Q&A For Digital Photography
Digital Help is designed to aid you in getting the most from your digital photography,
printing, scanning, and image creation. Each month, David Brooks provides solutions
to problems you might encounter with matters such as color calibration and management,
digital printer and scanner settings, and working with digital photographic
images with many different kinds of cameras and software. All questions sent
to him will be answered with the most appropriate information he can access
and provide. However, not all questions and answers will appear in this department.
Readers can send questions to David Brooks addressed to Shutterbug magazine,
through the Shutterbug website (www.shutterbug.com), directly via e-mail to:
or by US Mail to: David Brooks, PO Box 2830, Lompoc, CA 93438.
Is Your Computer's CD Drive Up To Every Challenge?
Q. I recently offered to make some prints for a friend. She burned several files to a CD and mailed them to me. To my surprise when I opened them they had, for want of a better description, short lines about a pixel high and 10-50 pixels in length. These lines were alternately light and dark shades, scattered throughout all the files. These lines print, by the way.
I printed the files for her and pointed the lines out. When I returned the disc to her she reported she does not see the lines on her system nor on the system of another acquaintance. So at my request she returned the disc to me. Lo and behold I still see them on my system, but not on my wife's.
What are these lines? Why do they only appear on my system? Are they on the disc? I've never seen anything like it before and have no other difficulties with my system.
Note: Screen shots were included with the reader's e-mail clearly illustrating the problem artifacts.
A. Thanks for providing all of the details and screen shots
describing the problem you are having. First of all, consider an image file
is a matrix of square pixels and that your computer "reads" the
data the same way you read a page of type--text left to right one line
at a time. If you are reading under artificial light and the power connection
to the light is partially shorting out so the light flickers a bit, as you scan
the page line by line, letter by letter, you might miss some words or parts
Being that the files on the disc can be read cleanly by some computers other than your own, then I would look to your CD drive as the likely source of the problem. And if your CD drive reads other discs OK, then it may be the CD-R from your friend has a weaker "image," which is very possible because a CD-R is recorded in a very thin layer of dye, and different brands and types do vary one from another. Also, a few fibers of lint may have gotten into your CD drive and attached to the head (reader). This could intermittently get in the way of the laser beam reader. This would yield skips of garbled data that would record like the lines that are in the images you sent.
From the information you provided, what I described seems to me the most likely cause of the problem, but it could be something else with a similar effect, like an electrical connection that is intermittently weak. But I would suggest that the CD is OK if it can be read by other computers, and that the most likely culprit is your CD drive. And it could be as simple as some fine dust in the drive.
Copying Slides With A Digital SLR
Q. In the January 2005 issue of Shutterbug, Roger W. Hicks makes reference to a slide copier carrier for his Nikon D70 ("Studio Update" article on pages 104 and 106). My father, who has 15,000+ slides, would purchase the D70 tomorrow if he could locate this slide copier carrier. He presently uses an attachment made by Nikon for his Coolpix 5400. Is there a slide copier carrier that works with the D70, and which lens is needed?
A. I really have no idea which brand slide copier attachment Roger Hicks referred to. However, as far as being able to copy slides with a digital SLR it is really no different than with a film SLR and about any of the same slide copier attachments should be adaptable. Using a slide copier attachment usually functions best and most effectively with a macro lens if it is the type that attaches to the adapter screw ring of a lens. Some slide copiers, however, have been available that have their own lens built-in. I would suggest inquiring as to what is available in slide copier accessories from at least a couple of our advertisers: B&H and Adorama. And of course check out the Nikon website (www.nikonusa.com) to see if a Nikon slide copier is available.
Resolution Means Different Things To Film And Digital
Q. I have a long-term gripe having to do with writers of all types who state with unequivocal authority that wide angle lenses have greater depth of field than standard focal length lenses or that long focal length lenses have less depth of field than shorter lenses. In fact, for the same size image at the film plane all lenses have essentially the same depth of field; e. g., a 25mm lens at 5 ft from the camera has the same depth of field as a 50mm lens at 10 ft, since the image size at the film plane is essentially the same in each case.
My point is that one should not necessarily acquire a short focal length lens in order to get greater depth of field; one only has to back away and make the image at the film plane smaller. One should acquire a wide angle lens, for example, because it provides an interesting perspective at the same subject distance or because there is no way to fit everything in the picture without it.
For the reason that greater depth of field may be desirable in many situations, many photographers use 35mm in lieu of 6x6 or larger cameras without considering why they do so. It also explains why digital cameras with small sensors have become so popular: they provide greater depth of field compared to 35mm and larger film sizes. On that point, the amazing thing about the current digital cameras are their excellent large print quality from such small sensors, making me think that these sensors must have a higher inherent resolution than most 35mm films. Has anyone compared the resolutions of the better digital sensors with 35mm or 120 film?
Laguna Niguel, CA
A. The "resolution" of a digital sensor and film
is not directly comparable as there is no physical correspondence between the
media. Film records images by physical means on a medium which is modified by
light to produce an image composed of grains or dye clouds. A grain image is
just organized noise. With digital the medium is a matrixed recording device
which records the color and brightness of light divided in a pattern of cells
(pixels) which once recorded is just pure information, usually free of any noise.
The term "resolution" applied to film references the film's ability to "resolve" subject image information popularly referred to as sharpness, or acutance and definition.
The term "resolution" applied to digital refers to the size of the image produced in pixels. In other words, a digitally recorded image is measured by how many pixels are involved to make up the matrix which represents the record of a subject. Digital resolution, although indirectly an influence on final image acutance and sharpness, does not actually say anything about how sharp the image is, except that the more pixels, the more information, which is a corollary of increasing the image format (film) size, say from 35mm to 120, or 4x5.
What Is Digital ISO Film Speed?
Q. We have read in magazine captions under photographs taken with a Nikon D70 that the camera was set at a certain ISO. Since digital cameras don't use film, we don't know what they are talking about. We would appreciate learning what the gap is in our comprehension. Thanks.
A. These days with all but the least expensive, most basic digital cameras, the imaging sensor used in the camera is variable in its sensitivity to light. And through the controls that are a part of the camera, a range of effective film speeds can be chosen. Many digital cameras these days have a base default effective film speed the equivalent of ISO 100, and options to increase the sensor sensitivity to as much as an effective ISO 1600. And like film, the slowest (default) ISO speed setting on a digital camera produces the best image quality, and as higher settings are used the image quality degrades, mostly in the form of noise in the shadow areas of the image produced.
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