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Medium format resolution

Matt McCarthy , Feb 10, 2007; 10:00 p.m.

Got a situation here -

I need to be able to produce images of archaeological excavation pits. The size on these things is 8 meters by 8 meters. The challenge is to raise a camera above it, photograph downward, and provide visible resolution down to 1 centimeter. This will require a VERY wide lens. I've found that at a 35MM camera with an 18MM lens at 9.5 meters away will encompass 8 meters by 8 meters - but the resolution, no surprise, is useless. So I may need medium format. Cost might not be an issue; I may be able to gain access to high-end gear ( like a Hasselblad H3 digital setup ). I know that the 6 x 6 format of a Hasselblad is better suited for that than a 645 like a Pentax or Mamiya, but I will still need to raise the camera pretty high to do so ( a platform has already been devised to raise a camera to 10 meters. Shorter height would be better, though ). Assuming a 9.5 meter distance from the surface, do any photo.net people know if medium format or high end digital can resolve a 1 centimeter increment? ( tack sharp resolution isn't required here, by the way ).

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Stuart Richardson , Feb 10, 2007; 11:11 p.m.

Your best bet might something like an Alpa 12, a Cambo Wide DS or a Horseman SWD. These are all dedicated wide-angle cameras. Most of them have some shift capabilities which may be useful. They take large format lenses which gives you a lot of flexibility. The lenses can go VERY wide, and the quality will most likely be even better than the best hasselblad lenses. They take digital backs, or they will shoot 4x5. If you use a fairly large sensor digital back with the SWD and use a 24mm lens, it is equivalent to about a 17mm lens on 35mm, so enough for your purposes.

Trent Whaley , Feb 11, 2007; 12:33 a.m.

Err... you've just described a 1600x1600 pixel image. Just about any modern camera can handle that. 6x6 MF should be able to handle ~1mm pixels on an 8m x 8m field if the scanner is good enough (ie Nikon 9000).

Russ Britt , Feb 11, 2007; 01:14 a.m.

I would think a superwide would be perfect....

Beepy . , Feb 11, 2007; 01:57 a.m.

I'm perhaps a little confused here... as someone else mentioned:

8 m * 100 cm/m = 800 cm length, you say tack sharp resolution is not required - so even say 4 pixels per cm? to resolve = 3200 * 3200 = 9 megapixels.
I guess I'm curious why a well shot (stable mounted, mirror lockup) fine grain 35mm image and well scanned (4000 dpi, no ICE - may blur details, clean neg/slide first) doesn't almost get you what you want - which implies that a Canon 1Ds MkII might be sufficient?

Maybe I'm looking at this entirely wrong?

Medium format would give you more resolution and room for error - but I'm wondering if there is something wrong with the method of capture. Do you have an example bad image and can you explain how it was produced (I get the impression from your message that a digital result in the end is desired).

I could be completely be screwy in how I am working this out... But I shoot a 4x5 and scan that at 2040 dpi when I want detail.

Kelly Flanigan , Feb 11, 2007; 02:45 a.m.

theta = approx 1cm/950cm = 1/1000 radian to slide rule accuracy. In military theodolites this arc angle is a mil; with 6400 mils being a full circle. In army gunnery a mil is about 1 yard in 1000 yards.

Guns, cannons and military sights and theodolites such as the Wild Heerbrugg T2 are often in mils instead of degrees, minutes and seconds. Math is easy using mils when in the heat of battle. If one misses the target by 120 yards to the left at a range of 2400 yards then you move the gun over by 50 clicks ; ie 50 mils; ie 1 mil at 2400 yards is about 2.4 yards.

With a 18mm lens on a full frames Canon 5D 1 mil is 18 microns. The sensor pitch is way less than this; about 8.2 microns. Thus with a decent high quality L series canon lens; or Nikon one with an adapter you probably will resolve a 1 mil object.

Kelly Flanigan , Feb 11, 2007; 02:53 a.m.

What is the 1 cm objects shape? are you trying read type thats 1cm high? or locate rocks, fissures, asps in the raiders of the lost arc pit?

How much "design margin" one needs in a photo capture project radically depends on the contrast and shape of the objects. If one wants to read text with a poor font and ill lighting then one needs alot more design margin. If the 1cm objects are just mice, asps or marbles then one needs less margin, unless the asps are hungry.

Matt McCarthy , Feb 11, 2007; 06:32 a.m.

Few more details - What needs to be photographed within the dig site is a measuring stick - a ruler with centimeter increments. My initial results with 100 -speed film and with digital (6.3 MP) gave me a image that when I zoomed in on the ruler, the result was so pixelated as to be impossible to accurately gauge the centimeter increments. The other details to note here are this: If possible, I'm trying to create a setup that "Joe Archaeolgy" can use - and generally, that knowledge is limited to PHD ( press here, dummy ) cameras. Gotta be simple. The other tricky factor is that two shots, one with ruler, and one without, of the same subject might be needed - two shots from 9.5 meters up. That's going to require an auto-advance film model ( if film is the answer ), with a remote trigger device. I know this is difficult, but I'm trying to come up with something very new for the world of archaeology, and experimentation is needed. Thanks to all for the answers so far!

Ivan Dzo , Feb 11, 2007; 07:52 a.m.

Matt, interesting challenge. I shoot film and scan at 5400 ppi. So your 800cm plot will be 7654 pixels across or 10pixels per cm. I've just looked at a techpan 35mm shot done on a tripod with a zeiss lens. The gaps in brickwork at 30m on a 45mm lens (about 1cm across) are quite obvious.

Moving up to 6x6 gives you 20 pixels per cm, if you can scan at the same resolution. This sort of scanner however is big money. If you scan at 2700 then you're no better than 35mm (although grain will be better but lenses will be worse).

So I find that I can get the same resolution with 35mm and 6x6 if I use the right film and are scrupulous with technique - not phd cameras though. Ideally you need a large format scanning back which would be ideal for this. Just have to mortgage your home to pay for it.

Stephen W. , Feb 11, 2007; 10:14 a.m.

Hassy SWC, which gives you a digi-back option.


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