 Josh |
How to calculate zoom Is there a way to calculate or figure out what a photo taken at 135mm (or 80mm, 200, 600mm, etc...) would look like? I am fairly new to digital photography, shooting with a 350D, 35-55mm lens, and would like to get a better idea on how much of a telephoto lens I need to buy. So, I'm trying to figure out from my photos what it would look like if I was able to zoom in more. There has to be some kind of conversion scale. For instance, if I open one of my images in Photoshop and view it at 100%, would scaling the image up to 135% be similar to a 135mm lens? Probably not, but hopefully you get the idea of what I'm asking. Thanks in advance
|
|
|
|
||
|
Justin G. |
well Josh I'm sure there's a way but I don't think it's simple. it would involve using some geometry and trig. see for a 50mm lens we know that is has an angle of view of 46°, a 100mm has a 24°, and a 135mm a 18°. I don't exactly know how to do it but I learned it a couple years ago in physics in high school. I mean there is a way to do it but i'd have to be at home crunching numbers and diagrams. when I get home i'll try to illustrate what i'm thinking, sorry I couldn't help more now. i'm sure one of the pros here knows how.
|
|
|
|
||
|
Michael H. Cothran |
Josh, Let me share some info another way: Lens focal lengths are related. Each time you halve the focal length you can see 4 times the image as before. Each time you double the focal length you can see 1/4 of the image as before. A 50mm lens on a 35mm camera is considered a "normal" lens. It sees close to what the human eye sees, except for all the periperal stuff. If you're looking at a large wall, let's say you're at a distance with your 50mm lens attached, so that you see 80' high and 120' wide. Standing in the same spot, if you switch to a 100mm lens, you will now see 40' high by 60' wide. If you switch to a 200mm lens, you will now see 20' high by 30' wide. A 400mm lens will see 10' high by 15' wide. Going the other way, a 25mm lens will see 160' high by 240' wide. This should at least give you some perspective. In between focal lengths can be figured with a little math. In short, each time you halve the lens' focal length, you double both the height and width of the area you can see. Hope this helps a little. Michael H. Cothran
|
|
|
|
||
|
Justin G. |
Michael, you really should author a Photography for Dummies book.
|
|
|
|
||
|
Justin G. |
wow after I hit submit (when it was too late) I realized I should proofread. Josh I didnt' mean you're a dummy! lol. I wanted to clarify that I meant Mike has a very appealing way of explaining things in lamens terms so we can all understand it. just wanted to clear all that up.
|
|
|
|
||
|
John P. Sandstedt |
Go into Google and search for "calculate zoom." There are several sites in the thousands listed that do include the formula that's based on arc-tangents and radians, and relates to image dimensions. I'd try to explain, but my trigonometry is 50 years old.
|
|
|
|
||
|
Josh |
Michael, thank you very much. That helps a lot. Justin is right, you have a great way of explaing things. Thank you all for responding. I'm going to search google for now. Josh
|
|
|
|
||
|
This old forum is now archived. Use improved Forum here
Report this Thread |
||