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Olympusman
Joined: 15 Jan 2012
Posts: 4090
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 Posted: Fri Dec 22, 2017 12:10 pm Post subject: Horseshoe Crab |
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Horseshoe Crab, one of the dinosaurs among us.
Captured on a Visioneer OneTouch 8820 flatbed scanner.
Scanography is an interesting discipline. Flatbed scanners have remarkable depth of field and the lighting is pretty much axial lighting. All you need to do is to construct boxes to put above your specimens so you can scan with the lid open.
Mike
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Michael Reese Much FRMS EMS Bethlehem, Pennsylvania, USA |
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mygale
Joined: 02 Aug 2016
Posts: 66
Location: Germany NRW
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| Posted: Sat Jan 20, 2018 2:01 am Post subject: |
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Oh thats really nice!
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Sumguy01
Joined: 28 Jan 2013
Posts: 1335
Location: Ketchikan Alaska USA
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| Posted: Sat Jan 20, 2018 9:22 am Post subject: |
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 Very nice.
Thanks for sharing. |
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rjlittlefield
Site Admin
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Posts: 19763
Location: Richland, Washington State, USA
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| Posted: Sat Jan 20, 2018 11:53 am Post subject: Re: Horseshoe Crab |
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Very nice image of an interesting subject!
| Olympusman wrote: | | Flatbed scanners have remarkable depth of field |
I am curious about this comment. The DOF of a scanner should be just the same as for a camera system whose lens is stopped to the same subject-side f# as whatever is in the scanner. Have you run some comparison that says otherwise?
--Rik |
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Pau
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Location: Valencia, Spain
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| Posted: Sat Jan 20, 2018 12:43 pm Post subject: |
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There are different kind of flatbed scanners (I read it years ago and I can't remember the technologies names) but I've experienced it:
My previous scanner was an Acer (SCSI ...) that did very well scanning leafs and even rocks with some relief, but my current Canon (printer combo) despite having much higher resolution is a true disaster if anything is not in contact with the glass: not only lack of DOF (this can be expected) but lots of artifacts
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rjlittlefield
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Location: Richland, Washington State, USA
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| Posted: Sat Jan 20, 2018 2:19 pm Post subject: |
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| Pau wrote: | | despite having much higher resolution is a true disaster if anything is not in contact with the glass |
That's exactly what I would expect. It's the usual tradeoff, with high resolution requiring a wide aperture which gives small DOF, versus low resolution which permits a narrow aperture giving large DOF.
Checking specs, I see that the Visioneer OneTouch 8820 that Mike used for this image is on the low end of resolution by current standards. The published specs are nominal 1200 x 2400 dpi, but reviews from 2002 suggest the actual resolution is a lot less. The low resolution means that it can use a small effective aperture, which a designer would probably choose because it would reduce costs and give the greater DOF.
Also relevant is that flatbed scanners are typically used to scan relatively large subjects, corresponding to low magnification with a camera system.
I don't know how big this particular specimen is, but if it's say 9 inches total length, then that would be around magnification 0.1X on APS-C, and f/16 at 0.1X has diffraction limited DOF around 68 mm, over 2.5 inches. It would be interesting to know how the DOF on Mike's scanner compares to that.
BTW, I think it really doesn't matter whether the scanner uses a single lens or an array of lenses over a scanning sense head. Either way, it's the angle of the light cone for each pixel that determines DOF and max possible resolution.
--Rik |
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