Why no built-in ND filters?

I am about to set out this "simple" question, in the hope that, in so doing, I will suddenly get the answer myself (as often happens with me!).

Why don't digital cameras offer built-in ND filters? In other words, why can't the electronic eye just be less sensitive and need a longer exposure? Is it because the technology of the chip means it produces too much noise with long exposures?

I get that you wouldn't see the ND-ness in the viewfinder, but that'd be a good thing, surely....

Maybe I am missing the point somewhere. Enlighten me.

The original Q has a built in ND filter.

The Q does have one

Ah, beat me to it I see

That was close

OK, so it CAN be done, yet I have never seen it mentioned in the dslr press.

I ony started thinking about this as I have decided I really would like to get a set of NDs.

Hmmm, it seems the ND filter on the Q is built into the 01 or 02 lens and not the actual camera.

Quite a few compacts have built in ND filters - probably because the smallest aperture is only f/8.

I wonder why most Dslrs don't have panoramic sweep. Some say it's a bit rough/crude compared to dedicated software that does the job but it'd be better than not having it I think.

the one on the Q is built into the lenses, not the camera.

going below the base sensitivity on the sensor would cost dynamic range, and as we have all no doubt observed, digital sensors behave better with underexposure than they do with overexposure.

It doesn't necessarily require an ND filter, a lower ASA setting would surely do the job?

but the base ISO is a physical property of the sensor.

I can't remember if any Pentaxes do it, but occasionally you see DSLRs with "expanded" ISO at both ends of the range, accessible via a custom function. This is the same thing, and it costs dynamic range.

Lower ISO can be as noisy as a high ISO (higher than the noise you get at 800 or even 1600 on my K5) which is why it's in the extended ISO range, there's an optimum setting for ISO vs noise which varies from sensor to sensor, minimum noise is not at 100 or even 200 with most sensors.

The ND filters in the Q lenses is so that you can use a wide aperture (to minimise DOF) in bright Sunlight as it's minimum ISO is 125 and it's fastest shutter speed is 1/2000th of a second.

For the opposite reason (increasing DOF in bright light with flash) you can use ND filters for that too.

http://strobist.blogspot.co.uk/2010/06/using-nd-filters-to-kill-depth-of-field.h...

Though as the Q can sync at 1/1000th of a second it's less necessary for this.

I use variable ND filters, the cheapest I have found with negligible colour cast are those from 7Day Shop

http://stores.ebay.co.uk/Go-to-7dayshop/_i.html?_nkw=variable+nd&submit=Search&_...

Another tip is to buy the filter to fit your largest lens and use much cheaper step up rings to fit the filter to your smaller lenses.

Lower ISO can be as noisy as a high ISO (higher than the noise you get at 800 or even 1600 on my K5) which is why it's in the extended ISO range, there's an optimum setting for ISO vs noise which varies from sensor to sensor, minimum noise is not at 100 or even 200 with most sensors.

The ND filters in the Q lenses is so that you can use a wide aperture (to minimise DOF) in bright Sunlight as it's minimum ISO is 125 and it's fastest shutter speed is 1/2000th of a second.




Not the case on any DSLR I've ever had

also the small form factor of the Q means that apertures smaller than about f/5.6 suffer from a loss of image quality due to diffraction.