Digital Zoom question

lurchlarson · 10-10-2010, 01:02 PM

My local congregation asked me to teach a photography class next month. I'm going to be keeping it pretty simple and because I only have 45 minutes.

One of the things I was going to do it to talk about why digital zoom is a bad thing. I'm not going to do the math for them, just the results and I wanted someone to check my math for me.

With digital zoom isn't the amount of zoom squared the reduction in number of megapixels? I.e. frame 10x10 units across with a 2x zoom results in a frame that is 5x5. Because it is a rectangle this equals a 75% reduction in the number of pixels you use.

10x10=100 units
--------------------
5x5=25 units

falconeye · 10-11-2010, 02:30 AM

Originally posted by lurchlarson

I wanted someone to check my math for me.

Your math is correct.

However, that's not the one reason why digital zoom is bad.

E.g., if you have a 16MP camera like the K-5 and do a 2x digital zoom, you'll end up with a 4MP image. Which may still be good enough for many purposes and actually might be on par with the output from a 2x teleconverter; or a 2 digital crop from a prime lens might be on par with the output from a zoom lens.

However, focus accuracy and a camera's P automatic setting may not be adequate for that 2x crop then. I.e., an actually longer focal length can result in better image quality. Even if you had an unlimited number of pixels to work with.

10-10-2010, 01:02 PM	#1
lurchlarson Veteran Member Join Date: Nov 2008 Location: Oregon, USA Photos: Albums Posts: 681	Digital Zoom question My local congregation asked me to teach a photography class next month. I'm going to be keeping it pretty simple and because I only have 45 minutes. One of the things I was going to do it to talk about why digital zoom is a bad thing. I'm not going to do the math for them, just the results and I wanted someone to check my math for me. With digital zoom isn't the amount of zoom squared the reduction in number of megapixels? I.e. frame 10x10 units across with a 2x zoom results in a frame that is 5x5. Because it is a rectangle this equals a 75% reduction in the number of pixels you use. 10x10=100 units -------------------- 5x5=25 units

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10-11-2010, 02:30 AM	#2
falconeye Veteran Member Join Date: Jan 2008 Location: Munich, Alps, Germany Photos: Gallery Posts: 6,871	Originally posted by lurchlarson I wanted someone to check my math for me. Your math is correct. However, that's not the one reason why digital zoom is bad. E.g., if you have a 16MP camera like the K-5 and do a 2x digital zoom, you'll end up with a 4MP image. Which may still be good enough for many purposes and actually might be on par with the output from a 2x teleconverter; or a 2 digital crop from a prime lens might be on par with the output from a zoom lens. However, focus accuracy and a camera's P automatic setting may not be adequate for that 2x crop then. I.e., an actually longer focal length can result in better image quality. Even if you had an unlimited number of pixels to work with.