Jan van Dijk (janvdijk@bart.nl)
Wed, 16 Jun 1999 13:33:35 +0200
-----Oorspronkelijk bericht-----
Van: Jan van Dijk <janvdijk@bart.nl>
Aan: Gary Miller <gmphotos@earthlink.net>
Datum: woensdag 16 juni 1999 12:48
Onderwerp: Re: Optics and depth of field
>See the Focal Encyclopedia of Photograhy under optics, etc. and lots of
>other books.
>
>Basicly DOF can be calculated via one or more formulas, in which the circle
>of confusion is one element.
>With different film sizes there will be different values defined for it. (A
>large negative will be enlarged less than a small one).
>
>So in the three examples given: if the circle of confusion would be defined
>equal, there would be a large difference in the DOF (a shorter lens will
>have a larger DOF).
>But because the different definitions of the circles of confusion it will
>compensate somewhat for that.
>So the total result will be that the 35 mm. lens has a greater DOF,
>depending how one defined the circle of confusion.
>That is one of the reasons why there are different DOF tables.
>
>
>Jan van Dijk.
>
>
>Van: Gary Miller <gmphotos@earthlink.net>
>Aan: Alternative Photo Group <alt-photo-process-l@usask.ca>
>Datum: woensdag 16 juni 1999 6:25
>Onderwerp: Optics and depth of field
>
>
>>I have a few questions about optics and depth of field for those on the
>list
>>that are into these areas. I know that we do not discuss optics too often
>>so maybe this can open up some new areas.
>>
>>I wanted to know how depth of field varies between formats. Let me
>>elaborate. I know that DOF decreases as you get closer to an object,
hence
>>one of the difficulties in macro work, and also decrease with longer focal
>>length lenses. But how would the DOF differ, or not, between the
following
>>three situations;
>>
>>1) a 35 mm lens on a 35mm camera
>>2) a 65 mm lens on a medium format camera (35mm equivalent field of view)
>>3) a 120 mm lens on a 4"x5" camera (35mm equivalent field of view)
>>
>>All three of these lenses have equivalent fields of view around 55
degrees.
>>Thanks for enlightening me.
>>
>>Gary
>>
>
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