How exactly does a digital ND work?

Does it lower the ISO of the image sensor?

I know that it does not adjust the shutter speed or the f stop.

As far as I know there is no such thing as a digital ND filter. I believe the XA10 has optical ND filters which are moved into the light path between f4 and f4.8 if the 'ND Filter' setting is set to automatic.

Digital ND filter is an interesting concept, if by digital you mean electronic. It could fuction by changing the gain of the circuits that read the sensor. Alternatively it might function a bit like an LCD display where in by changing the bias you can change the transparency. Think in terms of the photo-sun lenses used in eye glasses.

As far as I know there is no such thing as a digital ND filter. I believe the XA10 has optical ND filters which are moved into the light path between f4 and f4.8 if the 'ND Filter' setting is set to automatic.

Impossible, if it is true what you are saying it means that this camera must have like 20 different ND filters and it manages to switch between all of them without making a single noise and without distorting the image.

Why do I say 20 ND filters? Because if it was only 3 optical ND filters the switch between them would be very obvious.

This camera has a digital ND filter not a optical ND filter.

Digital ND filter is an interesting concept, if by digital you mean electronic. It could fuction by changing the gain of the circuits that read the sensor. Alternatively it might function a bit like an LCD display where in by changing the bias you can change the transparency. Think in terms of the photo-sun lenses used in eye glasses.

So what you are basically saying is that the ND filter on the xa 10 is basically the same as negative gain?

Then why don't they just call it negative gain instead of a Digital ND filter?

I have 2 theories to this.

First theory, the camera lowers the ASA or the ISO sensitivity of the cmos sensor.

Second theory, it uses a special static glass which has the ability to change its Neutral Density without moving, but I am not sure if that would count as digital.

Impossible, if it is true what you are saying it means that this camera must have like 20 different ND filters and it manages to switch between all of them without making a single noise and without distorting the image.

Why do I say 20 ND filters? Because if it was only 3 optical ND filters the switch between them would be very obvious.

This camera has a digital ND filter not a optical ND filter.

The ND filter option in the menus is only available in aperture priority and manual modes i.e. when you select the aperture (and ND filter). I don't think the camcorder ever switches ND filters in automatically during recording. As for noise, the motors that change the aperture and focus the lens are silent (at least to me!) so I don't see why the motor that controls the ND filters shouldn't be. I have read somewhere that if you shine a torch into the lens of a Sony HVR-A1 you can see the ND filters switch in when you adjust the aperture but I can't find the reference now. I think that if Canon had really invented an electronic ND filter they would list it as a feature.

Possibly the same technology used in auto darkening welding hoods. So yes, there can be digital ND filters. The only thing is, my AD welding hoods have a greenish tint so they aren't strictly neutral in that they do affect color reproduction.

-gb-

So what you are basically saying is that the ND filter on the xa 10 is basically the same as negative gain?
...

No. I am speculating as to what a "digital ND filter" might be were there such a thing, considering the way marketing folks occasionally misuse technical terms.

Stop and think about light sensors (CMOS or CCD) for a minute or two. The sensor latitude is driven by its dark current and its saturation point. It cannot meaningfully "see" anything darker than its dark current or brighter than its saturation point. And further its linearity may have rate effect (slew rate) limitations as well, sort of like reciprocity with film.

Playing with gain will effect the final image brightness, but will not be the same as a true ND filter with respect to keeping the light reaching the sensor within the desired sensitivity range of the CMOS/CCD. Playing with the physical aperture woud come closer to ND-like effects with respect to exposure, but has other effects on the image (e.g., depth of field). Playing with shutter speed is somewhere in between and its effect would depend in part on how the shutter speed is implemented within the camera in question.

At a 60i frame rate there is plenty of time to drop a small physical ND filter into the light path between successive fields on demand, all it needs to be is like a partly transparent between the lens leaf shutter blade.

At a 60i frame rate there is plenty of time to drop a small physical ND filter into the light path between successive fields on demand, all it needs to be is like a partly transparent between the lens leaf shutter blade.

I really doubt that, I have the PAL version and I record mostly 25p.

Keep in mind that the iris is not a replacement for the spinning shutter on a film camera.

I know that 1/50 shutter speed is considered as the standard SS when you record 25p, this is because a real film camera with a 180 degree shutter will have a shutter speed of 1/50 if you shoot at 25p.

The thing is, a film camera needs a rotating shutter to flick to the next film slide and a digital camera doesn't. This is why I mostly record with a 1/25 Shutter speed.

Lets do some basic maths: 1/25 x 25 frames = 25/25 = 1 second of footage with CONSTANT exposure to the CMOS sensor, if you go any slower the image will start to jitter because it has to duplicate the frames.

