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Equipment: Nikon D7000 with a 18-105mm lens that comes with it. Level of photographer: novice

I've read that the aperture levels change depending on focus. Is there any way in manual mode to stop this?

I tried taking photos of some cardinals and had it originally set at f3.5 but when I looked my screen it was at f4.5 and I couldn't get it any lower.

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The aperture changes because of focal length not focus.

Your lens has a widest aperture of f/3.5 at 18mm but to due physical properties of lens design, the widest aperture becomes f/5.6 at 105mm.

Because the lens aperture was at f/4.5 it means you were at a focal length of about 35mm when you took the photo.

It is possible to buy lenses that have a constant aperture as you zoom, but they are generally Professional grade and come with a premium price tag.

enter image description here

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  • \$\begingroup\$ This answer would be even better if it included a link to where you got the table from. \$\endgroup\$
    – user
    Dec 18, 2015 at 23:48
  • \$\begingroup\$ The table is from a review by Ken Rockwell: kenrockwell.com/nikon/18-105mm.htm \$\endgroup\$
    – Mike Sowsun
    Dec 19, 2015 at 15:59
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The description of the lens is: Nikon AF-S DX NIKKOR 18-105mm f/3.5-5.6G ED VR Lens

It should also say that marked on the lens. That means its maximum aperture is f/3.5 at widest angle, but f/5.6 at the telephoto end (and in between if in between). It is very normal (for that lens). Some lenses have a fixed maximum aperture at any zoom, but that one, and several others, do not.

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  • \$\begingroup\$ So here is a follow up question: due to aperture changes in response to zoom, so photographers avoid using the zoom as much as possible or do they make adjustments by establishing zoom first as then changing ios and shutter speed around that? Or am I missing something else entirely? \$\endgroup\$
    – Danny Rodriguez
    Dec 18, 2015 at 5:08
  • \$\begingroup\$ @DannyRodriguez, if you are using a variable aperture lens and are trying to shoot with the widest available aperture, and you shoot full manual, yes, you would have to adapt your camera settings if you zoom in or out. If, on the other hand you shoot on f5.6 or higher, you would not have to change the settings anymore. This aperture variability applies ONLY to the widest value of the aperture. Just for future reference, there are lenses offering constant aperture on the whole zoom range, but those lenses are way more expensive. \$\endgroup\$
    – Dragos
    Dec 18, 2015 at 10:12

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