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My current camera body is a Nikon D300 and my longest lens is the Nikon 70-200 f2.8 vrII. I'm planning a trip to Africa and I am considering buying a 2.0x teleconverter to get bit more reach. But for not that much more money I could get a D7100 that has twice the pixel count and crop the images when needed.

Advantages of getting a tele-converter:

  • Cheaper

Advantages of getting a D7100:

  • All advantages of having a more modern sensor.

  • Not having to attach the teleconverter when needed.

  • Not losing an f-stop or 2.

  • Possibly less camera shake because the physical length of the lens is shorter than with a teleconverter attached to it.

  • Less stuff to carry.

Is my reasoning correct? Or am I missing some advantages of a teleconverter?

An alternative option altogether is of course buying a longer lens, but I'm afraid I won't use it enough to make it worth it.

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1  
Do both! You'll have even more "reach." –  Paul Cezanne Aug 16 '13 at 14:42

3 Answers 3

up vote 3 down vote accepted

To be able to crop the equivalent of a 2X teleconverter you would need a camera with 4X the pixels: twice as many both vertically and horizontally. With twice the pixels using the D7100, you can crop to the equivalent of a 1.4X teleconverter + D300 and wind up with the same number of pixels.

Another answer already covers the theoretical side very well, so we'll talk about the practical side here.

Most of the time when you see similar questions it is posed with assumption the camera body will remain the same and the comparison is either cropping vs. a teleconverter or longer lens vs. teleconverter. In most comparisons I have read that did fairly objective testing, the high quality teleconverter won out over the same lens + same body + cropping. But usually not by a lot. Although it reviews Canon extenders rather than Nikon, here is one such comparison.

By throwing a different body into the mix, it alters the parameters. The D7100 has roughly twice the pixels of the D300. The pixel pitch for each camera is 3.9µm vs. 5.4µm (Hmm... there's that 1.4 ratio again). I would expect that will make enough of a difference to push the quality (in terms of acutance) of a D7100 cropped to 3018x2010 (6MP) to that of the D300 with a 2X convertor unless the final viewing size is large enough to reveal the lower resolution. You would additionally gain the advantage of not having to deal with the drawbacks of a teleconverter: Loss of two f-stops of light at the time you are shooting, decreased contrast, loss of edge sharpness, additional vignetting, etc.

In terms of comparing the D7100 to the D300:

  • You gain two stops of ISO on the high end and one on the low end. The native sensitivity of the D300 is ISO 200. ISO 100 on the D300 is ISO 200 divided by 2 (with no increase in S/N ratio, dynamic range, etc). ISO 200 on both cameras is really ISO 145 as measured by DxO Mark. ISO 100 on the D7100 is measured as ISO 69. Both cameras' actual ISO is measured about one half stop less than rated across their entire ISO range.
  • S/N ratio is slightly better set at ISO 12800 (21.9db) with the D7100 vs. ISO 6400 (21.1dB) with the D300, so you gain a little more than a usable stop in terms of noise on the high ISO end, and just under a full stop on the low end (D7100 @ ISO 100 = 41.1dB; D300 @ ISO 200 = 36.8dB).
  • The D7100 has about 1.5 stops better dynamic range at ISO 200 and moves to a two stop advantage at the high ISO extremes. Again, you gain another stop with ISO 100 on the D7100.
  • Tonal range and color sensitivity show similar gains as S/N ratio does with the D7100 vs. the D300.

Here's a link to a comparison of the sensor performance of the D7100 vs. the D300 at DxO Mark. Click on the Measurements tab, then each of the parameters to view a graphic comparison.

Of course the big comparison is this:

  • D7100 = $1,200USD
  • TC-20E III AF-S 2x = $480USD

The question to be answered thus becomes, "Are the advantages of the D7100 vs. the D300 that you will enjoy with all of your lenses in all of your photography after returning from your trip to Africa worth the extra $720USD?" Assuming you can sell the D300 used for around $500USD, the difference is only about $220USD. In those terms I would opt for the D7100.

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@AJHenderson A 2X teleconverter costs 2 stops. But it is already in the answer: "You would additionally gain the advantage of not having to deal with the drawbacks of a teleconverter: Loss of two f-stops of light at the time you are shooting, decreased contrast, loss of edge sharpness, additional vignetting, etc." –  Michael Clark Aug 16 '13 at 17:15
    
yes, I was referring to the 1.4x that would be equivalent to double the MP count. Sorry if that wasn't clear. I was flat out ignoring the original 2x since it wasn't comparable to the resolution gain. I guess I didn't read closely enough though. (I skimmed since your answer seemed very good already. :) ) –  AJ Henderson Aug 16 '13 at 18:04
    
Accepted this response as the answer because it's closest to the lines of thought I was having. –  Rene Aug 19 '13 at 7:03

Firstly a sensor with twice the pixel count would be equivalent to a 1.4x teleconverter, in terms of the number pixels on your subject so a 2x would give you more detail. But lets keep things equal and consider the case of a 1.4x TC.

Fundamentally the advantages of cropping are flexibility and less gear to carry/swap. You can correct the composition, or decide you prefer a wider shot, neither of which are possible with a TC. Teleconverters also slow down AF performance, by quite a lot in the case of a 2x.

Fundamentally the same process is going on in both cases - the TC spreads out the image, the cropped high resolution sensor finely samples a small region of the sensor. Thus a good quality TC and well matched lens should be able to match the quality you get (or thereabouts, the lens elements in the TC will impart some aberrations).

This equivalence also applies to light gathering. It's true you lose a stop of light with a TC, however the higher resolution sensor will have smaller pixels which gather less light, in fact the amount of light from your subject falling on the sensor is the same in both cases. The only advantages when it comes to noise will be from improvements in sensor technology.

The same situation occurs with camera shake, the TC based solution has a longer focal length, but a higher resolution sensor is more sensitive to motion blur, so both systems will behave similarly.

An alternative option altogether is of course buying a longer lens, but I'm afraid I won't use it enough to make it worth it.

In that case have you considered renting a lens? It generally doesn't cost that much for just a couple of weeks (compared to the total cost of the trip) and you can get all the reach you'll ever want (only risk is you wont want to give it back).

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A little different perspective from the other two answers: the 70-200 VR II results are less than stellar with the TC-20E III used wide open. Even stopped down to f8 it's only "good," in my opinion. In contrast, the TC-14E II (1.4x teleconverter) is excellent with the 70-200 -- wide open it's a minor hit in quality, and stopped down to f5.6 it's still very, very good. I never hesitate to use the TC-14E but always debate whether I need to use the TC-20E -- will the faster speed, better quality, and cropping with the 1.4x be enough to negate the increased reach of the 2.0x?

If you consider that the D7100 is "not that much more money" than the TC-20E (perhaps you're considering selling the D300 or something), then let me point to an option that's "not that much more money": buy a D7100 and a TC14E. The increased pixel count of the D7100 is basically an added reach of 1.4x, and the TC14E is an added 1.4x, effectively giving you a 2.0x teleconverter when used in combination.

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Since in photography 1.4 is really √2, in terms of photography 1.4 X 1.4 = 2 –  Michael Clark Aug 16 '13 at 13:58
    
Teleconverters really just truncate the actual conversion value, which is, as Michael stated, √2. Since the actual square root is 1.4142135623730950488016887242097, tacking two 1.4x TCs onto a lens, or using a cropped sensor and a TC, really is exactly like using a 2x TC on FF (rather than 1.96x). –  jrista Aug 16 '13 at 18:57
    
Thanks for the insight, guys; edited! –  Dan Wolfgang Aug 16 '13 at 23:31

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