This means that if there is really a optical ND filter in the xa10, you should be able to see it in your footage when you change the ND filter while recording at 25p with a SS of 1/25.

I tried it out and I can't see any distorted frames or images in my shots.

Myth Busted...

Specs for the camera say it has a "built-in gradation filter". That sounds like an actual physical filter.

Specs for the camera say it has a "built-in gradation filter".

A built in graduation filter can also be a built in "Digital" graduation filter.

PAL, with the slower frame rate, may actually give a bit more time in which to drop a physical filter into the light path unnoticed.

Considering the speed of small mechanical shutters, it should be possible to drop a filter into place in a small fraction of a field duration. For example, the rather large focal plane shutter in a 35mm still camera can move the full frame width in less than the maximum flash synch speed, on the order of 1/250 (0.004 seconds) with good current SLRs. Think how fast it can move the much smaller distance require if in the camcorder lens.

The physics of photon-to-charge convesion in CCD/CMOS argue against using gain as a viable ND filter mechanism, although gain can be used to adjust image brightness. Keep in mind that a ND filter is intended to adjust the brightness of the light reaching the CCD/CMOS (or film), not how the light reaching the CCD/CMOS is interprreted.

A built in graduation filter can also be a built in "Digital" graduation filter.

It could mean that, but seems unlikely. I can find no reference anywhere on the web to a digital ND filter. Do you know of other cameras that use one?

PAL, with the slower frame rate, may actually give a bit more time in which to drop a physical filter into the light path unnoticed.

You missed my point.

What I am saying is if you record with a 1/25 shutter speed @ 25p, you Sensor will have "CONSTANT" exposure.

When I say CONSTANT I mean, the sensor makes use of 100% of the possible exposure time without duplicating any frames. In other words, there is NO TIME for a ND filter to jump into frame without seeing it in the footage.



Let me try again with two examples.

First example (Max shutter speed for a film camera with rotating shutter) (1/50shuttersped @ 25p)

1/50 x 25 = 0.5 seconds of expose for one second of footage.
(The other 50% of the light goes through the viewfinder.)


Second example: (Max shutter speed for a DIGITAL camera WITHOUT a spinning shutter, just like the xa10 or any other digital video camera)

1/25 x 25 = 1 second of exposure for ONE second of footage. And 0 time for a optical ND filter to jump into frame.

It could mean that, but seems unlikely. I can find no reference anywhere on the web to a digital ND filter. Do you know of other cameras that use one?

Yes,go to camcorder reviews/tests and comparison with test images and technical data (http://camcorder-test.slashcam.com/compare.html) and select the Canon xa10, scroll down to ND filter.

The canon xf100 is also Digital.

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.

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.

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.

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.

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.

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 (http://www.canon.co.uk/For%5FHome/Product%5FFinder/Camcorders/professional/XA10/index.aspx?specs=1)

Canon Professional Network - Canon XA10: at Canon Europe (http://cpn.canon-europe.com/content/product/camcorders/XA10.do)
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.

[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.

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

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)

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.

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.

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.

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.

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.

What I don't understand is how a DSLR can adjust its ISO but a Digital video camera can't.

gain = ISO. Same basic thing.

I would say that gain is more like processing time,0 dB gain representing the nominal rcommended developer and processing time; increased gain being a bit like push processing.

ISO would correspond to the sensitivity of the sensor picture elements; e.g., aperture, shutter speed, and incident light on the subject,required to produce an optimal imge at 0 dB gain. Of course traditionally video does not speak to ISO, more often the ratig has been the aperture required to produce something like 50 IRE from 1000 LUX on a 50% gray card at 1/60 shutter (or somethign like that, the figures I gave are not actuals to my knowledge).

A bit more on the ND thing.

If we set the camcorder to Manual and manual exposure mode we get the Aperture, shutter, and gain displayed and can adjust them. They can be adjusted independently. The ND setting is coupled with the aperture setting, not separate.

As we adjust the aperture we find that after f/4 we get steps in ND (and marks for 1/2, 1/4, etc.) until we run out of ND filter range, then the aperture stops continue to f/5.6 etc. We can see changes in image brightness as we move between ND setting marks inplying that the filter effect is continuous, e.g. a ND wedge that moves through the light path.

It all make sense now. It is one less thing the user has to manage, fitting for a camcorder at this price point, and I am content to NOT have to deal with turning the ND ON/OFF it for the shooting I do..

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.

I can only see the iris working, I don't see a ND filter in the lens.

The xa10 gives the F-stop / ND value. it is not combined into the f-stop reading as you say it is.

