Question about analog lenses

Helloa there!

I've always liked photography and was always shooting pictures with my parents points and shoot camera and later on my own (Panasonic DMC-TZ7, or the ZS3 in the US). Sure enough I had a lot of fun, but it wasn't the real deal. I've had that camera for a year now and lately I've been getting more and more interested in *real* photography, so I picked up my mums old Nikon FG (Argh Nikon, get outta here!) and being just a youngster, I had no idea of analog photography. Turned out it wasn't all that different and I really like photography more than ever.

I only have on question, why are the F stops so different on an analog lens? I have a 52mm prime lens with F/1.8-22. How is that possible? As in, most digital lenses have like a F/4-5.6, but my lens pretty much covers the whole range!

Now I just need to save up for my first Digitral SLR I think, because this really is something I want to continue with; probably going for the T2i/550D.

Regards from the Netherlands

Greetings.

What you're dealing with is not "analog vs digital". There is really no such thing as "digital" when considering lenses. All lenses that I have ever seen on cameras use analog technology to bend the light rays.

Cameras can use film or digital technology, but within the same generation of cameras - such as the Canon EOS family - the very same lenses can be used on film cameras or on digital cameras.

What you've run into is a difference in the maximum aperture of lenses. The maximum aperture (smallest f-stop number) for a lens is the widest opening a lens can be adjusted to. Usually, that's what is advertised in the "name" of the lens. The minimum aperture (maximum f-stop number) for a lens is rarely, if ever advertised.

Another thing that may be confusing you is the fact that the Nikon lens has a manually adjusted aperture. Therefore, there is a control ring on the lens that is marked with all of the possible aperture (f-stop) settings. Modern camera systems and the lenses for them are different in that the camera actually "tells" the lens what aperture (f-stop) to use, so there is no manual control for that function on the lens. The camera "knows" what the maximum and minimum aperture for the attached lens happens to be and won't let you adjust the values beyond those limits.

If this answers your question, great. If not, fire away with more questions and you'll get all the help you need.

As SkipD says you're confusing the maximum possible aperture of a lens with the markings for setting a lens aperture.

The f/4-5.6 lens will do f/4 to around f/22 (some do more and some do less) at it's shortest focal length and will do f/5.6 to around f/22 at it's longest focal length but the aperture for that lens is set electronically via the camera and as such the marking for the aperture setting will be shown on the camera body.

You'll probably find that the manual lens has 1.8 (and the focal length of the lens) marked on the front of the lens somewhere which is the equivalent marking to the 'f/4-5.6' marking on modern lenses. Older lenses are often identified as 50mm 1:1.8 or 1.8/50 rather than as a 50mm f/1.8.

Ah this explains a lot! So, pretty much what you guys are saying, that when there's a range of F-stops mentioned, for example f/4-5.6, that mean's that the f/4-22 will be used for the shortest focal lengths and the f/5.6 for the longest, thus meaning, that whenever there's a range of focal lengths mentioned it's always a zoom lens. And that would also be why prime lenses always have one f-stop mentioned (the minimal f-stop), because the higher range of focal lengths are available no matter what? The number indicates the minimal f-stop.

SkipD wrote in post #11245234
Another thing that may be confusing you is the fact that the Nikon lens has a manually adjusted aperture. Therefore, there is a control ring on the lens that is marked with all of the possible aperture (f-stop) settings. Modern camera systems and the lenses for them are different in that the camera actually "tells" the lens what aperture (f-stop) to use, so there is no manual control for that function on the lens. The camera "knows" what the maximum and minimum aperture for the attached lens happens to be and won't let you adjust the values beyond those limits.

But you CAN use manual settings if you want to right? I know stuff like USM and AF can do it all for you, but you can put that off right?

One thing that you picked up is that it is not "usual" to see a zoom lens with such a wide aperture -- I've never shot with a lens like that and don't know the details, but it may have something to do with the manual aperture ring that was mentioned.

For modern lenses, including the Canon EF lenses that work with all our DSLRs, your "normal" fast zoom will typically have a wide aperture/low f-number of f/2.8. These lenses tend to be expensive, because they are more expensive to manufacture lenses where it all "works" for that wide of an aperture. So, EF zooms are f/2.8 at the widest. EF primes, though, can be made for a much wider aperture -- Canon has a couple with an f/1.2 aperture, in fact, although again the cost of those lenses is a lot higher than, say, a similar focal length at say f/1.4 or f/1.8.

