HMC40 - First Look

Well... I'll be pimp-slapped by a monkey...

Okay, so here's what the iris actually does: from fully open to f/2.8, it performs exactly as I expected -- each tiny motion of the wheel equates to a very tiny closing of the iris, in 1/6-stop increments.

Up until f/2.8.

Then, when you get to f/3.0, the iris itself stops changing. It stays at an actual f/2.8, and instead, a little ND filter comes gliding in from below and covers up the very bottommost section of the open iris window. And each tick you move the iris wheel, causes the filter to slide more into position, until it's all the way in, which is at f/6.4. So at f/6.4 the physical iris is still open to an f/2.8, but the neutral density filter is fully in place, so the actual light transmitted is the equivalent of f/6.4. Then, if you stop the "iris" down any further, it commences actually closing again.

So -- score one for Professor Bob and Cranky.

Not 100% sure how I feel about this. I mean, I know exactly why they've done it, they've done it for the sake of video quality because diffraction is a problem enough on a 1/3" camera, packing 1920x1080 pixels on a 1/4" camera can cause serious resolution differences due to diffraction. So they're attempting to keep the video as clean and sharp as possible for as long as possible throughout the iris range. Using the ND filter instead of actually closing the iris ... well, I guess it does give the user what they want, while preserving the highest video quality... it's just that it doesn't feel right that closing the iris doesn't necessarily actually close the iris, y'know?

I guess we just have to think about the display readout as T-stops instead of physical f-stops...

More disclosure would have made this perfect -- as Bob said, f/2.8 + ND.01, then f/2.8+ND.02, etc... but then again that might make things confusing. Technically it's doing what you want, it's controlling exposure the way you'd expect, it's just that the physical iris isn't closing. And with 1/4" chips, you're going to have deep DOF no matter what you do, and - frankly, - most of us spend our time trying to get the iris as OPEN as possible, and here the camera does it by default...

I guess I just chafe at any auto feature where I don't have 100% control over what the camera is doing, but at this price point, with the limited space for buttons, and the very serious image quality impairment that happens due to diffraction, it's probably a perfectly reasonable compromise. Of course, I'd prefer an HMC150-style three-position physical ND filter wheel that I can swap in at any time, but at this price point that just doesn't happen.

What this means from a practical aspect is that we should be diffraction-free from (display readout of) iris:OPEN to iris:f/6.4. Any deeper than f/6.4 and you're probably giving up some res to diffraction. Which may mean keeping a 3-stop ND filter on you would be a good idea if you're going to be shooting outdoors.
 
So, Panasonic decided to keep a wider aperture at f/2.8 instead of f/4.0 or f/5.6 like Sony and Canon are doing. AFAIK, values chosen by Sony and Canon provide the least distortion, while the value chosen by Panasonic veers to the side of shallower DOF, given that the chips are only 1/4-inch. Works for me. BTW, f/2.8 is aperture that is accessible both at full zoom and full wide. Any larger aperture will not be accessible at full zoom, so Panasonic chose the widest aperture that is available at all focal lengths. It wanted to provide as wide aperture as possible. Geez, why did not Pana just use larger chips?

On the HMC40 the ND filter absorbs about 2-1/3 of stops, less than 4 stops on the Canons, but this seems to be enough, the lens is not that fast.

> it's just that it doesn't feel right that closing the iris
> doesn't necessarily actually close the iris, y'know?

You are not closing the iris, you are darkening the image :)

> I guess we just have to think about the display
> readout as T-stops instead of physical f-stops...

Bingo! Panasonic should have put exactly that in the operation manual.

> Of course, I'd prefer an HMC150-style three-position physical ND filter
> wheel that I can swap in at any time.

The old-school ND filter with fixed position is worse, because when you engage it you darken/brighten image for how many? 4 stops? ND16 ==> 2^4. Then you have to immediately adjust aperture to correct brightness. With auto ND you get smooth change of brightness in the whole exposure range. For small chips auto ND is a much better approach.

Now the bonus question: does the consumer TM300/SD300/HS300 have the same ND filter inside?
 
The HMC150 has three two-stop filters.

As for what the consumer cams have, I have no idea, but I would be surprised if they engineered it differently as they'd have to face the same problem -- diffraction.
 
Barry_Green said:
As for what the consumer cams have, I have no idea, but I would be surprised if they engineered it differently as they'd have to face the same problem -- diffraction.
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They might just not care. The TM300 closes down to F16. Those who want wider iris can use screw-in ND filters like in the olden times.
 
Barry, thank you for taking the time to post all that information. I just got my HMC40 and really look forward to learning all that it can do. Will be using it this weekend for the first time at a car meet and drive.
 
Barry,

First of all thank you for all the work in testing the camera.

Second, given the higher pixel count and the smaller image sensors, diffraction comes into play a lot sooner than on the HMC-150. So, I'm happy to see the ND filter kick into place BEFORE the diffraction appears. As long as we know what is going on, I'm happy.

