Stoopid Noob Question about aperatures

[DiamondSCattleCo]

I pulled the trigger on a Nikon D50 the other day, and while I'm waiting for it to come, I've been snooping around looking for lens recommendations. While reading reviews, I keep seeing reference to "open all the way" and "closed up a bit" on fixed aperature, prime lenses.

So, dumb question: Is a fixed aperature lens like a Nikkor 50mm f1.8 not "open all the way" all the time? Or what exactly is being referred to?

Thanks in advance. Learning very much from this website, and for every question I get answers for, I end up with 10 more questions.

Rod

[jekostas]

The Nikon 50mm F1.8 isn't actually a fixed aperture lens. In fact, there are very few true fixed aperture lenses besides cadiotropic-type (mirror) lenses.

The Nikon 50MM has an aperture range of F1.8-F22. Normally you don't shoot a prime lens "wide open" (at maximum aperture) unless the conditions you're in absolutely demand it, since probably 90% of wide primes benefit optically from a slightly smaller aperture. This is especially prevalent of the lower cost 50MM primes from Nikon and Canon - very good optically for the price, but they really start to shine at F2.0-F2.4 or so.

[TheWengler]

The number listed is the max aperture not a fixed aperture. So f/1.8 is wide open, but that lens is still capable of stopping down to something like f/22. Lenses that have aperture listing like f/4-5.6 are variable max aperture. This is only for zoom lenses. At the short end of the focal range the max aperture is f/4 and at the long end of the focal range the max aperture is f/5.6

[Csae]

A wide open aperture, ie the smallest number the lens can do = the smallest DOF, and the least amount of light required.

Example, shooting portraits usually uses lower numbers, so that the background is out of focus and blurry. Shooting indoors also uses a lower number because of the small amount of light available.

A large number, ie stopped down, will give you a large DOF, but will require alot of light.

DOF = Depth of field.

[DiamondSCattleCo]

So f/1.8 is wide open, but that lens is still capable of stopping down to something like f/22. Lenses that have aperture listing like f/4-5.6 are variable max aperture. This is only for zoom lenses. At the short end of the focal range the max aperture is f/4 and at the long end of the focal range the max aperture is f/5.6

Ah, thank you much. Now I can continue my hunt for a macro lens and a prime. The D50 I bought comes with a Nikkor 28-80mm f3.3-f5.6 G AF and a Nikkor 70-300mm f4-f5.6 G AF. I'm given to understand that the 28-80 is a pretty fair lens, however the 70-300 gets soft at 200. I'm concerned about being able to isolate the subject with the f3.3, so I'm snooping for a good prime as my first purchase.

So is there a decent beginners guide around that would explain that sort of thing? Or a decent book to buy? I've been reading like mad for a couple months, however there doesn't appear to be a good "one stop shopping" website or book.

[Rooz]

Understanding Exposure, Bryan Peterson. read that with your camera handy. most importantly practice and experiment. good luck and enjoy your new camera.

[fionndruinne]

Here's another detail to throw out there for ya... depth of field is enhanced at longer focal lengths, e.g. your 70-300mm will isolate the subject rather well @ 300mm, especially at f/5.6, which will be the maximum (largest) aperture you'll be able to use with that lens at full zoom.

[K1W1]

So is there a decent beginners guide around that would explain that sort of thing? Or a decent book to buy?

Understanding Exposure has already been mentioned but I also highly recommend Thom Hogans D50 ebook (http://www.bythom.com/d50guide.htm). Not only will it explain all the things the user manual doesn't but it also gives you plenty of general photographic tips.

[mattdm]

Here's another detail to throw out there for ya... depth of field is enhanced at longer focal lengths, e.g. your 70-300mm will isolate the subject rather well @ 300mm, especially at f/5.6, which will be the maximum (largest) aperture you'll be able to use with that lens at full zoom.

Depth of field doesn't actually change with focal length — it just seems like it decreases with longer focal lengths because you're usually using the longer focal length to make the subject fill the frame. If instead you just moved closer, perspective would change but the in-focus depth would be identical.

[DonSchap]

Depth of Field (DOF) is comprised of three (four) variables, not just one or two:

Aperture
Focal Length
Distance to subject (center of focus - COF)
Sensor size (minute issue, usually)


When you move in on a subject, with the same aperture selected and same focal length of the lens, you are changing the center of focus (COF), when you refocus to get the subject. That changes the DOF ... you get something different.

