Question About Full Auto Operating Priority in HMC40

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Denniscasey

Well-known member
Loaned my HMC book to a friend so can't look this up. The thread about HMC80 overexposure made me wonder again about how HMC40 handles exposure when it is set to full auto. Is following about right??

1. In bright light is ND applied first to try to keep iris within some pre-defined "optimal" (for high definition or depth of field) range?? If that is not enough to limit light, iris will close down; and if there is still too much light shutter will change from default 1/60 (in USA) to faster speed or will shutter stay locked at 1/60?

2. In low light ND naturally not applied, iris opened until at some point gain is applied if needed, and does shutter speed ever change from default 1/60?

Again, this is when HMC40 is set to full auto.
 
1. The ND filter is not automatic, it is integrated. I think the word "automatic" confuses people. It doesn't decide whether it's needed or not; it is always absolutely always added whenever you stop down the lens past f/2.8. Period. Even if you were in pitch black zero light conditions, if you stopped the iris down past f/2.8, the ND filter would be added.

2. In full auto the HMC40 can change the shutter speed.
 
Hi Dennis

Point the camera at a bright subject in auto, switch to manual and then push the iris wheel in once to see what shutter and iris the camera applied...then do the same in lower light etc etc and you can easily see what settings auto "has decided" It gives you a neat understanding as to what shutter and iris is applied in various conditions. AS Barry says the camera doesn't decide the ND ...it's all integrated....Obviously in very low light the iris will be open and gain applied in auto BUT I you went fully manual and physically closed the iris, the ND would come into play as it's linked to the iris and not decided by the camera (In a dark room at midnight you normally would have the iris open anyway unless for some reason you manually selected a VERY low shutter spped in manual) My trick to get nice low light footage is always shoot manual iris and what I do is crank to gain to no more than 10db or 12db then light the subject with a video light so my blacks are still black and not noisy.

Our AC-90's have just become available so I will definately have to get myself one as the PAL HMC80's also have vanished, along with the HMC42, off the dealers stock list.

Chris
 
Thank you Barry and Chris. I will run the experiment but I always like to understand the "theory" behind what happens or in this case how the camera "thinks." Dennis
 
Dennis,

One thing to keep in mind when in manual mode is to keep your iris above f/8. If you close down below that, your image will go soft since you are out of the sweet range of the lens. This behavior is true of most all lenses, but in the case of the 40/80, the ND thingy takes you there when it runs out of ND capability so it can bite you. The cams need more ND capability, I guess the sun doesn't shine as bright in Japan. So on any bright day, you will want to have an nd filter or possibly a polarizer in your kit. A .6 or .9 seems to be enough for most circumstances. If you stay around f/4, the cam will really produce amazing results.

Grant
 
Very good point Grant!

It was suggested with the AC-130/160 that the sweet spot was F5.6 and that has 1/3" chips so F4 or even more open should be pretty sweet on the 40!! You however CAN get away with using a smaller F stop too..I was doing a wedding on Saturday with the 80's and left the main camera in manual so shutter was fixed at 1/50th...it had been stormy but the sun came out and my iris closed down to F10.8 ... I quickly changed shutter and it dropped back to F6.8 but on the footage you cannot see the change at all. However it that was done in lower light you would have seen the softness immediately. Just for interest the camera seems to favour F6.8 in full auto in bright light.

Chris
 
On the HMC40/HMC80 and AC90, you can close down the iris to f/6.4 with no worries about diffraction at all. Anywhere from f/1.5 to f/6.4 should result in no diffraction issues. This is because of the way they've developed the integrated ND filter; normally you'd only be able to go to about f/2.8 on a camera with chips this size, but the integrated ND filter lets you stop down to f/6.4 while still avoiding any softening problems due to diffraction. And, truth be told, you can go a little further without it being an issue, I think f/8 is perfectly usable.
 
Barry_Green said:
1. The ND filter is not automatic, it is integrated. I think the word "automatic" confuses people. It doesn't decide whether it's needed or not; it is always absolutely always added whenever you stop down the lens past f/2.8. Period. Even if you were in pitch black zero light conditions, if you stopped the iris down past f/2.8, the ND filter would be added.

2. In full auto the HMC40 can change the shutter speed.
Click to expand...

Barry, Chris, Grant; In reading your latest helpful comments on keeping iris opened more than f/6.4 (or possibly f/8 per Barry) and the role of the "ND thingy" (to use Grant's technical term ) I thought more about the theory (I say theory because this may have no practical application) of HMC40 operation.

