Closest focus distance @ inifinity for 17mm


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superdave

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#1
Hi,

I was wondering what the closest distance a 17mm lens can shoot clearly when the focusing is set to infininty?
 

blurblock

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#2
superdave said:
Hi,

I was wondering what the closest distance a 17mm lens can shoot clearly when the focusing is set to infininty?
What camera? 35mm SLR, 35mm DSLR, Medium Format camera? What aperture?
 

superdave

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blurblock said:
What camera? 35mm SLR, 35mm DSLR, Medium Format camera? What aperture?
I'm using a Canon 10D. Does the aperture setting and camera type (film or digital) affect the focusing distance? I tot it should be the same....
 

blurblock

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superdave said:
I'm using a Canon 10D. Does the aperture setting and camera type (film or digital) affect the focusing distance? I tot it should be the same....

Yes it will .... so what aperture setting? The camera type affects the focusing distance due to difference in the circle of confusion. How far are you away from the subject as well ....
 

superdave

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blurblock said:
Yes it will .... so what aperture setting? The camera type affects the focusing distance due to difference in the circle of confusion.
ok... I'm probably looking at a 2.8...

To better give an idea of what I plan to do... below is a sample picture of a shot I took while wakeboarding. I'm being dragged behind a little dinghy about 5 feet from the rider and my camera is being enclosed in a wet case which after its sealed, I am unable to make any adjustments to the camera settings. The shot was taken with a cheapo russian fisheye, so results are not great and it doesn;t work well with my flash.

I was thinking of getting another wide angle lens, something like a 17mm f2.8 for this kind of shots. Because the action is so fast and the framing difficult, I'd prefer to set the lens to infinity so the subject is in focus, regardless of how far they are from me... which is subject of course, to my question of what the min focusing distance is when the lens is set to infinity....

I was able to get the subject in focus (set to infinity) from just 5 feet away on the fisheye.

 

blurblock

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superdave said:
ok... I'm probably looking at a 2.8...

To better give an idea of what I plan to do... below is a sample picture of a shot I took while wakeboarding. I'm being dragged behind a little dinghy about 5 feet from the rider and my camera is being enclosed in a wet case which after its sealed, I am unable to make any adjustments to the camera settings. The shot was taken with a cheapo russian fisheye, so results are not great and it doesn;t work well with my flash.

I was thinking of getting another wide angle lens, something like a 17mm f2.8 for this kind of shots. Because the action is so fast and the framing difficult, I'd prefer to set the lens to infinity so the subject is in focus, regardless of how far they are from me... which is subject of course, to my question of what the min focusing distance is when the lens is set to infinity....

I was able to get the subject in focus (set to infinity) from just 5 feet away on the fisheye.
I don't think you can get the subject to be in focus at infinity from just 5 feet away at f/2.8, you mean that person is only 1.5 meters away from you? If you want to set to infinity from just 5 feet at 17mm you need to be at f/8.

For f/2.8, you are required to have a distance of about 2.7 meters or 9 ft away to get infinity. That is cutting it very thin as this is the distance of the near limit of acceptable sharpness where the focus point is not the subject.

I don't think there is anything wrong with your lens and your flash. Look at all those back light, chances are the flash is fooled by the background lighting to produce very little power to lighten up the subject. I suggest you switch to manual for your fill in flash instead.

 

student

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I don't know about the 17 mm.

On my Canon 1V, using my 14 mm at f4, focus will be ok from about 4-5 feet away.
 

blurblock

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student said:
I don't know about the 17 mm.

On my Canon 1V, using my 14 mm at f4, focus will be ok from about 4-5 feet away.
For 35mm film camera, at 14mm f/4, the subject need only to be at 5.5 feet to get infinity, but the minimum nearest acceptable sharpness (the out of focus subject that is sharp) is 2.8 feet :D.
 

superdave

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blurblock said:
I don't think you can get the subject to be in focus at infinity from just 5 feet away at f/2.8, you mean that person is only 1.5 meters away from you? If you want to set to infinity from just 5 feet at 17mm you need to be at f/8.

