Lens Format Equivalents pt III – Ilustrated
I’ve put together a few images to illustrate a scenario of format equivalents. This example uses an extreme example of someone starting on 4×5 who wants to move to 6×17. The options we discussed were 1) using the ratio of the short edges 2) using the ratio of the long edges 3) using the ratio of the diagonals..
First of all here is the 4×5 sample shot.. we’ll presume this was taken with a 150mm lens
The ratio of the long edges would give 120mm (for the 4×5) to 170mm (for 6×17) which is 1.4:1 – so if we were to use a 210mm lens we would get the following
If we use the ration of the short edges we us 95mm (for the 4×5) and 60mm (for the 6×17 we get 0.63:1 – so we use a 94mm lens and get …
finally we try the ratio of the diagonals 1.17:1 which gives 175mm which gives
Now I would think it fairly obvious that the typical choice would be to scale by the short sides… But this is just one instance and hence it’s wise to know why a choice is made..
Let’s take a look at 35mm to Large Format conversion.. firstly here is the 35mm picture taken with a 35mm lens…
The long side ration is 36mm to 120mm which gives approx 1:3.3 which is a 116mm lens.. (nice length on 4×5) which would result in this picture
If we use the short sides, we get a ratio of 95mm to 24mm which gives approx 3.96:1 which gives a 138mm lens..
Using the diagonal gives a ratio of 3.5 to 1 which gives 122mm lens.
Which of these makes sense…. Well
1) if you are used to cropping your pictures already, the short edge comparison recreates this. 1:3.96 (~4:1)
2) if you like to get a lot of forground and background in portrait mode, then you’ll want to get the comparison of the long side. 1:3.33
3) if like the amount your current lenses encompass width ways (on a landscape orientation shot), you should use the long side conversion. 1:3.33
