Sunday, April 1, 2012

Fast lenses are meant to be shot wide open? ... or?




"The Nikon 85mm ƒ/1.8G AF-S provides excellently sharp images, though to achieve maximal sharpness you must stop down to at least ƒ/5.6."


This comment published in a well known web magazine set me thinking. Stop down a 1.8 lens to 5.6 for more sharpness?  In my book fast glass should be used wide open, otherwise why pay the premium for a fast 1.8 prime lens?

At around F 4.0 /5.6 Nikon has a number of extremely competent lenses at different price points:  18-105 VR,  18-55 VR, 18-200 VR II, 16-85 VR, 20-120 VR, 28-300 VR  to name a few. So if a photographer is happy to shoot at around 5.6 then why would he need a 1.8 lens?

Though it is axiomatically true that lenses improve stopped down, it is also true that fast primes are optimized to be used wide open – think of the legendary Nikon 300 f2.8, the 600 f4, 85 f1.4, the 24 f1.4 etc all of which produce superb results and bokeh wide open.

Fast glass and VR
" I have VR so should I need a fast lens?"  is a question which is put to me often.

VR will not work if the subject is moving and  if you want to freeze motion, you need to crank up the shutter speed and so a faster lens is needed. If you want to use lower ISOs in the same light conditions then you would need a faster lens.

If you look at a 5.6 lens with VR and a 1.8 lens without VR the difference is  around  3 stops. This difference means that you can shoot at ISO 200 with the 1.8 lens and ISO 1600 with the 5.6 VR lens keeping the shutter speed the same. It also means that keeping the ISO the same in both situations the speed would be 1/1000 of a sec with the 1.8 lens and 1/125 of the sec with the 5.6 lens. So can you see the possibilities?

My opinion has always been that if you buy a fast lens use its capabilities to the maximum. Do not hesitate to go wide open because that is what the lens is capable of doing. Many wildlife photographers I know shoot a 2.8 lens always at 2.8 and adjust with the shutter speed and ISO. A high shutter speed for wildlife ensures that camera shake is reduced and also freezes whatever motion there may be with the subject. The massive Nikon 600 F4 is routinely set at aperture priority F4 and the ISO and shutter speed decided on the available light.

Bokeh              
An issue which is not often discussed is the bokeh or the out of focus background with a fast lens. The creamy bokeh of a Nikon 85 1.4 is to be seen to be believed and well worth the investment in the lens if you need photos of this type.

Downside of fast glass?
The lenses are usually heavy and very often to get the best results you  need to monopod or tripod mount the lens especially the big telephotos and zooms. Further, fast glass does not come cheap and sometimes the huge difference in price does not justify the cost of a fast lens.  For example,  consider the Nikon 70-200 f2.8 VR and the 70-300 f4.5/5.6 VR. Both lenses at their middle apertures e.g. 6.3, 8 etc would produce similar photos but the fast zoom would come into it’s own in low light situations when 2.8 becomes mandatory and you would get a photo with this lens only. Wildlife and sports are examples of this type of photography.

Fast glass or a new body?
This is a question which often crops up – should I buy a new fast 2.8 zoom or keep my old lenses and buy that new Nikon 36 mp body?  I am firmly of the view that if your existing body does not allow you to do certain things which the new body will allow you to do and which you need desperately,  e.g. shoot acceptable photos without flash at ISO 12, 800 for example, then you may seriously think of upgrading to a new body. However, if it is just the lure of mega pixels then I say refrain!

Bodies come and Bodies go but fast glass lives on forever! 

2 comments:

  1. I think that the "utility" of the lens is more important than the quality.

    Would you rather have the right focal length or more sharpness? Fast enough aperture or better contrast? I think getting the shot you want in the first place trumps choosing lenses and settings for sharpness any time.

    But I have to admit that if selective focus/low-light shooting or a large depth of field aren't priorities for the shot at hand I tend to "f/8 and forget" about the aperture...

    ReplyDelete

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