I started a post in dpreview.com in Jan 2015. It was controversal, but then Thom Hogan of dslrbodies.com concur with the conclusion in his website few days latter. Updated post where there was more agreement, and members contribute with more data to support this idea.
Common belief is that a full frame DSLR camera is too expensive and too heavy,
and is only for the price no object photographer. Most people lean towards APSC
crop sensor camera to save money. Is true that APSC cameras are cheaper with
the kit lens. However, once you get into the nicer lens, APSC camera's price
advantage diminish, and in some cases are even more expensive. Here is a quick
You can quickly see that to get the equivalent light gathering ability from the full frame camera, you can use a more economical higher f-stop lens. The larger sensor compensate for the smaller aperture high f-stop lens. While the initial camera purchase may cost more, you make up for that with each lens you get.
Use the Nikon D7200 APS-C with top quality 17-55mm f2.8 lens for the baseline
The 17-55mm f2.8 lens weights 755g, and is 111mm long. It is the equivalent of 27.2-88mm for full frame camera. The 17-55mm is a nice lens, but is heavy because is f2.8. Why would you want to go to a full frame camera? The answer is that with the new Nikon D610 and D750 full frame cameras, the size of the camera is exactly the same as a D7200. The D750 is only slightly heavier at 760g vs 675g for D7200 camera. Both the D7200 and D750 are almost identical as far as focus ability and features. The D610 is a full frame, but with somewhat lower autofocus ability, and lower price. Both make for an attractive full frame alternative.
These are the proposed equivalent lens for the full frame camera to replace the heavy 17-55mm f2.8 APSC lens:
Choice A: 24-120mm f4 lens is 710g and 104mm long.
Choice B: 24-85mm f3.5-4.5 is 485g and 82mm long.
The above two full frame lens are lighter because they have higher f-stop, but because you are using a full frame sensor, they are equivalent in light gathering ability.
Base on the theory of equivalent in graph below, a theoretical f4.3 full frame lens gathers as much light as f2.8 APS-C camera lens. However, because you are using f4.3, you will have to use higher ISO to get the same exposure. To compensate for f4.3, you will need exactly ISO 235 to equal to ISO 100 on a f2.8 APS-C lens. Looking at data from DxO lab, real life tests proves that both cameras have about the same amount of noise.
Now realize that using higher ISO on a full frame camera may affect dynamic range performance. From DxO data, ISO 200 on the D750 full frame camera has about the same dynamic range as ISO 100 on D7100. Maybe only a hair less looking at their graph. This tells you there is pretty much no penalty for going with a f4 lens, and using ISO 200 on a full frame camera.
Show me the Money - No Pun Intended:
You can see, there is not much cost diference between APSC and full frame!
Show me the Weight:
Nikon DSLR Study Conclusion:
If you are considering either the D5500 or D7200 APSC camera, be sure to look at the full frame D610 and D750 cameras. The initial purchase price for the camera body may be more, but when you add in equivalent lens, the cost is just about even. The weight is not much different either. Some case lighter, some case heavier.
What about Other Cameras Besides Nikon?
Somewhat similar argument can be made with Sony full frame:
Sony A7 full frame with kit 28-70mm f3.5-5.6 weights 416g+295g=711g total, and cost $1598.
Sony A77II APS-C with kit 16-50mm f2.8 weights 726g+577g=1303g total, and cost $1598.
Full frame and APS-C cost exactly the same with these two cameras. You loose about equivalent of half a stop with the full frame lens at f5.6 end, but gain slight amount of light at the f3.5 end. However, remember that the A77II has a translucent mirror in front of the sensor that takes away about 1/2 stop of light. Therefore, these two cameras are exactly equivalent. Now look at the weight, 711g for the full frame versus 1303g for the smaller sensor, but heavier APS-C camera. Full frame is almost half the weight of APS-C for the same price!
The same argument can be made with these two cameras:
APS-C Fujifilm X-T1 440g $1300 with a 16-55mm f2.8 at 655g $1200 -> Total cost: $2500, weight: 1095g
Sony A7 416g $1298 with 24-70mm f4 430g $1198 -> Total cost: $2496, weight: 846g
Again, the full frame cost exactly the same down to the dollar, but weights less than the APS-C.
My conclusion is don't buy an APS-C camera, go directly to a full frame with the recent drop in full frame price. Once you get into prime lens, full frame will blow APS-C away in image quality.