Please consult with the online DOF Calculator (http://www.dofmaster.com/dofjs.html) (<- Click on this link) to inspect how these variables and their impact on your photography.

[mattdm]

Depth of Field (DOF) is comprised of three (four) variables, not just one or two:

Aperture
Focal Length
Distance to subject (center of focus - COF)
Sensor size (minute issue, usually)


It's true that the balance of area in focus in front and behind the plane of focus change at different focal lengths (assuming a subject with the same magnification), but the overall DOF doesn't change significantly.

Print/View size is also important. If you make a 1" thumbnail, the entire scene may seem in focus, but if you print large, some of it won't be. (And this is directly related to the sensor size factor, because to get a same-sized print from a smaller sensor, you have to expand more.)



Please consult with the online DOF Calculator (http://www.dofmaster.com/dofjs.html) (<- Click on this link) to inspect how these variables and their impact on your photography.

I like the one at http://www.tawbaware.com/maxlyons/calc.htm .

[DonSchap]

Matt ... consider a simple diagram at this DCRP Thread link (http://www.dcresource.com/forums/showthread.php?t=44064). Post #1 and #16.

[mattdm]

Don, your diagrams are missing the example of changing focal length but constant magnification. That is, move to stand where your focal length makes the subject the same size in your viewfinder. Do the math and you'll see that depth of field remains virtually constant.

[DiamondSCattleCo]

Thanks for the help on the books (and DOF theory). Next time I'm in the city, I'll find the Understanding Exposure book. I DLed the D50 guide, and its great, so I'll be shipping more money off to the author :)

Rod

[Norm in Fujino]

Rod, I gotta say, you're in for an adventure. And "google is your friend." There's a wealth of info on the net, just try googling for stuff like "beginner photography tutorial" and you're set.

[DiamondSCattleCo]

<chuckle> My first stop was Google. I've got about a decade worth of reading bookmarked, but I'm finding sites like this useful for narrowing down the useful articles from the trash. I DL'ed 30 photography eBooks a few weeks ago, and found a couple (I think) gems, so I shipped some dollars off to the authors of those.

Now I just need to convince the wife I need another thousand dollars for a good prime :) If she'd known that buying me a Canon A590 (my first good point and shoot) for Christmas was going to lead to this, I suspect I would have gotten socks :)

Rod

[Rooz]

Now I just need to convince the wife I need another thousand dollars for a good prime :)

no you dont. the 50/1.4 afs, 35/1.8 afs and even the 60/2.8 micro afs all come in at well under $1k. the 35 is only a couple of hundred.

[DiamondSCattleCo]

no you dont. the 50/1.4 afs, 35/1.8 afs and even the 60/2.8 micro afs all come in at well under $1k. the 35 is only a couple of hundred.

Shhhhh... I thought maybe I could convince her that I needed a good prime for a grand, but sneak in a decent macro lens while I was at it :D

<chuckle> I joke around about my wife, but shes good with my hobbies. To be honest, I'm not real sure what I'm going to need next, at least not until I get the camera and lenses in hand. I do a whole mixed bag of shooting, so we'll see if the aperture on either of the lens is enough to satisfy me. I may actually end up needing a decent macro lens first, as I don't think either of the included lenses will work well in a macro situation.

Rod

[DiamondSCattleCo]

and even the 60/2.8 micro afs all come in at well under $1k.

Ok, so next dumb question after I was snooping around today during lunch hour:

I see plenty of "prime" lenses that are micro/macro, such as the Nikkor 60/2.8. Do these lenses generally function well as both prime AND macro lenses? Or should I really be looking at a dedicated macro lens and a dedicated prime?

Rod

[mattdm]

I see plenty of "prime" lenses that are micro/macro, such as the Nikkor 60/2.8. Do these lenses generally function well as both prime AND macro lenses? Or should I really be looking at a dedicated macro lens and a dedicated prime?


I think there's a basic misconception here. These are very different concepts.

A macro lens is any one that's able to focus close enough for its focal length that you get an image that's close to the real-world size of the object (that is, that size on your film/sensor — when you print, possibly much bigger.) The closest distance a lens is able to focus is one of the many factors that goes into making a lens (which is a study in compromise). So, lenses which can focus usefully-closely are generally labelled as macro lenses.

