Crop vs. FL

This is maybe a stupid question, but I wonder if I really need that lens with extra reach when I have a 18mp camera. I used to shoot with my 30D and 8 mp. Now I have 18mp and I never print above A3 format. I like to shhot birds and my longest lens is 300mm. I know you will all say that is to short for this purpose, and I really consider buying the 400/5.6. But I guess a 400 on a 8mp camera is no better than a 300 on a 18mp camera right?

celter wrote in post #11692262
This is maybe a stupid question, but I wonder if I really need that lens with extra reach when I have a 18mp camera. I used to shoot with my 30D and 8 mp. Now I have 18mp and I never print above A3 format. I like to shhot birds and my longest lens is 300mm. I know you will all say that is to short for this purpose, and I really consider buying the 400/5.6. But I guess a 400 on a 8mp camera is no better than a 300 on a 18mp camera right?

What about slight misfocusing ? Or lens aberrations ? Or motion blur ? Or noise ? Or scores or other artifacts that on the crop sensor are magnified 2.6 times compared to FF ?

Refresh Image wrote in post #11692306
What about slight misfocusing ? Or lens aberrations ? Or motion blur ? Or noise ? Or scores or other artifacts that on the crop sensor are magnified 2.6 times compared to FF ?

I'm pretty sure they aren't magnified, crop just has a smaller field of view

When I originally wanted a telephoto longer than my 55-250mm kit lens, I found a used Sigma 170-500mm with a non-adjustable aperture (stuck at f/6.3 because the lens couldn't communicate with my camera).

Testing showed that cropped shots with the 55-250mm were much sharper, with less CA, than the uncropped shots taken with the longer lens. And the keeper rate was way higher with the 55-250mm lens.

Then, when I bought a new Sigma 150-500mm I did an informal comparison with a friends 70-200mm with 2X teleconverter and found that I preferred the shots taken with the Sigma.

My opinion (for what little it's worth) is that there are too many variables involved to reduce the decision down to megapixels versus focal length. Have you thought about renting a couple of lenses and testing them in the field? I wouldn't be surprised if lens weight and auto-focusing speed became equally important considerations.


Edit: I re-read the original post. You will definitely be able to crop more with the 18mp sensor. I'd be interested in seeing your results. Also, is it practical to use a prime lens for shooting birds in flight? I would think it'd be really tough to find them in the viewfinder.

celter wrote in post #11692262
This is maybe a stupid question, but I wonder if I really need that lens with extra reach when I have a 18mp camera. I used to shoot with my 30D and 8 mp. Now I have 18mp and I never print above A3 format. I like to shhot birds and my longest lens is 300mm. I know you will all say that is to short for this purpose, and I really consider buying the 400/5.6. But I guess a 400 on a 8mp camera is no better than a 300 on a 18mp camera right?

If you can get the results you want with the gear you have, why spend more?

yjt wrote in post #11692321
I'm pretty sure they aren't magnified, crop just has a smaller field of view

That's true, but in order to reach a given print/display size, the cropped image would need to be enlarged more, magnifying imperfections (and reducing the ultimate DoF as the blur discs are also magnified more).