It would be interesting to see what happens to the resolution at F1.8, F2.8, F8, F11, and F16. Or at least when the camera says F8, F11, and F16.

(2.8 x 2.8) / (6.4 x 6.4) = 7.84 / 40.96 = about 1/5.22 or about 19.1%

So the ND drops the light by a bit more than 2 F-Stops; roughly 2.38 F-Stops

Now, if F6.4 = F2.8 with maximum ND filter
F9.1 is really F4 with maximum ND
F12.7 is really F5.6 with maximum ND
F18 is really F8 with maximum ND (F16 is the maximum, right?)


Bob Diaz
 
Barry_Green said:
What this means from a practical aspect is that we should be diffraction-free from (display readout of) iris:OPEN to iris:f/6.4. Any deeper than f/6.4 and you're probably giving up some res to diffraction. Which may mean keeping a 3-stop ND filter on you would be a good idea if you're going to be shooting outdoors.
Click to expand...

Thanks Barry, loads of great info there. I actually quite like the sound of this as it makes the controls simple, and the ability to have greater depth of field is not something I ever use on the HMC151 anyway. This actually keeps the DOF relatively shallow which is nice.

Just one thing though, if the ND filter is partially applied (lets say 80%), don't you effectively have a small aperture 20% of f/2.8 with no ND filter?

In case what I am asking is confusing. What I mean is that wouldn't you get diffusion at the edge of the ND filter? It would be like having 2 apertures at the same time, one small, one large.
 
Just one thing though, if the ND filter is partially applied (lets say 80%), don't you effectively have a small aperture 20% of f/2.8 with no ND filter?
Click to expand...

for my understanding there are multiple ND filters with different values, you're not actually covering only a percentage of the area with only one. It keeps applying the next higher value!

So at no moment you would have a filter covering only part of the lens/sensor. At least that's how i understand it!
 
Superfresa66 said:
for my understanding there are multiple ND filters with different values, you're not actually covering only a percentage of the area with only one. It keeps applying the next higher value!

So at no moment you would have a filter covering only part of the lens/sensor. At least that's how i understand it!
Click to expand...

That's not what Barry said, but I hope you're right, as that would be better.
 
Barry_Green said:
I'll shoot a 12233 chart at various apertures, so we'll know what the diffraction issues are.
Click to expand...

Thanks Barry. :dankk2:


For users it will be helpful to know how high up on the F-Stops (T-Stops) one can go before diffraction sets in and kills the resolution.

Subject to what you find, users may need to up the shutter speed or use ND Filters in full sunlight. Then again, maybe the hit isn't as bad as one might fear.


Bob Diaz
 
It actually slides in from below, and occludes only a small portion of the aperture. It's diamond-shaped, and so is the aperture (4-bladed iris). So the top point of the ND filter slides up and translucently covers up the bottom corner of the iris, just a little bit; at f/3.0 I'd guess that the ND filter is covering up maybe 5% of the total area of the iris. Then, as you stop down more and more (well, as you roll the iris wheel more and more closed) the ND filter slides up and covers more of the iris, until by f/6.4 the ND filter is fully covering the entire iris.

Looks really weird and seems quite illogical, but it works and works well.
 
Sorry Barry, this is hard to explain. But I was wondering if, as the ND filter covers most of the aperture, don't you get diffusion from the small remaining gap, not yet covered?
 
By diffusion, do you mean diffraction? No, because the iris hasn't changed iris size. If you mean is there some ancillary image effect caused by the edge of the filter and where the "two apertures" meet -- I haven't noticed anything out of the ordinary. It does sort of look like there's two apertures, a "clear" one and an "ND" one, but the resulting image on the monitor looks simply fantastic. I don't know what downside I should be looking for, but my initial examination doesn't show any visible downside at all...
 
Wow, big difference... so the HMC40 for outdoors and the HMC150 for indoors =)

when you say you had to adjust the light, how much difference between them?
 
Barry_Green said:
Oh, and for those following along, be sure to check post #2 for the first image -- a res chart comparison.
Click to expand...
With the difference in sensor resolution the result was to be expected, but it is nice to see real-life confirmation, about 700-800 lines, while the 150 hovers around 600 lines. CCinfo obtained similar results with the TM300/HS300. With the tiny Canon HF200/20 CCInfo measured about 900 lines in good light, almost EX-like! But your "change of lightning" would be even more serious in the latter case.

So you don't have a Sony prosumer cam, but do you have one of the Canons, like the HV20/30/40 or the HG10, the one with the 2MPixel 1/2.7-inch chip? This is a well-known camera and stacking the HMC40 against it would be something many people could relate to. CCInfo measured that the TM300/HS300 has about the same light sensitivity as the HV20/30 and HG10 (around 7-8 lux needed for 50 IRE) but they keep changing their procedures every year, so there is still a bit of uncertainty.

This camera will be the first foray into pro world for many amateurs, so comparing it to well-known consumer cameras would be immensely beneficial. Thanks for all your work!
 
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