Doug,
How large are you originally scanning your slide (dimensions and resolution). It sounds to me like you might be scanning the slide at too small a size/resolution and then resampling as you increase the image dimensions.
If that’s the case, here’s what I suggest.
1> Make sure your slide is clean from fingerprints and oils. 2> Scan your image at the size and resolution you need.
3> Failing that, scan your image at as high a resolution as possible. 4> Then, in Photoshop, set your image to the desired size, but UNcheck the resample image option. This way, you force Photoshop to use existing pixel information to achieve the desired size. As a result, as your image gets larger, the resolution drops. If you’ve scanned your image with sufficient resolution, you should be okay.
5> Clean up any unnecessary file resolution in a second step. Once you have the image dimensions to what you want it to be, rerun the Image Size dialog and check the resample image option and set your image to the desired specs (300ppi for print; 180 for newsprint; 72 for screen, etc…).
Hope all that makes sense. Let me know if you need further clarification or have more issues.
By which Colin means 2400 ppi at 100% of the slide (24mm x 36mm), not 2400 ppi at your final size. Scanning interfaces vary in their ability to allow the user to define an enlargement and the resolution at that size.
If you use the 300ppi benchmark for final rez, then Colin’s suggestion will support an 800% enlargement of your slide, or about 7.5" x 11.3" at 300ppi after resizing your input without resampling.
