I find it most convenient to scan my images from within Photoshop so that the image automatically appears in the Photoshop window.
In Photoshop select File>Import and then select your Twain source.
The intent when scanning is to obtain as much information in the scan as is possible. Your image editing software can't work on information that your scan doesn't collect so get to know your scanner's software and use it to collect the maximum amount of detail in both shadows and highlights. It will have controls with which to optimise the quality of the scan, experiment with settings to find those that suit you best.
I suggest that scanning be done at the highest optical resolution your scanner will allow. My flatbed scanner has a main scan (across the moving bar) of 1200dpi. It has a sub scan of 2400 dpi (it takes 2400 samples per inch as it moves down the document being scanned). According to it's menu it can scan up to 9600dpi which means it scans at 1200 dpi and interpolates (invents) the rest. I find that if I need to increase the file size in this way 'Photoshop' does it better than the scanner software.
When scanning prints, negatives or slides use RGB mode. Monochrome, or grayscale images, typically turn out better if you gather the colour information in the scan and then change from RGB to Grayscale in Photoshop.
An A4 colour print at 300 pixels per inch needs a file size of about 22/3 megabytes which should give a reasonable guide to scanning resolution. If your scanner won't give you this size at it's optical best then let it do the best it can and increase the file size in Photoshop.
If scanning in all your latest batch of slides don't forget to save the imported images at regular intervals. There iis little more annoying than to spend an hour scanning only for the computer to crash leaving one to do it all again.
Having scanned your image and saved it I suggest that the first thing to do when you start work on the image is to create a duplicate layer. Layer>Duplicate layer. This means that if whatever you do doesn't appeal you can always drag the duplicate to the trash can and be left with the original. (Don't forget to create another duplicate.)
I thought it might be useful to illustrate the process I go through when scanning an image with my film scanner. First a word about dpi and ppi. Inkjet printers print at dpi i.e. dots of ink per inch. Scanners scan at pixels per inch (ppi). The two are not related. Unfortunately in scanner software ppi is often referred to as dpi which can cause some confusion. So scanner dpi (as below) is nothing to do with printing dpi.
When the final adjustments have been made the scan button is pressed, the image scanned and automatically transferred to the image editing programme, Photoshop in my case.
Unfortunately with the advent of Windows 7 Konica Minolta no longer supplied drives for the SCSI Scan Dual and Scanspeed film scanners. However I was able to acquire an Adaptec PCI SCSI card with Windows 7 driver and Hamricks excellent 'Vuescan' software includes drivers for many (Most?) scanners. So my Scan Speed and Scan Dual are happily now back in use with the excellent Vuescan software. Highly recommended! Find it at: