Samyang 24mm f/1.4 is really a f/1.8 lens

Started Mar 23, 2012 | Discussions thread
Henning W
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Re: Samyang 24mm f/1.4 is really a f/1.8 lens
In reply to JEMD, Mar 24, 2012

This issue is not new with digital, just exacerbated. If you measure the aperture/shutter combinations on any through the lens metering camera from the old Spotmatic on you will see a similar progressions of shutter speeds/apertures. An f/1.4 lens set to f/1.4 didn't result in a shutter speed half as long as the same lens set to f/2. However, the metering usually compensated somewhat for the vignetting that all lenses have wide open, and is usually worse for fast lenses due to the need to keep the size of the lens within reason. So you would find that the centre of the picture would be slightly overexposed but the corners would receive closer to the correct exposure.

With digital sensors and their 'wells' the problem is often a bit worse because more of the light rays from a very wide aperture lens come at oblique angles even at the centre of the image. Recent sensor designs have gotten around this better by placing microlenses over each photo site.

The 24/1.4 lens is truly an f/1.4 lens. That is determined by the focal length and entrance pupil, and does not take into considerations sensor efficiencies. If you had an f/1.8 lens, and used it at f/1.8, you would still see it needing more exposure time than the same lens at f/5.6 and whatever would lead you to believe.

There is no deception involved, and you do get the benefits of the fast lens. Whether those benefits are enough to justify the price of the lens is up to you.

Just for reference, I have quite a number of fast lenses between f/1.4 and f/1, and have been using such lenses for a long time. I now use them on digital cameras and appreciate the images that they enable. And it's not just about shooting at higher shutter speeds.

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