Using F2.0 combined with manual focus to inf

[shniks]

Hi all,
I am still trying to grasp the concepts of photography, and I need a little help with something. I know that using an apeture of f2.0 results in a short depth of field. However, what happens when you set manual focus to infinity while using f2.0. What will be in focus? What range will be in focus? I will appreciate any replies.

[maderito]

Answer: 1/2 the hyperfocal distance to infinity.

For a Canon 10D with a 50 mm lens at aperture 2.0 and focused at infinity:
- 108 ft. to infinity in focus
- hyperfocal distance = 216 ft.

The hyperfocal distance is that distance when focused at will cause everything from 1/2 hyperfocal distance to infinity to be in focus. It varies depending on the focal length (and crop factor) of the lens and the aperture.

It wasn't obvious to me, until you asked, that when focusing at infinity, the hyperfocal distance concept still applies. (I hope I have that right :) ).

See http://dfleming.ameranet.com/dofjs.html to figure this out for your camera.

[Yance]

It is almost completely dependent on the focal length of the lens. Different length lenses will have different DOF for the same aperture.

[Scottes]

For a Canon 10D with a 50 mm lens at aperture 2.0 and focused at infinity:

Actually, you probably want to befocused at the hyperfocal distance. If you focus at something 216 feet away, everything from 108 feet to infinity will be in focus.

According to http://dfleming.ameranet.com/dofjs.html, a 10D with a 50mm at f/2 focused at infinity (I used 100,000 feet as a subject distance) then everything from 215 feet to infinity would be in focus. Using as subject distance of 10,000 feet that changed DoF to 211 feet. Using 1000 feet changes DoF to 177 feet.

So focus at the hyperfocal and you'll have the largest depth of field. 108 feet and beyond.

[maderito]

According to http://dfleming.ameranet.com/dofjs.html, a 10D with a 50mm at f/2 focused at infinity (I used 100,000 feet as a subject distance) then everything from 215 feet to infinity would be in focus. Using as subject distance of 10,000 feet that changed DoF to 211 feet. Using 1000 feet changes DoF to 177 feet.

Scottes --

Thanks for picking up the error.

If focused at infinity, everything from the hyperfocal distance (not 1/2) to infinity is in focus.

When focused at infinity, the appropriate DOF equation reduces to:

D(near focus of acceptable sharpness) = H - f

where H is the hyperfocal distance and f is the lens focal length. When all units are converted to feet, that works out to be 215.8 feet in the current example in which the hyperfocal distance is 216 feet.

[stopbath]

It varies depending on the focal length (and crop factor) of the lens and the aperture.

Sorry, crop factor has nothing to do with depth of field of hyper focal distance.
A 1/10 crop of a 50mm lens (factored to 500mm) retains the properties of the 50mm lens and does not adopt the properties of the 500mm lens other than the image size. Distortion, depth of field, hyperfocus angle of view all remain true to 50 mm.

[Scottes]

It varies depending on the focal length (and crop factor) of the lens and the aperture.

Sorry, crop factor has nothing to do with depth of field of hyper focal distance.
A 1/10 crop of a 50mm lens (factored to 500mm) retains the properties of the 50mm lens and does not adopt the properties of the 500mm lens other than the image size. Distortion, depth of field, hyperfocus angle of view all remain true to 50 mm.

Since the crop factor affects the size of the circle of confusion I would think that it would have an effect on Hyperfocal Distance.

And the DoF calculator above seems to think the same thing. With 35mm film, subject distance 1000', 50mm at f/2 has a low of 120 feet.

http://tangentsoft.net/fcalc/help/Hyperfocal.htm, lists Circle of Confusion in it's Hyperfocal Distance formula.

And Bob Atkins says (http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=000glM) that the CoC is also part of the calculation.


A *crop* does not change anything, but the crop factor of the smaller format sensors does change the CoC - this directly affects DoF and Hyperfocal Distance.

[stopbath]

It varies depending on the focal length (and crop factor) of the lens and the aperture.

Sorry, crop factor has nothing to do with depth of field of hyper focal distance.
A 1/10 crop of a 50mm lens (factored to 500mm) retains the properties of the 50mm lens and does not adopt the properties of the 500mm lens other than the image size. Distortion, depth of field, hyperfocus angle of view all remain true to 50 mm.

Since the crop factor affects the size of the circle of confusion I would think that it would have an effect on Hyperfocal Distance.

And the DoF calculator above seems to think the same thing. With 35mm film, subject distance 1000', 50mm at f/2 has a low of 120 feet.

http://tangentsoft.net/fcalc/help/Hyperfocal.htm, lists Circle of Confusion in it's Hyperfocal Distance formula.

