Help calculating a crop???

[Monkey]

I cant get it right in my head!!!

Lets say ive took an image at 50mm, and i want to see what it would have looked like at 200mm....

How do i work out what to crop to get the result.

I appreciate the quality will drop, it is merely for comparing focal lengths to give an indication to what telephoto zoom to buy.

 

[Jonno_dudley]

Hi monkey

That's a question i've never really thought about and am not sure about the answer. But when I was on the market for a telephoto lens, i used a link on the Tamron site for comparinng different focal lengths. The address is below. Although i can't seem to get onto Tamrons site at present. Maybe you can. Hope it helps

http://www.tamron.com/lenses/learning_center/tools/focal-length-comparison.php

 

[pxl8]

200/50 = 4 so you need to crop the image by a factor of 4 or 0.25

So take the original width, multiple it by 0.25 and that's the width you'd need to keep in the cropped image.

 

[Grockle]

Is this any use to you? http://www.acapixus.dk/photography/angle_of_view.htm

 

[Monkey]

cheers, all sorted now..

This is why i needed to work it out, was trying to figure what lens was needed to fill the frame with this shot took at 50mm

 

[grumpybadger]

But remember that a cropped 50mm gives a different image to a 200mm when you consider foreshortening and depth of field.