Having gained a little bit of experience with scanning film recently (when switching back from digital photography to analogue photography), I would like to share what I would think are the most important pre-condition for sucessful scanning:
Summary: Use Nikon Coolscan 9000, available at most scanning services.
1. Do not used Minilab or comparable; they are still expensive and the results are not usuable, because all curves tend to be cropped. (That means that not the entire dynamic range per colour channel is registered, but only a smaller band of it, resulting in tint, drowned shadows, burned highlights, and in particular no way of correcting this, as it simply means "lost information". The result is comparble to a distorted audio recording due to exceeding maximum recording level.)
2. Though drum-scanners are known to be the best scanners at all, I cannot say that I have found the necessity to use such expensive devices for my needs to this point.
3. All my experiments with using my Canon 5D II for scanning images through using high-quality macro lenses have resulted in the preliminary finding that it relatively difficult to light the film correctly (not to produce vignetting) and to maintain equal distance to the focal plain (to avoid unsharp areas, which requires exact parallelity). In addition, you'd lose the option of lossless dust reduction and the entire process is too time consuming anyway.
4. My experience that the Nikon Coolscan 9000 to this point has provided me with scans which seem to be equal or even exceeding the professional scans I had let made previously for 30+ EUR per image in quality. Nikon Coolscan 5000 did not deliver results of the same quality.
II. Image Format
1. IMPORTANT: Always use TIFF 48BIT (16BIT per channel); 8BIT TIFFs or JPGs will not provide sufficiently high colour depth to perform the necessary colour corrections without creating artefacts in colours. This effect clearly shows in the curves: 8BIT imagery creates gaps when adjusting the input-output-relation (you will see the previously smooth curves change in to a row of isolated pillars; meaning lack of information); which mostly leaves you with imagery losing subtelity, esp in difficult colour spaces (such as the subtle shades in the shadows of night-time imagery).
2. IMPORTANT: Make sure ALL AUTO CORRECTION is SWITCHED OFF! This applies to BOTH COLOUR CORRECTION and SHARPENING (unsharp mask, etc). You can perform any of these yourself at any point in time, but if they have been applied to your raw data during scanning already, they are irreversible. Usually auto color correction increases contrast by cropping the shadows and the highlights (and worse: not equally for all three colour channels), which leaves you with a significant, undesirable and permanent loss of colour information. Generally film should be scanned with a bit of "headroom" left and right of the input-output-curve; meaning that the darkest point on the film does not equal Colour #000000h and the lightest point does not equal #FFFFFFh.
There are two reasons for this: a) neither is the darkest point necessarily pure black, nor is the lightes pure white on each image (think of a sunset, when the sun itself appears orange or red) and b) in many cases there is still information in the space left and right of the main curve (esp. regarding night-shots). Moreoever, the reduced contrast of certain motives (shadows after sunset) requires only part of the available colour space being used, as otherwise you'd blow up colours and contrast to a degree which not only makes the image very grainy and low-fi, but also does not ressemble the ambiance you originally tried to catch. The same applies (in particular) for film which has the characteristics of vintage film, e.g. ADOX COLOUR IMPLOSION film, which lives from the fact that it does not use the entire range of brightness, but reagrding which instead esp. highlights run out very smoothly and with quite some headroom before the maximum of bright white would have been reached.
3. IMPORTANT: in order to achieve II.2. you will need to let all your film be scanned as "positives", meaning that colour negative film needs to be scanned as colour slide film. The results should look like the original film, including the organge or magenta mask. I will describe in a different thread how to remove these masks. Any automated removal of the mask will - in my experience - result in the negative effects described under II.2.
4. A resulotuion of 4000 dpi is desirable for most films, and even not sufficient for film such as Fuji Velvia (which can't be helped as usually a higher resolution is not available anyway). Even regarding film with larger grain, 4000 dpi tends to be preferable to 3000 dpi, because it allows more subtle application of an unsharp mask, should you wish to use that (which I don't), or to have made big enlargements, which do only show analogue artefacts, but no digital artefacts (meaning details may be slightly blurred and grain becomes very visible, but aliasing through clearly visible pixels does not occur). There are some exceptions, such as KODAK HIE and ADOX COLOUR IMPLOSION, both of which in my expierence have such large grain that 3000dpi are truly sufficient. However, I even let the KODAK HIE be scanned @4000dpi, because I like blowing it up overly large for printing, and I would not want to have digital artefacts. After all, it only costs a few cents and some MB more per image to have the images scanned @4000 dpi instead of 3000dpi, while oppositely you will need to rescan should you need a particular images @4000 at some point. For Adox Colour Implosion, 3000 dpi truly is sufficient.
... the echo of a distant time ...