So, it was a good observation and question, and I hope we helped!

TijmenDal wrote in post #11245579
Ah this explains a lot! So, pretty much what you guys are saying, that when there's a range of F-stops mentioned, for example f/4-5.6, that mean's that the f/4-22 will be used for the shortest focal lengths and the f/5.6 for the longest, thus meaning, that whenever there's a range of focal lengths mentioned it's always a zoom lens. And that would also be why prime lenses always have one f-stop mentioned (the minimal f-stop), because the higher range of focal lengths are available no matter what? The number indicates the minimal f-stop.

So that you can fully understand what I'm about to explain, you need to first understand that the f-stop numbers are actually a ratio. A setting of f/4, for example, means that the len' effective internal opening diameter is 1/4 of the focal length of the lens. F/22 means that the lens' effective internal opening diameter is 1/22 iof the focal length of the lens. I say "effective internal opening diameter" instead of the diameter of the lens' iris diaphragm because it's my understanding that today's optical design wizardry can effect how much light gets through a lens in addition to using the iris opening. I could be wrong on that point, though.

Regarding the aperture settings, there are two types of zoom lenses. The more common type of zoom lens (including almost ALL "consumer-grade" zoom lenses) will be marked like your example of f/4-5.6. This is because the ratio of lens opening to focal length changes as the focal length of the lens is adjusted. In the "olden days" where the lens' aperture was set with a manual ring (such as that on the Nikon lens you have), the photographer had to compensate when adjusting the focal length of a zoom lens. With today's automagic cameras, most of this is dealt with by the camera. If you tell the camera that you want f/8 when using an f/4-5.6 lens, the lens will be adjusted to an effective f/8 at all focal lengths. It's only when you want a wider opening than f/5.6 that the camera will actually show you that you cannot get your desired f-stop at some focal lengths.

There are high-end zoom lenses (such as the three Canon "L" class zoom lenses that I use) that have some intricate mechanics in them that mechanically adjusts the iris diameter as the focal length is changed. The result is that there is no change in the light level getting through the lens as the focal length is changed. These zoom lenses are marked with a single f-stop number (all of mine are f/2.8 ) on the front of the lens. This does not make these lenses into a fixed focal length (often called "prime" on photo forums) lens, of course.

As Tony alluded to above, there are no zoom lenses with maximum apertures larger (smaller f-stop numbers) than f/2.8. To get any "faster" lenses, one needs to choose fixed focal length lenses.

TijmenDal wrote in post #11245579
But you CAN use manual settings if you want to right? I know stuff like USM and AF can do it all for you, but you can put that off right?

You can manually set the aperture of all lenses used with EOS cameras. However, when using lenses designed for these cameras the setting is made IN THE CAMERA and not on the lens like your Nikon lens. You just have to select the right exposure control mode on the camera's dial. Either Av or M positions will let you define the aperture setting that you want to use. The Av position makes the camera choose the shutter speed while the M position requires the photographer to choose a shutter speed in addition to the aperture setting.

TijmenDal wrote in post #11245579
Ah this explains a lot! So, pretty much what you guys are saying, that when there's a range of F-stops mentioned, for example f/4-5.6, that mean's that the f/4-22 will be used for the shortest focal lengths and the f/5.6 for the longest, thus meaning, that whenever there's a range of focal lengths mentioned it's always a zoom lens. And that would also be why prime lenses always have one f-stop mentioned (the minimal f-stop), because the higher range of focal lengths are available no matter what? The number indicates the minimal f-stop.


But you CAN use manual settings if you want to right? I know stuff like USM and AF can do it all for you, but you can put that off right?

You seem to have a pretty good grasp -- lenses with the range of apertures as part of their description, that range is the widest aperture possible over the range of focal lengths, the widest possible at the shortest focal length. So an EF lens that has a range of f/4-f/5.6 means the widest aperture of f/4 will be limited to the shortest focal lengths, whereas the longest focal lengths will push that to f/5.6.

