CFLs and UHF interference

[:Jerry:]

How about citing some facts Mr Hansen rather than some anti oil, anti capitalist, anti motor vehicle, **opinions**.

[David Hansen]

On Mon, 16 Jun 2008 13:12:10 +0100 someone who may be ":Jerry:" wrote this:-

I quoted several facts. However, you snipped them, presumably because you were unwilling or unable to counter them. Instead you responded with a little tirade. That may fool some of the people some of the time.

Unless some arguments replace the tirade you may have the last word. My last word is to point people at

which is a link from the page I have already quoted and read for themselves.

[:Jerry:]

No, you are citing opinion.

However, you snipped them, presumably

Because they were opinions, not facts.

Instead you

Whilst you only ever cite opinions that back your 'anti' agenda, and don't try and hide the fact that you are about as anti motor vehicle as it's possible to be without actually engaging in direct action - a simple Google groups search will turn up your opinions on 'those idiots who drive'.

"Welcome to the Web Site of Depletion Scotland. We are a group of individuals based...."

As I said, Mr Hansen cites opinion rather than facts, and at that, solely opinions regarding Scottish oil production...

[Arfa Daily]

All of what you say is quite true, but the colour temperature must be taken in conjunction with the CRI, which for a CFL is less than the ideal of 95 -

100, by quite a margin. It is this shortcoming, rather than the colour temperature, which gives rise to the 'sick' quality of the light, no matter how close it is to matching daylight, at any time of the day, in terms of colour temperature.

LED lighting suffers similarly, because again, like the individual phosphors in the tricolour mix used to coat the CFL's discharge tube, each individual LED colour used, has a narrow spectrum of output, giving rise to an overall 'peaky' spectrum, rather than the much 'smoother' ones of daylight and incandescent light.

Arfa

[Tony Quinn]

In message , Andrew Gabriel writes

Colour Temperatures out of which textbook? I've seen exteriors at 8000K at which Colour Temperature I needed gain in the camera.

[Andrew Gabriel]

Well, the sun isn't that hot. You can get colour temperatures that high by filtering out the direct sunlight which has more of the red components (e.g. in the shade), and just using the blue light scattered in the atmosphere (i.e. the blue sky). Generally when people talk of midday colour temperature, it's the average across the sky, but the splitting of the red and blue by the atmosphere can make it much more complicated when the object being illuminated can't see all of the sky.

[Mortimer]

That's interesting because I've found that twilight/dusk are actually very blue (ie higher colour temperature): if I white-balance my still camera off a sheet of A4 paper that's outside at dusk, tungsten interiors (real tungsten or tungsten-balanced CFL) look horrendously red. Using the same white balance in daylight (either sun or shade) also looks quite orange.

[The Natural Philosopher]

Thats true for dusk, but not sunset/sunrise.

Dusk is in any case a time when our own colour receptors start to pack in: we tend to see grey only.

Even more amusing was taking time exposures by moonlight: the film itself (pre digital) would give an overall green cast to the picture.

[Tony Quinn]

In message , Mortimer writes

Correct, they are .. it's the scattered light that does it. The broadcasters reading this will know that - the d-i-y types probably not.

[Andrew Gabriel]

See my other post about having to average across the sky. Of course, once the sun has set, you only have the blue sky as you are in the earth's shaddow (hence my reference to "just before twilight", or perhaps I should have said, just before sunset). That is unless you have clouds which can still see the sun and reflect the direct red path back to ground (i.e. "red sky at night")!

[Andy Champ]

I recall once many years ago waking up in the night, and looking out at the moonlit garden with the frost on the plants, getting out the tripod, and taking a picture. When I got it back I spent about 5 minutes wondering why the heck I'd taken a picture of the garden. All that nice silvery effect had gone, it looked just like daylight!

Not a touch of green though. I suspect it was Agfa slide film, as I usually used it because (a) cheaper than prints and (b) the mounts were nicer than Kodak.

Andy

[SpamTrapSeeSig]

In article , The Natural Philosopher writes

Reciprocity failure proportionately worse on some layers than others. AKA "crossed curves", although strictly speaking it's not the latter.

[Mortimer]

Yes, you need to be careful not to just trust the meter and expose as if it was daylight. I've been amazed with my digital camera to take pictures at dusk when it's quite hard to see details with the naked eye but find that a sufficiently long exposure can result in pictures that could easily have been taken on an overcast day during normal daylight.

Kodakchrome slide film seems to have a very mucky green cast to the shadows in under-exposed or night-time pictures. Agfachrome or Kodak Ektachrome are much better in that respect.

I wonder if some of the colour cast of moonlight pictures was down to the infamous "reciprocity failure" that film is prone to in very low light, whereby the normal rule that halving the aperture requires a doubling of shutter speed no longer works and the three emulsions respond differently to light. Mind you I once took some very long exposure shots (eg f11 for 2 mins on 200 ASA) of Christmas lights and other street scenes and didn't see any colour cast that couldn't simply be attributed to the non-tungsten street lights.

[John Rumm]

This page makes it quite clear why there is such a subjective difference:

[SpamTrapSeeSig]

In article , Mortimer writes

I forgot this was cross-posted away from UTB.

It's crossed-curves, not just reciprocity failure. R.F. means you have to increase long exposure times by a compensation factor (as you say), but of itself it won't cause colour casts.

The cast comes from a large number of other factors, including the illumination, temperature of the film, the change in UV content of the light (often filtered out however), and the fact that RP doesn't affect the emulsions identically for all of the colours.

If the above is a bit rough, I've forgotten much of it. I need to dig out my books on colour processes...

[Bill Wright]

I took a series of these and the processor went mad trying to balance them.

Bill

[Paul Ratcliffe]

I've seen 'em higher than that. 12000 and even 15000. Of course, it doesn't last very long.

[Tony Quinn]

Of course not - I wasn't suggesting otherwise - merely that the OP didn't have much real world experience of CT variations, as experienced by the typical OB racks man.

[dennis]

Shadows are always bluish from the scattered "sky" light. Sunshine gets redder as the sun gets closer to the horizon. The only time people notice the shadows are blue is in pictures of snow.

[The Natural Philosopher]

Yes, it was reciprocity failure. It would have been Fuji 400 negative film.

I remember also stopping to take a snap shot of an oil tanker against the sunset in Scapa Flow. There of us took it - two with 'point and shoots' and me with a 200mm lens, and a lot of care over the exposure. Their shots looked dull. Mine is a riot of sepia and orange. Ive still got the print hanging on the wall.