A prime lens is any lens with no zoom. They cover all of the possible ranges a zoom can cover — from ultra wide, to wide, to normal, to telephoto, to extreme telephoto. As I said, designing a lens is juggling many different compromises. Since prime lenses only have one focal length to deal with, there's far fewer compromises to make, so prime lenses generally have less distortion, wider max apertures, better bokeh, less color aberration, are smaller and lighter, and are often cheaper. The design choice of close-focus distance still remains, so depending on what the manufacturer chooses, prime lenses can be made as macro lenses just like zoom lenses can.

It sounds to me like you have a list of "must-have lenses", and the list has "macro lens" and "prime lens" on it. Unfortunately, the list is oversimplified.....

[Rooz]

Ok, so next dumb question after I was snooping around today during lunch hour:

I see plenty of "prime" lenses that are micro/macro, such as the Nikkor 60/2.8. Do these lenses generally function well as both prime AND macro lenses? Or should I really be looking at a dedicated macro lens and a dedicated prime?

Rod

Rod, micro lens', as a general rule, focus a little slower than a regular prime lens. the primary advantge of a macro prime lens is that the minimum focus distance is very small so it can double as both a macro lens and a low light prime.

the other thing about macro lens' is that they are only 2.8 lens'. with a prime imo, you're better off with a faster lens like a 1.4/1.8 or f2. so for example, a 50/1.4 and 60mm/2.8 maro are similar focal lengths and will have pretty similar quality ouput. the BIG difference is that 1.4 is 2 stops faster than 2.8. so in other words, thats the diference between allowing you to shoot at iso400 or iso1600.

step one is to determine what focal length you want, next step is work out which one suits you best.

[mattdm]

Rod, micro lens', as a general rule, focus a little slower than a regular prime lens.
[...]
the other thing about macro lens' is that they are only 2.8 lens'


These aren't necessarily magically true, of course — they're just examples of the typical compromises.

[Rooz]

which is why i said "as a general rule" matt. ;)
i'd say 95% of macro lens' focus slower than regular lens'....i;ve used and owned quite a few aswell. the only macro lens i know of faster than 2.8 is tamrons new 60/2. do you know of any others ?

[mattdm]

which is why i said "as a general rule" matt. ;)

:) Yeah, I just thought I'd point that out because 1) it illustrates my earlier point, and 2) since there seems to be some confusion it seemed best to be extra explicit.


i'd say 95% of macro lens' focus slower than regular lens'....i;ve used and owned quite a few aswell. the only macro lens i know of faster than 2.8 is tamrons new 60/2. do you know of any others ?

That's a good example. :) There's also a Canon f/2.5 macro (although it's only 1:2) and some older Olympus lenses. Probably more, but I bet it also falls roughly into the 95%-are-slower category.

Although it's worth mentioning that f/2.8 is faster than most zoom lenses (especially zoom lenses in the same price range as many macro primes), because removing zoom from the equation makes it easier/cheaper to design that way.

[DiamondSCattleCo]

Thanks for the info Matt. While I understand what a prime is, I was using the term "prime" when I really should have been using the term "portrait".


It sounds to me like you have a list of "must-have lenses", and the list has "macro lens" and "prime lens" on it. Unfortunately, the list is oversimplified.....

Actually I don't, but I am trying to follow the lens buyers guide from this site(and others). I know what I normally take pictures of (family portraits - variable lighting, action shots of the kids, cattle shots from intermediate range, some close in macro shots) and what I plan to take pictures of (much more macro photography in my future. No bugs. I hate bugs).

Since the camera comes with a 28-80 and a 70-300, my intermediate range shooting should be handled, as well as longer range stuff (that I don't currently do). My portrait requirement may even be handled, but I won't know until I actually get the camera in my hot little hands. Since neither of the included lenses has macro capability, I'll _likely_ need a shorter range macro lens, like a 50mm or 60mm. My thinking is if I can find a really good prime macro lens that would double as an acceptable portrait lens, I'd kill two birds with one stone and save a little money, making my banker and my wife happy.

BTW, thanks for the depth of field calculator link. You have no idea how many questions that cleared up...

Rooz posted:
"Rod, micro lens', as a general rule, focus a little slower than a regular prime lens. the primary advantge of a macro prime lens is that the minimum focus distance is very small so it can double as both a macro lens and a low light prime."

Thanks Rooz, this is exactly what I was looking for. I just gotta learn to use the jargon properly so I don't confuse the people I'm looking for help from. BTW, thanks for the earlier book recommends. Extremely useful.

Rod