Daniel Reetz, the founder of the DIY Book Scanner community, has recently started making videos of prototyping and shop tips. If you are tinkering with a book scanner (or any other project) in your home shop, these tips will come in handy. https://www.youtube.com/channel/UCn0gq8 ... g_8K1nfInQ

Zoom lens vs prime lens - what's the disadvantage to zoom?

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jonwilliamson
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Re: Zoom lens vs prime lens - what's the disadvantage to zoom?

Post by jonwilliamson » 16 Feb 2010, 22:23

Misty wrote: Even given the quality advantages a prime lens's optics have that you bring up, Jon, I'm thinking that a zoom lens might be better at dealing with that kind of size variation in my specific case; however, prime lenses might have an advantage for people dealing with mostly similarly-sized items.
Not necessarily, I actually look at it a bit differently. It really just depends on your requirements - If you want to shoot every image at the maximum available resolution, absolutely you need a zoon. However, if you want to scan all images (regardless of size) at a constant resolution then a prime may work just fine. For example, I normally scan pages 11x14 and smaller, and seldom scan anything larger than that. I normally scan at 300 dpi, so at 11x14 that translates to about 3300x4200, which puts me right at the 15 megapixel range to accomplish that resolution.

Now assuming that I scan something smaller such as a 4x6 page, I would still normally scan it at 300 DPI. Zooming in with the full resolution available on the camera would increase the DPI because you are applying the same amount of pixels to a smaller area, so using the previously calculated 3300x4200 that would translate to over 800 DPI. I don't increase resolution for smaller pages, so for me it makes sense to scan smaller documents the same exact way I would for the larger size and just crop the image, pretty much the same as with a flatbed type scanner but in post processing. As such, this should be good for any size page up to the max size I have configured the setup for.

Now if I needed to scan something larger than my configured size or needed a higher resolution for a smaller page then that is really where a zoom may come in handy, just not for my application where I want to maintain a constant archival standard of 300 DPI regardless of page size.

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Misty
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Re: Zoom lens vs prime lens - what's the disadvantage to zoom?

Post by Misty » 17 Feb 2010, 10:07

Yes, that's what I meant - in my case, I deal with some very oversized items, like the 40 inch-wide maps I was mentioning, but also with standard-sized items. Being able to cope with those and with smaller pages is probably going to work better with zoom.
The opinions expressed in this post are my own and do not necessarily represent those of the Canadian Museum for Human Rights.

DDavid

Re: Zoom lens vs prime lens - what's the disadvantage to zoom?

Post by DDavid » 17 Feb 2010, 11:47

Antoha this likely won't apply but I have a Nikon film SLR zoom
lense that had that problem but it has a small flathead screw
that can be tweaked a little tighter. The screw was located
on the side of the barrel that moves. May have been more than
one screw.

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Antoha-spb
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Re: Zoom lens vs prime lens - what's the disadvantage to zoom?

Post by Antoha-spb » 18 Feb 2010, 02:31

DDavid wrote:a small flathead screw that can be tweaked a little tighter.
mine doesn't have a screw. Just some kind of 'stopper' fixing the moving barrel only in the most-compact-lens-size position (for safe carrying).

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