trouble seeing DoF in viewfinder...how do you do it?

i'm a noob with an XTi, kit lens and my 85 1.8 just came in the mail yesterday. i had a few opportunities to shoot with the 85 last night. anyway, i noticed with both of my lenses, when i'm shooting and focusing, i can't tell what my depth of field is in the viewfinder. if i'm shooting my dog at f/4, how do i know if his whole body will be in focus, or just his head? is it only when you upload the photos that you can tell?

also, what does the DoF button on the camera do. sometimes i press it and it does nothing, other times it turns the viewfinder dark...i dont understand how to use it.

any tips or insight is appreciated. thanks!
-Dan

With an XTi you really just have to get a feel for it based on experience.

The problem lies with the VF, which has a lot of problems:

1. The VF on all of the 1.6X bodies (and especially the Rebels) is tiny. It's so small that it is nearly impossible to evaluate DOF. The only solution here is to move up to a larger format with a bigger VF, like the 5D. The 5D has a viewfinder that is about as big as what your would have gotten on a mid-grade film camera of yesteryear. The 1Ds is like a good film camera of yesteryear. Nothing matches the best film cameras from before like the OM-1.
2. Even with a big VF, all autofocus VFs make for poor DOF viewing. Because they assume you will be autofocussing, they give you a smooth grind on the AF screen. This smooth grind 'lies' to you about the DOF and even makes it hard to assess if you have nailed focus. You can solve this with a rougher ground screen like the EE-S screen for the 5D. Be aware that rough ground screens get dark fast with slow lenses. At f/4 it's pretty dim and by f/5.6 it's almost too dark to compose with. Rough screens and slow kit lenses do not get along.

And finally - once you get that rough screen, if you hit the DOF preview button at say, f/11, the VF will pretty much turn black.

While we are on the topic, also keep in mind that DOF is not a hard number. DOF is subjective and depends on how big you will print, how closely you will view the print and how picky you are. The standard DOF calculators assume 8x12 prints viewed at about 18 inches. If you print bigger you will need to stop down more. If you view your monitor at 100% from a few inches, you will need to stop down a ton as this is equivalent to peering at a 20x30 print from 6 inches away.

Well, it's good you took a few minutes and found that DOF button. The reason you don't "see" the DOF usually is because cameras maintain their state at the widest aperture until you press the shutter button. This is so you can have a nice bright viewfinder to properly compose your photos..

The DOF button stops the aperture down to whatever you have set so that you should be able to preview the DOF. "It just turns the viewfinder dark" is a very common thing to hear so you're not alone!

More thorough explanation here:

http://www.naturephoto​graphers.net/articles0​905/rb0905-1.html

...which is why I'd like a digital DoF preview giving me a number in ft/inches so I know how much will be in focus. Perfectly doable with today's cameras. Even the distance to subject when you've focused is returned with many lenses.

mrklaw wrote in post #6195728
...which is why I'd like a digital DoF preview giving me a number in ft/inches so I know how much will be in focus. Perfectly doable with today's cameras. Even the distance to subject when you've focused is returned with many lenses.

That would be a great feature. Input your own CoC number in the menus. Then while shooting the LCD screen could give a constantly updating range of near - far acceptable sharpness based on selected aperture and focus distance.

Given that most lenses return focus distance info to the camera, this should be a simple bit of software. Using the LCD like this will eat the battery a bit though.

mrklaw wrote in post #6195728
...which is why I'd like a digital DoF preview giving me a number in ft/inches so I know how much will be in focus. Perfectly doable with today's cameras. Even the distance to subject when you've focused is returned with many lenses.

Yes indeed, that sounds like a good idea and should be quite simple to add.

mrklaw wrote in post #6195728
...which is why I'd like a digital DoF preview giving me a number in ft/inches so I know how much will be in focus. Perfectly doable with today's cameras. Even the distance to subject when you've focused is returned with many lenses.

thanks for the tips everyone. and this ^ sounds like a awesome idea! someone forward that to Canon.

timrocks311 wrote in post #6195672
...... if i'm shooting my dog at f/4, how do i know if his whole body will be in focus, or just his head? is it only when you upload the photos that you can tell? also, what does the DoF button on the camera do. sometimes i press it and it does nothing, other times it turns the viewfinder dark...i dont understand how to use it.....

As the poster said before any lens (prime or zoom) will always default to the largest aperture (e.g. f/1.8). So even if you are shooting at f/4, f/8, f/16 or f/32 what you are LOOKING through in your VF will always be f/1.8.

So if you wanted to see what your composition looks like when at f/4 then you set it to f/4 and you press the DOF preview button. The REASON it goes dark is coz f/4 lets in LESS light than the default f/1.8. But you are supposed to look beyond the darkness and see if the background or foreground of your composition which would have been blurred at f/1.8 come into focus at f/4 when looking through your VF.

Also if you are shooting at say f/2 and you press the DOF preview button it may do little or nothing (you should still hear the blades closing) since the default is f/1.8 and you are going down 1/3 stop. While f/4 like 3.33 stops down.

Since you are new, and want to see it work, go out on a bright sunny day. Look though the VF at f/1.8 and then stop down to f/4 and you will still have enough light to actually SEE that your background has come into focus when you press the DOF preview button. And for dramatic effect set it to f/22 (or f/32) and press the DOF button and you will see a dramatic difference.

timrocks311 wrote in post #6195864
thanks for the tips everyone. and this ^ sounds like a awesome idea! someone forward that to Canon.

Probably have better luck forwarding to Nikon these days.

But that would be a pretty sweet feature.