You will also see zoom lenses with just one aperture spec -- these are lenses that are capable of having a "constant" aperture through its focal length. They are more spendy.

As to Manual vs Automatic, you'll see two built-in "modes" where you can do certain things manually -- the Auto Focus/Manual Focus switch on the lens lets you turn the AF controlled by the EOS camera on and off so if you want you can control the focus only with the focus ring.

You are likely wondering more about Manual Exposure, though, where you set the cameras aperture and shutter speed and typically the ISO. The lens is then "instructed" by the camera to use that aperture.

The limits with the EOS cameras and EF lenses as far as widest allowed apertures are still in place becase of the actual design limits of the lenses.

tonylong wrote in post #11245682
You will also see zoom lenses with just one aperture spec -- these are lenses that are capable of having a "constant" aperture through its focal length. They are more spendy.

So, these lenses don't have any aperture apart from their set aperture? Like, they have only one type of diaphragm and that's it? Or am I completely missing the picture here?

The rest is all crystal clear, thanks a lot!

TijmenDal wrote in post #11245986
So, these lenses don't have any aperture apart from their set aperture? Like, they have only one type of diaphragm and that's it? Or am I completely missing the picture here?

The rest is all crystal clear, thanks a lot!

Almost all photographic lenses have adjustable iris diaphragms to control the amount of light that is allowed to go through them. There are only a very few lenses that have a fixed aperture.

Older manually controlled lenses like your Nikon lens have a control ring on the lens to adjust the aperture. When using these on the original cameras they were designed for, the iris diapragm usually stayed wide open until the shutter release button was depressed. Then the iris would close down to the chosen aperture.

Most (all?) of the lenses designed for today's automated cameras do not have manual aperture control rings on them. The camera communicates with the lens and "tells" it what the photographer has chosen for the aperture to use for the exposure (by settings made to the camera). The lens' iris is still kept wide open until the shutter release button is depressed so that there's more light coming through the lens for focusing and viewing.

All of the automated lenses can be set to any aperture in a range, just like the Nikon lens you have. It's just that the setting is done via camera automation instead of a manual ring.

All of the lenses stop way down. For instance the 18-55mm f/3.5-5.6 has an aperture range of 3.5-22 at 18mm and 5.6-36 at 55mm.

My understanding is that 'constant aperture' means the aperture does not change as you zoom, which is nice. Not having that feature on the lens I describe above, I could set up the photo just the way I want it at 18mm f/3.5 and if I zoom in I will end up with a slower shutter speed whether I like it or not because the f-stop will increase. Unless I change the ISO of course, but you see what I mean.

TijmenDal wrote in post #11245986
So, these lenses don't have any aperture apart from their set aperture? Like, they have only one type of diaphragm and that's it? Or am I completely missing the picture here?

The rest is all crystal clear, thanks a lot!

The aperture "spec" refers to the widest the lens can go at a given focal length. As Skip points out, the physical opening has to adjust as you change the focal length, until it hits the limit of the physical design. The "constant" lenses have a design that allows the blades of the physical opening to continue opening the aperture as the lens goes through it's focal length range so that (if you are in Av or Manual and select the widest aperture) the f-number, the ratio of the opening to the focal length, will stay constant.

As you've seen, most zoom lenses are not designed so "wide" so their openings can't enlarge enough to give, say, an f/4 aperture throughtout the focal length -- the physical opening can give f/4 at, say, 70mm but as a lens is extended toward, say, 300mm the physical opening is already as wide it can get so that the f-number will show a "narrow" aperture/higher f-number. Less light is making it to the sensor because of this combination of extended focal length and limited opening. So, these lenses get forced to expose at the higher f-number and give us the higher f-number calculation.

Canon does have a series of zooms that are capable of maintaining a "constant f/2.8" and another series that is capable of maintaining a "contstant f/4". Needless to say, the f/2.8 lenses are more expensive because they have to be built with a wide enough pysical opening structure to allow the aperture blades to keep going wider as the lens focal length goes from, say, 70mm to 200mm, and the lenses are hefty because ot this. The f/4 lenses are also very nice for the constant feature -- and because they don't require the very large opening of the f/2.8 series, they are less expensive/less hefty than the f/2.8 and so are quite popular -- they constitue the "second tier" of Canon L zoom lenses and are known for sharp, high quality glass.