1. I understand that as soon as iris approaches f2.8 the ND filter is added "absolutely." My original question assumed camera in full auto mode, but as Chris mentioned even if you are in manual mode and wanted to select f/11 for some reason, the ND would override manual setting and be added to try to bring effective exposure back to some wider opening than f/6.4? Is that right?

2. Now, back to full auto operation and assuming very bright light. As soon as iris approaches some point, maybe f/5.6 , ND is added (linked to iris) to try to keep iris in the "sweet zone" (assume f/2.8 to f/6.4). If ND is not enough to keep iris wider than f/6.4 will camera automatically begin increasing shutter speed (to Barry's point that camera can change shutter speed in full auto) to keep iris in sweet spot or will it just stop iris down as much as it can and then if that is not enough in bright light it will begin increasing shutter speed?

This is just me trying to understand more about how HMC40 prioritizes or orders its settings. Practically speaking, I do have both polarizing and ND filters but sometimes in chaotic situations I do not have time to add various filters. Dennis
 
1. I'm not sure what question you're asking? The ND filter is not optional, it's integrated. The numbers that the camera reports for what the iris are, are not, in fact, what the actual dimensions of the iris are. When you choose f/11, it is not stopping down to f/11. It is stopping down to about f/4.8 or so, and the rest of the exposure compensation is added by the ND filter, to where it is exposing AS IF it were at f/11, but in fact the actual diameter of the iris is more like f/4.8. (I'm making that number up, it may or may not be f/4.8, but it's probably in that ballpark).

So it doesn't matter whether you're in automatic or manual, that makes zero difference whatsoever. Whenever the camera reads anything from f/1.5 to f/2.8, that is the actual iris diameter. Whenever it reads anything from f/2.8 to f/6.4, the actual physical iris size is locked at f/2.8, and the difference in exposure is caused by the ND filter being progressively brought more and more into view. At any point after f/6.4, the iris starts closing down again, but the ND filter remains fully engaged. So f/6.4 is, in fact, f/2.8 iris + 2 1/2 stops of ND filter (roughly, I don't remember the exact number off the top of my head but it's in the book). So if you go from f/6.4 to f/7.2, it would in fact be an f/3.1 iris + 2 1/2 stops of ND filter. If you go to f/8, it will in fact be f/3.4 (ish) plus 2 1/2 stops of ND filter.

There is no choice about it, there is no differentiation, and whether it's automatic or manual makes no difference whatsoever.

2. Again, it works exactly as I described before, regardless of the light conditions. There is no "if" about the ND filter. It is an integrated part of the exposure system. If you go past f/2.8, the ND filter will be added, doesn't matter if you're shooting the sun or at the bottom of a coal mine. The ND filter has nothing to do with responding to the lighting conditions, it is an integrated part of the iris system. It is a way to keep the iris as open as reasonably possible, in the sweet spot of the iris range to minimize diffraction.

Now, that said, there isn't enough ND filtration integrated in the camera to handle all scenarios. So once the ND filter is fully engaged (at f/6.4), any further "stopping down" does in fact result in the iris closing down more.

When in auto mode, the camera tries very hard to avoid diffraction-inducing tiny apertures. It will choose to shorten the shutter speed rather than stop down the iris, after a certain point. On the AC90 I think that point is f/7.2, but again, that's off the top of my head. So it'll stop down to about f/7.2 IIRC, and any further brightness compensation will be handled by shortening the shutter speed, up until about 1/500. I don't think the system will reach for a shorter speed than 1/500. Once it's at 1/500, if it needs to further cut the brightness, it will close the iris more, all the way to f/11 if necessary. (but again, that isn't a physical f/11, as the image would be so soft from diffraction that it'd probably look like VHS if you did that! When it says f/11, it's really somewhere around f/5.6 + 2.5 stops of ND).
 
Barry, thank you for complete explanation (and patience). I had not really linked all this together before to fully understood high priority HMC40 places on keeping iris from diffraction-inducing tiny apertures (hence the excellent resolution camera is known for). Also in your last sentence example it is helpful to understand when camera displays f/11 the iris is really open to around f/5.6 with with ND (no choice) added in (I understand these are approximations). Regards, Dennis
 
Hi Dennis

Just be very careful working in manual. I did a wedding in a Church that had huge windows on one side and switched from auto to manual ...the shutter on the darker side was happy at 1/50th and the iris was F2.8 I think..the readers then came up to the lectern on the sunny side and I swung the camera around still in manual and the iris shot to F10.8 and being in manual the shutter stayed where it was ...exposure was still OK but the IQ was terrible compared to the previous shots ...if you stay in manual and move to different lighting flip the switch back to auto so the camera can adjust the shutter itself or manually adjust the shutter so the iris doesn't close so much...makes a huge difference!!

