Photography 101 - The Penarth Problem

Mine exploration, photographs and mining history for mine explorers, industrial archaeologists, researchers and historians

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Vanoord
54.4% (Neutral)
Newbie Topic Starter

17 years ago

Now then, I've been looking at Nimrod's pics of Penarth, for example, this one:

🔗Penarth-Slate-Mine-User-Album-Image-019[linkphoto]Penarth-Slate-Mine-User-Album-Image-019[/linkphoto][/link]

This seems to exhibit the same strange green tint that I had problems with in Penarth. It seemed to be a very difficult mine to photograph, perhaps due to copious quantities of light grey dirt.

Any thoughts what might cause this green tint?

Hello again darkness, my old friend...

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Captain Scarlet
50.2% (Neutral)
Newbie

17 years ago

Yep. I know exactly what caused it. A combination of using the highest ISO setting with a very long exposure time (1min plus), something I now no longer do. The problem manifested itself not just in Penarth, but other slate mines too so it was not location specific.

STANDBY FOR ACTION!!!!...

Vanoord
54.4% (Neutral)
Newbie Topic Starter

17 years ago

What ISO?

Hello again darkness, my old friend...

Captain Scarlet
50.2% (Neutral)
Newbie

17 years ago

"Vanoord" wrote:
What ISO?

The max on the 8400 ..... (400 from memory ??)

😉

STANDBY FOR ACTION!!!!...

Vanoord
54.4% (Neutral)
Newbie Topic Starter

17 years ago

Interesting... I got the same effect at 200 ISO: I wonder if the slate has some sort of green which is brought out by the Light Cannon? I took a few pics in there which were (I think) lit with a 1,000,000 candlepower cheapie torch and they don't exhibit the same symptoms.

The other place that had a similar hue was Moel Fferna, although some of those pics had an exposure of over 2 minutes, so the camera is forgiven for that.

Hello again darkness, my old friend...

LAP
50.2% (Neutral)
Newbie

17 years ago

The colour and wetness of the rock does have an affect. For instance - in Cumbrian workings - mines with blue slate seem to be much lighter than mines with green slate. For instace compare pics of Hodge Close to ones of Stainton Ground. Hodge Close being green.

regards

Linden

Ps - I've worked out high power torches are mush better if you're trying to light up mucky chambers such as those at Penarth. I had the same problem at Elterwater. Though the light colour isn't very natural.

Kein geneis kanaf - Cain gnais canaf
Byt vndyd mwyhaf - byth onddyth moyav
Lliaws a bwyllaf - Líows o boylav
Ac a bryderaf - ac o boryddarav
Kyfarchaf y veird byt - covarcav yr vairth
Pryt nam dyweid - poryth na'm dowaith
Py gynheil y byt - Pa gonail y byth
Na syrch yn eissywyt - na soroc yn eishoyth
Neur byt bei syrchei - nour byth bai sorochai

Barney
50.2% (Neutral)
Newbie

17 years ago

Don't you think its just a general problem with digital cameras as opposed to a 35mm slr?
fast films/long exposure times on a 35mm just results in 'grain' whereas digital images do all sorts of weird things generally, distorted colours etc..

LAP
50.2% (Neutral)
Newbie

17 years ago

"Barney" wrote:
Don't you think its just a general problem with digital cameras as opposed to a 35mm slr?
fast films/long exposure times on a 35mm just results in 'grain' whereas digital images do all sorts of weird things generally, distorted colours etc..

ie, you've got a good point there - though if you use a light cannon in a chamber for a long exposure - I guess there will be some blurring etc... due to the way in which the light paints the chamber walls - when coming from a device of this sort. This is a little difficult to explain.. but I hope you get the idea.

diolch

Linden

Barney
50.2% (Neutral)
Newbie

17 years ago

The only problem i have found with the canon is that if you adopt the painting method with an apperture of f8, an exposure time of about 180 seconds is about right, due to the slow ingress of light to the camera, the picture will come out nice and equally lit (or the area painted at least) Swap to f2.8 and the time is reduded drastically <30 seconds, so with the amount of light being kicked out, the painting has to be smooth and equal other wise it will show slightly on your pics.
A couple of my 180 second exposure shots have turned purple in the top of the pic, this only seems to happen at around this time scale and more.

Vanoord
54.4% (Neutral)
Newbie Topic Starter

17 years ago

#10

What were you lighting the pic with Barney?

We've usually put the purple haze down to the use of the Light Cannon, which has a gas discharge bulb (???).

Hello again darkness, my old friend...

Barney
50.2% (Neutral)
Newbie

17 years ago

#11

My lighting was done with the cannon, but reading various tests on dpreview, it would appear to be a trait of some digital cameras