Digital ND filter question xa10

[Jeff Harper]

Are you referencing the ND filter entry under "External Controls"? If so, that entry has to do with whether the camera has an external switch to control the ND filter. It does not specify what type of ND filter it has.

I noticed they also say the camera has no switchable MF/AF switch. That is true, but not really accurate. There is a button that serves the same purpose, so they should have noted that.

[Jeff Harper]

The ND filter is ACTIVATED digitally for sure. But that doesn't mean the actual filter is digital. A digital ND filter would not be a ND filter, it would be a fake ND filter.

[Rainer Halbich]

Originally Posted by Jeff Harper

The ND filter is ACTIVATED digitally for sure. But that doesn't mean the actual filter is digital. A digital ND filter would not be a ND filter, it would be a fake ND filter.

That is what I am trying to figure out, If it is a "FAKE" ND filter, how does it work?

I know it is not optical.

[Rainer Halbich]

Originally Posted by Jeff Harper

The ND filter is ACTIVATED digitally for sure. But that doesn't mean the actual filter is digital. A digital ND filter would not be a ND filter, it would be a fake ND filter.

If it was a optical ND filter you will hear it changing for sure, even if it has a digital activation.

AND, if it was optical you won't be able to have the "in between" ND settings. That is why I referred earlier to a very unrealistic 20 ND filters.

[Jeff Harper]

It might be a seemingly logical assumption that the ND filter is fake, and you might be right. But the assumption is still based on presumptions that may or may not be true. In other words, you (we) can guess what is happening inside the camera, but we cannot know without more information.

More information is why you posed your original question, of course, but the question was based on the assumption the ND filter is digital. I admit you could be right, but we just don't know.

[Richard Stone]

The Canon UK website specifications for the XA10 describe the ND filter as "Built-in gradation filter (Auto or off)". I would guess that this is some sort of graduated optical filter which rotates in the optical path to give more or less effect. If the filter has a "clear" position then it could always be in the optical path and need never be switched in and out.

Canon XA10 - Professional Camcorders - Canon UK

[Don Palomaki]

Canon Professional Network - Canon XA10: at Canon Europe
calls it: "... a built-in, automatic graduated ND filter."

Sure sounds like a physical filter to me. Graduated probably just means it has areas of different density.

[Rainer Halbich]

[QUOTE= I would guess that this is some sort of graduated optical filter which rotates in the optical path to give more or less effect. [/QUOTE]

Makes the mist sense so far, but what makes more sense to me is if the ASA or ISO sensitivity is reduced.

If it is a rotating filter the one side of your footage would be darker than the other side.

[Kawika Ohumukini]

Apparently some of the Powershots have a physical ND filter that moves in and out of the opening. I guess if there's room for something like that in the XA10 then it's possible it has two of them. I sent an email to Canon asking but that may fall under trade secret category. Cheers

[Don Palomaki]

If it is a rotating filter the one side of your footage would be darker than the other side.

That presumes a uniform gradient filter rather than a filter with steps (segments) of uniform density. Think of slices of pizza, with each slice being a different density. You rotate the filter to bring in the appropriate density slice. That would be an approach.

FWIW: Gradient ND filters are sold for the specific purpose of modifying exposues such as reducing sky exposure relative to areas below the horizon.

Playing with ASA/ISO sensitivity presumes a CCD/CMOS element with variable sensitivity (e.g., photons per electron), which is different from adjusting gain of the circuits that read the CCD/CMOS.

You cannot change the ISO/ASA of a piece of film, that is determind by the the chemistry of the film emulsion and the standred used to determine ISO. However, you can expose that film at any ASA/ISO you like, and then try, by varying the development time, temperature and developer, to get a usable image on the film.

To use a photographic comparison;
CCD/CMOS sensitivity is like film speed.
Gain is like push processing film
Grain is a combination of pixel pitch, electronic noise, and variations in individual pixel sensitivity
Aperture is aperture
Shutter speed is like shutter speed (although it may be implemented differently)

[Rainer Halbich]

Originally Posted by Don Palomaki

You cannot change the ISO/ASA of a piece of film, that is determind by the the chemistry of the film emulsion and the standred used to determine ISO. However, you can expose that film at any ASA/ISO you like, and then try, by varying the development time, temperature and developer, to get a usable image on the film.

To use a photographic comparison;
CCD/CMOS sensitivity is like film speed.
Gain is like push processing film
Grain is a combination of pixel pitch, electronic noise, and variations in individual pixel sensitivity
Aperture is aperture
Shutter speed is like shutter speed (although it may be implemented differently)

I just want to mention that I have shot on supper 16mm film before, I understand these things.

Keep in mind that you get different films with different sensitivity, when I expose to film I expose according to the ISO of my film in my Arri SRII and I use the 1-10 zone system to refine my exposure. I don't really understand how you expose at any iso, it makes no sense to me or I did not understand you.

What I don't understand is how a DSLR can adjust its ISO but a Digital video camera can't. Film cant change ISO just like that, but the xa10 is a digital camera, this should not be a problem.

Just a interesting fact: a film camera has a spinning shutter and a digital camera does not, because of this you can get double the exposure from a digital camera without loosing any frames.

[Don Palomaki]

Movie film is a series of single exposures on a strip of film. The film moves past the gate for each exposure. If I recall correctly some cameras did allowed the film to be backed up a bit to allow a multiple exposure, I think this was mainly for what was a lap dissolve (transition) between clips.

What I don't understand is how a DSLR can adjust its ISO but a Digital video camera can't...I don't really understand how you expose at any iso

ISO is a rating of the film based on a standard - so much light for so much negative density with specified processing. It is used to communicate to the film user how much light on the film is needed to reproduce the specified density in the film. The digital camera has replaced the film with a sensor (CMOS or CCD) and a RAW file on some form of storage media (e.g., SDHC card). And digital signal processing has replaced the developer.

My understanding is that the ISO change is not a change to the physical film, CCD, or CMOS, it is really a change in the exposure determining process that takes the "light meter reading" and based on the selected ISO determines the exposure settings; i.e., shutter, aperture, ND filter, and (for digital photography) gain.

In an auto metered still film camera) you can dial in a different ISO setting, and the camera will expose the film at what it thinks is the optimal exposure for the new ISO rating. It may actually be under exposed, or over exposed compared to the film manufacturers nominal specifications. Thus, I could say that I expose ISO/ASA 100 film at ISO 200, or I could that I underxposed ISO 100 by one stop. You can use a separate light meter to obtain similar settings.

Video does not have a legacy of using ISO thanks to real time feedback on exposure. ISO/ASA ratings exist in part to facilitate meter readings to calculate satisfactory exposures in adance because with film you had to wait for it to be souped before you knew if the exposure was right. The skill was in knowing the properties of the film and the scene to adjust the exposure and processing as necessary if the photographer wanted to achieve something other than the film makers standard result.

[Tom Hardwick]

I'm with Richard Stone on this - there's no such thing as a digital ND filter. Negative gain comes close but it's not really the answer because the laws of optics show that you mustn'ts shoot at apertures smaller than f/4.5 or so if you want to avoid the softening effects of diffraction and you're using a tiny 1/3" sensor as this Canon does.

You can bet your dog's life on the fact that if a camcorder doesn't have a manually operated ND filter switch on the lens barrel then (undocumented, generally) internal ND is being added. I first saw this on Canon's Super-8 cameras way back in the 70s and it's been a tried and tested way of keeping the iris blades wide and the picture sharpness up.

Bear in mind that the v'finder aperture readout is an extrapolation of ND + iris blade position. You may well be told you're shooting at f/5.6 but that's because the camera's actually shooting at f/2.8 with 2 stops of light being soaked by internal ND.

It's pretty easy to see the ND filter at work if you look down into the lens, and my Panasonic MX300, SD900, Sony PDX10 and so on have all had undocumented ND and unreliable aperture readouts.

Rainer said, 'If it is a rotating filter the one side of your footage would be darker than the other side', but of course when the filters in the same physical place as the aperture blades this just isn't so.

tom.

[Don Palomaki]

On can of course run some simple tests to help identify what is happening.

For a fixed shutter speed, a uniform target field and changs in illumination
Changes in physical aperture will result in a change in DOF.
Changes in the form of a real ND filter at the same aperture will result in a change in exposure without change in DOF.
Changes in the form of gain adjustments or other DSP will result in changes in the grain and noise floor of the video.

Use a uniform target such as a white or gray card to evaluate noise floor.

[Tom Hardwick]

What's this camera got - a 4 to 40mm lens (or thereabouts?) Even at full tele it's going to be mighty difficult to measure dof changes, after all, a 40mm f/2.8 lens is not noted for its differential focus capabilities.

Much better to look down into the lens using an LED light and watch what's happening as you vary the iris control wheel.

tom.