The strategy you choose is a personal "need" decision ultimately. But there is a principle involved; and that is you can always make a smaller print from a large size file, and quite easily, but if the file size is small, and lacks the information, you can't really make a bigger print successfully.

So if you scan at the scanners highest resolution you have all the information that can be reproduced from the original. At 7200dpi that potentially makes a very large print. But if you only scan to print at 4x6 inches at 300dpi, the information in the scan is nsufficient to make a print much if any larger.

In the old, early days of digital storage space for large files was expensive, now with Gold/Gold CD's at less than a dollar each for blanks, permanent storage is cheap. So there is no good reason not to scan at the scanner's maximum optical resolution and archive an original scan that will make any size print you might ever want.

Always scan at the optical resolution of the scanner if you're archiving your transparencies. The theory is to scan once and save it as a master. Then resize based on your needs and save it under a new name to not overwrite the original. The last thing you want to do is to have to rescan a slide because you needed a larger print.

Quote:
I'm working on scanning old 35mm transparencies both to ensure that we have the image if anything happens to the transparency, and to be able to share images with family. I'm wondering what might be the best resolution and image size for these scans.

• Do I scan at 100% of original size and 7,200DPI?
  
• Or do I scan at lower resolution (say 300DPI) and size for likely future printing (say 4x6 or 5x7)?

Normally I would scan directly to the target size for printing, but in this case I don't know the ultimate use for the image, so I suppose the optimal choice is small size and high resolution. Recommendations?

Followup:
I've been experimenting with my new Epson V500 with some old B&W negs, and have hit an interesting anomaly. These negs are from an old Kodak camera, and are about 2.4" x 4.2" image size. I had to make my own negative holder, of course. But the interesting thing is that Silverfast will not make a usable image at 6,400 DPI. The image is solid black. I reinstalled the Epson Scan software, and was able to make a 6,400 DPI scan, but now the Epson software refuses to make more scans, saying there isn't enough disk space, although there is plenty of space for these 800MB scans. I've logged this as an issue with Silverfast, but meanwhile I'm thinking perhaps I should drop back to 3,200 DPI for these negs, if only to get the file size down to something more manageable. Silverfast does scan successfully at that resolution.

Further followup:
The Epson Scan software refuses to scan an 800MB image when the temp drive has about 3GB of free space. Weird. When I switched the temp drive to another drive with 300GB+ of free space, the Epson Scan software had no problem completing a 6,400 DPI scan. So the problem is with Silverfast AI Studio and this scanner. Silverfast replied very promptly to say they cannot reproduce the problem, and ask whether I had deleted the Silverfast preferences folder (which seems to be their answer to all problems), and whether I'm using the latest Epson drivers. The answer was yes to both questions. So unless Silverfast has other suggestions, I'm left being unable to scan above 3,200 DPI with this scanner.

My question remains: am I likely to regret scanning these medium-format negs at 3,200 DPI? I'm not sure I want to try to find space for dozens of files in the 800MB range each. It's very unlikely that anyone would ever want to make a large print from any of these images. I'm thinking that 3,200 DPI may be adequate for archiving these old negatives. Any thoughts?

Sorry Steve, but I must ask are you expecting to make billboard size prints. I have the scanner and use SilverFast to drive it, and my printer only goes up to 17" wide, so I set the width of the scan size to 16 inches by 300dpi, and at whatever the length happens to be depending on whether a 6x9cm or 6x7cm negative. Scans are excellent, file size manageable and prints, I could not ask for better.

So I must ask what is the point in what you are trying to do?

Good point. I'm making archival, digital copies of these images to share with family and try to ensure that copies survive for a long time, somewhere, and in a format that will meet anyone's needs for a long time. So I don't have a specific output in mind at this time. It's sort of like my question about scanning 35mm slides. What resolution? Your suggestion was 7,200 DPI because the highest resolution gives the most flexibility for future use. I was following the same logic with these negatives -- scan the negs at 100% of original size, at highest resolution. However, your approach makes intuitive sense. I'll experiment a bit and see how file sizes compare.
Thanks,
Steve

The logic is good for 35mm because the film image is small, with larger film sizes the logic needs to be tempered by what image output size can one actually use or want. In your case I would just set an arbitrary limit to image sizing scanning any film larger than 35mm, maybe as I do. Then you will have no problems caused by exceeding file size limits, which is what you really described - not a problem with the software.