CX vs DX for bird photography

When it comes to bird photography for hobbyists, there are two quite new choices: The Nikkor CX 70-300mm f/4.5-5.6 (my review) for Nikon 1 cameras, and the Sigma 150-600mm f/5-6.3 Sports for DX cameras with an APS-C sensor size.

The lenses are pictured below in the transport positions, as compact as possible, with the Nikkor CX 70-300mm being the smallest, obviously:

Even if the lenses have so different focal lengths, they still have a similar equivalent reach, due to the smaller sensor size of the Nikon 1 cameras. Here is a diagram illustrating the reach and maximum aperture of the lenses:

So, is there any practical difference in the image quality between these combos? With the Sigma 150-600mm weighting 5 times as much, is it worth lugging along? To answer this, I have some comparison pictures taken at the same time with both lenses. (Click for larger images.)

Nikkor 70-300mm on Nikon V3, ISO 800, 300mm, f/5.6, 1/250s	Sigma 150-600mm on Nikon D3300, ISO 3200, 600mm, f/6.3, 1/500s
100% crop:	100% crop:
In this example, I could safely push the ISO higher with the APS-C sensor equipped Nikon D3300. With the higher resolution, I also get more details. However, with the Nikon V3, I had the 20FPS option enabled, giving me a lot of images to choose from later. That way, I got a higher number of images with the bird posing as I preferred.

Nikkor 70-300mm on Nikon V3, ISO 800, 300mm, f/5.6, 1/500s	Sigma 150-600mm on Nikon D3300, ISO 3200, 600mm, f/6.3, 1/1000s
100% crop:	100% crop:
I had both cameras in the same settings: Auto ISO up to 3200, aperture priority mode, and +1/3 stop exposure. I also used the centre spot focus mode. Still, the Nikon V3 kept the ISO lower, quite sensibly, since anything above 1600 is quite difficult to use. The V3, in the automatic mode, prioritizes to keep the ISO low, over increasing the shutter speed. You can of course override this, if you want. With the better high ISO capabilities of the APS-C camera, you can more easily use faster shutter speeds, anyway. The V3 also appears to underexpose a bit more than the D3300. Again, the Nikon D3300 gives vastly better resolution. Even if the Sigma lens has a smaller f/6.3 aperture in the longest extension, the depth of focus (DoF) is still thinner due to the larger sensor size of the DX setup. In this application, I would say this is not necessarily a good thing: With such an extreme tele lens, it is more common that you need a deeper DoF to cover the entire bird, especially at close focus ranges.

Nikkor 70-300mm on Nikon V3, ISO 200, 300mm, f/5.6, 1/500s	Sigma 150-600mm on Nikon D3300, ISO 500, 600mm, f/6.3, 1/1000s
100% crop:	100% crop:
Again, both cameras were set up the same way: Auto ISO up to 3200, aperture priority mode, and +1/3 stop exposure. I used the centre spot focus mode. The Nikon V3 prioritizes to keep the ISO lower, and sets the shutter speed as low as 1/500s, unless there is a lot of light. With the image stabilization, a shutter speed of 1/500s at an 800mm equivalent focal length is usually quite ok. Here is an example where the thinner the depth of focus (DoF) of the DX setup is an advantage: The twig in front of the bird is more blurred away. With the more generous lightning here, we also get more details with the Nikon 1 rig. However, the Nikon D3300 with the Sigma 150-600mm still gives you significantly more details.

The lenses

The specifications reveal that the Sigma lens is five times heavier, not nearly as easy to bring along when hiking:

Lens	Nikon 1 70-300mm	Sigma 150-600mm Sports
Mount	Nikon 1 CX	Nikon FX/DX, Canon EF
Max aperture	f/4.5-5.6	f/5-6.3
Equiv focal range	190-820mm	225-900mm (1.5x crop)
Crop factor	2.7x	1x-1.5x
Lens elements/groups	16/10	24/16
Minimum focus distance	1m	2.6m
Optical image stabilization	Yes	Yes
Weight	560g	2860g
Diameter	73mm	121mm
Length	108mm	290mm
Filter thread	62mm	105mm
Hood included	Yes	Yes
Tripod collar	Optional, Nikon TR-N100	Yes, built in

The cameras

I used the Nikon D3300, which is the least expensive Nikon DX DSLR camera. Is there anything to be gained by using a more expensive camera?

