Sony DSLR users may, or may not know they don't get any visual benefit from
sensor-shift type image stabilization, that is, the Sony SteadyShot stabilization only begins its job once the mirror is up
and out of the way, after you press the shutter button. Canon and Nikon DSLR users have grown accustomed to seeing the
smoothing effects of their lens based image stabilization, which runs independently from the shutter action, although it will
not run continuously, and may need to be restarted by a shutter half press. Not included in the above statement, but
worth mentioning; sensor-shift stabilization is visible in pocket cameras on the EF or LCD, or in current Sony DSLR and SLT
cameras in movie mode, but not in still image capture mode.
Sigma and Tamron have recently come out with
their own versions of lens based IS systems available in the Sony alpha mount, Sigma calls their system OS for "Optical
stabilizer" and Tamron uses VC, or "vibration compensation."
I've long had questions about
how these lens based image stabilization devices would work with Sony, such as; does it offer additional compensation from
movement as opposed to the Sony system, and most importantly, what happens when you use both systems simultaneously!!
Fortunately, I have a copy of the Sigma 70-200mm F/2.8 HSM OS lens to help answer those questions.
In the test below, I've used all available options for each system.
the first column is no image stabilization or sensor-shift stabilization, both have been turned off. In the second
column I'm using Sony's SteadyShot sytem only. The third column is Sigma's OS1 system only. The fourth column
is Sigma's OS2 setting, which is used primarily for horizontal panning, and is meant to better stabilize vertical shifts.
the fifth column I'm using both SteadyShot and Sigma's OS1. The last column is both SteadyShot and Sigma's OS2.
The
first four columns below show results that were taken at 200mm, (hand-held of course) and about 7' (2.1m) away form the subject,
with a shutter speed of 1/15sec, an aperture of F/4, and ISO set at 200. I chose this combination to get the most noticeable
results going from no stabilization, to sharp images using stabilization. The last two columns were taken at 160mm with
the same camera specs. I used a shorter focal length to see if it made any difference when using both systems together;
it didn't. I took ten shots of each set to get a good look at what I would consider the average result. The Target is
a magazine back, with a 100% center crop. Most of the Sigma OS1 crops are very sharp, although they don't look like
it because the page and print aren't super sharp in real life.
The results are pretty
clear. With no stabilization, there are no sharp images. When using Sony's SteadyShot system, there was a big
improvement in usable images. The Sigma's OS1 produced the sharpest shots, and offered the most compensation. OS2 was
less effective because it's not meant for static subjects. When using both systems together, you'll probably ruin the
image, apparently both systems are working against each other, although that's no surprise. This is true when using
movie mode also, so make sure you turn off SteadyShot when using the lens based system, or vice versa.
So
which system is better? You'll probably be quick to say the lens based system, but that might be a mistake. I
noticed when using Sigma's OS lens based system it takes more than a second to fully activate after it's switched on, or is
awakened by a shutter press, and if you quickly press the shutter button to take a picture, there may be little or no effect,
so for fast action, make sure the system is active before you're ready to shoot. The Sony SteadyShot system is ready
instantly, and may produce better shots under certain circumstances. Note: Sigma claims a one second start-up time in
their lens manual, but that's not going to give you the best results based on my testing here.
To sum
this up; YMMV, meaning my results here may not be the same as what you'll get using the same exact testing procedure.
You may be more steady, or more shaky than I am. For the crops below I took a shot or two, then rested, and repeated
until I was done with each set. The results from top to bottom, in each column are in the order that I took them.
I'm
guessing SteadyShot is giving me about a 1.5-2 stop improvement at this focal range and shutter speed. Sigma's OS1 gave
me about 2-2.5. Sony and Sigma both claim (marketing fluff) about 4 stops of improvement, but again, it will all depend
on the individual.
