why so many of us can't function without a tripod, lol.
So that's it, Photography 101 and what aperture numbers mean. There's a LOT more to it such as balancing that trio of ISO, shutter and aperture, but now you know the mechanics. BTW, the FILTER size is totally separate, that just means how wide you lens barrel is where the filter threads are.
Isn't this a great hobby??
Each lens should have its own protective filter, so that it's always there whenever you need the lens, and all your lenses may have different thread sizes anyway. Needless to say, a bad-quality filter may affect your photos, so investing in good quality will pay off.
Hey Katja - That's certainly a valid viewpoint, but I'd prefer not to put any more glass between my subject and the sensor. The possible drawbacks to image quality aren't worth it to me, and I'm much more likely to damage the lens barrel than the front element. I think if you search you'll find some threads discussing both sides of things, and I'd guess - and it's just a guess - that the majority (i.e. more than 50%) of people don't put "protective" filters on their lenses.