For f/2.8, you are required to have a distance of about 2.7 meters or 9 ft away to get infinity. That is cutting it very thin as this is the distance of the near limit of acceptable sharpness where the focus point is not the subject.

I don't think there is anything wrong with your lens and your flash. Look at all those back light, chances are the flash is fooled by the background lighting to produce very little power to lighten up the subject. I suggest you switch to manual for your fill in flash instead.
Ok thanks. The shot i took above is without flash because it was all weird when i tried to use with that fisheye lens. Haven't tried manual with flash yet though. I had set it to aperture priority. How do you manage to calculate so accurately anyway (when you said: If you want to set to infinity from just 5 feet at 17mm you need to be at f/8.)?

Another question if you know.... I have 420EX Speedlite. I realise I can shoot bursts of flashes in P mode, but in the other modes, its just a single flash (even though the shutter continues with bursts)... why is that so?

Thanks.
 

knoxknocks

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#10
you thinking of using a 17-35 f/2.8?

if I'm not wrong, what blurblock is talking about is calculating the hyperfocal distance and then dividing that by 2 to get the near limit of acceptable sharpness. When you focus at the hyperfocal distance, anything from 1/2 of the hyperfocal distance to infinity is in focus. Unfortunately, the 17-35 doesn't have a DOF scale, so you'll have to compute.

There are quite a few DOF calculators on the web. The one I like is DOFMaster http://www.dofmaster.com/dofjs.html.

If you want to calculate hyperfocal distance manually, use this formula:

focal length x focal length
-------------------------- + focal length
CoC * aperture

For your 10D, you can use something like 0.019mm as the Circle of Confusion. Circle of Confusion for digital camera is calculated by

35mm CoC
----------------------
Focal Length Multiplier

A value of 0.03 is normally used for the 35mm CoC. So for your 10D,
CoC = 0.03/1.6 = 0.01875 about 0.019mm
 

blurblock

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#12
knoxknocks said:
you thinking of using a 17-35 f/2.8?

if I'm not wrong, what blurblock is talking about is calculating the hyperfocal distance and then dividing that by 2 to get the near limit of acceptable sharpness. When you focus at the hyperfocal distance, anything from 1/2 of the hyperfocal distance to infinity is in focus. Unfortunately, the 17-35 doesn't have a DOF scale, so you'll have to compute.
Whatever gives you the idea near limit of acceptable sharpness is Hyperfocal distance divided by 2?

Hyperfocal Distance = ((Focal Length of the Lens x Focal Length of the Lens) / (Aperture x Circle of Confusion)) + Focal Length of the Lens

Near Focus limit = (Hyperfocal Distance x Distance of Subject in Focus) / (Hyperfocal + (Distance of Subject in Focus - Focal Length of the Lens))


Thus when you want to know thread starter wanted to know what is the minimum distance for infinite, I need to know the Aperture, Camera Type and Focal Length.
 

superdave

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thanks for all the help guys.... this is a lot cheemer than I had expected. I guess I have to spend a little more time reading up on your posts again.... right now, the only circle of confusion that I know is the one ringing in my head :bsmilie:

Cheers!
 

enzochang

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blurblock said:
Whatever gives you the idea near limit of acceptable sharpness is Hyperfocal distance divided by 2?

Hyperfocal Distance = (Focal Length of the Lens x Focal Length of the Lens) / (Aperture x Circle of Confusion)

Near Focus limit = (Hyperfocal Distance x Distance of Subject in Focus) / (Hyperfocal + (Distance of Subject in Focus - Focal Length of the Lens))


Thus when you want to know thread starter wanted to know what is the minimum distance for infinite, I need to know the Aperture, Camera Type and Focal Length.
If far focus is infinity ... Hyperfocus is 10 feet ... nearest limit is 5 feet ...

If you have a DOF scale lens ... take a look .. its always half ..
 

blurblock

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enzochang said:
If far focus is infinity ... Hyperfocus is 10 feet ... nearest limit is 5 feet ...

