Another interesting snippet gleaned from the KAP forum I look at concerning camera image resolution may be of use to UG photographers.

In the quest to achieve well focused, good depth of field shots one would think that high numbered f stops with long exposures would be the order of the day. But it appears that in the digital world this is not always the case. Apparently smaller apertures give bigger points of light on the image sensor and if the point of light covers several pixels (sensors) you loose resolving power. A fuller reference is here.
http://www.tracyvalleau.com/blog/?p=16 
Simply put for the non technical the answer is to to use an f stop of 5.6 and just either side to provide the optimum focus with a reasonable depth of field. Wider angle lenses help too.

Peter.

Just thinking out aloud, f5.6 would be ok for a side on shot of an item like ore chute, an old wheel etc where most of the object would be within the depth of field. Taking a photo of a tunnel, stope, etc would require a deeper DOF and a higher numbered f stop would it not?
I am thinking from a DSLR point of view.
A f5.6 on a fixed lens digital camera is equivalent to f22 on a SLR. This is probably why compact cameras are better for taking photos underground. 5 - 8 seconds with a compact is something equivalent to 1.5 mins on a DSLR.

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Apparently not, I like you have always understood that better depth of field comes with smaller aperture setting (bigger numbers). This may be the case with film emulsion. With digital you have a sensor which must not react the same way.

From a practical, end user & observer view point, while editing Simon's & Colonel Mustard's photos I noticed that both had incredibly good depth of field focus. It would be interesting to analyze the exif info on the original shots to see what the f stops are.

I'm going to run some tests on this as I am also aware that to get good depth of field with focus on wider angle lenses a friend of mine also recommends an f stop of 5.6. Again he produces some great images.

The rule of thirds still applies though.
focus range is a third in front and two thirds behind.
personally i would be looking for a greater depth of field than 5.6.
To get round this ditch a 35 or 50 mm lens and get at least a 28 mm or 12-24 zoom with an auto focus easier still is a straight wide angle like the nikon 10.5mm.

If you do a search on flickr for nikon 10.5 mm wide angle you willsee many results.

Of course many other makes and models are available.

The 11-16 tokina looks the bizz but its mega expensive.

pace

I don't quite follow the "bigger points of light" idea.
However there is what is known as the "useful aperture" after which stopping down does not increase the depth of focus to any great extent. It does, however, increase the possibility of diffraction, the bending of light around the edges of the iris which leads to a general decrease in the level of sharpness.
There is an excellent article about this, somewhere on the Olympus web site. Sorry, I've printed it off and I can't re-find the address!
The maths are fairly simple and it is possible to create an Excel worksheet that will do all the calculations to give near and far depth of field points as well as hyperfocal distance.
This can be put on a small, handheld computer for use in the field but I doubt that many will want to go to that extreme! It is however most useful to peruse these tables and relate them to the lenses that one uses.
As a gross generalisation most Olympus 4/3 lenses have a "sweet point" between f11 and f16. I try to use them in manual mode having set a hyperfocal distance. With a 14mm focal length focused to 2m at f7.1, near focus is 0.97m and far is infinity, hyperfocal point being 1.88m. I'd expect the figures for other DSLR's to be similar to this example of "useful aperture".
Hope this helps!
Edit: found it! www.olympus.co.uk/consumer/dslr_Depth_of_Field or just put "depth of field of the Olympus E-1" into a search engine. Enjoy!

If you do a search on flickr for nikon 10.5 mm wide angle you willsee many results.

Of course many other makes and models are available.

The 11-16 tokina looks the bizz but its mega expensive.

pace

I don't think my pension would cover the Nikon 10.5mm either. 🙂

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i got mine second hand and it cost me 300 quid. !!

