Focus points when stopped to, say, f22

[mrpiano]

Hi everyone,

I have a question in regard to using focus points when stopped down to let's say, f22 or so. My question is this:

If you are stopped down to f22, and you are focusing on something that's 3 or so feet away, does that mean that the object that's 3 feet away will be in sharper focus than everything behind it? I'm trying to get a sense of what the focus points on my 30d are really achieving when you're NOT trying to throw the background out of focus, but want everything in sharp focus instead.

Or put another way: do focus points matter when you stop down that much, or shall I manually focus in those instances?

Thank you!

Gino

[OsmosisStudios]

Focus still matters.

General rule is to focus 1/3 of the way into the scene.

An example: Lets say youre taking a long shutterspeed shot of a waterfall. The waterfall is 30 feet away. The general rule would then mean you focus on an object about 10 feet from your camera.

I believe this works from f8 on, but for best results dont go above f/16

[mrpiano]

Thanks for the quick reply...I'll experiment with that a bit and see what kind of results I get...

[dcclark]

Do remember that, even if you're going with a very small aperture (say, f/16 or f/22), you still will have a hard time getting EVERYTHING in focus. Instead, you need to figure out your hyperfocal distance. Focusing there will get everything from half that distance through infinity in focus. But that does mean that anything closer than 1/2 the focus distance will be out of focus, and if you focus at the wrong point, even more things will be blurred.

[inkista]

Depends on your focal length.

A depth of field calculator can help you figure out the best place to focus to get everything to infinity sharp ("hyperfocal distance"), but it will only really be useful if your lens has a distance scale on it so you ca set how far away you're focusing precisely.

[mrpiano]

Yeah, actually, I'm guessing all my lenses have a distance scale, they're pretty new Canon lenses, some "L" glass...so I'm poking around trying to find the best tutorial on how to interpret all those numbers on the lens...any tips/urls?

Thanks!

GG

[inkista]

I gave the link in my post. And DOFMaster on the iPodTouch/iPhone and the PalmOS version both rock, since you can carry them around with you out in the field when you need them.

You enter your:

• crop factor
• focal length
• aperture
• focus distance

and it spits back your DoF near and far limits, and the hyperfocal distance.

If you set the lens to focus at the hyperfocal distance, everything from half the hyperfocal distance to infinity should be inside your depth of field. However, if your subject is really close, or your lens is really long, you may not be able to achieve close focusing and infinity focus at the same time.

And then you need to go get a tilt-shift lens. (just kidding).

[mrpiano]

Perfect, thank you for the link!

[kencaleno]

Originally Posted by mrpiano

Hi everyone,

I have a question in regard to using focus points when stopped down to let's say, f22 or so. My question is this:

If you are stopped down to f22, and you are focusing on something that's 3 or so feet away, does that mean that the object that's 3 feet away will be in sharper focus than everything behind it? I'm trying to get a sense of what the focus points on my 30d are really achieving when you're NOT trying to throw the background out of focus, but want everything in sharp focus instead.

Or put another way: do focus points matter when you stop down that much, or shall I manually focus in those instances?

Thank you!
Gino

You will need to use manual focusing
-because you are going to be focusing on an object at a certain distance-that object may differ in tone from your overall subject, so if you don't use manual focus,exposure will be recorded from the focal point, too-so set your focus,then recompose and take/make your shot. Or, on second thoughts, you could use autofocus,then holding shutter button halfway down, switch to manual focus. This will lock the focus, so you can let go the button,then recompose and shoot,getting the correct exposure.

If you want to have everything sharp from 750mm (2 feet six inches) to as far as you can see, use F 11 and focus on a point 1500mm (5 feet away) if you stop down any further than f11,diffraction occurs and softens the apparent sharpness THIS IS FOR A 18-55 KIT LENS , SET AT 18mm Regards, Ken

PS. Below is a chart for hyperfocal distance for 18-55 and 70-300 lenses .Lenses set at these distances will produce an image that is acceptable sharp from 1/2 the noted distance to as far as you can see

[mrpiano]

Originally Posted by inkista

I gave the link in my post. And DOFMaster on the iPodTouch/iPhone and the PalmOS version both rock, since you can carry them around with you out in the field when you need them.

You enter your:

• crop factor
• focal length
• aperture
• focus distance

and it spits back your DoF near and far limits, and the hyperfocal distance.

If you set the lens to focus at the hyperfocal distance, everything from half the hyperfocal distance to infinity should be inside your depth of field. However, if your subject is really close, or your lens is really long, you may not be able to achieve close focusing and infinity focus at the same time.

And then you need to go get a tilt-shift lens. (just kidding).

Ok, Inkista, I picked up the DOFMaster for Iphone, since I have the Iphone anyway...

Question in regard to what a few of the settings are asking for:

Format: Canon DSLR (i get it)
Lens: If I'm using a 28-135mm, do I set this to 135mm, or to whatever focal length I'm choosing to use?
F/stop: I get it
Focus: Now, the value that I put in, let's say, 10 feet, means, "My subject is 10 feet away?"

And once I setup DOFMaster using these settings, it tells me

Focus Distance is 10 feet (again, not sure if that means my subject is 10 feet away or what)

Near limit is 4.6.1 ft (meaning everythiing from 4.6.1 feet from where I am standing will be sharp?)


Far Limit and Total DOF is "Infinity" meaning everything beyond 4.6.1 feet to infinity will be sharp?

Hyperfocal distance is 8.55 ft...so, not sure what that means in terms of where I should be focusing (do i focus at 10 feet since that's my focus distance, or 8.55 feet)

Getting there, I think...thanks to everyone for their help so far!

GG