# Calculate the length of an object that can fit into my frame.

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#### dRebelXT

##### New Member
Here is the specs of my lens, and cam is 350D. I need to calculate the
diagonal distance of the smallest box (W/L = 3/2) which can exactly fit
into the frame. Is this formula correct?

D = 2 * (220cm * tan(6.2/2)) / 1.6 = 14.89cm.

http://www.sigmaphoto.com/lenses/lenses_all_details.asp?id=3275&navigator=3
Angle of View 18.2 - 6.2 degrees
Minimum Focusing Distance 200- 220cm
Maximum Magnification 1:5.3
:think:

##### Senior Member
dRebelXT said:
Here is the specs of my lens, and cam is 350D. I need to calculate the
diagonal distance of the smallest box (W/L = 3/2) which can exactly fit
into the frame. Is this formula correct?

D = 2 * (220cm * tan(6.2/2)) / 1.6 = 14.89cm.

http://www.sigmaphoto.com/lenses/lenses_all_details.asp?id=3275&navigator=3

:think:
Duh ... hmm ... what does this has to do with photography?

#### dRebelXT

##### New Member
Duh ... hmm ... what does this has to do with photography?
Well, can decide what is the minimum subject I attempt to point my cam towards. ;p

#### swhyge

##### New Member
dRebelXT said:
Here is the specs of my lens, and cam is 350D. I need to calculate the
diagonal distance of the smallest box (W/L = 3/2) which can exactly fit
into the frame. Is this formula correct?

D = 2 * (220cm * tan(6.2/2)) / 1.6 = 14.89cm.

http://www.sigmaphoto.com/lenses/lenses_all_details.asp?id=3275&navigator=3

:think:
If I can refine your equation:

You must also consider the angle of line D and axis of the lens. Assume this angle as theta, then the max distance D' = D/sin(theta).

You may further refine it by considering the perspective angle effect.

If you box has sharp edges, then light diffracts, you may also wish to factor the wavelength of the light which you taking your shot.

And lens has also pincushion and barreling effect, you will must also consider to a better approximation of D.

Finally, because of the finite size of the photosites, your best accuracy will be +/- 2 photosite distance..

#### LittleWolf

##### New Member
dRebelXT said:
Maximum Magnification 1:5.3
Isn't this what you're looking for?

#### ortega

##### Moderator
Staff member
take a picture of a ruler?
or a tiled floor?

easier no?

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