Sigma 17-70 f2.8-4.5 (FL and f-stops)

fLyIr · 03-06-2011, 09:54 AM

Hi to everyone, but question is for sigma 17-70 owners

I'm going to buy this lens but would like to know the steps of f-stops through all focal lenght.
Especially which FL is ending with 2.8 and 4 and what aperture does 50mm have.

Thanks for your answers.
Best regards.

Adam · 03-06-2011, 11:07 AM

It doesn't vary in fixed increments, but is actually analog. The camera will usually round up in the viewfinder, so shortly after 17mm you'll see 3.5. At 50mm the true aperture will be around 4, but in the viewfinder you may see 4.5- it really depends on the lens. I haven't used this one so I can't tell you for sure.

fLyIr · 03-06-2011, 12:20 PM

2 Adam
Thank you!

For exapmle, camera shows that f4 covers 30-60mm, so real f4 @ 30mm won't be the same real f4 @ 60mm (aperture continuously closing as focal length increasing and camera changes number of aperture only when passing certain FLs) ? Am I right ?

I hope you understand what I mean

Adam · 03-06-2011, 12:24 PM

Right- but the difference is probably neglibible anyway. Lens manufacturers tend to approximate apertures and focal length, so there's definitely leeway in there.

fLyIr · 03-06-2011, 12:49 PM

Thanks again, now it's clear for me

pop4 · 03-07-2011, 04:45 PM

These are some rough values I got from varying the focal length and seeing what max aperture I could get;

f/2.8 from 17 to ~21mm
f/3.5 from ~23 to ~34mm
f/4.0 from ~34mm to ~70mm
f/4.5 at ~70mm

So basically when I turn the zoom ring, at just a bit before 70mm, the figure on the display jumps up to f/4.5.

Originally posted by fLyIr

Especially which FL is ending with 2.8 and 4 and what aperture does 50mm have.

So the lens quite quickly loses it's f/2.8 max aperture, and at 50mm, the max aperture is f/4.0. The focal range makes the lens a quite useful everyday/walk-around lens, but if you NEED f/2.8 in that range, then you're probably better off getting one of the 16-50 or 17-50 or 18-50 constant f/2.8 lenses out there.

Hope that helps.

jjdgti · 03-09-2011, 09:42 AM

Originally posted by pop4

These are some rough values I got from varying the focal length and seeing what max aperture I could get;

f/2.8 from 17 to ~21mm
f/3.5 from ~23 to ~34mm
f/4.0 from ~34mm to ~70mm
f/4.5 at ~70mm

So basically when I turn the zoom ring, at just a bit before 70mm, the figure on the display jumps up to f/4.5.

So the lens quite quickly loses it's f/2.8 max aperture, and at 50mm, the max aperture is f/4.0. The focal range makes the lens a quite useful everyday/walk-around lens, but if you NEED f/2.8 in that range, then you're probably better off getting one of the 16-50 or 17-50 or 18-50 constant f/2.8 lenses out there.

Hope that helps.

Thanks for the info. I did not have the time to do this in mine. But it is nice to know other people observations.

03-06-2011, 09:54 AM	#1
fLyIr New Member Join Date: Oct 2010 Location: Almaty Photos: Gallery Posts: 20	Sigma 17-70 f2.8-4.5 (FL and f-stops) Hi to everyone, but question is for sigma 17-70 owners I'm going to buy this lens but would like to know the steps of f-stops through all focal lenght. Especially which FL is ending with 2.8 and 4 and what aperture does 50mm have. Thanks for your answers. Best regards.

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03-06-2011, 11:07 AM	#2
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,595	It doesn't vary in fixed increments, but is actually analog. The camera will usually round up in the viewfinder, so shortly after 17mm you'll see 3.5. At 50mm the true aperture will be around 4, but in the viewfinder you may see 4.5- it really depends on the lens. I haven't used this one so I can't tell you for sure.

03-06-2011, 12:20 PM	#3
fLyIr New Member Join Date: Oct 2010 Location: Almaty Photos: Gallery Posts: 20 Original Poster	2 Adam Thank you! For exapmle, camera shows that f4 covers 30-60mm, so real f4 @ 30mm won't be the same real f4 @ 60mm (aperture continuously closing as focal length increasing and camera changes number of aperture only when passing certain FLs) ? Am I right ? I hope you understand what I mean

03-06-2011, 12:24 PM	#4
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,595	Right- but the difference is probably neglibible anyway. Lens manufacturers tend to approximate apertures and focal length, so there's definitely leeway in there.

03-06-2011, 12:49 PM	#5
fLyIr New Member Join Date: Oct 2010 Location: Almaty Photos: Gallery Posts: 20 Original Poster	Thanks again, now it's clear for me

03-07-2011, 04:45 PM	#6
pop4 Veteran Member Join Date: Aug 2007 Location: YMML Photos: Gallery Posts: 1,879	These are some rough values I got from varying the focal length and seeing what max aperture I could get; f/2.8 from 17 to ~21mm f/3.5 from ~23 to ~34mm f/4.0 from ~34mm to ~70mm f/4.5 at ~70mm So basically when I turn the zoom ring, at just a bit before 70mm, the figure on the display jumps up to f/4.5. Originally posted by fLyIr Especially which FL is ending with 2.8 and 4 and what aperture does 50mm have. So the lens quite quickly loses it's f/2.8 max aperture, and at 50mm, the max aperture is f/4.0. The focal range makes the lens a quite useful everyday/walk-around lens, but if you NEED f/2.8 in that range, then you're probably better off getting one of the 16-50 or 17-50 or 18-50 constant f/2.8 lenses out there. Hope that helps.

03-09-2011, 09:42 AM	#7
jjdgti Veteran Member Join Date: Jun 2008 Location: NJ Posts: 1,824	Originally posted by pop4 These are some rough values I got from varying the focal length and seeing what max aperture I could get; f/2.8 from 17 to ~21mm f/3.5 from ~23 to ~34mm f/4.0 from ~34mm to ~70mm f/4.5 at ~70mm So basically when I turn the zoom ring, at just a bit before 70mm, the figure on the display jumps up to f/4.5. So the lens quite quickly loses it's f/2.8 max aperture, and at 50mm, the max aperture is f/4.0. The focal range makes the lens a quite useful everyday/walk-around lens, but if you NEED f/2.8 in that range, then you're probably better off getting one of the 16-50 or 17-50 or 18-50 constant f/2.8 lenses out there. Hope that helps. Thanks for the info. I did not have the time to do this in mine. But it is nice to know other people observations.