Regarding low light shutter it won't change any lower than 1/50th in full auto ...to go lower you have to do it manually ...if it's at 1/500 in sunlight and you walk into a dim room the cam will drop the shutter to default only, no lower ..that's your baby if you want to shoot at 1/25 or 1/30 to get better low light.

Chris
 
ChrisHarding said:
Hi Dennis

Just be very careful working in manual. I did a wedding in a Church that had huge windows on one side and switched from auto to manual ...the shutter on the darker side was happy at 1/50th and the iris was F2.8 I think..the readers then came up to the lectern on the sunny side and I swung the camera around still in manual and the iris shot to F10.8 and being in manual the shutter stayed where it was ...exposure was still OK but the IQ was terrible compared to the previous shots ...if you stay in manual and move to different lighting flip the switch back to auto so the camera can adjust the shutter itself or manually adjust the shutter so the iris doesn't close so much...makes a huge difference!!

Regarding low light shutter it won't change any lower than 1/50th in full auto ...to go lower you have to do it manually ...if it's at 1/500 in sunlight and you walk into a dim room the cam will drop the shutter to default only, no lower ..that's your baby if you want to shoot at 1/25 or 1/30 to get better low light.

Chris
Click to expand...

Hi Chris,
Very good cautionary note particularly for relative novice like myself. Your example of rapid lighting changes at wedding (and impact on IQ when in manual ) has similarities to race car events I film--cars moving in and out of bright sun and shade, clouds moving over sun, etc. Plus it is not like we are in a studio setting where we can redo a shot (despite cost penalty) if necessary--we get one shot.

Would appreciate comments on my evolving technique given my level of experience and rapidly changing lighting conditions at races. I have experimented quite a bit with shutter speed impact on motion blur and "natural appearing" motion look. For racing events I find that race car motion appears natural even at 1/500 and motion blur is minimal. That does seem counter intuitive that I do not see strobing or anything at high shutter speeds--I have also filmed spinning ceiling fans and there I can see strobing and other "unnatural" motion look. So from what I learned in this thread, I am thinking I will put camera in manual mode, set shutter speed to maybe 1/250, put on polarizing or ND filter, set iris to push auto, do a manual white balance, but leave focus in auto setting (just in case far to near movement of cars exceed depth of field for manual focus setting). I will check iris display for sun and shady portions of track and verify it stays more open than f/6.4 or thereabouts. With those settings what could have I forgotten that could cause a problem? Dennis
 
I didn't even realize how the shutter speed would change in auto mode since I don't use it much. But the whole not enough built in nd with this cam is a surprising shortcoming from Panna. I mostly use this cam outside and generally just leave some sort of filter parked on it, but if you need to add or remove the filters much, it is a PITA. The scenario that Chris mentions would be pretty frustrating; the last thing you want in the look of your video is a huge change in the look mid-clip. I have toyed with moving on from the 40, but for a very light and compact cam that can really deliver great IQ at a reasonable price, I'm not so sure there are any better options despite some issues. When first announced, I was pretty hyped up on the AC-90 until I realized it was closer in size to a HPX170.

Grant
 
Hi Grant

Sadly at that wedding the image quality changed and it was fairly seamless but you can see the image deterioration but probably the bride won't even notice it Yeah I got excited with the AC-90 initially but after finding out that there is no auto level control on the XLR audio like the HMC40/80 has it was scratched off my list.

Dennis, I doubt whether people will even notice moving stuff like fans or vehicle wheels at higher shutters so it probably a lot better to keep the shutter high and the iris low and get a decent image rather than get a really bad image and "correct" motion. The safest way to get the shot in manual is to let the camera get the shot in full auto and then switch to manual and fiddle and tweak. There is nothing wrong when working in bright light to add an extra ND filter..It has already been said that the AC-90 when being used outdoors needs an ND filter

Chris
 
Gentlemen, Thank you again for all the information and advice which contributes a lot to my improving camera skills. Regarding the HMC40 itself, admittedly I have no basis for comparison, but when I do things correctly I am still impressed with IQ. The small form factor is one reason I bought the HMC40 and it provides a great combination for me. My lack of experience/skill continues to be the limiting factor, not the camera. Regards, Dennis
 
Glad to help, and yes, when used properly the HMC40 produces impressive imagery. Best of luck on your journey to improve your skills!
 
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