Three 14-bit RAW image merge
Paintshop Pro X4 Tonemapped
Camera Nikon D700
Lens Sigma 24-70mm f/2.8
Exposure 1/60th, 1/125th, and 1/250th of a second
Focal Length 24mm
ISO Speed 200
I do like my Nikkor glass, however as an engineer my choice to purchase a Nikkor or after market lens for my Nikon bodies is not based upon if I can afford the lens, I have the means to purchase any lens I desire. Rather, my choice is based upon an understanding of optical physics, the manufacturer’s design, function, and physical construction of the device.
A lens is basically pieces of special glass, (elements). The cost of the optical glass blanks used to make the very best lenses in the world, such as Leitz or Zeiss, is very high. The cost of the glass that goes into a lens other than these type lenses (even Nikkor) is priced lower, and aren’t as Great as Leitz or Zeiss glass. I do understand that lenses that are similar in most other qualities are not built out of equal components. There is also the concept of a difference in precision grinding for lenses, however, that difference has narrowed between high cost lenses and medium priced lenses in the last few years, because of computer based grinding technologies.
Nikkor lenses, as with the less expensive manufactured Sigma and Tamron lenses I own vary according in quality with different names and letters, designating one class over another. Nikkor, Sigma, and Tamron are not the best lenses out there. With noticeable exceptions, they aren’t priced as high as the finest lenses either. $5,500 for a Leitz lens is not uncommon – that being said, in comparison a $2,000 Nikkor lens could be considered a ‘budget’ lens.
After market companies such as Tamron or Sigma make some Great lenses, but few are at the highest quality level. My experience with after market Sigma and Tamron lenses is that the image quality of pictures taken with the glass is quite Great, better than passable. However, I have purchased Nikkor glass, because you get what you pay for. I have also found to obtain that final 15% of lens performance in my Sigma and Tamron glass, I would have to pay more than double the cost for a Nikkor.
Finally, two lenses that are par performers in most ways could be very unequal in build quality and resistance to the environment. Sometimes the difference between prosumer lenses and professional lens, or camera bodies, may come down to only that. Build quality for after market lenses like my Sigmas and Tamrons is why they are less expensive, rather than their features and specifications. In fact, build quality aside, image quality for the Sigmas and Tamrons are fine (and in my experience – par to ‘superior’ glass like Nikkor).
I recommend doing some research. Identify what is being measured in comparison of the glass you are considering purchasing, such as types of distortion, vignetting, sharpness across the field, meaning on the edges of the image compared to the middle, etc. Some of these specification differences are far from critical, others can make a huge difference. Of course a large factor is what you are taking pictures of and, in what conditions.