What the F/Stop?

[Swanky]

Hey there. I just found this board a few days ago and I have to admit it blows the "other" candid board away. After browsing through some posts--it's apparent guys like L Digital, Archman, Wetmac, and Nightshade (just to name a few) not only take excellent candids, but produce pure unadulterated artwork. :bowdown:

Anywho, I'm getting ready to finally buy my first DSLR; probably the 20D. I've owned a Nikon 4500 for almost three years and I've hit the proverbial wall as to what I can capture with a point and shoot camera. I won't waste your time asking for an exact len recommendation, but I did have a question concerning f/stops.

WTF, indeed. I've read this site http://www.uscoles.com/fstop.htm and understand the basics slightly better. Now I'd like to know how that translates into using the right lens for the right situation. I know you need a fast lens (yes, and higher ISO / shutter / monopod / hands of steel) for low light / indoors shooting, but what about the outdoors. Should I be shooting in a larger f/stop range more along the lines of 4 to 5.6f? Also, is the general rule of thumb to use a smaller f/stop on telephotos compared to larger f/stops on smaller lenses? Why are most of the popular lenses a fixed f/stop instead others that contain a range?

Perhaps I'm overthinking the whole concept, but I'd like to know before I plunk down my money. Personally, I love the depth of field produced from 2 and 2.8f lens. Mmmmm, sharp foregrounds and blurry backgrounds make my toes tingle. I'll probably end up getting a 50mm walkaround and a 70-200mm zoom. Obviously, I haven't decided on the right f/stop yet. ;)

I appreciate any help.

[archman]

The best way I've found so far (and God knows I've got a lot to learn) is to experiment. I shot most of this summer (my first with the 20D) using Aperture priority, where I chose the aperture setting and the camera chooses the shutter speed.

But, towards the end of the summer, I reversed and started using Tv mode, in which I choose the shutter speed and let the camera choose the aperture. And personally, I like the results I'm getting much, much better.

But by all means...don't trust me on this! There are many others here who have a lot more knowledge on this stuff than I do (DP, Pez, and Olympus come quickly to mind).

Welcome to the board and thank you for your kind words :)

[deliriouspixel]

Welcome to cO Swanky. :banana:

About that outdoors shooting
youre still going find the need/want for the faster glass (f2.8 vs f4 or f4-5.6)
not only because of the background blur afforded by a thin depth of field
but also so that you can still shoot your lens stopped down
meaning not at its widest aperture
in less than fully sunlit situations where f4 is necessary
to get fast enough shutter speeds for
a clean handheld shot of a moving subject

[You want to shoot your lenses stopped down
for better image quality
especially consumer grade lenses]

You might be thinking that since youre intending to always shoot at f8
the faster glass may not be a requirement
but realistically f8 needs good light and often times
results in shutter speeds too slow to be held for razor sharp images
including many of the varied daylight conditions you'll want to shoot
especially on longer focal lengths

You are after sharp pix, right?
If so, then the faster the glass you buy will
expand your camera's light gathering performance
and should net you more keepers
over the range of shooting conditions that you will encounter
even if you dont shoot indoors or at nite

Variable aperture zooms are less desirable than the fixed aperture zooms
for the same above reasons

I suggest you get your cam with the kit lens
and a single modestly priced 2.8 or faster lens
like a 85/1.8 or 50/1.4 or even the inexpensive 50/1.8
then learn what you can do with these
and experience for yourself the relationship
between aperture and shutter speeds :thumbup:

[Assman]

Yup - all the above advice is sound.

To summarise, use the kit lens in TV mode
(Play with shutterspeeds, but a rule of thumb is to use a shutterspeed inverse to the lens length - a complex way of saying a 200mm lens should have a 1/200th or faster shutterspeed)

Of course, AV mode has its benefits, but its best used in special circumstances.

Even the full-auto without flash [P] mode is probably quite usable.

After you have played with the kit lens for a while, you will know where it doesn't meet your expectations and get a new lens that fits them better.

Oh, as for the great depth of field the 2.0 lenses produce, you also have to realise that focusing is critical. You may find its much good for quick snaps. BTW, you can get a F1.4 50mm lens from Canon. Beautiful little lens. ;)

[Benjammer]

It sounds like you may be confused about one thing, I dont know if I just mis-interpreted what you meant, but if not than this should clear a concern up.

When a lens says its 5.6, or 2.8 etc that is the smallest f/stop number it can go to (which means the most wide open it can go to, to let in more light, its kinda backwards).

But even though it says its a 2.8 lens, that doesn't mean your stuck at 2.8, they usually go from 2.8 all the way to 28 or something really closed. So if your shooting in bright outdoors the 'iris' of the camera can close a little to let in less light. Using a larger fstop number.

The apperature is always variable, although theres some zoom lenses that allow a maximum (like the lowest number) to be 2.8 at one end (I think wide angled) but when you zoom in the max is now 4.0 or something else.
So if it says 2.8-4.0 thats just the maximum amounts and not the whole range.

Get what I mean?

OR did I confuse you... or you already know all this and it is totally irrelevent?

[Swanky]

Thanks guys. I truly appreciate the input.

Benjammer--Ahhhhhh haaaaa, now I finally get it! Yep, I thought a fixed 2f lens was truly stuck at 2f; hahaha. *slaps forehead* I couldn't find any info about that question so I began to assume that's how lenses worked. For a second I thought I was going to need like 7 or 8 lenses because of all the different f/stop ranges.

Now that I feel like a complete idiot--guess I'll try to make it up by going through my old photos and start posting. :lol:

[Benjammer]

:) Glad I could help.
It's actually pretty cool how lenses work, its kind of like the pupil of an eye how it opens and closes based on how much light it needs (yep your eyes do that). But the camera lenses do it very very quickly.

With all the money you saved from not having to buy 8 lenses you can donate some to me :p

The 20D is a great camera, just remember to turn up the sharpening, (or get an expencive L series lens). some people say the noise reduction makes images look a little soft, but ive seen some nice sharp images from a 20d, as well as alot of softer looking ones, but its a nice look.