Lens info.

[Salleke]

If I set my lens in Manual Focus mode and focus on infinity what
is the minimal distance from witch the lens focus on a subject?

Is there a formula or a calculation method to know that for every lens?

[jfrancho]

Try here: http://www.dofmaster.com/dofjs.html

[Salleke]

Try here: http://www.dofmaster.com/dofjs.html

Jfranco - Thank you for the intresting link. But I would like to know if there is a easy way to know what the shortest focus distance is of a lens that is been put in manual focus and set at infinity focus.

[jfrancho]

The DOF calculator is the easy way to find this out. What you are asking for will be determined by what aperture you are using. You wil have no choice to use a DOF calculator to find that information. B&H Photo or Canon will have minimum focus distance listed in the specs, but that isn't the answer to your question.

[Citizensmith]

Something else to bear in mind is that the zone of acceptable focus (or Depth of field) extends both in front of and behind you plane of focus. So if you focus on infinity you won't actually be getting the best available DOF.

For instance, with my 24 f/2.8 set at f/16, if I focus on a subject 6.5 feet from the camera everything from 3.2 feet to infinity will appear in focus. If I was to focus on infinity it would push my minimum acceptable distance out further.

[jfrancho]

Excellent point, C.Smith. There are many revelations to be found when using the tool. Learning how to apply this information in field is the fun part.

[jfrancho]

He is asking for the closest distance that will be in focus when the lens is set to focus on infinity. Assuming your subject is in focus at infinity, you can ignore the actual focus setting and get this number with focal length and aperture. The aperture will be the variable that will determine how close to the lens the DOF will extend. The hyperfocal distance will be where to focus to acheive optimum focus in the DOF. The tool is quite simple: type in the known constants, and choose an aperture. Alternatively, you can print up the chart for use in the field.

Salleke, if you put up a real world example, we may better be able to answer the question with an example.

[jfrancho]

Assuming your subject is in focus at infinityRent, I addressed this as well. Your statement disregards aperture, and it is not accurate to say that aperture does not affect nearest acceptable focus, but in fact is critical in this calculation. I suggest you spend some time plugging numbers into the calculator to see for yourself. For example, with a 50mm lens set as high as f/16, and a distance as short as 28 feet, the DOF is infinite. However, the minimum acceptable sharpness occurs at 13.8 feet, not infinity, as you are claiming. This what I think is the answer to Sellek's query. If I'm wrong about my interpretation of the question, then I apologize.

[jfrancho]

If I set my lens in Manual Focus mode and focus on infinity what
is the minimal distance from witch the lens focus on a subject?
I would like to know if there is a easy way to know what the shortest focus distance is of a lens that is been put in manual focus and set at infinity focus.I think it is pretty clear what he asking. I used that distance as an arbitrary example. Again, I think we need a little more "real world" info from Selleke to really give a definitive answer, since it appears based on the interpretation of semantics, we are both correct.

[LastLine]

Have to say this thread has answered a few questions for me. Thank you all.

[Salleke]

I think it is pretty clear what he asking. I used that distance as an arbitrary example. Again, I think we need a little more "real world" info from Selleke to really give a definitive answer, since it appears based on the interpretation of semantics, we are both correct.

First of all thank you all for the answers, I have learned a lot out of the discussions.

This question came up to me when I was trying to take a picture of the lightning a week ago.
There was someone who suggested to put the lens on manual and focus on infinity.
My problem was and still is: If I put the lens on manual and set the focus ring on the infinity mark
where does the lens start to see everyting in focus?

For example: I have a 50 mm 1.4. If I set this lens in manual focus and set the focusring on the infinty mark
wich is the nearest distance from where the subjects start to be in focus? In focus from the nearest distance to infinity?

Next week I will receive my 85 mm 1.8, how can I know it from this lens what the nearest focus distance is if put it on infity focus?

I'm am sorry for the strange way to ask this but inglish is not my native launguach.
Again thank you all for the comments ... :)

[jfrancho]

The only way to figure this out is a DOF calculator. Using a 300d/XT/20d as an example:
50mm f/8 minimim limit of acceptable sharpness is 27ft, subject distance 54ft.
50mm f/1.4 minimum acceptable sharpness is 150.3, subject distance 297ft.
50mm f/16 minimum acceptable sharpness is 13.8 ft, subject is distance 28 ft.
The subject distance was not an arbitrary number. I chose the minimum subject distance that provided an infinite depth of field. As you can see, aperture will affect the minimum acceptable sharpness range. In fact, minimum acceptable sharpness is just part of DOF. I'm not entirely sure if this helps with your specific problem, or that the suggested solution will even work.

[rent]

okay, i've deleted my previous messages in this thread as they now appear misleading upon clarification of the questin.

what salleke is asking is the hyperfocal distance for a given focal length and aperture. hyperfocal distance, by definition, is the distance to the nearer plane of DOF when lens is focused at infinity; in another word, when lens is set to focus at infinity, everything from hyperfocal distance all the way to infinity will be considered in focus.

the DOF calculator does this very nicely, punch in the film format (XT/10D/20D/1D, etc), lens focal lenth and aperture the hyperfocal distance is displayed automatically. for example, for XT/10D/20D, a 50mm lens at f/16 has a hyperfocal distance of 27 ft. this means everything from 27 ft to infinity will be in focus when you focus the lens at infinity.

-alex

[jfrancho]

okay, i've deleted my previous messages in this thread as they now appear misleading upon clarification of the questin.

what salleke is asking is the hyperfocal distance for a given focal length and aperture. hyperfocal distance, by definition, is the distance to the nearer plane of DOF when lens is focused at infinity; in another word, when lens is set to focus at infinity, everything from hyperfocal distance all the way to infinity will be considered in focus.

the DOF calculator does this very nicely, punch in the film format (XT/10D/20D/1D, etc), lens focal lenth and aperture the hyperfocal distance is displayed automatically. for example, for XT/10D/20D, a 50mm lens at f/16 has a hyperfocal distance of 27 ft. this means everything from 27 ft to infinity will be in focus when you focus the lens at infinity.

-alexI don't think that is the proper application of hyperfocal technique. See here (http://www.dofmaster.com/hyperfocal.html).The concept of hyperfocal distance is easy to understand: focus a lens at the hyperfocal distance and everything in the photograph from some near distance to infinity will be sharp. Landscape photographs are often taken with the lens focused at the hyperfocal distance; near and distant objects are sharp in the photos.So, actually you would focus at the hyperfocal point, and the minimum limit of acceptable sharpness is 13.6ft all the way to infinity. Your description of hyperfocal distance is completely irrelevent and incorrect if the camera is set to focus to infinity.

[rent]

jf: i can assure you that what i stated is the answer to the original question, if focused at infinity, everything between H and infinity will be in focus. this is the very definition of hyperfocus and also can be mathematically shown using the formula at http://www.dofmaster.com/equations.html

using the second formula in this page which calculates the near distance of acceptable sharpenss: D(n) = s(H - f) / (H + s -2f), when s (focus distance) is infinity, D(n)=H (actually, it is H-f where f is lens focal length, but unless we are talking about macro here, f is very small compared with H).

i do want to point out that what i stated is definitely not the appropriate way to apply the hyperfocal distance to get the *maximum* DOF. to do so, just like you stated, one should focus at hyperfocal distance (H) and then everything between H/2 and infinity will be in focus.

-alex

I don't think that is the proper application of hyperfocal technique. See here (http://www.dofmaster.com/hyperfocal.html).So, actually you would focus at the hyperfocal point, and the minimum limit of acceptable sharpness is 13.6ft all the way to infinity. Your description of hyperfocal distance is completely irrelevent and incorrect if the camera is set to focus to infinity.

[jfrancho]

Bottom line: Aperture will influence the minimum range of focus. Setting the focus to infinite is not going to net you the nearest range of acceptable sharpness, nor will you necessarily get the picture from it. Furthermore, I don't know what value this advice has for your application, as the details were vague. I think the best solution was addressed and answered already before there was a discussion, debate, retraction, and new debate. I'm really glad that we able to simplify this whole DOF thing. I know I'll never waste my time using the online calculator, when it can be solved algebraically.

[jfrancho]

everything between H and infinity will be in focusI just noticed this. The statement is incorrect. You meant to say: The hyperfocal distance is the point of focus where everything from half that distance to infinity falls within the depth of field. Which is why a 50mm lens fitted to a 300D set at f/16 set to focus at infinity (the minimum that infinity can be on this lens is 27.1ft, which you've found through your calculations) will net you a near focus range of.......13.6ft. Still don't get it? You almost had me convinced I was completely wrong, until I made my own function using the formulas provided on the site and tested it out.

[jfrancho]

Where this all gets interesting is when you use f/22. H becomes 19.2, and nearest focus is 9.61. Interesting apples, huh?

[jfrancho]

One final addendum. All of this math really moot when applied to real world photography. You need to determine what aperture will give the desired depth of field, FIRST. once that is determined you would focus at the hyperfocal distance. This where the old 1/3 in front/2/3 behind the focus rule comes from. I know I always thought of it incorrectly in the beginning. Establish DOF, and focus at H. But this is not hard fast rule, just a tried and treu technique for landscape photography. We can mess with formulas and numbers all day, but the math must be used as a tool support the photograph. [John: steps off the soapbox]

[Salleke]

Jfrancho & Rent,


Thank you both for your answers and discussions. It is bin very learning
and now I have some understanding in this matter.
Thanks goes to all other members as well.

[jfrancho]

Jfrancho & Rent,


Thank you both for your answers and discussions. It is bin very learning
and now I have some understanding in this matter.
Thanks goes to all other members as well.Your welcome. I'm sorry if I come off like crazy person....now go take some pics so we can see just what the heck you're trying to photograph! Good luck.

[rent]

Originally Posted by rent
everything between H and infinity will be in focus

I just noticed this. The statement is incorrect. You meant to say: The hyperfocal distance is the point of focus where everything from half that distance to infinity falls within the depth of field. Which is why a 50mm lens fitted to a 300D set at f/16 set to focus at infinity (the minimum that infinity can be on this lens is 27.1ft, which you've found through your calculations) will net you a near focus range of.......13.6ft. Still don't get it? You almost had me convinced I was completely wrong, until I made my own function using the formulas provided on the site and tested it out.

hi jf, you didn't quote my statement completely, i said, *if the lens is focused at infinity*, everything between H and infinity will be in focus. this is the definition (well, at least one of the mathematical equivalent definition) of hyperfocal distance. and this is the correct answer to the original question (which asks about when lens is focused at infinity).

you statement about hyperfocal distance being "the point of focus where everything from H/2 to infinity falls within DOF" is correct. but it is only correct when focus is set to the hyperfocal distance!! if you look at the illustration below the DOF calculator, the bottom picture illustrate this exact point -- focus at H, DOF is between H/2 to infinity.

i don't know how else to put it more clearly... using the example of 50mm lens at f/16:

1) if lens is focused at infinity, DOF is from 27.1 ft (hyperfocal distance) to infinity.
2) if lens is focused at hyperfocal distance of 27.1 ft, DOF is from 13.6 to infinity.

hopefully now we can agree. :D

-alex

[rent]

now go take some pics so we can see just what the heck you're trying to photograph! Good luck.

this i definately agree. :p

sorry to all who's reading if this thread has become somewhat of an academic exercise. now the weekend is here we should all be out shooting.

-alex

[jfrancho]

this i definately agree. :p

sorry to all who's reading if this thread has become somewhat of an academic exercise. now the weekend is here we should all be out shooting.

-alexI also apologize for my stream of conciesness posts. No more late night POTN sessions.