And Bob Atkins says (http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=000glM) that the CoC is also part of the calculation.


A *crop* does not change anything, but the crop factor of the smaller format sensors does change the CoC - this directly affects DoF and Hyperfocal Distance.
Are you referring to the fact that a 50 mm lens on a SLR is normal but wide angle on a 4x5?

The focal plane is different on these beasts. A 50mm on an SLR with a full frame sensor will focus the same as an SLR with a 2/3 frame sensor. Both SLRs focus the same, with the same depth of field it's only the 'amount of the image used' that is changed, the lens image and properties have stayed the same.

[Scottes]

Are you referring to the fact that a 50 mm lens on a SLR is normal but wide angle on a 4x5?

I'm referring to the Circle of Confusion, which affects the DoF and HDistance.

http://tangentsoft.net/fcalc/help/CoC.htm
"f/Calc calculates the CoC using the "Zeiss formula": d/1730, where d is the diagonal measure of the film, in millimeters. This formula yields acceptable values for most uses."

Since the 10D's sensor is smaller than a 35mm's film camera's, then the CoC will be smaller, thus changing the results for DoF and HDistance calculations.

[stopbath]

Are you referring to the fact that a 50 mm lens on a SLR is normal but wide angle on a 4x5?

I'm referring to the Circle of Confusion, which affects the DoF and HDistance.

http://tangentsoft.net/fcalc/help/CoC.htm
"f/Calc calculates the CoC using the "Zeiss formula": d/1730, where d is the diagonal measure of the film, in millimeters. This formula yields acceptable values for most uses."

Since the 10D's sensor is smaller than a 35mm's film camera's, then the CoC will be smaller, thus changing the results for DoF and HDistance calculations.
But the projected image from the lens is the same, it's just that the sensor is smaller (thus cropping the image.) The properties of the lens do not change. Using the film size is just a quick and easy way of doing the calculation, and is misleading when some cameras use only a portion of the lenses image. The formula should read "designated image size of the lenses format" (but heck film size is so much easier) so that popping a 35mm or medium format sensor in a 4x5 swing camera will still result in the correct calculations (that of a 4x5 image.)

[Scottes]

Here's a fantastic explanation, with pictures and diagrams.

http://dfleming.ameranet.com/dof_dslr.html

I believe it. I'm done.

[stopbath]

Here's a fantastic explanation, with pictures and diagrams.

http://dfleming.ameranet.com/dof_dslr.html

I believe it. I'm done.
"Digital SLR (DSLR) cameras use lenses designed for 35mm SLR cameras. The physical performance of a lens doesn't change when you mount it on a DSLR. And yet, we see more depth of field (DOF) in photographs taken with the DSLR. Why? Because we change the DOF with our feet; we move further away from the subject."
So nothing changes (including CoC), as the 'moving back' always increases depth of field... Done too. :)

[shniks]

Thanks for the replies.......but this discussion has gone way over my head! However, thanks for the links, I'm going there now to read up on all this. But its good to hear that depth of field isnt as shallow as I thought, because there are times I need smaller apetures when taking landscape shots.

[maderito]

Why? Because we change the DOF with our feet; we move further away from the subject."
So nothing changes (including CoC), as the 'moving back' always increases depth of field... Done too. :)
Gee, I'd hate to see friendships lost over a DOF argument. :o

I wrote the original statement: [depth of field] varies depending on the focal length (and crop factor) of the lens and the aperture.
I added the crop factor parenthetically so that those who insist on accuracy would be satisfied.

The same shot (field of view - FOV) composed in the viewfinder of a film SLR will have a smaller DOF than a DSLR since the DSLR shooter must back up to get an identical FOV. Because the DSLR shooter is further from the subject but using the same lens, the DOF increases.

On the other hand, if the image is taken from the same distance by film and DSLR cameras, the DSLR will have a smaller DOF. The image appears magnified in the DSLR viewfinder and in the final image. It is the magnification that creates the subjective perception of a smaller DOF.

You can invoke the Circle of Confusion or you can talk about crop factor magnification, or you can rant on in other directions. The simple fact is that the central portion of 24 X 36mm image when cropped out and enlarged back to 24 X 36mm will always look less sharp - all other things being equal. DOF is about what is sharp and what is not. Starting from that simple principal, all the rest follows.

[mr_clean001]

OK - for a newbie like myself I have to agree that this is a little over my head, but I have to ask - what the hell is "circle of confusion"? Sounds like the name to a bad punk band but a simple definition will do.

