Stanfan

As a walk around lens I use a Nikon 18-70mm Which was part of my D70 kit. On my other lenses 50mm & 85mm,
I can choose the aperture I want but on the 18-70 it's controlled by the zoom. How can I choose the aperture
and still have the use of the zoom on my D-7100?

Winslowe

Ditch the el cheapo and get a constant aperture zoom.

Stanfan

Well, I didn't realize they were available. Thank's for the quick response

oldtigger Loc: Roanoke Virginia-USA

Why don't you just change the aperture setting on your camera?
It worked fine on my D7100 with the 16-28, 18-55, 24-70, 55-200, 28-300, 70-300, 85-200, and 70-200.
Probably works on yours also.

Linary Loc: UK

I guess you are referring to the fact that when open to 18mm, the widest aperture is f3.5 and when zoomed out the widest aperture is f4.5.
A constant aperture lens will at the widest angle open to (say) f3.5 and when zoomed out will still be at f3.5. The problem with constant aperture lenses is cost. They are a lot more expensive than variable aperture lens (such as the one you have).

Reinaldokool Loc: San Rafael, CA

You can. However because of the change of focal length, the largest f-stop is controlled by the lens. However, you can set a smaller aperture (larger number)

Alternatively, you can spend a wheelbarrow full of money for a constant aperture lens. (Also much heavier.)

John Gerlach Loc: Island Park, Idaho

Every variable aperture lens I have used didn't vary if I was stopped down at least one stop because the lens varied the size of the aperture to maintain the f/number. Of course, if you are set wide open, then zooming out requires a larger hole with the longer lens and that isn't possible since the aperture is only so big which forces the lens to switch to a smaller aperture in this case.

amfoto1 Loc: San Jose, Calif. USA

Hi and welcome to UHH...

What you probably mean is that the 18-70mm zoom is a variable aperture design... an f3.5-4.5, to be exact. That's a difference of only 2/3 stop, not really all that big a deal. Variable aperture designs are cheaper, smaller and lighter and less complex than non-variable aperture zooms.

But, if you set f4.5 or smaller aperture (f5.6, f8, f11, etc.) on your camera, the aperture shouldn't change when you zoom. I think you'll find it is only when you set it wide open or nearly so, at f3.5 or f4 in this case, that you're limited in any way when you change the focal length. This is only between 1/3 to 2/3 stop difference so typically only becomes a concern if you're using fully manual exposure techniques (where you set the aperture, shutter speed and ISO) or when using fully manual lighting equipment such as studio strobes. In those circumstances the changing aperture might be a minor inconvenience that requires you to make some slight adjustments to other settings on the camera or to the lighting.

Otherwise, when using any sort of auto exposure mode with the camera or through-the-lens metered and controlled flash, the slight change in aperture when you zoom the lens is automatically corrected and becomes pretty much a non-issue.

If it were a much larger aperture that rendered shallow depth of field effects and where the change in aperture was greater, it also might be more of a concern... But that's not a very big deal in this case, either.

There are "constant aperture" zooms available, if you prefer. Just be prepared for a considerably higher price, as well as larger size and more weight to carry around.

The Nikkor AF-S 18-70mm f3.5-4.5 DX lens (3" long and 14 oz.) is no longer in production, but can be found selling for around $100 or less.

The AF-S 18-55mm f3.5-5.6 DX VR has replaced it as a kit lens, costing about $250 when bought separately. It's smaller, lighter and has stabilization added... but also has less range of focal lengths and a much greater variation in aperture (up to 1-1/3 stop) when set wide open and zoomed.

D7200 are usually offered in kit with a different, slightly more upgraded AF-S 18-140mm f3.5-5.6 DX VR lens, also variable aperture. It's a little larger & heavier, but has a wider range of focal lengths plus image stabilization and sells for about $500 when purchased separately.

A Nikkor AF-S 17-55mm f2.8 DX lens maintains constant aperture at all settings, with a reasonable large aperture for lower light shooting or stronger background blur effects, but is both longer and larger diameter and weighs over a half pound more... and costs $1500.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

On the 18-70, which is a very good lens by any standard, both optically and build quality, you can choose the aperture and have it remain constant as long as you do not choose an aperture that is larger than F4.5 - which is the max aperture at 70mm. Setting it to F4.5, F5.6 or smaller will not result in it changing as you zoom.

It is only 2/3 of a stop to go from F3.5 to F4.5, not one full stop as Amfoto incorrectly stated.

Sigma has a 17-50 F2.8 that you can buy at B and H for $370.
Nikon has a 17-55 F2.8 that you can get new for $1500, or used for around half that.
Tokina has 16-50 F2.8 that you can get used for around $250.
Tamron has a 17-50 F2.8 for around $300.

for the most part, any zoom that starts out at or near 18mm and goes to 70 or more will likely be a variable aperture zoom.

Here are a couple of nice reviews on your lens btw.

http://www.bythom.com/1870lens.htm
http://www.photozone.de/Reviews/235-nikkor-af-s-18-70mm-f35-45-g-if-ed-dx-review--test-report?start=2

RWR Loc: La Mesa, CA

Whatever aperture is set at 18mm will be 2/3 stop slower at 70mm.
https://www.dpreview.com/products/nikon/lenses/nikon_18-70_3p5-4p5g_ifdx

Apaflo Loc: Anchorage, Alaska

That is not the case at all. If zoomed to 18mm an fstop of f/4.5 can be set and it will remain at f/4.5 if zoomed to 70mm. If set to f/3.5 at 18mm it will change to f/4.5 as the lens is zoomed to 70mm.

But less known is that the minimum fstop at 18mm is f/22 but at 70mm it is f/29. When zoomed to 70mm if the fstop is set at f/29 and the lens is then zoomed to 18mm the fstop will change to f/22.

Again, when set to between f/4.5 and f/22 the zoom will not change the fstop.

RWR Loc: La Mesa, CA

Yep! Apparently the newer zooms are different than the first (and only) variable aperture lens I tried. My apologies to all.
Edit: Thanks for the correction.

Stanfan

Thank's to all for the wealth of information!

sueyeisert Loc: New Jersey

I had the Sigma 17-50 f2.8 and loved it with my Nikon,I've since moved on toFuji mirrorless. Get constant aperture lenses.

billnikon Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont

Think of your lens as two lenses in one, at 18mm you have a 3.5 lens, at 70 you have a 4.5 lens. Your camera will automatically make the aperture change as you zoom, you can always stop down to a smaller aperture if you want.