I can not get HD out of the HPX300

Cees Mutsaers

Cees Mutsaers

Veteran
My skills with the HPX300 are still very limited. Therefore i am not able to get the crisp footage out of it which I have seen on this forum. Ok I will give you an example (http://www.vimeo.com/15737268). Make it full screan to judge it. The focus was set ok (also back focus is ok), i am sure because I checked it many times before shooting. To me it looks very very soft. The settings were :

Scenefile CINE D
Resolutie 1080
Codec AVC-I-100
DETAIL LEVEL +1
V DETAIL LEVEL +2
DETAIL CORING +5
CHROMA LEVEL -2
CHROMA PHASE 0
COLOR TEMP A-CH 0
COLOR TEMP B-CH 0
MASTER PED 0
A.IRIS LEVEL -3 (used manual iris)
DRS effect +3 (but this does not work in 1080 right)
GAMMA CINELIKE-D
KNEE high
MATRIX Cinelike
SKIN TONE DTL ON
V DETAIL FREQ THIN
Zebra 1 70%
Zebra 2 90%
FRAME RATE 25p
SHUTTER OFF
GAIN -3 dB
white balance manual/ white
Flash band compensation OFF
ND 2
iris 8

What is optimum iris setting of the HPX300 with respect of resolution?
 
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Hi Cees,

with 1/3 " Native HD sensors like the 300 series the max F stop to go to is F4, beyond that the picture can start to degrade (soften due to Iris diffraction). I try to keep it at F4 or lower if i can, i was shooting
by the sea here in the Uk recently and i was at max Nd + polariser and i barely managed to keep it low.
I got this from the excellant article by Alan roberts on the HPX300 for the BBC.

Another way to deliver crisp video is how you export to say Vimeo or Youtube.

I use H264 and if its 720p i keep it at 8Mbit/sec for 1080 i use 20Mbit/sec (or lower if file size gets a little crazy), im using Edius 5.5 but it should be similar for other editors.

p.s. i just noticed you said you were using F8...way to high mate.

cheers Andy
 
Hi Garion,

Thanks for your reaction.
So the hpx300 gives only maximum resolution betweeen f/4 and f/1.6 ??? Actually this is the first time on this forum I hear that the iris window to get HD results is so small !!! If this is true than indeed my F/8 is way to small.
It also means that this cam is not really suitable for making high depth of focus shoots (I know most of you even don't want this but sometimes I do).
I used 20 Mb/s H.264 for export so that will not be the problem moreover in FC it looks exactly the same.
Can you send me a link to this article of Alan Roberts?


cheers
Cees
 
Hi there, i tried to pm you the link last night but it said you didnt have that turned on. F4 on the 300 is probably closer to f7.5-8 on a 35 mm slr but dont quote me.Im at work at the moment so havent got the link unless others have it to hand.

The smaller sensor affect both the field of view and depth of field. Now im coming from a photography background here so bear with me.

If you matched up the field of view on the 300 to an equivalent lens on an SLR, the 300 would need a much lower F stop to get the same DOF as the SLR.

In the scene you posted above on vimeo, if you zoomed in and focused on the distant buildings then pulled right back, all should appear to be in focus at F4. :)
 
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Hi Garion,

That is great info. I will reshoot all my footage at F/4 - F/1.6 and hopefully it will be better. I will also decrease the "detail corning" from +5 to +1, increase the "detail level" a bit from +1 to +2 and switch off the "skin detail" (by the way I thought "skin detail" worked the opposite way namely you get more skin detail when turned on but it is just the other way around, very confusing name). I will let you know about the results.

thanks again Garion :)
 
The BBC document says it is best to use up to f4 and f5.6 at the most, if you want shallow DOF you need it as wide as possible anyway. I tend to stick to this rule and have been very happy with my footage that I upload to you tube at 720p 5mbs.
 
Getting deep focus shouldn't be a problem with an HPX300/370... it's a 1/3" camera. Even at f/2.8, shooting wide-angle at 7mm, setting focus at 6 feet, everything from 3 feet to infinity will be in sharp focus.

You don't need to (or want to!) go to f/8 to get deep-focus wide-angle shots.
 
Thanks Barry you comfirmed what Garion explained me in this thread. I tried to get a high DOF in the shot and shot at f/8 - f/16 (like you do in photography) but I understand now that from f/4 and higher the resolution of the HPX goes down fast and it is even not necessary to get a high DOF (as i understand it is determined by the NA (numerical aperture) in DOF = lambda/(NA)square). Leaves the question in what circumstances do you use the f/5.6 - f/16 iris range ?, only as an emergency solution in cases when ND4 gives you still to much light and you can only give up some resolution? In this case you could also go to higher shutter speeds as a kind of solution right ?

