DSLR 101 3.0

[RobertTheFat]

Those numbers you're throwing around are the focal lengths (in millimeters) of the lenses you're using. They have nothing directly to do with the distance from the camera to the subject - in yards, feet, meters, rods, fathoms, furlongs, or any other units. Where on earth did you get the idea that they do? I hope it wasn't from me or Ernie.

If what you're doing is trying to calculate the depth of field for various distances and focal lengths, there are tables for that. I don't refer to them much, but I believe the camera-to-subject distances are usually quoted in feet.

[jazzman1]

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@RobertTheFat wrote:

Those numbers you're throwing around are the focal lengths (in millimeters) of the lenses you're using. They have nothing directly to do with the distance from the camera to the subject - in yards, feet, meters, rods, fathoms, furlongs, or any other units. Where on earth did you get the idea that they do? I hope it wasn't from me or Ernie.

If what you're doing is trying to calculate the depth of field for various distances and focal lengths, there are tables for that. I don't refer to them much, but I believe the camera-to-subject distances are usually quoted in feet.

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I'm trying to figure the actual distance from an object I'm shooting.  As in one of the pics I posted of the jazz fest of the band on stage.  Whenever I shoot at a distance, just a example, a tree, that may in my opinion be 100 yds away in real distance.  My lens only shows distance in mm.   Maybe I'm wrong here, maybe it's non issue I should'nt worry about, I don't know.  It's just something I would like to know, how fto determine how far away from whatever I'm shooting is in ft. and yds.  I've looked at what the lens says in mm when I zoom in but that's no help.  I guess maybe you guys never understood the question.   Sorry if I was'nt plain.

BTW...Nobody told me any of the stuff you mentioned, nor have I asked that, or wanted to know.  I think this question of mm has been an issue of mis-communication...between us all.   I don't think you guys understood my question, so your answers did'nt appy for me.  If so, I'm very sorry keeping this running so long.  Actually it seems like a very simple question with an easy answer.  But maybe i'm wrong about that.

[jazzman1]

Re: DSLR 101 3.0

19m ago

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@RobertTheFat wrote:

Those numbers you're throwing around are the focal lengths (in millimeters) of the lenses you're using. They have nothing directly to do with the distance from the camera to the subject - in yards, feet, meters, rods, fathoms, furlongs, or any other units

I know this Bob....the mm reading on my lens tells me nothing about my distance from my camera to a subject or scene.....far away.  That's why this question.   I'm mostly trying to know the actual distance from my camera when taking a shot.  The question came to mind when I saw gear called "range finders".   So I thought those may be helpful to learn distance when taking long range shots.  My thinking is knowing our distance, say 100 yrs.....may be helpful in getting the right camera settings for the shot.   And those settings might change depending on the light.  I'm thinking knowing my distance for any given shot, would help determine the best settings, of my camera to use, for that shot.

Maybe this is a nonsense question, if so, I'm very sorry to have bothered you and Biggs with it.

[jazzman1]

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@RobertTheFat wrote:

Those numbers you're throwing around are the focal lengths (in millimeters) of the lenses you're using. They have nothing directly to do with the distance from the camera to the subject - in yards, feet, meters, rods, fathoms, furlongs, or any other units

I know this Bob....the mm reading on my lens tells me nothing about my distance from my camera to a subject or scene.....far away.  That's why this question.   I'm mostly trying to know the actual distance from my camera when taking a shot.  The question came to mind when I saw gear called "range finders".   So I thought those may be helpful to learn distance when taking long range shots.  My thinking is knowing our distance, say 100 yrs.....may be helpful in getting the right camera settings for the shot.   And those settings might change depending on the light.  I'm thinking knowing my distance for any given shot, would help determine the best settings, of my camera to use, for that shot.

Maybe this is a nonsense question, if so, I'm very sorry to have bothered you and Biggs with it.

[jrhoffman75 · Accepted solution]

Unless there is only one item in your viewfinder, which is next to impossible, there are an infinite number of distances between you and the items.

Only one distance is in perfect focus, and depending on depth of field, a range of distances will be in acceptable focus.

Zooming the lens doesn't change the distance anymore than it compresses the distance between objects.

Maybe it's my imagination, but I often feel a tugging on my leg when I read some of these postings.

[jazzman1]

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@jrhoffman75 wrote:
Unless there is only one item in your viewfinder, which is next to impossible, there are an infinite number of distances between you and the items.

Only one distance is in perfect focus, and depending on depth of field, a range of distances will be in acceptable focus.

Zooming the lens doesn't change the distance anymore than it compresses the distance between objects.

Maybe it's my imagination, but I often feel a tugging on my leg when I read some of these postings.

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Hey jrhoffman75.  Thanks for the help and this does help.  Guess you're saying my distance should not be an issue in taking any of my shots.  That's good to know, I feel a little relief.  Bugs me to no end when there's something I think I should know and can't figure the answer. 

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I often feel a tugging on my leg when I read some of these postings

Guess you mean you help lost causes, stray dogs, and newbies like me (LOL)

BTW.....Thanks much.

[ebiggs1]

"... depending on depth of field, a range of distances will be in acceptable focus."

This called the hyperfocal distance. It is the closest distance at which a lens can be focused while keeping objects at infinity acceptably sharp. When the lens is focused at this distance, all objects at distances from half of the hyperfocal distance out to infinity will be acceptably sharp.

[jrhoffman75]

Negative. That's not what I want talking about. I was talking about when you focus at a particular point that distance is perfectly sharp and a range around that is acceptable based on the circle of confusion that establishes DOF. One might control DOF by choosing aperture to selectively highlight the subject.

Hyperfocal distance you select a focus point so that the closet and furthest item of interest is in acceptable focus relying on DOF.

I know you know this; I just to be sure all readers do.

[ebiggs1]

Not negative.  They are really extremely related to each other. Most people wil be happier with hyperfocal distance than COC.  COC depends on the sensor size and viewing medium.  Hyperfocal distance is lens driven.

[RobertTheFat]

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@ebiggs1 wrote:

Not negative.  They are really extremely related to each other. Most people wil be happier with hyperfocal distance than COC.  COC depends on the sensor size and viewing medium.  Hyperfocal distance is lens driven.

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a.  Isn't the whole concept of hyperfocal distance based on the CoC (i.e., the appearance of being in focus because other factors keep you from telling the difference)?

b.  Hyperfocal distance is useful only if the in-focus range has to extend to infinity. Or am I missing something?