TijmenDal wrote in post #11245100
Helloa there!

I only have on question, why are the F stops so different on an analog lens? I have a 52mm prime lens with F/1.8-22. How is that possible? As in, most digital lenses have like a F/4-5.6, but my lens pretty much covers the whole range!

As Skip mentioned, there is no such thing as digital vs analog lenses.. Both are interchangable depending of course on the camera body and the lens itself..

Most lenses are normally rated by focal length and by maximum aperture..

For example you can have 50mm prime lenses with a maximum apertures of anything from f/1 to f2.. Most 50mm primes are around f/1.2 to f/1.8 maximum aperture.. With prime lenses, the aperture is always constant..

Zooms are a different kettle of fish.. Some zooms the maximum aperture will remain constant when you zoom in from wide to telephoto. The Canon EF 70-200mm f/2.8 is such a lens.. Other zooms, the maximum aperture will change when you zoom.. At 70mm the maximum aperture could be f/4 but at 300mm the maximum aperture could be f/5.6.. The Canon EF 70-300mm f/4-5.6 is such a lens.. These lenses are easier to design and manufacture,, therefore a little cheaper..

Without getting into the physics and mathematics of lens design, let's look at a 50mm f/1.4 prime.. At f/1.4 the lens "lets" in twice the light than at f/2, f/2 will let in twice the light than f/2.8 and so on..

Check out the diagram below..

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An interesting question that could be spurred by all this is something I can ask but can't answer because I don't have the technical knowledge of optics and lens design involved.

So, considering the fact that the wideness of the aperture/physical opening is related to and limeted by the focal length. So, at least in the Canon DSLR world, primes begin to hit a "limit" at, say, the 85 f/1.2 -- a big heavy lens that apparently "maxes out" the ultra-wide engineering for longer focal lengths. The next-longer wide primes in the Canon lineup are f/2 -- the 100mm f/2, the 135 f/2 and the 200 f/2, and longer than thatthey goe to f/2.8, f/4 and f/5.6.

Now, the point of this and the question it raises is why a zoom within the range of one of these longer primes can't actually be built with the wider spec of the prime? For example, why can't the 24-70 f/2.8 be, instead, the 24-70 f/1.2/1.4/1.8? Or the 16-35 f/2.8 be the 16-35 f/1.2/1.4/1.8?

Of course the obvious question is that they would be costly, but duh...is that it? Or is there a design/engineering problem that holds things back? I mean if it's just cost, how much more would it cost for the 24-70 f/1.2 beyond what people pay for a combination of the 85 f/1.2, the 50 f/1.2 and the 24 f/1.4 -- a combination that plenty of people have paid out a good ~$5000 for?

Well, like I said I have the question but not the answer, so you guys who know stuff and such are invited to toss out thoughts!

tonylong wrote in post #11246620
Now, the point of this and the question it raises is why a zoom within the range of one of these longer primes can't actually be built with the wider spec of the prime? For example, why can't the 24-70 f/2.8 be, instead, the 24-70 f/1.2/1.4/1.8? Or the 16-35 f/2.8 be the 16-35 f/1.2/1.4/1.8?

Compare the size difference of the 24-105 f/4 compared to the 24-70 f/2.8. Now imagine how much bigger a 24-70 f/2 would be. Now imagine how much bigger a 24-70 f/1.4 would be.

Forgetting about the size for a second, why pay $10,000 for a 24-70 f/1.4 when you can spend way less on a set of f/1.4 primes.

Cost/weight coupled with what would surely be a tiny target market are the main barriers to f/1.4 zooms.

tonylong wrote in post #11246620
I mean if it's just cost, how much more would it cost for the 24-70 f/1.2 beyond what people pay for a combination of the 85 f/1.2, the 50 f/1.2 and the 24 f/1.4 -- a combination that plenty of people have paid out a good ~$5000 for?

The 85/1.2, 50/1.2 and 24/1.4 are already quite large lenses. Combining those lengths (and the in between lengths if you want a continous zoom) into a SINGLE lens would weight/cost WAY more than what you have in mind.