what's the point of fast lenses (small DOF) indoors?

I'm a relative newbie so forgive me...

I was just thinking...people make such a big deal about f/2.8 zooms or faster primes because it allows them to shoot in low light, indoors and stuff. But what is the point of worrying about them, when your DOF becomes so small and essentially useless in a lot of situations? Don't get me wrong, I like a small DOF for a lot of creative shots.

For example, I like to take shots of my dogs (or portraits) indoors...and i've been trying to get away without a flash when possible. So i think about buying fast primes to accomplish this. But with an 85mm @ 2.2 @ 8 ft my DOF is like .16ft...enough to get the eyes in focus but the rest of the head is blurry. So why worry about the fast prime when i need f/10 and a flash to get the whole head/face in focus? i can save money on all those fast, expensive lenses and buy a flash and some cheaper, f/4 lenses.

If you want everything in focus, or a large amount you can set the focus on the hyperfocal distance where everything past a certain point would be in sharp focus. I haven't ran into a DOF problem yet but an F/4 lens cant go to 2.8 but a 2.8 can go to 4. If you want the best sharpness, you stop down one or two, and with a 2.8 you can still mantain a fairly fast speed. If you can justify the price difference, the 2.8 is invaluable for situations that need it.

yeah, but say you're using a 50 @ f/2...your subject is 5 feet away and your hyperfocal distance is 216 ft...with 108-infinity in focus. that doesn't work.

i guess your right though...the appeal of those lenses is that you have the capability of using f/2, or whatever, if you want to. i guess for taking my indoor portraits of my dogs, i really do need a flash.

Keep in mind the fact that a lot of photos are taken at some longer distance than portraits. At 20', with a 50mm f/2 lens the DOF is 3' deep. So the ability, for a photojournalist, to capture the photo without flash, permits a shot to be made where a slower shutter speed (for slower aperture) just does not work due to subject motion.

A Canon 18-55 lens would be fine to use in a church- if you could use a FLASH with it. Since you can't during a ceremony, you need a prime or wide angle zoom with f/2.8 aperture and still have to shoot at ISO800 or 1600. I wish I could afford the 17-55 IS !!

This is really all about using available natural lighting. I suppose in the next 5-10years ISO performance will be so great that we won't need expensive lenses.

Ultimately, it is often better to learn how to use off-camera and/or bounced flash to shoot stopped down a bit indoors. It is certainly a fact that super shallow DOF isn't always desireable.

That said....I can also get perfectly useable shots at f/1.4 to f/2 IMO. Often so long as the eyes are exactly at the plane of critical focus some tolerance of softness at the nose tip and ears is OK.

Sounds like a Tokina 11-16 2.8 might be what you're looking for--low-light, with large DOF. At 11mm 2.8 the hyperfocal is 7ft and at 5 you have a DOF of 3-15ft. Fast, large DOF, and focus close-up.

The point of the fast lenses is that you can capture shots that you otherwise could not catch. If I was using an f4 zoom at a concert I would not be able to capture the moment because usually it would be to dark to have an adequate shutter speed. At concerts they do not allow media to use flashes. Also at weddings their are churches that do not allow flash so you are left using fast lenses. I personally do not have a problem with using an extremely shallow dof. I think that you recognize that the lens has a limit and you respect it.

The above poster pretty much says it all.

This is not normally the case though. Sure it becomes shallower but you can increase the distance to your subject to compensate for this - if you need more dof.

As stated above it allows you to capture shots you may otherwise not get.

I do weddings and the ability to shoot with f2.8 lenses compared to f4 really does make a huge difference at times.

My reason for preferring fast lenses is a better view of the viewfinder. You know - old eyes, & focus is more accurate for me with fast lenses whether it be manual or auto.

2 more points to consider

The cross type precision AF sensors only work with a 2.8 or faster lens.

Canon lenses focus wide open--so all things being equal a larger aperture lens will focus faster and more accurately in low light.

I primarily shoot low-light action indoors at a theatre. Fast lenses are absolutely required in order to not be using flash for everything. Here's a good example. This was shot at ISO 1600, 1/125, f/2.0 with a 50mm lens. I'm fine with the small depth of field. I wouldn't have been fine with blowing out the existing lighting with my own flash.

IMAGE LINK: http://www.austinrocky​.org …ontent/IMG_6804​_large.php

timrocks311 wrote in post #6386961
i guess for taking my indoor portraits of my dogs, i really do need a flash.

You won't be able to shoot moving dogs indoors without a flash, most likely. If they're lying down, you can use available light. I notice you already have a 85mm f/1.8, which is my absolute favorite lens for outdoor portraits. Here's another example. This was shot at ISO 100, 1/2000, f/1.8 with the 85mm. On a Rebel XTi, even. And it's still probably my favorite dog shot. Sometimes the tiny depth of field can work to your advantage.

IMAGE LINK: http://shawn.mchorse.c​om …ntent/IMG_0428_​large.html

More theater, less dogs!

Well, think of it this way...

An f/1.4 can always stop down to f/4, f/8, f/16, f/22 while an f/4 lens can never go anything larger.