Sunday, April 11, 2010

HS10 vs dSLR – same depth of field? *updated*

I saw an incorrect statement on the FTF this morning from someone who seems to have fallen prey to the hype surrounding the HS10 from Fuji.

By the way, I have toned down my rhetoric because the original author is generally a nice guy these days on the FTF and does not deserve to be ridiculed as could be interpreted from my post. In this instance, though, I am quite certain he is simply wrong.

The statement in question was:

The long lens on this camera has a shallower depth of field so the background is slightly thrown out of focus... like a DSLR... but not as much! Detail is very good and the slight blurring in the background is not in-camera NR... its is the shallow depth of field playing here.

The image he showed is *not* linked here to avoid any acrimony (despite his giving me permission to post it later on), but it is a little girl sitting on a couch watching TV. I’ll show a diagram of it here, with the subject circled for future reference.


The vital statistics of the image are: Manual, f/2.8, 1/2.5s, 100iso, no flash, focal length 4.2mm

My point with this post is to address the depth of field available with a camera of this type, and the ludicrous claims made above, which – to summarize – are:

1. This camera has a long focal length and therefore gets shallow depth of field almost like a dSLR – not true at all

2. The slight blurring of the background is not noise reduction, but rather this shallow depth of field – not true at all

To address point 1:

The “range” of a lens (and this one is spectacularly long) has *nothing whatsoever* to do with its ability to get a shallow depth of field at normal focal lengths.

To show you what I mean, this image comes from the excellent depth of field master web site, which can tell you the exact field of focus for any shot (and we’ll get to this shot in a moment.)


So, if he shot anywhere near the hyperfocal distance at that focal length and aperture, then his claim is false.

This specific image was shot at a focal length of 4.2mm, which is approximately 24mm in 35mm camera terms. That’s *very* wide. And this is confirmed by his use of the widest aperture possible, f2.8, which is only available at the widest focal length.

Even a dSLR is hard pressed to get shallow depth of field in a wide shot with the subject a fair distance from the camera, occupying only a small portion of the middle of the frame -- as his shot shows. So let us see what DOF Master says …


I chose 1/2” sensor, which gives a *shallower* depth of field than the HS10 would actually have with its 1/2.3” sensor. I chose a subject distance of only 3 feet, which is probably showing a *shallower* depth of field than is actually present in this image. And I chose 4.3mm (4.2 was not selectable) which again shows a *shallower* depth of field. So all of these advantages to his statement should have resulted in a close call, no?

No. The hyperfocal distance for the HS10 at that setting is 1.3 feet … and *everything* from the subject onwards is therefore in crystal sharp focus. Except when noise reduction kicks in, as it always does with these tony sensors.

Depth of field get shallower as the magnification increases, not as the “potential magnification if a different focal length or camera to subject distance were used” increases :-)  Sheesh …

Longer focal lengths increase magnification. Shorter subject distance increases magnification (duh.) And that’s pretty much the story. Subject distance must go down or focal length must go up to get some background blur. This image has neither of those properties … very wide focal length plus moderate subject distance (small in the frame) makes for everything being sharp.

I ran a second scenario for this sensor … even at 100mm (equivalent to over 500mm effective) and 12 foot subject distance (the baby would fill the frame and then some), the back wall would be in focus if it is 12 feet away. Ye canna change the laws of physics!

To address point 2:

Of course that slight blur is probably noise reduction. What else can it be? That part of the frame should be crystal sharp because of the relatively long subject distance and very short focal length. See above.

But that part of the frame is darker than the rest and thus is likely attacked by the aggressive noise reduction that this camera must employ, even at base ISO. That’s just the price of such tiny sensors.

So … why do people continue to make claims like the above? Especially people who should know better? Beats me … but right now there is a rush to be popular on the FTF, and that comes from ownership of the HS10 for the next few months.

Until, that is, they realize that the image quality at low ISO is shite and the camera is too big to conveniently carry into venues that do not allow larger cameras.

For further study … you don’t need to believe me after all if you read up on this yourself …


Someone pointed out to the author of that comment that I had “torn him a new one” on my blog. I did not mention names etc, therefore I did not tear anyone a new one, but I have toned down my rhetoric because the author responded with aplomb. Impressive, to be honest. Of course the usual moronic echoes from others were not so impressive :-)

However, he continues to push the theory that this separation comes from a shallow depth of field.

This slight DOF separation property seems to be a unique optical property of the HS10's lens when used at its widest angle (24mm)! Seems to be some new optical design responsible for this optical phenomenon!

I am quite happy with this slight background separation. I can understand how this effect can be easily mistaken for in-camera NR on a hurried look... which it is NOT!

It is hard to argue with “an advanced design that defies the laws of physics.”  But I still believe that he is incorrect.

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