I agree, a rotating ND filter directly behind the iris is a possibility, but if this is true is must be a EXTREMELY close to the iris and I doubt that this is the case. This will also need to be a very large graduated filter because the effect will be different if the iris is wide open vs a small iris. A larger filter can make it more gradual. It is a possibility but I feel 20% positive about the theory.

gain = ISO. Same basic thing.

Are you sure? It makes sense to me bacause more gain = more niose and more litht, just like hight iso + more niose and more light.

But why not call it the same thing?

Yes, ISO and gain mean the same thing for our purposes. Why different names? Who knows. Wikipedia will have the answer, for sure.

ISO would correspond to the sensitivity of the sensor picture elements; e.g., aperture, shutter speed, and incident light on the subject,required to produce an optimal imge at 0 dB gain. Of course traditionally video does not speak to ISO, more often the ratig has been the aperture required to produce something like 50 IRE from 1000 LUX on a 50% gray card at 1/60 shutter (or somethign like that, the figures I gave are not actuals to my knowledge).

I am not sure about your ISO theory, According to me the ISO is ONLY the light sensitivity of the film/ digital image sensor. It has nothing to do with SS, Aperture, ND value, WB or frame speed. Or maybe I don't understand what you are saying?

A bit more on the ND thing.

If we set the camcorder to Manual and manual exposure mode we get the Aperture, shutter, and gain displayed and can adjust them. They can be adjusted independently. The ND setting is coupled with the aperture setting, not separate.

As we adjust the aperture we find that after f/4 we get steps in ND (and marks for 1/2, 1/4, etc.) until we run out of ND filter range, then the aperture stops continue to f/5.6 etc. We can see changes in image brightness as we move between ND setting marks inplying that the filter effect is continuous, e.g. a ND wedge that moves through the light path.

It all make sense now. It is one less thing the user has to manage, fitting for a camcorder at this price point, and I am content to NOT have to deal with turning the ND ON/OFF it for the shooting I do..

That is all good and I also think it is awesome, but it does not answer the question.

If this is a digital ND filter which lowers the iso/gain, many people will fry their sensors because they filmed the sun rise or sunset thinking that it is a optical filter...poor camera sensor...

I can only see the iris working, I don't see a ND filter in the lens.

The xa10 gives the F-stop / ND value. it is not combined into the f-stop reading as you say it is.

All the camcorders I've looked at that have no external ND switching use internal ND Rainer. I'd be very surprised if the XA10 bucked the trend. But I haven't looked at this camera so I didn't list it as one of these.

Any internal ND placed at the iris blade position can be tiny. Even when wide open it still only needs a tiny filter. And it doesn't have to be graduated - the ND is just inserted into the light path a little bit at a time. It's completely out of focus, as are the iris blades of course.

tom.

Rainer - you started this thread asking about a 'digital ND filter' and I thought we'd all talked you out of it. Obviously we haven't.

Rainer - you started this thread asking about a 'digital ND filter' and I thought we'd all talked you out of it. Obviously we haven't.

One day when AVCHD becomes outdated I am going to strip my camera and I am going to find out.
I will report back in 5 years.

For now I will assume that it has something to do with the sensor sensitivity, because I don't want to burn my sensor when I record the sunset.

Ranier, I believe that in science they say that the simplest explanation is the most likely the correct one, or something to that effect.

In this case, the most likely and commonsense approach would be that Don is correct. First, no one here, so far, has ever heard of a ND filter that is purely electronic, but I understand that just because we've not hear about it does not mean it is not so. But the very idea sounds, well, to not seem logical, at least to me, but I'm no expert, so what do I know.

Secondly, if this were a new type of ND filter that operates the way you fear that it does, Canon would likely mention it, if not brag about it. It would likely be well known.

Thirdly the characteristics of the ND filter on the XA10 seen to be that of a genuine ND filter. When it kicks in the images look like a real ND filter is being used. If it acts like a rabbit, and smells like a rabbit, it is probably a rabbit.

Fourth, if the sensor was particularly more sensitive and prone to danger from sunsets, etc, then Canon would probably mention it, because they would not want to deal with the many returns of damaged cameras.

Long story short, the safest, most logical bet is that the camera uses a traditional ND filter. Just because you can't see it doesn't mean it is not there.

Just turn it off, buy a variable ND filter or a regular one, and you won't have to worry at all.

Yes, ISO and gain mean the same thing for our purposes.

Not quite, except perhaps in the narrow taxonomy of the DSLR that has morphed the definition of ISO. In the DSLR they use ISO to refer to how the image exposure was calculated (see the past paragraph below) and factor in DSP results as well.

ISO ~ sensitivity of the CCD/CMOS in absolute terms (e.g., microvolts per photon)
Processing time/temperature ~ Gain, 0 dB gain being the recommended developer time/temp point.for the rated ISO, or amplification of microvolts in the pixel sensor.

