Image stabilization on zooms: F, A, FA, ...

leodp · 05-20-2021, 04:55 AM

Hi, two quick questions, which I could not find completely answered.

On which zooms the IBIS is working correctly?

I expect that a correct communication of the focal length should happen between camera and lens, so probably only at least FA type lenses? Or maybe not all of them? What about third-party lenses?

Second point: optical image stabilization is said to give me 4 to 5.5 steps of gain in exposition time, depending on the camera model.
But on zooms the focal length is communicated to the camera in steps, and even primes may have a mismatch of also 5% in the reported Vs actual focal lenght. This in turn affects the IBIS accuracy. IS anybody aware of any measurement of this effect?

Thanks, Leo

**Lowell Goudge** · 05-20-2021, 05:02 AM

IS will or should work on all zoom lenses in the F and FA range.

A lenses do not communicate anything really, they have a fixed coding of minimum and maximum aperture. but that is all. for an A lens you need to enter the focal length yourself, and for zooms this will be a compromise you can pick minimum focal length, the meadian focal length, or if you intend to shoot at a fixed focal length set it to that value.

leodp · 05-20-2021, 05:14 AM

Originally posted by Lowell Goudge

IS will or should work on all zoom lenses in the F and FA range.

A lenses do not communicate anything really, they have a fixed coding of minimum and maximum aperture. but that is all. for an A lens you need to enter the focal length yourself, and for zooms this will be a compromise you can pick minimum focal length, the meadian focal length, or if you intend to shoot at a fixed focal length set it to that value.

I shoot with old zoom lenses in the past, and that's what I did too: enter a middle value between min and max zoom focal lengths.

But I am going to buy a generic zoom which I will use in darker situations, and would like it to have the IS working correctly at any zoom.
I already own a Sigma 17-70 2.8/4.0, which communicates its focal length stepwise to the camera, and the camera IS works accordingly.
Is anything similar possible on older zooms? Does a FA type zoom, for example, tell the camera its actual focal length (not the range)? And a F, an A, an M zoom?
This is what I would like to know before deciding which zoom to buy.

**boriscleto** · 05-20-2021, 05:22 AM - **1 Like**

F and FA zooms communicate the focal length. A and M lenses do not.

Fogel70 · 05-20-2021, 06:04 AM

I believe any AF lens should communicate focal length to camera, both Pentax and third party lenses.
Except for Pentax first AF lens SMC Pentax-AF 35-70mm F2.8.

kypfer · 05-20-2021, 07:18 AM

Originally posted by Fogel70

I believe any AF lens should communicate focal length to camera, both Pentax and third party lenses.

Exactly my experience. I use FA and FAJ lenses as well as some older Sigma a/f lenses on my modern digital Pentax cameras with no problem

It's only manual-focus zooms that are any problem … either make a compromise and hope, take a little longer and do it properly, or disable Shake Reduction and keep the shutter speed up

**UncleVanya** · 05-20-2021, 01:51 PM

There are a few third party manual focus lenses that communicate some information to the camera using the serial data pin. Most I think are primes and send exact aperture data rather than relying on the passive mount contacts.

**Lowell Goudge** · 05-20-2021, 05:27 PM

Originally posted by leodp

I shoot with old zoom lenses in the past, and that's what I did too: enter a middle value between min and max zoom focal lengths.

But I am going to buy a generic zoom which I will use in darker situations, and would like it to have the IS working correctly at any zoom.
I already own a Sigma 17-70 2.8/4.0, which communicates its focal length stepwise to the camera, and the camera IS works accordingly.
Is anything similar possible on older zooms? Does a FA type zoom, for example, tell the camera its actual focal length (not the range)? And a F, an A, an M zoom?
This is what I would like to know before deciding which zoom to buy.

