Is a 300mm @21mp same as a 600mm@10mp?

Started Nov 14, 2008 | Discussions thread
LeonXTR Contributing Member • Posts: 820
Re: Is a 300mm @21mp same as a 600mm@10mp?

If I am shooting with lets say a 300mm f/2.8 that is 20+ MP camera is
that about the same as shooting with a 10mp camera using a 600mm lens?

i am assuming you mean if you crop the image from the 20mp cam will it be the same as an image from 10mp with a higher zoom

20mp is 50% more resolution on each side versus a 10mp,so 300mm +50% equals to a 450mm lens on a 10 mp.


The reason I ask is I have a 1D MK III and a 300mm f/2.8 IS lens. IF
I were to switch to say a 1Ds MK III at 21MP is it ABOUT equal to a
using a 500-600mm Lens on my 10mp 1D MK III?

Definitely not,because:

300mm on your 1DIII is equal to 300mmX1.3(cameras crop factor) this means its like using a 390mm on a 1DsIII.

Now if you put your lens on a 1DsIII and crop each side by 50%,thus making a 10mp image it would give you 50% more zoom,300 X 150 / 100=450mm

So switching to a 1DsIII will give you 450mm(on 10mp crop) versus the 390mm you are getting now,plain speaking 60mm more,or 15.384% more zoom.

Less than getting a 1.4X converter on your 300mmF2.8 which will make it a 420mmF4(546mm on your cropped 1DIII),or even a 2X converter and get a 600mmF5.6(780mm on your cropped 1DIII)

I find that shooting small birds/animals I have to REALLY crop to get
anything worthwhile. I know a longer focal length would solve the
problem but would more MP do the same thing?

no because you will loose the 1.3X crop,gain 50% more,but that's it.No big difference.

Other than the 1.3 crop factor what am I missing here?

P.S. I already have a 40D and it is not nearly as good as the MKIII
so I don't want to go the 1.6 route.

You are correct,1DIII is excellent,no comparison with an xxD model

Get a 1.4X or a 2X converter,for about $300,and you get either 546mmF4 or a 780mmF5.6


hope this post helps you make the right decision(and i apologize for all the mathematics)
Let there be light

 LeonXTR's gear list:LeonXTR's gear list
Canon EOS 5D Mark II Canon EF 200mm f/2.8L II USM Canon EF 70-200mm f/2.8L USM Canon Extender EF 2x II Sigma 105mm F2.8 EX DG Macro +5 more
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