Re: image circle relative to focal length/fstop

Would then a thick material create a smaller circle with the same image
quality (or not) as a thinner material? These may be simple questions but I
want to be able to control the size of my image circle, either through
pinhole size or focal length. It now sounds like material thickness could be
a 3rd variable to play with, and possibly the most productive. Any other
advice out there? Thanks for the responses so far. Thom
----- Original Message -----
From: "G.Penate" <penate@rogers.com>
To: <pinhole-discussion@pinhole.com>
Sent: Monday, 25 March, 2002 22:54
Subject: Re: [pinhole-discussion] image circle relative to focal
length/fstop

> But if your aim, Thom, is to have a circular image in the middle of your
> paper/film format, the bellow mentioned rule will not work for you, in
such a
> case you should perhaps assume a 5 times the focal length or even more.
Use
> also thick material to make your pinhole.
>
> Guillermo
>
>
> PS: it was somewhat hard to answer this nature of question without
recurring to
> use "derivative calculus" which BTW, I thought it was called trigonometry,
> taught in grade 8 to me. My friend Juan use to say: "why are we learning
this
> stuff we would never use", he was probably right ;-)
>
>
> ----- Original Message -----
> From: "Tom Miller" <twmiller@mr.net>
>
>
> > The rule of thumb is that, on a flat film plane, the circle will be
> > 3.5 times the focal length. So, if the focal length is 1" the circle
> > will be 3.5", if the focal length is 2" the circle will be 7", and so
> > on. The f-stop doesn't really matter for this rule of thumb.
> >
> > ----- Original Message -----
> > From: "Thom Mitchell" <tjmitch@ix.netcom.com>
>
> > How can I quickly determine the size of the image circle for a given
> > focal length and f/stop. I want to be able to keep an image circle
> > from getting too big, i.e. I want it to be 2' or 3''. Any quick help
> > would be appreciated as would simple rules of thumb as opposed to some
> > of the derivative calculus I sometimes see. Thanks for your help in
> > advance. Thom
>
>
>
>
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Received on Mon Mar 25 23:02:49 2002