Barry_Green said:
Getting deep focus shouldn't be a problem with an HPX300/370... it's a 1/3" camera. Even at f/2.8, shooting wide-angle at 7mm, setting focus at 6 feet, everything from 3 feet to infinity will be in sharp focus.

You don't need to (or want to!) go to f/8 to get deep-focus wide-angle shots.
Click to expand...
 
I would only go to f/8 on an HPX300/370 if shooting standard-definition, or in an emergency situation where the ND isn't enough.
 
Has nothing to do with CMOS, it has to do with the lens, and the size of the pixels on the sensor. The smaller the iris and the tighter you try to focus light, the sooner diffraction kicks in.

However, on the HVX200, the final overall resolving power isn't as high, so it can deal with some diffraction and still be performing at its sharpest. On an HVX, you can go to f/8 easily, and even f/9.6, before diffraction starts to become an issue.

If you want to see the severe effects of diffraction on an HVX200, try f/11 right before the iris closes. Not regular f/11, but f/11 plus a couple of ticks. Stop down the iris until right before it closes fully, and compare that to a shot at f/5.6, and you'll see a huge difference.

The HPX370's pixels are tiny tiny tiny compared to the HVX200's. They're about 1/4 the size, so diffraction kicks in about 2 stops sooner.
 
Ok lets see if I understand it. Diffraction at > f/4 deteriorates the MTF. If the pixel size is smaller, diffraction has a larger impact on the MTF. The pixel size is of coarse fixed in the HPX300 but buying a better lens should help?? Question is how far can you stretch the iris setting you still can get HD resolution, maybe one stop to f/5.6 at most ??? and this is probably not worth while buying a lens which is probably twice as expensive as the whole HPX300 ???

This higher sensitivity to diffraction of smaller pixels is probably also the reason why the HPX300 has one ND filter more than the HVX, so to prevent that you have to use iris settings > f/4.




Barry_Green said:
Has nothing to do with CMOS, it has to do with the lens, and the size of the pixels on the sensor. The smaller the iris and the tighter you try to focus light, the sooner diffraction kicks in.

However, on the HVX200, the final overall resolving power isn't as high, so it can deal with some diffraction and still be performing at its sharpest. On an HVX, you can go to f/8 easily, and even f/9.6, before diffraction starts to become an issue.

If you want to see the severe effects of diffraction on an HVX200, try f/11 right before the iris closes. Not regular f/11, but f/11 plus a couple of ticks. Stop down the iris until right before it closes fully, and compare that to a shot at f/5.6, and you'll see a huge difference.

The HPX370's pixels are tiny tiny tiny compared to the HVX200's. They're about 1/4 the size, so diffraction kicks in about 2 stops sooner.
Click to expand...
 
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Changing the lens won't change anything. We're talking about physics here. Squeezing light through a too-tiny hole (the iris in the lens) causes it to spray around loosely-focused. It has nothing to do with the HPX300, nothing to do with your particular lens, nothing to do with anything that you can control. Just don't stop down the lens that far. The smaller the pixels on the chip, the more sensitive the imager will be to diffraction, and the HPX300 has tiny pixels. That's what gives it great resolution, but it also makes it more susceptible to diffraction.

The larger the pixels on the chip, the more you can stop down the lens before encountering the limits of diffraction. With a 2/3" chip camera, the pixels would be 4x as large, and you could accordingly stop down more before diffraction started to limit your resolution. With the tiny pixels on the small chip, the effects of diffraction are noticed sooner.

There's really nothing you can do about it. Just don't go that deep in the f-stop range and you'll avoid it. The only way to gain more flexibility with the iris would be to buy a camera with bigger pixels (either something like an HVX200, or a larger chip like an HPX3100).
 
But the wavelength of visible light (400 - 700 nm) is way smaller than the smallest iris setting you can set, so I am surprised that the very small amount of diffraction you get has such big impact on the very small HPX300 pixels (are the pixcel just 3.84 * 3.84 microns if i did the math correct? ) ? I don't doubt you Barry just curious and want to understand the technology I am working with so I can use it to my benifit :))
 
Chromatic Abberation also comes into effect more with smaller chips and being stopped down, it is also mentioned in the BBC report.
 
Today I reshot everything keeping the iris between f/open and F4 and indeed the results are much better resolution wise (I also increased the detail level from +1 to +2, decreased "detail corning" from +5 to +2 and switched "skin detail" off (although the latter probably does not do a lot for what I was shooting). I am still not able to get the extremely sharp images I have seen here on this form from other members (for instance the animal shots Barry made when he tested the cam in Africa). Probably I have to improve my skill further. Anyway you all were a big help :))) Thanks again.
 
Faulty camera isn't too likely though; that should be rare. How about lens back-focus? If you're new to video you may not be aware of the need to set lens backfocus...
 
Back focus with the 300/370 can be a little touchy compared to other cameras. Get a good siemens star chart and have the iris near wide open for setting back focus for starters.
 
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