Why does my Tokina 100mm f/2.8 Macro show a smaller maximum aperture at close focus?
Asked 4/22/2016
2 views
2 answers
0
On my Nikon D610 with a Tokina AT-X Pro 100mm f/2.8 Macro, the lens is marked f/2.8, but when I focus closer than roughly 9 feet the reported maximum aperture starts getting smaller. At extreme close-up / 1:1 macro, it appears limited to about f/5.6, even in Manual mode. Why does this happen, and is the camera choosing an aperture automatically or is this normal macro-lens behavior?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
10y ago
2 Answers
2
As the others have alluded to here, the aperture number (aka. f-stop) indicated on the physical aperture ring only indicates the effective aperture when focused in the non-macro range - i.e. at distances greater than perhaps 1 meter or so. The reason why the camera reports a narrower aperture than the lens setting is because of the effective lengthening of the lens when focusing in the macro range, making the effective aperture smaller than you might otherwise expect.
In other words, your 100mm lens effectively becomes a 100~150mm lens when focused up close, and the area of the aperture is therefore smaller in proportion to the length of the fully extended lens.
You can visualise this effect simply by looking down a cardboard tube. Cut the tube in half and look down it again; the diameter of the tube hasn't changed but hole at the other end appears effectively much larger simply because the tube is shorter.
Originally by user38928. Source · Licensed CC BY-SA 4.0
user38928
10y ago
0
Generated from our catalog & community — verify before relying on it.
This is normal for macro lenses. The camera is not overriding your manual setting or choosing an “ideal” aperture for you.
At close focus, a macro lens extends internally/optically to achieve higher magnification. As the lens’ effective focal length/extension increases, the effective aperture becomes smaller, so the reported maximum aperture changes. That’s why a lens labeled f/2.8 at normal distances may only be effectively about f/5.6 at 1:1 macro.
So the f-number you see at close distances reflects light transmission geometry at that magnification, not the camera taking control away from you. In other words, the physical aperture setting corresponds to a smaller effective aperture when focused very close.
This behavior is common with macro lenses, and your Tokina 100mm doing this is expected.
Recommended products
UniqueBot
AI10y ago
Your Answer
Related Questions
Why does my macro lens show a smaller maximum aperture at close focus?
How useful is image stabilization on a 100mm macro lens?
Do internal-focusing macro lenses keep their maximum aperture at close focus?
Why does Live View exposure simulation look too dark at 1:1 with the Canon 100mm f/2.8L Macro?
Why does my Canon 100mm macro look closer than my 18-200mm zoom at the same focal length?