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  1. #21

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    Quote Originally Posted by avandesande
    How did you figure your 'best focus distance'? It won't be the same as it would be with air.
    I figured my best focus by using the following method. First, I wet-mounted a negative emulsion down to the platten of the scanner and then made a scan. Next, I wet-mounted the negative base side down to the platten and made a scan. Comparing the two scans showed that the base-down scan was sharper than the emulsion down scan, which means that the "best focus" lies above the platten of my scanner, which is a very good thing. I've heard that some people found that their best focus point was below the platten, although I don't know how they tested this. Next, I wet-mounted to a glass plate as I suggested early, using shims to get various heights and measuring with a precision caliper. Finding the best scan gave my my ideal height. I will say that scans from about .25mm to .75mm were very close, although I could detect a small bit of improvement at .5mm . Just FYI, the Canon negative holders hold the emulsion about 1 mm above the platten, which is not ideal, at least with my scanner.

  2. #22

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    Quote Originally Posted by avandesande
    How did you figure your 'best focus distance'? It won't be the same as it would be with air.

    I use a chrome on glass resolution target. I scanned it at maximum resolution at different heights, from zero position on the glass to 4mm above the glass, and looked at the resolution on screen to evaluate resolution at the various distances. There is not really much difference because the lens of the scanner has great depth of field, but from my reading the best resolution was obtained when the emulsion of the negative was about 1mm from the surface of the scanner glass.

    Sandy

  3. #23

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    Quote Originally Posted by Peter De Smidt
    Sandy,

    By shimming the glass one can get the negative at the best height even though it's under the glass sheet. If you tape all of the edges of the Mylar and wipe up any excess, there's very little chance of any Kami getting on the scanner platten. If you're really worried about it, you could seal all the edges of the platten with Kami tape. Won't you have a dry glass to glass surface with your method? Might this not lead to Newton's rings?

    Regards,
    Peter
    Peter,

    I have never seen any Newton rings from the glass to glass interface. I worried about this initially but it is no problem at all. On the other hand, I have often experienced Newton's rings with dry scanning when placing the negative in contact with the glass.

    BTW, I do not place fluid mounted mylar over the base of the film with my method. I just place the negative emulsion side down on the mounting glass, tape the negative down, and scan. I tested with mylar fluid mounted on top (on the base) but could not see any advantage at all with 5X7 negatives.
    With the Leafscan 45 and roll film negatives I do fluid mount the mylar over the base of the negative.

    Sandy

  4. #24

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    maybe steal the glass out of an old scanner. won't cost you anything.
    art is about managing compromise

  5. #25

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    Quote Originally Posted by sanking
    Peter,

    I have never seen any Newton rings from the glass to glass interface. I worried about this initially but it is no problem at all. On the other hand, I have often experienced Newton's rings with dry scanning when placing the negative in contact with the glass.

    BTW, I do not place fluid mounted mylar over the base of the film with my method. I just place the negative emulsion side down on the mounting glass, tape the negative down, and scan. I tested with mylar fluid mounted on top (on the base) but could not see any advantage at all with 5X7 negatives.
    With the Leafscan 45 and roll film negatives I do fluid mount the mylar over the base of the negative.

    Sandy
    Hi Sandy,

    I too have experienced Netwon's rings when dry scanning with the negative on the platten. I'm glad that there's no problem with glass. I like the fact that your method requires no expensive Mylar. Unfortunately, I doubt that I'll find a sheet of glass .5mm thick, and even if I did it would be very delicate. Still, I may spring for the new Epson 750 scanner, and it's best focus point might be higher. Thanks for sharing your method!

    -Peter

  6. #26

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    Quote Originally Posted by Peter De Smidt
    Hi Sandy,

    I too have experienced Netwon's rings when dry scanning with the negative on the platten. I'm glad that there's no problem with glass. I like the fact that your method requires no expensive Mylar. Unfortunately, I doubt that I'll find a sheet of glass .5mm thick, and even if I did it would be very delicate. Still, I may spring for the new Epson 750 scanner, and it's best focus point might be higher. Thanks for sharing your method!

    -Peter

    Peter,

    The 750 looks very interesting. But I am going to wait to see how effective the scanner is in terms of ration of dpi to lppm. The Epson 4800 is less than 50%. 4800 dpi (at pixel to lppm of 2.5:1) should give about 80 lppm, but by my tests, actual lppm is less than 40. If the 750 increases the efficiency to 65-70% I will consider it a good buy, otherwise will stay with the 4800 until the next generation.

    Sandy

  7. #27

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    I already posted a link to S. I. Howard Glass, Co., (http://www.howardglass.com/) but with the description of the application, their products looks fully appropriate. I don't think you need optical flatness, meaning measured in wavelengths of light. Certainly the scanner manufacturers aren't using that grade of glass.

    Their soda lime glass is available in thickness of 0.40, 0.55, 0.70, 0.90, 1.1, 1.2, 1.6 mm, all the way up to 19 mm. Typical prices for thicknesses around 1 mm are $1.15 per square foot. Sizes are various, such as 20 x 20 inches. I think they cut to the size that you want.

    Perhaps their B270 super white crown glass is better. They emphasize its optical clearness. It costs a lot more.

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