IS/VR and shutter speed

[John Chardine]

I think I remember BPN moderator Roger Clark say once that IS/VR has little effect past a certain shutter speed and that he will turn IS/VR off at that point. Is there an advantage to turning IS/VR off in terms of IQ or does it just save battery power? Also, it would be of interest to know what this shutter speed is and how it varies with focal length. With modern digital cameras and the ability to view at 100%, I don't think the old rule that the shutter speed was fast enough if it was faster than 1/focal length works any more for critical sharpness. Is it possible to work this out from first principles- camera shake ultimately causes the image projected by the lens on the sensor to move so what is the relationship between the amount and type of camera/lens shake (rotational, lateral etc) and the amount of image movement this causes on the sensor and how does this vary with focal length? What is the limit of detectability of sensor image movement (i.e., blur) at 100%. Is it around the sensor pixel size or somewhat bigger?

Anyway lots of questions and I hope some answers to follow! I fully expect Roger to direct me to a web page he has written on the subject, and which I have not yet found!

Thanks.

[Jim Neiger]

I think I remember BPN moderator Roger Clark say once that IS/VR has little effect past a certain shutter speed and that he will turn IS/VR off at that point. Is there an advantage to turning IS/VR off in terms of IQ or does it just save battery power? Also, it would be of interest to know what this shutter speed is and how it varies with focal length. With modern digital cameras and the ability to view at 100%, I don't think the old rule that the shutter speed was fast enough if it was faster than 1/focal length works any more for critical sharpness. Is it possible to work this out from first principles- camera shake ultimately causes the image projected by the lens on the sensor to move so what is the relationship between the amount and type of camera/lens shake (rotational, lateral etc) and the amount of image movement this causes on the sensor and how does this vary with focal length? What is the limit of detectability of sensor image movement (i.e., blur) at 100%. Is it around the sensor pixel size or somewhat bigger?

Anyway lots of questions and I hope some answers to follow! I fully expect Roger to direct me to a web page he has written on the subject, and which I have not yet found!

Thanks.

John,

Most lenses detect tripods and shut off IS/VR and have modes that detect panning and turns off horizontal IS. If you have a canon lens that does this you can just set IS mode 2 and leave it on. I have heard some photogs say that IS slows down AF speed slightly, but I can't tell the difference, so I just leave mine on mode 2. I like to leave it on so I don't forget to turn it back on when I need it.

[Fabs Forns]

John, also disengaging IS or VR would give you faster acquisition. OR so I've heard. I never turn mine off.

[Desmond Chan]

This seems to be a subject that gets discussed/debated a lot. I've seen some on dpreview just recently. However, in the technical guide for Nikon D3, it suggests - if I remember correctly - turning VR off when shutter speeds are faster than 1/500s. I have a feeling that if your camera handling skills are not up to par, so to speak,:D perhaps leaving VR/IS on all the time could help. I do, except when shooting macro with camera on tripod.

[Alfred Forns]

I think at the end you will do more harm than good turning it off. Would suggest to keep on all the time.

Keeper ratio with or without I have not been able to tell any difference and have tired with both Nikon and Canon.

[Roger Clark]

Hi John,
I have done some experiments regarding image sharpness and shutter speed. I had noticed that sometimes my 300 f/4 L IS images seem less than sharp. I traced the problem to IS on at fast shutter speeds above about 1/2000 second or so. The IS on the 300 f/4 is an older version and I have not seen this effect on my 500 f/4 L IS or 300 f/2.8 L IS. While I only have seen this effect on the 300 f/4, when I remember I do turn off IS on all my lenses at high shutter speeds, just in case.

I think the problem has to do with the servo loop in the IS system. It must be slower in the 300 f/4

It is a simple test. On a clear day, choose a static target with lots of detail, e.g. a brick wall. As the sun rises and the light increases, hand hold your lens and photograph the target. Boost ISO if necessary. Take several images at each exposure, but keep f/stop constant through the whole test.

Roger

[John Chardine]

Thanks for all the replies. I was aware of the automatic switching off of IS when mounted on a tripod in some Canon lenses, although I don't think most tripods out there are capable of keeping a lens like the 500/4 steady enough for this to take effect. If you don't believe me, lock down your 500 on a Wimberly head and heavy-duty Gitzo tripod and then turn on Live View and see how much movement there is, even in a light breeze.

My question really boils down to how fast a shutter speed do you need with a certain focal length of lens before you obviate the need for IS? Maybe the answer is that it's always beneficial to have it on even at 1/4000s for example. I'll try Roger's suggested test.

[Sabyasachi Patra]

Supplementary Question:
What do you guys do when you are clicking with a 500mm +1.4x or 600mm +1.4x at 1/30 or 1/40th of second on a tripod or bean bag. Do you keep IS on or off?

Cheers,
Sabyasachi

[Roger Clark]

Sabyasachi,
I keep IS on at the slow speeds. Here is a 1/10 second exposure of a Lilac Breasted Roller with a 500 mm + 2x TC taken from a rocking safari vehicle on a Wimberly mount sittign on top of the vehicle. I did have to use mirror lock-up at that slow speed.
http://www.clarkvision.com/galleries...1500b-700.html

Roger

[Sabyasachi Patra]

Thanks Roger!

I too keep the IS on all the time. I use mirror lock up if the tiger is not moving. Recently I tried without IS +mirror lock up and without IS and without mirror lock up with mixed results. As of now, I am convinced that IS on is the best for me. Thanks for the confirmation.

Cheers,
Sabyasachi