Why won’t my Tamron 90mm macro on Nikon D5500 open wider than f/3.0 or f/3.5?
Asked 1/27/2018
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I’m using a Tamron 90mm f/2.8 macro lens on a Nikon D5500. In Aperture Priority or Manual mode, I sometimes can’t set the aperture as wide as f/2.8—the lowest available value changes to f/3.0 or f/3.5 depending on the situation. Why does this happen, and is there anything wrong with the lens or camera?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
8y ago
2 Answers
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The lens is reporting the effective aperture at your current focus distance. Note that as you focus closer, the reported maximum aperture reduces; the closer you focus, the higher the f-number you'll get.
This is actually a good thing, particularly if you are relying on external metering. It saves you having to calculate the true exposure based on the "bellows draw" (that is, how far the lens is being moved away from the sensor or film plane as you focus). If you are shooting things at low magnification, the difference between the exposure at infinity and the exposure at your focusing distance is negligible no matter how the lens works, but at higher magnifications - as you move into macro territory - the difference between an internal-focus (rear-focus) lens and a unit-focus (traditional-type) lens becomes important. If the lens is moved far enough away from the sensor or film to focus at 1:1, you lose two stops of effective aperture. So a "90mm f/2.8" lens focused at 1:1 is either not 90mm anymore, or not f/2.8 anymore.
If a lens intended for macro shooting keeps a constant reported maximum aperture, it could be telling you one of two things:
the focal length of the lens is being reduced as you focus closer, in which case the effective aperture for exposure purposes remains the same, but you lose working distance; or
the focal length of the lens is remaining constant, but you will be underexposing unless you figure out the bellows factor and compensate if you are not using TTL metering at the time of shooting.
Some lenses are a little bit of both, too, so you can't just look at the focus distance and make a quick calculation. If the focal length is being reduced, but not as much as in a "pure" IF lens, while the lens as a whole is effectively being moved further from the sensor, you'll have had to do some testing ahead of time to know what compensations to make with external metering, or take test shots as you go.
It's best, then, if the lens tells you what's really going on. Even if that seems somewhat counter to your expectations.
Originally by user71889. Source · Licensed CC BY-SA 4.0
user71889
8y ago
0
Generated from our catalog & community — verify before relying on it.
Nothing is wrong. With macro lenses, the maximum available aperture often changes as you focus closer. At or near infinity, the lens can open to f/2.8, but at close-focus and macro distances the camera may show a smaller effective maximum aperture such as f/3.0 or f/3.5.
This happens because close focusing increases the lens extension/effective light loss, so the reported aperture changes with focus distance. The closer you focus, the higher the effective f-number becomes.
So if you’re shooting very close subjects, especially in macro range, it’s normal that f/2.8 is no longer available. As you focus farther away, f/2.8 should return.
In short: the lens is behaving normally, and the changing minimum aperture is expected for close-up/macro work.
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AI8y ago
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