Some help with lens markings, please

[xpatUSA]

Although I am an old geezer, I was never a knowledgeable guy until recently and that only on matters digital.

So, this oldish Sigma lens has me beat on exactly how to use the 'R' mark:



I can see that the f-number curves provide a nominal DOF at the various zoom settings. And it's not too hard to guess that 'R' refers to the use of Infrared sensitive film back in the day.

Fast forward to my Sigma DSLRs where changing to IR photography is a simple matter of popping out the hot mirror with my thumb on the SD14.

While knowing that the camera can auto-focus with some types of IR lens filters in place, how exactly would I use the 'R' mark on this lens for manual focusing?

[rpcrowe]

You would focus normally and note where the focus line (your lavender mark) aligns with the distance scale. Then you would move the focus ring so that the R mark lines up with where the normal focus line was on the distance scale. That should (more or less) place your focus in line with where the IR is focusing...

[xpatUSA]

Thanks, Richard,

Useful to know because when the lens has a filter on it, you can't see to manually focus. So, it's a case of filter off, then focus (I prefer manually) then turn the focus ring that little bit more then put the filter back on. Quite a game, almost beyond my limited patience

Which is why I tend to shoot with the lower wavelength filters such as the 700nm because they'll often auto-focus in decent light. 950nm - no chance.

[William W]

. . . how exactly would I use the 'R' mark on this lens for manual focusing? . . .

In addition - I want to underscore and also make it crystal clear that because it is a Zoom Lens, the IR Marker will change depending upon the FL that is set.

Prime Lenses have only one IR Marker.

So for the IR re-focussing procedure on a Zoom Lens, one will need to take into account the imaginary lines which I have drawn on you image:



*

Some modern lenses still have IR markers. The IR refocusing procedure for a zoom lens, is kind-of outlined here, in Canon’s 70 to 200 User Manual:



WW

[xpatUSA]

Thank you, Bill, for taking the time and effort to confirm what I indeed thought was the case.

It's amazing how much "good stuff" has almost disappeared from lens exteriors!

OT, but I was looking some pics of an older Sigma 50mm macro lens that I sold about 5 or 6 years ago and it actually had an aperture ring on it. Fortunately, I did know what that was for ;-)

[William W]

. . . OT, but I was looking some pics of an older Sigma 50mm macro lens that I sold about 5 or 6 years ago and it actually had an aperture ring on it. Fortunately, I did know what that was for ;-)

Continuing OT:

Funny how now, with a "modern lens" (i.e. sans aperture ring) if we want to use it reverse mounted via connection rings to another lens to make macro . . . we have to use a "work around" so the "modern lens" holds it stopped down position.

Previously, we'd just use the aperture ring and maybe if the lens was really fancy and had "connections" to the Camera we'd have to lock a little leaver, too.

WW

Addendum - just checking I still know how to do it:



Don't know about other brands, but with Canon EF hold the DoF preview whilst releasing the lens from the camera.

Yes I know that 'but you're not supposed to remove a lens without powering off the camera' but that's only one of the many 'rules' that I break, daily.

[rpcrowe]

You could focus first, place filter on lens and then move the focus point. However, it was easier just to leave on the filter and use the focus scale for focusing.