To keep the response short any af lens communicates focal length

05-20-2021, 04:55 AM	#1
leodp Junior Member Join Date: Jan 2013 Photos: Gallery \| Albums Posts: 39	Image stabilization on zooms: F, A, FA, ... Hi, two quick questions, which I could not find completely answered. On which zooms the IBIS is working correctly? I expect that a correct communication of the focal length should happen between camera and lens, so probably only at least FA type lenses? Or maybe not all of them? What about third-party lenses? Second point: optical image stabilization is said to give me 4 to 5.5 steps of gain in exposition time, depending on the camera model. But on zooms the focal length is communicated to the camera in steps, and even primes may have a mismatch of also 5% in the reported Vs actual focal lenght. This in turn affects the IBIS accuracy. IS anybody aware of any measurement of this effect? Thanks, Leo

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05-20-2021, 05:02 AM	#2
Lowell Goudge Site Supporter Join Date: Jan 2007 Location: Toronto Photos: Gallery \| Albums Posts: 17,891	IS will or should work on all zoom lenses in the F and FA range. A lenses do not communicate anything really, they have a fixed coding of minimum and maximum aperture. but that is all. for an A lens you need to enter the focal length yourself, and for zooms this will be a compromise you can pick minimum focal length, the meadian focal length, or if you intend to shoot at a fixed focal length set it to that value.

05-20-2021, 05:14 AM	#3
leodp Junior Member Join Date: Jan 2013 Photos: Gallery \| Albums Posts: 39 Original Poster	Originally posted by Lowell Goudge IS will or should work on all zoom lenses in the F and FA range. A lenses do not communicate anything really, they have a fixed coding of minimum and maximum aperture. but that is all. for an A lens you need to enter the focal length yourself, and for zooms this will be a compromise you can pick minimum focal length, the meadian focal length, or if you intend to shoot at a fixed focal length set it to that value. I shoot with old zoom lenses in the past, and that's what I did too: enter a middle value between min and max zoom focal lengths. But I am going to buy a generic zoom which I will use in darker situations, and would like it to have the IS working correctly at any zoom. I already own a Sigma 17-70 2.8/4.0, which communicates its focal length stepwise to the camera, and the camera IS works accordingly. Is anything similar possible on older zooms? Does a FA type zoom, for example, tell the camera its actual focal length (not the range)? And a F, an A, an M zoom? This is what I would like to know before deciding which zoom to buy.

05-20-2021, 05:22 AM - 1 Like	#4
boriscleto Loyal Site Supporter Join Date: Dec 2009 Location: North Syracuse, NY Photos: Gallery Posts: 16,476	F and FA zooms communicate the focal length. A and M lenses do not.

05-20-2021, 06:04 AM	#5
Fogel70 Pentaxian Join Date: Sep 2009 Location: Stockholm, Sweden Photos: Albums Posts: 3,062	I believe any AF lens should communicate focal length to camera, both Pentax and third party lenses. Except for Pentax first AF lens SMC Pentax-AF 35-70mm F2.8.

05-20-2021, 07:18 AM	#6
kypfer Pentaxian Join Date: Jan 2018 Location: Jersey C.I. Posts: 3,595	Originally posted by Fogel70 I believe any AF lens should communicate focal length to camera, both Pentax and third party lenses. Exactly my experience. I use FA and FAJ lenses as well as some older Sigma a/f lenses on my modern digital Pentax cameras with no problem It's only manual-focus zooms that are any problem … either make a compromise and hope, take a little longer and do it properly, or disable Shake Reduction and keep the shutter speed up

05-20-2021, 01:51 PM	#7
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,452	There are a few third party manual focus lenses that communicate some information to the camera using the serial data pin. Most I think are primes and send exact aperture data rather than relying on the passive mount contacts.

05-20-2021, 05:27 PM	#8
Lowell Goudge Site Supporter Join Date: Jan 2007 Location: Toronto Photos: Gallery \| Albums Posts: 17,891	Originally posted by leodp I shoot with old zoom lenses in the past, and that's what I did too: enter a middle value between min and max zoom focal lengths. But I am going to buy a generic zoom which I will use in darker situations, and would like it to have the IS working correctly at any zoom. I already own a Sigma 17-70 2.8/4.0, which communicates its focal length stepwise to the camera, and the camera IS works accordingly. Is anything similar possible on older zooms? Does a FA type zoom, for example, tell the camera its actual focal length (not the range)? And a F, an A, an M zoom? This is what I would like to know before deciding which zoom to buy. To keep the response short any af lens communicates focal length