But anyone can use it if i,m on a trip together someday.

poor and happy

The best advice I can give on this subject, which dosen't seem too different from the film option, is to take some time out and investigate Hyperfocal distance. I was shooting a Canon A1 with a Tokina 28mm lens. I had the aperture set to f8 and the focus set to the hyperfocal distance ,and taped up so it could not move, which gave me a DOF from 1.3 Metres to infinity. A GN 45 flash set to auto and the whole thing became a high quality point and shoot set up with remarkable results. This was really good when working in crappy or wet conditions where you could just whip it out of the ammo box fire it off and get it back before it got too messy.
Once familiar with it (hyperfocal distance) it changes your outlook when buying lenses. Some 28mm lenses had a better Hypf dist than some 24mm ones. It makes you a little more choosey, but the finished product really shows. 😉 😉

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Thanks for the comments and references, there is some good info there. What is very obvious is that most of you are using DSLRs with larger sensors. From reading Gwyn's link and Roy's comments it appears to hold true in other words the larger the sensor the more like traditional SLR with film.

In my case at the point and shoot camera end of things the sensor size is smaller so there will be a difference it would seem. Found this link while following up Gwyn's suggestion http://photo.net/learn/optics/dofdigital/ 

I'm obviously going to have to do some tests as I'm limited financially as to what I drop down a flood shaft! Having said that I want to try to do the best I can. Up to now I've only ever taken video with the camera and have had mixed results when using the G7 for normal UG shots, preferring the A640 for regular use. Part of the problem is the use of conversion lenses which I've found can give wildly varying results something the DSLR owners will not suffer from if using proper lenses.

From a practical, end user & observer view point, while editing Simon's & Colonel Mustard's photos I noticed that both had incredibly good depth of field focus. It would be interesting to analyze the exif info on the original shots to see what the f stops are.

Simon and Colonel Mustard have a fixed lens camera as you have. Call them Compact, Bridge or whatever. They are (quote from Understanding Exposure by B. Peterson) 'hopelessly plagued with the ability to render a tremendous amount of depth of field, even when you set your lens to f2.8 - an aperture of f2.8 is equivalent to an aperture opening of f11 on a SLR(/DSLR) camera! And,when you're at f4, you're able to record a depth of field equivalent to f16. At f5.6, you're equivalent to f22. At f8, you're equivalent to f32, and if your lens goes to f11, you're at a whopping f64! Those of us who use SLRs can only dream of the vast depth of field that would result from apertures like f64.'
So when you are taking photos with your compact camera at f5.6 you are really taking photos at f22.

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Thanks for explanation, I have always used Fujifilm cameras with fixed lenses since giving up on film. And like you say have always got tremendous results when doing serious photography as I get great depth of field even at slow speeds and in bad weather.... I always seem to be able to get a reasonable shot in the worst of conditions.
Now I understand why my friends when we are doing railway shoots sometimes get fed up as I often get a better result in overall picture terms (as all in focus and great overall exposure) even though I might not get quite as sharp an image say as they do.
Regards ICLOK

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im afraid i dont really understand all these settings i use a fuji finpix s8000 set on f2.5 and 400 asa and it seems to work ok for me although im clueless to the f setting as it shows up in red on my screen for some reason but the results i think are ok....see below..
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🔗Personal-Album-252-Image-049[linkphoto]Personal-Album-252-Image-049[/linkphoto][/link]

🔗Personal-Album-252-Image-051[linkphoto]Personal-Album-252-Image-051[/linkphoto][/link]
but i am thinking of getting a camera with a 28m lens as that gives wide angle if i read the bumth correct.

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im afraid i dont really understand all these settings i use a fuji finpix s8000 set on f2.5 and 400 asa and it seems to work ok for me

Switch to 100 ASA and increase your shutter speed by x3, (E.G. 2 secs on 400 = 6 secs on 100 approx) you will see a big improvement! Im not knocking your photo's Bograt, far from it, There is less 'noise' at a slower asa.

if it helps you can veiw the text around these pics (exif data)
these where taken on a nikon dslr this weekend. They may give you a better inclination of time v exposure.
they average out at about 20-30 secs on 5.6 and fucused to infinity.

http://www.flickr.com/photos/pacef8/