Thanks...

[Scottes]

But its good to hear that depth of field isnt as shallow as I thought, because there are times I need smaller apetures when taking landscape shots.

Take a look at the DoF calculator before you think that.

For a 35mm with 50mm lens at f/8 focusing on a subject 20 feet away, your near limit of accetptable sharpness is 12.7 feet, while the far limit is 47.7 feet. You have 35 feet of DoF.

On your G5, same lens same aperture same distance, your near limit is 17.9 feet and the far is 22.6 feet. You have 4.7 feet of DoF.

Huge difference.

But I honestly have no idea of the aperture and real lens size of the G5. Do they say it's 50mm, or say it "effectively" 50mm? Hold on, Canon says "With a 35mm equivalent range of 35 – 140mm..." so you can't really use the calculator until you know what the "real" lens length is. I would guess that you should use 35mm film format when calculating DoF.

[stopbath]

OK - for a newbie like myself I have to agree that this is a little over my head, but I have to ask - what the hell is "circle of confusion"? Sounds like the name to a bad punk band but a simple definition will do.

Thanks...
As I understand it Circle of Confusion refers to the blur generated by an out of focus point of light (reflected or direct). If a point is focused (through depth of field) it will render as a point. As it gets out of the depth of field, it starts dispersing and is no longer a single point. This dispersion is the circle of confusion. The Circle of confusion can be measured and when it hits a size, the point is deemed "out of focus". Thus .001 width is focused, .004 is focused too, but .1 is out of focus and 1. is way out.

Now magnification of the image seems to play a part in this. If you magnify your image twice as big, you'll figure more of the image is blurry, thus cropping the original image and enlarging it, creates the need for a smaller 'circle of confusion.' I don't see the need for this. Magnifiying also increases the grain and other artifacts.

Personally, I don't like the phrase, not because it reminds me of the song "Ball of Confusion" (which I like) ... but I feel it is not accurate.

When using a regular lens, the out of focus point will render in the shape of the aperture which may well be a circle, or may be a hexagon. With a reflex lens, it will render as a donut. A circle is not always rendered from out of focus points. Perhaps "loss of clarity" is better.

[stopbath]

Why? Because we change the DOF with our feet; we move further away from the subject."
So nothing changes (including CoC), as the 'moving back' always increases depth of field... Done too. :)
Gee, I'd hate to see friendships lost over a DOF argument. :o

I wrote the original statement: [depth of field] varies depending on the focal length (and crop factor) of the lens and the aperture.
I added the crop factor parenthetically so that those who insist on accuracy would be satisfied.


Nope, nothing like a good round of head butting to keep friendship alive and thriving! :) :)

Perhaps a better statement would be: Depth of field varies on focal length of the lens, the aperture, and the focal distance.

Crop facter only 'seems' to apply as it may cause the photographer to choose a wider lens, or move back, which both increase depth of field, but on it's own, the depth of field is not affected by crop factor.

[Scottes]

Nope, nothing like a good round of head butting to keep friendship alive and thriving!

Perhaps a better statement would be: Depth of field varies on focal length of the lens, the aperture, and the focal distance.

I agree. We all have opinions.

I think that the second sentence says it best, particularly the "focal distance." When I compute DoF, I think about the distance from the subject. Hey, I have a 10D and that's all I've ever had. When considering the picture itself (ie; FoV) it's a different story.

If I take a picture of someone 20' away with both film and digital, the DoF will be very different, and the resulting picture will be very different.

If I take a picture with each camera so that this person's head exactly fills the frame, well, that's a whole different story.

[maderito]

Perhaps a better statement would be: Depth of field varies on focal length of the lens, the aperture, and the focal distance.


We're almost agreed but would probably need binding arbitration to come to a final memorandum of understanding. :D

Example with 50 mm lens at f=2.0

-With 35 mm camera focus distance = 100 ft: DOF = 58 to 371 feet

-Back up to 160 feet and reshoot with 10D: DOF = 92 to 617 feet

The size of the image is the same. But the DOF is quite different. You may say that's because you used your feet and backed up with the DSLR, thus giving you greater DOF. Correct.

Fundamentally, the DSLR camera with a 1.6 crop factor is not a true 35 mm camera. It is closer to a 22 mm camera. It has a smaller DOF at a given focal distance - until you back up and compose your shot as you would see it on a larger format camera.

A 35 mm camera is called such because that's the width of the film (including sprocket holes). Perhaps if we called the 10D a 22 mm camera, we could stop talking about crop factors.

I hate crop discussion posts - and I'm suprised and disappointed to see myself involved in one. :shock: