Specific distance ratio for a chosen focal length

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Permalink Reply by Papa Rotzzi on January 22, 2012 at 9:32am

I don't know that I can even wrap my head around the question. From my point of view, distance to subject is based on composition, not on lens design. 

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Permalink Reply by Fred on January 22, 2012 at 9:53am

It entirely depends on whether you want a close portrait of the face or full length body shot, a photographer knows what shot to take and takes it.

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Permalink Reply by nathan mccreery on January 22, 2012 at 10:51am

Bear in mind that as the distance of the subject to lens changes the image size changes and the depth of field, at a certain aperture, changes.  I am not sure what the intent of the question is, or why it would be important from this vantage point.  The distance of the lens to subject is much less significant than the composition you're  building.  My suggestion always is to move in close enough to the subject that cropping will be minimized.  I use close proximity to my subject very often when using a very wide angle lens to give more prominence to foreground material.  The time I can see this being an important consideration would be if you were trying to determine the hyperfocal distance for maximizing Acceptable Depth of Field at a particular aperture.  There were times when lenses of very old fashioned design were sharper at some distances than others, for instance in using a close focusing lens in large format photography.  However I think those lens designs are a thing of the past.  The other would be that macro and micro lenses used to be optimized for certain distances, however, and again, those designs are things of the past.

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Permalink Reply by John C on January 22, 2012 at 3:55pm

Thank you all guys for the replies, at least makes me think to focus more on the composition and not so much on doing the math :).  I was very curious of this and went to some searching at the internet and there were lots of those stuff describing 

how it is done, but I want to get advice from you guys, the most experience ones if do you really apply this when you get your pictures or do you ever give it a thought before getting your pictures? I want to share one of the link I came across and there you will find a focal length calculator in relative to the distance of the subject. It's a nice site, discussing about theories and stuff about photography. This is one of the reason I wanted to ask this question. Here's the link: http://www.cambridgeincolour.com/tutorials/camera-lenses.htm 

Thanks again guys, please let me know your thoughts of the link :)

Best regards,

John

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Permalink Reply by CameraClicker on January 22, 2012 at 6:53pm

Understanding the science of lens design won't hurt.  As a practical matter, you get used to looking through lenses and become able to predict what focal length might be useful for a given scene.

In the same way, it doesn't hurt to know the temperature gasoline burns at, how a four-stroke engine works or Newton's laws, but you don't usually think very much about any of those things when driving your car to the local mall.

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Permalink Reply by John C on January 23, 2012 at 8:16pm

Thanks CameraClicker. Well said. =)

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Permalink Reply by SRT30D on January 24, 2012 at 10:54pm

Also, remember that a lens will give different perspectives of distortion dependant upon the distance. Such as the 16mm in a facial close-up will distort the most prominent part of the feature- usually the nose.

A telephoto will make objects appear closer together than they actually are, shortening the perspective.

As for what would be classified as a 'normal' lens in relation to the eye, I recall it being somewhere in the 50-58mm range for a 35mm frame. Too, if I recall correctly,  the 35mm lens can be  considered normal 'wide angle' using the periferal vision as a guide.

Of course, these numbers could be way off, depending on your lens and chip size.

Measuring a distance- let your eye be your guide with an SLR- whatchya see is whatchya get, for the most part. Unless you're a math geek, then have fun coming up with some charts. ;)   There is the 'hyper-focal distance' that is a sweet spot for focussing to get maximum depth of field, which may possibly be what you're thinking of.

SRT

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Permalink Reply by John C on January 25, 2012 at 6:15am

Thanks SRT. True each type of lens can render different effects on the subject. I was thinking in the line between getting a good quality picture without diminishing the lens capabilities to focus clearly depending on the focal length  used say for example 85mm, 16mm etc and lens design. like for instance how far is far enough should I stand away from my subject and not compromising picture quality including sharpness. I believe that in any given situation, 50mm can also be use to take landscape but to comparably get the same picture as a landscape lens does, we need to pull back a little further to get the ideal picture that we want, but then again are we going beyond what a 50mm lens is supposed to be designed at? I also understand that to get a better shot, we would rather chose to set the aperture to f8, f11, f22 and so on but is this really enough?

You're also correct about the hyper focal distance, basically, I'm not used to it yet and perhaps that will be my next topic for discussion unless it's already been described here hehe. Right now, my only concern is if the lenses that we use are designed with a specific distance in mind and by violating it affects overall picture quality.

Then again, you're also right to point out that  "let your eye be your guide with an SLR- whatchya see is whatchya get" because that's where all the fun begins ;) Thanks for sharing.

Best Regards,

JohnC

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