Help Understanding My Distance Scale

Hello,

I have a Canon EF 28-135 lens and I've been starting to read more about focusing distances and hyperfocus lately (to think, you don't just set your focus to infinity all the time for a landscape!). So I understand the focal length of course, and understand the scale that shows your focus distance in feet or meters, but what do the little red scales do at the end of the scale that show different focal lengths? Also, how exactly do you dial in a hyperfocal distance when the jumps between feet and meters are so large? i.e. it will go from 15 feet to 50 feet with no markings in between. Below is a closeup pic of the lens linked from a website.

http://www.popphoto.co​m …uide/images/len​ses/52.jpg

The red scale is for use in infrared photography. You'd focus normally, then turn the focus so that what was next to the main indicator line moved next to the IR line for the FL in use.

As for how you set it given the available scale, you guess, keeping in mind that the scale is not linear.

The red marks are for IR correction. So if your shoot IR you focus on the subject 5m away with the zoom set a 50mm, you'd then turn the focus to line up the 5m on the scale with red 50 mark.

As for the scale and hyperfocus, you just have to estimate it(some lenses have better markings than others and most hyperfocus distances will fall into distances with smaller jumps on the scale) or you can focus on something that's at the desired hyperfocus distance.

Also note that on zoom lenses those distance scales are likely only correct for a particular focal length. Certainly for the 24-105L they can be quite misleading.

That scale will do you no good with hyperfocal distances, because it's a zoom lens. Take a look at the focus scale on a prime lens instead (Canon 20mm f2.8 for example). Notice anything that's not shown on your 28-135mm?

In order to use a lens' distance scale to set hyperfocal focusing distance, the scale also has to have indication of the f-stops, as can be seen on that 20mm lens. The reason you don't see those indicated on the 28-135 is that the f-stop scale will be different depending upon the focal length being used with the zoom. The f-stop scale would be radically different whether the lens were set at 28mm or 50mm or 100mm or 135mm.

There are printed hyperfocal charts or calculators that you can buy, then determine for whatever focal length and f-stop combination you happen to be using. That's the best you can do with most zoom lenses.

Hyperfocal calculators are pretty useless...try finding these APS-C hyperfocal distances on your lens distance scale, and tell us how many can be estimated pretty closely by looking at the scale...

28mm, f/4 hyperfocal = 41'
28mm, f/8 hyperfocal = 21'
35mm, f/4 hyperfocal = 64'
35mm, f/8 hyperfocal = 32'
50mm, f/4 hyperfocal = 131'
50mm f/8 hyperfocal = 66'

As for the DOF scales on fixed focal length lenses, again pretty useless when you own APS-C, as they are calculated for FF cameras.