In terms of the sensor, the D3300 has the state of the art 24MP APS-C sensor. It is as good as it gets now.

More expensive cameras, like the Nikon D5500, will give you more autofocus options, and better tracking of moving subjects. If you photograph stationary birds, this is not important at all. For birds in flight, the D3300 may not have what it takes, and you need a higher end camera.

More expensive cameras will give you better ergonomics, though. And better access to functions, without going through the menus. For example, quicker adjustment of ISO, drive mode, and autofocus options.

The Nikon 1 V3 is the high end Nikon 1 mirrorless camera at this time. Choosing this camera over the entry level Nikon 1 J4, is mostly about ergonomics: You get the option of using the extra grip, the electronic eye level viewfinder, and you get somewhat more buttons.

Nikon were quite late to the mirrorless party, with their Nikon 1 series. They took the rather bold step to use a fairly small sensor, the so called "1 inch sensor". Don't be fooled by the name. Just as the Four Thirds sensor is less than 4/3'' diagonally, the 1 inch sensor is less than 1'' diagonally.

This odd naming convention comes from the time when radio tubes were used for sensors: A 1'' sensor would be an radio tube with a 1'' diameter, while the actual imaging area would of course be much smaller than 1 inch.

Some speculate that Nikon chose to use a smaller sensor to protect their popular DSLR line. I think it was more due to a genuine desire to make the camera system small, which also differentiates it more from the DSLR cameras.

From the start, the Nikon 1 system left the market puzzled: Who is it for? Who would buy toy coloured camera kits with a poor ergonomy and a high price? To add to the confusion, Nikon did release high end lenses, like the Nikkor 32mm f/1.2 portrait lens. But with no enthusiast friendly camera layout, who would use them?

As it turns out, the Nikon 1 system has three strengths, in my opinion:

1. Very good implementation of PDAF from the start. When I tested the first generation entry model Nikon 1 J1, I found that it had vastly better autofocus performance than the later and premium priced Lumix GM1.
   
   The PDAF technology implemented means that you get very good autofocus performance during video recording, and, probably more essentially, for moving subjects in AF-C mode. The Nikon 1 cameras can rival high end DSLRs in this area. This autofocus performance is the most important when using long lenses.
   
   
2. Very fast framerates. The Nikon 1 cameras can take 60 frames per second in full resolution mode, and while saving the full RAW image. Of course, this only works in electronic shutter mode, but unlike the Panasonic Micro Four Thirds cameras, the E-shutter has a fast enough readout to avoid the rolling shutter issues.
   
   This makes the Nikon 1 cameras well suited for sports, for example, where you may want to take a 20 frame burst during a crucial moment, and then later pick the one you want to publish.
   
   
3. The Nikkor CX 70-300mm f/4.5-5.6 (my review) long tele zoom lens. With an impressive 810mm equivalent focal length, this is the smallest birder-friendly lens available currently.
   
   Combined with the very good PDAF AF-C performance, and the high frame rates possible, this lens makes the Nikon 1 system to a dream come true for anyone interested in photographing birds and wildlife, while wanting to keep the bulk of their gear down. The lens is also useful for spectator sports.

If you are not into any of these three areas, then I think you should not look further into the Nikon 1 system. There are other systems that are better suited, unless you are interested in the topics above.

Conclusion

Using the Nikon CX 70-300mm f/4.5-5.6 on Nikon 1 cameras is very convenient, giving an enourmous reach in a small and compact package. However, sometimes, you could wish for better high ISO performance, and more reach.

Using the Sigma 150-600mm f/5-6.3 Sports lens, on even an entry level DX camera body, gives you slightly more reach than the CX 70-300mm lens, and, more importantly, better image quality across the whole ISO range. And higher resolution to boot.

However, using the Sigma 150-600mm comes at a price: Twice the price, in fact, but more importantly, five times the weight. Mostly, you will prefer to bring the CX 70-300mm f/4.5-5.6, with the much smaller dimensions.

The Nikon 1 setup is small enough that you can put it in pretty much any camera bag. The Sigma lens, on the other hand, is so large that you need a special backpack for it. Using it requires more planning.

The CX lens is also much easier to use for birds in flight (BIF), with the smaller size and lighter weight, and with the sophisticated AF performance of the Nikon 1 cameras.