GH1 DOF Vs HMC-150/HPX170

[studio1972]

Not sure if anybody has already done this, but I was interested in what the GH1 might give me in terms of DOF compared to my HMC151. These calculations were done with the stock GH1 lens which is designed with video in mind. Obviously the results would be different with prime lenses etc.

Distance to subject = 5m
35mm equivelant focal length = 100mm
Aperture fully open in both cases

HMC = 2.45m at f/2 13.8mm
GH1 = 1.83m at f/5.6 50mm

Distance to subject = 5m
35mm equivelant focal length = 200mm
Aperture fully open in both cases

HMC = 0.7m at f/2.4 27.6mm
GH1 = 0.44m at f/5.6 100mm

I used this online calculator:

http://www.cambridgeincolour.com/tut...calculator.htm

It seems like the GH1 is capable of shallower DOF, but not so much as you might expect given that the sensor is 4 times as wide. I haven't done the maths, but I would imagine that an EX1 might come out with similar figures to the GH1 as it has a better lens than the HMC and a slightly larger sensor.

[Martti Ekstrand]

The fall-off of focus outside the DOF is greater with a bigger sensor than these numbers indicate. Which shows in the image.

[studio1972]

The fall-off of focus outside the DOF is greater with a bigger sensor than these numbers indicate. Which shows in the image.

Ok. I've just done the same calcs for the EX1, and it comes out at 1.68m and 0.41m respectively. This means it has slightly shallower DOF than the GH1.

Regarding your point about the larger sensor, I believe that this is counteracted by the narrow aperture of the GH1 lens. Of course, you can get other lenses for the camera.

Regards

Stuart

[Tim Joy]

You can get razor thin DOF with the GH1 and the right lens, so the question is- How much do you want?
Compared to 1/3" cameras, you have much more control, and you can get shallow DOF in almost any shot with a reasonably fast lens above about 35mm, or shooting CU with wide lenses.

[studio1972]

I was talking about the stock lens. Obviously with another lens the situation would be different. What I am saying is that if you intend to use the stock lens (which has a reasonable zoom range etc.) then you are going to get DOF in the same ball park as an EX1 and not much better than a 1/3 camera. The GH1 is much cheaper than these, so I'm not trying to slate it, I was just a bit surprised when I worked it out, and thought people might be interested as it seems most people seem to expect shallower DOF on the 4/3 camera.

[Ben_B]

The nice thing about a camera like the GH1 is that you can get shallow DOF in almost any situation if you need it. The HPX170 can get very shallow DOF if you need it, but you have to be shooting wide open, get far back, etc.

Here's some HPX170 screen grabs from a friend of mine when we were shooting around with the HPX and the GH1 that show off potential DOF of the HPX.

[Tim Joy]

Ahh. I see your point. Yes, it is close to the 1/3" cameras but just that little bit of extra shallowness is really nice sometimes.

[Barry_Green]

At the same aperture, the GH1 will be astoundingly shallower than the EX1 or HPX170 or HMC150. If you're going to go comparing f/2 to f/5.6, then of course you're going to end up with the results you got. But when are you going to be shooting f/2 on one camera, and in the exact same circumstances shooting f/5.6 on another camera? That's not gonna happen.

Aperture to aperture, the GH1 is going to be extremely much shallower.

[Ben_B]

And in the end, that's why many of us bought it.

[studio1972]

But when are you going to be shooting f/2 on one camera, and in the exact same circumstances shooting f/5.6 on another camera? That's not gonna happen.

Both cameras are fully open in this situation, I often have my HMC lens fully open, and I would do the same with the GH1 if I had one, seems like a perfectly reasonable comparison to me. Why would you not use the HMC at f/2.0 in a similar situation?

Surely you are not seriously arguing that you would have the same aperture in the same situation with a 1/3 camera as you would with a 4/3 camera?

Aperture to aperture, the GH1 is going to be extremely much shallower.

That's undoubtably true, but also a straw man. The EX1 has a lens with a wide zoom range at f/1.9, if such a lens could even be produced for a 4/3 sensor camera it would be enormous and would cost a fortune. The stock lens on the GH1 can go no more open then f/5.6 at the zooms I calculated.

Yes, you could use a prime lens on the GH1, but then you would have much less flexibility. An aperture to aperture comparison is really meaningless given that you would be falsely restricting the EX1/HMC to carry out this comparison.