# Number crunching, angle of view.

Started Jan 3, 2013 | Questions thread
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Number crunching, angle of view.

So (because i'm a big maths geek and do this sort of thing for fun) I was trying to work out what focal length of lens I'd need to fill my sensor (50%+) with the moon to take great detailed close up shots.

now I've stolen a bunch of info from various wiki/ website to cobble this all together so i just wanted someone to check my math as I can get a bit mixed up, I'm still learning/relearning a lot of theory i've forgotten. Alternatively, if there is an easier way to calculate it...

pentax K-30 with sensor size: 23.7*15.7

Equation from wiki: angle = 2 * atan[ (height of sensor)/(2 * Focal length)]

f = height/[2*tan(angle/2)]

height of sensor = 15.7mm

moon field of view ~ 32 arc mins = 32/60 degrees.

F ~ 1700mm equivalent focal length to fill the sensor top to bottom.

so as I'm not on full frame sensor this equates to an equivalent F = 0.65*1700  =  1100mm

so 1000mm would fill the vast majority of the screen top to bottom?

thoughts, comments corrections all welcome.  or i can get back in my corner and do some more math and leave you all alone...

JOJO

jojo81's gear list:jojo81's gear list
Pentax K-30 Sigma 120-400mm F4.5-5.6 DG OS HSM Pentax smc DA 18-55mm F3.5-5.6 AL WR +2 more