Reach from extender versus reach from higher density sensor

This is inspired by the thread about ISO performance, where the question came up what exactly the extender is doing to all this:
https://photography-on-the.net …/showthread.php​?t=1077251

Assuming you have a 70-200mm lens and you need more reach, is it better to...

• ... use a camera with a higher density sensor in the crop area, in this case the 7d? This leads to more noise at same ISO.
  
• ... use an extender, in this case on a 5d2? This leads to losing an f-stop in aperture, and assorted other to-be-assessed degradations.
  

• 1) using an aperture both can offer (f/5.6 or smaller), both at same ISO and shutter speed. This mostly tests the optical qualities of the extender.
  
• 2) in the 5d2 trade in the better noise performance for the lost f-stop (using f/4 and iso 1600 on the 7D and f/5.6 and iso 3200 on the 5d2)
  

Interesting test, however different lenses and different TCs don't produce similar results. I have had lenses that loved a 1.4x TC, and others where the IQ fell apart, all from the same TC. I don't know the exact reason why though.

I've always been a big believer in the "shoot tight & crop tighter" philosophy and MP don't matter.

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Well here is another piece in the puzzle. I think the 5d2 comes out on top in that test. Clearly the extender does less damage to the picture (including from the lost f-stop) than the high-density sensor - but not by much.

But the 7d package without the extender is quite a bit cheaper than the 5d2 package with the extender.

Consider this:

2500	5d2
1249	70-200 f/4 is
500	1.4x extender
---------------
$4249

1600	7d
1249	70-200 f/4 is
---------------
$2849

1600	7d
2400	70-200 f/2.8 is II
---------------
$4000

Uhm..i disagree..to my eyes the 7D image is a bit sharper in the 100% Not sure you'd see it in RL usage, but the fact you gain a stop in aperture is worth it...

There is another comparison done here by Juza using a 300mm f/2.8 + 1.4x and 2.0x TCs versus the 1Ds Mark III

http://www.juzaphoto.c​om …icles/canon_7d_​review.htm

He came up with roughly the same conclusion, its a HAIR better, But that hair is also letting you use an aperture 1 stop wider which sometimes is a bigger difference, IE because you can use ISO800 vs 1600 and etc

KenjiS wrote in post #12893895
Uhm..i disagree..to my eyes the 7D image is a bit sharper in the 100% Not sure you'd see it in RL usage, but the fact you gain a stop in aperture is worth it...

There is another comparison done here by Juza using a 300mm f/2.8 + 1.4x and 2.0x TCs versus the 1Ds Mark III

http://www.juzaphoto.c​om …icles/canon_7d_​review.htm

He came up with roughly the same conclusion, its a HAIR better, But that hair is also letting you use an aperture 1 stop wider which sometimes is a bigger difference, IE because you can use ISO800 vs 1600 and etc

Keep in mind that because of the sensor size difference between 1.6x crop and full frame, there's a bit over a stop difference in noise performance between the two when talking about sensors of the same resolution and technology level.

So being able to use a stop lower ISO on a crop camera isn't really the advantage one would think it is.

The biggest advantage crop has over full frame is that it will be able to autofocus in light that the crop camera wouldn't, when you use a teleconverter on the full frame camera to equalize the angle of view. The exception, of course, is if you're using a 1Ds series camera as your full frame camera, in which case the autofocus can deal with apertures as narrow as f/8, while the crop camera can nominally only autofocus down to f/5.6. That latter is almost certainly an artificial limitation. As far as I'm concerned, Canon has no business placing artificial limits into any of these cameras.

^- of course the greater pixel density and putting more pixels on target with a crop camera also means you might not have to crop as much, if at all... 1.6x is giving you a -slight- advantage in terms of field of view over a 1.4x tcon after all

The MORE interesting comparison would be a 1.3x Crop vs FF, Say a 1DIII or 1DIV vs the 5DII