Saturday, 20 August 2016

Landscapes: mathematical considerations about focusing and exposing

Recently I've bought a new lens for my collection, a SAMYANG 14mm F2.8 ED AS IF UMC. I think it could be a excellent choice for landscapes and night photography. It has been shipped while I am making my first calculations.

One of the most famous 'tricks' in landscape photography is the use of the hyperfocal distance. In my other blog, Astaroth's World, I wrote about hyperfocal previously but, What is the hyperfocal distance? Wikipedia says:

"The hyperfocal distance is the closest distance at which a lens can be focused while keeping objects at infinity acceptably sharp. When the lens is focused at this distance, all objects at distances from half of the hyperfocal distance out to infinity will be acceptably sharp."

Focus to the hyperfocal distance is a method to have a very large depth of field, and so, it's perfect for landscapes.

Source: DOF Master
It depends of focal length (the lens), the f-number (the aperture) and the circle of confusion (a parameter of the camera related with the range that you can consider that something is in focus in a approximated way).

I've made a table with the main situations for landscapes photography with my current photographic gear (for Nikon D7000, CoC: 0.02 mm).




Everything is cooler in a graphic:


The dependence with de focal length makes that shorter focal lengths have smaller hyperfocal distances. It means that you can focus nearest with short focal lengths and you will have in focus until the infinity.

Other interesting point in landscape photography and, mainly, in night photography, is the equivalent exposition when we change the ISO or the f-number. Night photography usually means long exposure photography. A trick is to take a picture at very high ISO as preview. If you like that image, you can repeat it with an equivalent exposure and a less noisy ISO.

The calculus of the exposure time for a different ISO is very easy:


The f-number have a direct effect in the depth of field and in the hyperfocal distance, so to know how depends the exposure with f-number could be so important. The calculus about this is a little harder (you can also view it in Astaroth's World, previously posted):


Summary


The theory is in the above lines. Now, it's time to practice! I hope to bring soon you more interesting pictures of landscapes and the night with the new gear.


Appendix


I've recently received my new camera: a Nikon D810. This camera has a circle of confusion of 0.03 mm and it affects to the above results. I show the new tables for Nikon D810 below.




I hope to be useful.

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