Mauricio,
Stan Halpin forwarded your message to the Pentax Discussion Mailing List,
from which I reply.
If I got this right, you wish to take photos of flowers at exactly 1:20,
then make a grid that you can print onto the slide afterwards to measure the
size of the flower.
I advice against using this method because the accuracy will be pretty low.
1/10mm * 20 is 2mm error margin. If your small flowers are eg. 10mm, that's
an error margin of 20%. That might be okay, but it's definately not
scientific standards.
May I suggest another method for you to consider:
Make a grid design that you can use in the field, and place right in front
of the flower. Like a tennis racket, only with a finer grid. Then photograph
the flower and the grid together. Then you can measure the size of the
flower correctly independent of scale in the photo. Your accuracy will only
depend on the accuracy of the grid.
You could also photograph the flower with any object of known size. Eg. an
ordinary liner or ruler, or a cylinder (filmbox etc.). As long as you know
the size of the object, you can calculate the size of the flower:
Oi/Or = Fi/Fr
or
Fr = (Or*Fi)/Oi
where
Oi = Object size on image
Or = Object size in real life
Fi = Flower size on image
Fr = Flower size in real life
If you project the slide on the wall and measure there, your accuracy will
be pretty good.
Hope this helps?
Best regards,
Jostein Øksne M.sci.
Norwegian Medicines Agency
> -----Original Message-----
> From: Stan Halpin [mailto:[EMAIL PROTECTED]]
> Sent: Friday, August 10, 2001 3:42 PM
> To: PDML
> Cc: [EMAIL PROTECTED]
> Subject: FW: focal lenght
>
>
> A query received for which I have no answer. I am not even
> sure I understand
> the question.
>
> I will be out for a week. Please send any responses to the
> original query
> author. Thanks!
>
> Stan
>
> ----------
> From: "Mauricio Bonifacino" <[EMAIL PROTECTED]>
> Date: Thu, 9 Aug 2001 15:49:40 -0300
> To: <[EMAIL PROTECTED]>
> Subject: focal lenght
>
> Dear Friend:
>
> I work with plants and i am needing to build a ruller that
> allows me to
> determine the size of small flowers. I need a ruller that
> measures 1/10 mm.
> I decided doing a reticule model at 1:20 and taking a picture
> and using the
> design printed on a slide as a ruller. I need to know the
> relation between
> the film position, the focal lenght of the lens and the
> object distance. I
> will be working with a 80 mm lense and I will place the
> object at 1,6 m from
> the camera in order to have a 1:20 scale.
>
> thanks in advance for considering my inquiry
>
> Mauricio
>
>
>
> -
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