The primary reason for ISO is to allow metering of light and then setting exposure for the optimal result on film. You need the meter and ISO because with film there is no instant feedback as you get with a camcorder in the viewfinder and zebra (if you use it). You have to soup the film to see the result.

Photons reaching the film/CCD/CMOS pixel is a combination of the aperture, exposure time, light on the subject, subject reflectivity, and any losses due to filters. It is a bit easier than speaking in photons per sqmm for, say, 20 IRE.

Because you can translate aperture and shutter speed for, say 20 IRE, you can compute an equivalent ISO.

Not to be confused with people exposing film at a different ISO and then push or pull processing to obtain the negative density they want, or art effect they are trying to achieve.

Don, on my DSLR type camera, I use the ISO setting exactly as I use the gain on my videocamera, the less the better. In that way it is the same thing for us, and for the many of us that don't know the differences between the two, the long and short of it is that they are the same thing, for practical day to day use, right?

I raise the gain on my Xa10 just as I will raise the ISO on my GH2, under the exact same conditions: when I need a brighter image and I can't increase exposure any further and I'm at the slowest advisable shutter speed for the conditions I'm shooting in.

I'm convinced this is a physical filter that moves completely in. I zoomed all the way in and put a rectangle HDV-Z96 LED light facing slightly off to the side facing into the lens. When I went one click past f/4 I could see a reflection of my entire rectangle light appear. When I went back a click the light reflection disappeared. It appeared to be a filter rotating from the bottom up to cover the opening completely. As I continued to increase the f-stop the iris didn't appear to change size so I'm wondering how they're handling the continuous change.

Kawika, well done sir. Excellent work.

The reflection you see is very common and it's because the internal NDs aren't coated (I know not why, they're another element in the multi-element lineup and need to be the best they can be). If the iris didn't appear to change size as you varied the f stop then the ND must be varying - even if you can't see it because of the reflections.

Ranier, I believe that in science they say that the simplest explanation is the most likely the correct one, or something to that effect.
Almost - "the simplest explanation that fully explains the observed facts is the most likely the correct one" is how it's normally expressed, and it's Occams Razor. (See Occam's razor - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Occam's_razor) ) But do note the "most likely" - SOMETIMES it may let you down!

As far as this goes, then forget about "digital ND". The concept can't work beyond a small amount (which is negative gain) and I'll try to explain why.

Increase the light incident on a chip and the output signal will increase - up to a limit when saturation is reached. There will be a certain maximum output voltage that can't be exceeded no matter the light intensity. For reasons of best signal-noise it's normal to operate the chip just below this light level to normally get full amplitude. More light would mean clipping, less will mean more gain needs to be used - hence a worse s/n figure.

So, if the light intensity doubles, then adding a stop of optical ND gets you back to square one. Don't add it and we're into clipping - and there is nothing that can then be done electronically to simulate the ND filter. That's why "digital ND" is a physical impossibility.

(Practically, there is a little headroom, hence the possibility of using a little negative gain, -3 or 6dB. Even this will likely come at the expense of highlight handling though.)

The "Canon A1 Digital" was a Hi8 camcorder from the early 1990s. The Digital in the name was with respect to the internal DSP. The read from the 1/2" CCD was analog, the signal on tape was analog, and all outputs were analog.

In the case of the XA10, digital refers no doubt to the method of controlling the ND filter. the "digital control" allows the camcorder to control the iris up to the point where the ND filter enters, stop iris change while the ND filter is changing value,. and result iris change when the ND filter is maximized. Easy to do digitally with stepper or servo motors, not as easy with simple mechanical schemes.

The "ISO rating" determines exposure required to produce a specified image based on certain exposure processing assumptions. The digital camera revolution has dumbed things down for Joe and Jane Sixpack in the transition from chemical to electronic photography. Gain converts the latent image on the CCD/CMOS into voltage, much as processing converts the latent image on the emulsion into silver (density) in the negative. Changing gain is like push/pull processing.

If you under expose an image, but increase developing time/temperature you can get a negative that shows a "normal" density range, but the density curve and grain structure may be different (typically larger gain and poorer shadow detail). Add gain to underexposed video and what do you see - usually more image noise and less satisfactory shadow details.

However, all this is an academic exercise in self abuse. Shoot and edit video, have fun, and make your clients happy with the end result. What counts is not the specifics of the technology but the end result on the end users' display of choice.

Here's a video I made of the action. It's at normal speed, slow and slower. I don't know exactly what it all means but here it is. Cheers.

Canon XA10 Internal ND Filter Test on Vimeo

p.s. The aperture changing size is actually me going past f/4 to f/3.7.