If you have a DOF scale lens ... take a look .. its always half ..
Correct, my bad ..... I fail to see the word Infinity behind.
 

knoxknocks

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#16
blurblock said:
Whatever gives you the idea near limit of acceptable sharpness is Hyperfocal distance divided by 2?

Hyperfocal Distance = ((Focal Length of the Lens x Focal Length of the Lens) / (Aperture x Circle of Confusion)) + Focal Length of the Lens

Near Focus limit = (Hyperfocal Distance x Distance of Subject in Focus) / (Hyperfocal + (Distance of Subject in Focus - Focal Length of the Lens))


Thus when you want to know thread starter wanted to know what is the minimum distance for infinite, I need to know the Aperture, Camera Type and Focal Length.
wah...i gong liao :bsmilie:. when focus at hyperfocal distance, DOF extends from 1/2 * hyperfocal to infinity no? sorry if i cause confusion.
 

blurblock

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#17
knoxknocks said:
wah...i gong liao :bsmilie:. when focus at hyperfocal distance, DOF extends from 1/2 * hyperfocal to infinity no? sorry if i cause confusion.
Correct :bsmilie: ..... I forgot all about the infinity clause ... hehehehe paisei ...... :sweat:

Anyway, that is just theory, in practical you can extend pass infinity :D....
 

#18
If anyone is still interested, I have a 16mm fisheye on my EOS 300D. At f8 my lens is (theoretically) in focus from @ .8M to infinity. The wider you open the lens, the less the DOF becomes. At f11, the DOF becomes .55m to infinity. The focal distance keeps moving closer. if you are focused on a subject Xm away, then rule of thumb is DOF in front of subject ( closer to lens ) is 1/3 the total and behind subject is of course 2/3. Focus at a subject @ .6M and all is in focus from @.4m to @1.3m at f 11. At same f11, if you focus the lens on 1m everything from .5m to infinity in focus. Comes up the same no matter which way you use for it. I set my camera at f8 and focus on 1.2m and I have the world in focus, or at least as much as I need.

As to flash, when you have the camera or flash on auto in your situation ( strong backlight) you will never get a correct exposure. The auto machinary is not able to cope with it. go to manual, set fstop and focus where you want and meter a patch of what looks like gray. set the shutter speed and ISO and bag that camera. You have point and shoot wideangle machine.

Also your flash is not able to light the angle of the lens. My lens has 180 degrees coverage, and I don't know of a flash which can do that. in the photos above, you don't need flash, you have enough light to get a good exposure.

Get out of the habit of using auto. Set the camera on manual and learn how to use it. There are a few times you can use program or whatever, but they are far between and very few. Better yet, get a good incident meter like a Gossen Lunapro which is reflected and incident. With incident you take the reading from what appears to be the subject direction and it always reads gray. ie... perfect exposure; doesn't matter back lighting or side or front.

LunaPro meters appear on ebay for about $20us to about $50us. I have 2 of them, one i have been using since 1972 and it is just as accurate as it was then. I calibrate my cameras with it.

Good luck

Michael :cool:
 

zhuangyan

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#19
???? sry, new here. wad is the Depth of Field , Circle of confusion and hyperfocal distance? if i am shooting something and i just set to the focal distance i want by turning the focus ring to make it sharp. y we need to many calculations?
 

#20
tHE REASON FOR WORRYING ABOUT IT IS SO YOU CAN REGULATE WHAT IS IN FOCUS IN YOUR PHOTOS. jUST FORGET THE CIRCLE OF CONFUSION AND HYPERFOCAL DISTANCE, THEY WILL JUST CONFUSE YOU.

iF YOU ARE FOCUSED ON A SUBJECT 2METER AWAY FROM YOU and you want everything from the camera to as far as you can see, then you have a large depth of field (DOF) If you are taking a photo of a lovely young lady and the background is confusing, you can change the depth of field to throw that background out of focus. This is called selective focus. As you learn more about photography you will see why these methods can be ueful to you.

If I didn't answer your questions, please re ask me.

Michael ;-)
 

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