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[Picture Rocks]

The two problems should be able to be seen right away!


Rock Creek River Jasper017crop4.JPG (101.32 kB . 300x446 - viewed 2156 times)

When you get the right balance of file size, resolution to output use, you will have already figured out not to get air bubbles and newton rings! A polished slab can work out well on the scanner bed without water but it helps to get clarity with an unpolished slab. Make sure the scanner is clean and the slab flat and clean, with no nubs. The farther away from the scanner surface the slab is the more out of focus it will be. I mean 2 millimetres could make a difference if you have a tiny nub.  Put a small puddle of water in centre of scanner glass and place the slab over. I didn't want to scratch my scanner glass so I also put an acetate sheet down first. The newton rings were cause by the acetate and glass but goes away if water is put down first. The bubbles go away if you pre-wet the slab as well as placing one edge first on scanner. A little soap or glycerine mixed first with the water can help if your're having trouble with fine bubbles. A light mineral oil can reduce bubbles instead of water but oh what a mess to clean up. I put a thin silicone seal on my scanner edge to prevent water from entering! You take full responisbility for possible wrecking your scanner! If you haven't given it a try, I recommend it, you will forget about ever getting lighting and focus messed up.

[irockhound]

If scanning slabs is the goal.  I wanted a digital library of agates and jaspers a long time ago when scanners were lower res but digital cameras were not invented yet. I made a glass tray and filled it with water and then sat the tray on the scanner.

[Picture Rocks]

If scanning slabs is the goal.  I wanted a digital library of agates and jaspers a long time ago when scanners were lower res but digital cameras were not invented yet. I made a glass tray and filled it with water and then sat the tray on the scanner.

Wouldn't the height above the scanner bed throw the focus off?

[irockhound]

A scanner glass is quite rigid.  I made the tray the width of the scanner glass to maximize the size of slab scanned but even if I hadn't the weight is so lite.  you could probably put a gold bar on the glass and it wouldn't affect the optics.  You would have to have a HUGE sheet of glass (feet square) and even then the flex would be so slight.  Also the scanner has a wider focal distance than you think, even at a very narrow focal plane it would still have enough even if there could be flex which again there won't be.

BTW why are you going this route?  I did this so long ago only because digital cameras hadn't been invented yet.  The resolution difference between a scanner and a camera is MASSIVE and you are not shooting through a sheet of non optic glass like you are in a scanner.

If you have seen Pat McMahons book he shot those pictures using a camera above a tray filled with fluid and the flashes on either side to not create reflections and look at the quality of those pictures.  The specimens don't have to be polished due to being immersed in the fluid.  The only issue as anyone who has tried photographing slabs web is not matter how many times you have cleaned them the always seem to shed some junk which means you are changing the fluid quite often to keep a clean environment for the photos.

[Picture Rocks]

A scanner glass is quite rigid.  I made the tray the width of the scanner glass to maximize the size of slab scanned but even if I hadn't the weight is so lite.  you could probably put a gold bar on the glass and it wouldn't affect the optics.  You would have to have a HUGE sheet of glass (feet square) and even then the flex would be so slight.  Also the scanner has a wider focal distance than you think, even at a very narrow focal plane it would still have enough even if there could be flex which again there won't be.

BTW why are you going this route?  I did this so long ago only because digital cameras hadn't been invented yet.  The resolution difference between a scanner and a camera is MASSIVE and you are not shooting through a sheet of non optic glass like you are in a scanner.

If you have seen Pat McMahons book he shot those pictures using a camera above a tray filled with fluid and the flashes on either side to not create reflections and look at the quality of those pictures.  The specimens don't have to be polished due to being immersed in the fluid.  The only issue as anyone who has tried photographing slabs web is not matter how many times you have cleaned them the always seem to shed some junk which means you are changing the fluid quite often to keep a clean environment for the photos.

I never mentioned anything about flex. It's the depth of field which is one issue. The scanner is designed to focus at the surface of the glass. I tried to scan a slab with an uneven surface and the high spots were out of focus - only a couple of mm above glass. Also, my scanner can isolate a slab area and create 4000+ dpi file which is way more resolution than my 21MP camera. I illustrate the procedure for those who are having trouble getting good slab shots and don't have an expensive setup. Haven't seen Pat's book yet, looking forward to it. Cheers.

[irockhound]

Lol I read weight.  silly me.

[irockhound]

You are right about the pixel count but with no control over lighting and depth of field I still think the camera will out perform the flatbed.  If you are doing isolated areas to get super high detail I could see the scanner being the go to.  I just remember all the color aberrations from the scanner lighting.  Like I originally mentioned it has been some time since I was using the flatbed for this. 

There are some flatbed scanners that do a better job with 3d.