ratts at uky.campus.mci.net
ratts at uky.campus.mci.net
Tue Sep 23 20:25:46 EDT 1997
Kenelm Philip wrote:
> I have received no new information in response to my earlier
> posting re digitizing, but I gather there is some interest in how this
> may best be done. So here are some hints:
> Definition: Direct digitizing = making digital images without
> going through the 'normal' procedure of making a photograph and then
> scanning the slide or print (or making a PhotoCD).
> Methods: 1) flatbed scanners, 2) digital cameras. There is a
> third method, using single frames from video cameras--I have nothing to
> offer regarding that approach.
> 1) Using flatbed scanners: These devices have sufficient depth of
> field (which may vary among different makes and types) to achieve reason-
> ably good focus on butterfly wings even though the body (of a spread
> specimen) keeps the wings from contacting the platen. Before attempting
> this on your scanner, you should calibrate the depth of field of field
> by scanning a ruler with one end on the platen and the other end propped
> up so the ruler is inclined to the platen. The image can then be examined,
> and a simple calculation will show you what the limiting distance from the
> platen is for acceptably sharp focus. When in doubt, make a print--the
> resolution on the print may be higher than on the screen.
> In my case (H-P ScanJet 4C) the depth of field does not allow me
> to scan pinned specimens--they must be depinned. A method for doing this
> was described in the News of the Lepidopterists' Society (1 May 1975, page
> 1). I have constructed a more elaborate version as follows: Take a Variac
> (autotransformer) and connect it to the 120V end of a 6.3V filament trans-
> former capable of producing at least 5 amperes at 6.3V. Attach a piece of
> zip cord to the low-voltage terminals of the filament transformer, and
> to its free end attach two very small alligator clips. You may find that
> having an ammeter in the low-voltage circuit can be a help. Attach the
> alligator clips to the pin above and below the body of the specimen, and
> slowly crank up the Variac. For black pins, you will have to scrape the
> paint off to make better contact where the clips are placed.
> Depending on the size of the pin, you should find that something
> around 2 to 4 amperes will heat the pin enough to soften the insect's
> tissues enough to let you withdraw the pin. Warning: letting the pin get
> red hot will produce a strong and unpleasant odor of roasting bug...
> You will then need to whomp up some kind of device to spear the
> butterfly through the (somewhat enlarged) hole left by the pin, and hold
> it just over the platen with the ability to adjust the height and angle
> of the wings wrt the platen.
> Very fine images may be made this way. For a butterfly with a
> two-inch wingspan, scanning at 600 dpi gives about 1200 pixels across the
> image. Printing at 300 dpi on a color printer gives you an approximately
> life-sized image of good quality.
> One problem, as Gary Anweiler reported today, is that the background
> tends to run gray since it's usually farther from the platen than the
> specimen. An ideal specimen-holder would thus have to let you have a back-
> ground (of whatever color you wanted) immediately behind the specimen.
> Gary was fortunate in that his scanner could handle a pinned specimen, which
> mine does not have the depth of field to do--or else Gary will be pleasantly
> surprised with the improvement if he tries to scan a depinned specimen.
> 2) Using digital cameras: Here the important parameter is the macro
> focusing ability of the digital camera. To date I have found three digital
> cameras with true macro capability: the Ricoh RDC series, the Sony DKC-ID1
> (about twice the cost of most consumer-grade units), and the new Sony
> Mavica MVC-RD7. Warning: many makes of digital cameras _claim_ macro
> capability, as the Olympus D200-L and D300L units, the Apple QuickTake
> series, etc. Some (i.e. Olympus) even show a butterfly closeup in their
> advertising brochure--which some experimentation with the camera, and
> careful examination of the figure in the brochure, indicate was almost
> certainly actually made with a conventional film camera. Most such units
> can focus down to about 3.5 inches, which means, with their somewhat
> wide angle lenses, that the horizontal extent of the field in the subject
> plane at closest focus is around 5 inches--not at all sufficient for
> butterfly shots.
> The three cameras listed above as having true macro capability
> can all focus to within 1 cm. The Sony Mavica (which is the one I am
> using) can cover a horizontal field of 1.25 inches at closest focus,
> giving a reasonably large image of even a Lycaenid with a one-inch wing-
> span. The main problem with these units is that their macro focusing
> is only obtained when in wide-angle mode. The Mavica has a 10 to 1 zoom
> lens (40mm to 400mm 35mm equivalent) but must be in its widest-angle
> mode for close focusing. This means that providing proper illumination
> of the subject is tricky, and will involve the construction of a special
> lightbox to get diffuse lighting directed at the specimen into the narrow
> space between the camera body and the specimen. I will know more about this
> topic later this fall...
> The Mavica has a 640x480 pixel CCD, so you can get over 600 pixels
> across the image of most specimens. Prints at 144dpi or 300dpi are ade-
> quately sharp for publication purposes. The Mavica is unique (to date)
> among digital cameras in storing its images on a 3.5" floppy disk (JPEG
> files on an HD MS/DOS disk). These images may be opened in Photoshop on
> either a PC or a Macintosh--no cables needed. You can get 15 to 20 full-
> resolution images on a floppy.
> The Mavica has auto-exposure (which may be locked out just before
> taking a picture) and either auto or manual focus, using a 2.5" LED color
> viewscreen on the back of the camera to check the image. The auto-exposure
> may be offset plus/minus 1.5EV, which allows you to compensate for the
> effects of a light or dark background.
> Preliminary results with the Mavica look encouraging, but a final
> evaluation will have to await construction of the lighting source, and
> trial shots of a number of different species of leps.
> Of course, the ultimate digital camera would be one of the Nikon
> (or other make) units which use a high pixel-count CCD inserted in a
> standard 35mm body. With prices running from $6K to $16K or so, these are
> not an option for 'the rest of us'! Color scanners, and consumer-grade
> digital cameras, are at least items that many of us can hope to purchase.
> I hope these notes prove helpful to someone contemplating direct
> digitizing of leps. I will be most interested to hear about results...
> Ken Philip
> fnkwp at aurora.alaska.edu
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