A short discussion on what the eye sees from a photographic point of view – this depends on the aspect ratio of the camera body as well as the camera lens field of view and the focal length of the lens being used.
Most DSLR cameras come with a kit lens which often has a zoom capability, giving the flexibility of a small wide angle to a short telephoto zoom. Most manufacturers make a standard lens; this is often a 50mm standard lens which of course changes in size for whichever camera body ratio you might have on your body. Although I own a 50mm E lens for my Nikon, which is a stunning manual focus lens if you can find a good one, I tend to use my 40mm Voightlander lens which is small, light in weight and very easy to use with filters. Why? Because this lens has a more realistic focal length for what my eye sees.
Tamron do make the SP 45mm F/1.8 Di Vc Usd Lens which has a lot faster aperture than the Voightlander. Also the Tamron has Image Stabilising and an ultrasonic motor for AF. If I had the money and room in my bag for another lens this lens would be on my short list.
In fact if you do your maths correctly, the correct lens for your eye on a full frame DSLR should in fact measure 43.27mm. So the Tamron at 45mm is just over this.
There are four images below taken at various focal lengths to show you just what I mean. The subject matter of the image may not appeal to you, but hopefully you will be able to see the differences between the four different focal lengths of lens used. It’s not easy to tell, but look closely at them. I did in fact use a zoom for this particular image. I found that the screen information on the back of my camera body did not always match up with what the Photoshop raw converter told me I had used. So with one image I am under by 1mm, with two images I am over by 1mm, and one image is dead on.
My conclusion is that you should use the best lens that you have and enjoy yourself whilst you are using it. If you don’t own a prime lens you are missing out on a lot of Fun.
Mark
Image on 40mm Voigtlander lens (actual focal length 41mm)
Image taken at 44mm (closest as practical to 43.27mm)
Image at 45mm as Tamron lens (actual focal length 46mm)
Image on 50mm standard lens (actual focal length 50mm)