focal distance (not focal length): I have often wondered why specifications for lenses only include minimum focal distance but not maximum focal distance. It would sure help me a lot...

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focal distance (not focal length)

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Mar 8, 2013 13:19:01 #

nat Loc: Martha's Vineyard, MA

I have often wondered why specifications for lenses only include minimum focal distance but not maximum focal distance. It would sure help me a lot if I knew this....or have I not learned anything?

Mar 8, 2013 13:29:39 #

rpavich Loc: West Virginia

nat wrote:

I have often wondered why specifications for lenses only include minimum focal distance but not maximum focal distance. It would sure help me a lot if I knew this....or have I not learned anything?

You mean "minimum FOCUS distance? MFD?

Mar 8, 2013 13:31:47 #

nat Loc: Martha's Vineyard, MA

rpavich wrote:

nat wrote:

I have often wondered why specifications for lenses only include minimum focal distance but not maximum focal distance. It would sure help me a lot if I knew this....or have I not learned anything?

You mean "minimum FOCUS distance? MFD?

Yes

Mar 8, 2013 13:33:00 #

Linda From Maine Loc: Yakima, Washington

Interesting point. Have always thought "infinity" but with footnotes about how you need to fill your frame with the subject for best results. Will follow this thread with interest.

Mar 8, 2013 13:34:09 #

nat Loc: Martha's Vineyard, MA

Linda From Maine wrote:

Interesting point. Have always thought "infinity" but with footnotes about how you need to fill your frame with the subject for best results. Will follow this thread with interest.

Whew! I thought it might have been the stupidest question known to the forum.

Mar 8, 2013 13:34:33 #

JR1 Loc: Tavistock, Devon, UK

!!!

Because when focused on infinity it is obvious that they will be sharp with subjects even 1000s of light years away that is why. Such as suns (stars)

It would be odd if manufacturers stated "only use this lens from 10' to 1 mile"

Mar 8, 2013 13:35:09 #

Searcher Loc: Kent, England

I have a lens which focuses from a few inches to twenty or thirty feet, but this is very rare. Surely most lens focus to infinity.

My lens is home made from old magnifying glasses.

Mar 8, 2013 13:37:00 #

rpavich Loc: West Virginia

nat wrote:

rpavich wrote:

nat wrote:

I have often wondered why specifications for lenses only include minimum focal distance but not maximum focal distance. It would sure help me a lot if I knew this....or have I not learned anything?

You mean "minimum FOCUS distance? MFD?

Yes

Well...then that's why...it's only useful to know how close you can get to your subject...not how far away they can be :)

Mar 8, 2013 13:37:45 #

Linda From Maine Loc: Yakima, Washington

nat wrote:

Linda From Maine wrote:

Interesting point. Have always thought "infinity" but with footnotes about how you need to fill your frame with the subject for best results. Will follow this thread with interest.

Whew! I thought it might have been the stupidest question known to the forum.

There are a few apparently unhappy souls who will let you know they think your question is "stupid" by their sarcastic comments, but most people on UHH do seem to try to be helpful because they know your question is sincere. And some will even say, "I'm sure glad you asked that because I wanted to know too!"

Mar 8, 2013 13:41:20 #

nat Loc: Martha's Vineyard, MA

JR1 wrote:

Well, !!!. I doubt that if I set my lens to infinity that I will get something 1000s of light years away. That is what the Hubble (sp?)telescope is for. And Yes, I would like the manufacturers to tell me at what distance my lens is likely to reach its peak, its focus peak, so to speak. Lenses have got to have limits. :twisted:

Mar 8, 2013 13:44:25 #

JR1 Loc: Tavistock, Devon, UK

1/4 of a million miles away

http://i928.photobucket.com/albums/ad121/jser1/Image1-15.jpg

92,955,807 miles away

http://i928.photobucket.com/albums/ad121/jser1/JPEGImage27328577.jpg

Mar 8, 2013 13:50:42 #

OddJobber Loc: Portland, OR

One notable exception. When using an adapter to mount a lens designed for a different camera, the lens to film plane distance will often change, resulting in loss of infinity focus. This will not, of course, be given in the lens specs. Nice shots, JR1.

Mar 8, 2013 13:52:52 #

nat Loc: Martha's Vineyard, MA

I take it, JR, that you vote YES on the stupidest question.

Mar 8, 2013 13:59:30 #

nat Loc: Martha's Vineyard, MA

rpavich wrote:

nat wrote:

rpavich wrote:

nat wrote:

I have often wondered why specifications for lenses only include minimum focal distance but not maximum focal distance. It would sure help me a lot if I knew this....or have I not learned anything?

You mean "minimum FOCUS distance? MFD?

Yes

Well...then that's why...it's only useful to know how close you can get to your subject...not how far away they can be :)

So, is it really a question of magnification? Sorry, I have trouble with spacial concepts...always have.

Mar 8, 2013 14:04:38 #

Linda From Maine Loc: Yakima, Washington

Assuming every lens will focus to infinity, why are some moon shots much sharper than others? That must have to do with quality of lens and the technique (tripod, proper exposure, etc). Anything else?

And if you aim both your 250 mm lens at distant hills and your 500 mm, will they produce equal sharpness at same enlargement (uncropped)? Or is my original mention of "filling the frame" a major factor in most cases? (thinking in terms of "how close you can get" per rpavich)

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