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I've been looking for focusing aids for IR and UV multispectral imaging, and while browsing on a whim at our local salvage store, Urban Ore, in Berkeley, I happened across an item that might be useful. It's a vintage face tanning device with both a UV lamp and IR resistance-heating sources. I'm guessing it dates to the '50s or '60s. It's a German made device by "Dr. Kern & Sprenger, KG" and it runs on 220V AC. I picked it up for $10. I haven't checked, but I wouldn't be surprised if you could find one of these on eBay. The IR heaters would radiate mostly in the thermal-range (3,000 to 30,000 nm, or 3-30 microns), outside the range of the CMOS sensors on most cameras, but they certainly also radiate in the near IR (700 to 1,300 nm). However, I'm thinking of disconnecting them or rewiring the switches because they draw a lot of watts and produce mostly heat. They can't be switched off while the UV lamp is on, unfortunately (the switches offer only IR "Wärme," or IR+UV "Sonne + Wärme"). I also have an IR LED flashlight from maxmax.com. I'm trying to find out more about the UV lamp in this device, particularly about the spectrum it emits and whether there are modern lamps that I can replace it with to get specific UV wavebands. It appears to be a high-pressure mercury lamp, but could also be a low-pressure lamp. A label on the back of the device identifies it ("Typ UV Brenner") as a "UV800". I've attempted, but haven't yet found a way to remove the lamp to replace it. It emits quite a bit of visible light, and while testing it I've been wearing sunglasses with a good UV-blocking rating to protect my eyes, and I avoid looking at the lamp directly. I'd also like to find out if I can attach dichroic or other filters in front of the UV lamp to specifically select certain wavelengths or wavebands of UV light. For safety reasons, I'd like to filter out any UVB and UVC. If anyone has experience with filtering for specific UV bands on the light source, I'd be interested to hear of your experiences. Other UV light sources for use as focusing aids would be welcome. I know others in this forum have made good suggestions for UV sources for actual imaging. For UV imaging, here's another example of a tunable UV light source: "High Power UV LED Radiation System: 365nm 385nm 395nm 400nm 405nm" http://photographyoftheinvisibleworld.blogspot.de/2012/09/high-power-uv-led-radiation-system.html Dr. Schmitt's blog is my favorite resource for UV photography, and his inventory of macro lenses is another fantastic resource: The Macro Lens Collection Database http://www.macrolenses.de/ Thanks to Dr. Schmitt for permission to link to his sites here. Anyway, apart from the novelty appeal and low cost, the tanning device is relatively small and light, and it has a nice hinge that allows the light to be directed at various angles. It's an interesting addition to my inventory for multispectral RTI.
For capturing high-resolution multispectral images of a 19th century landscape painting (36 x 50 inches), I found it helpful to create a spreadsheet for planning purposes, and also to supplement the shooting notes as a record of what was done. To get complete coverage of the painting at the desired resolution for RTIs and photogrammetry (500 ppi for RTIs, and up to 2600 ppi for certain details), it was necessary to take a series of overlapping images. The spreadsheet takes basic information about the object (size, material, UV sensitivity), camera and lens (format, sensor and pixel dimensions, focal length, and settings), and calculates various parameters (working distances for the camera sensor and light source, minimum size of the reflective spheres, number of images, and storage requirements) for the project, given the desired target resolution and various wavebands (UV, visible, and IR) to be captured. This information is useful for estimating the space and time requirements for capturing RTIs and photogrammetry. Since the painting is on the east coast of the U.S. and I'm in California, it was important to have a good understanding of these parameters before shipping equipment across country and for arranging studio space in which to do the work. The spreadsheet was also helpful for selecting the macro lens for the project. The storage requirements are based on a RAW image file size of 20 Mb (a slight overestimate for my 16 Mp camera) and don't take into consideration the processed file sizes. For example, generating .dng files with embedded RAW images approximately doubles the RAW file size, and exporting .jpg images adds approximately 50 percent to the storage. The final processed .ptm and .rti files range from approximately 250 Mb to 350 Mb per RTI, so accordingly, additional storage will be needed to process the files. The spreadsheet only estimates the storage needed for RAW image acquisition. Another variable is the amount of overlap for the images. For general imaging and RTIs at a given resolution, the spreadsheet uses 10 percent overlap, and for photogrammetry, it uses 66 percent overlap for the camera oriented horizontally. The spreadsheet calculates the distance to shift the camera in horizontal and vertical directions to get complete coverage of the object. It assumes three images per position for photogrammetry (horizontal and two vertical orientations) and 36 images per position for RTIs. These parameters can be adjusted for particular project needs. The input parameters are entered into the spreadsheet using metric units. A companion worksheet mirrors the format of the metric spreadsheet and automatically converts all the distances from metric to English units, for convenience. An example of the spreadsheet is attached, showing the calculations for this project. [see update below.]