Lenses
A lens that is good for photographic purposes is often not good for scanning purposes. This is because while photographic lenses are made to focus on 3D objects at distances from about 50cm, we are trying to focus on a 2D object at much closer distances. Most photographic lenses will not even focus close enough to fill the digital frame with the film and you would have to crop. Even if it does, or you use extension tubes, this is not enough.
An optimal lens for scanning projects a flat focus field, has high resolution at close focus distances and has high contrast. These are complex concepts, but by looking through the price ranges that you are interested in, you should get a good overview of what will work for you.
General Points
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Normal photographic lenses are not very suited for scanning
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Stay away from vintage Zoom (variable focal length) 'Macro' lenses - they are not true macro lenses
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Using extension tubes on a normal photographic lens will not give very high quality scans
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Some macro lenses, vintage and modern, are excellent
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You will find a lot of misinformation about lenses on the Internet and on forums
VALOI Recommendations
Note: That the categories you will find below are are ordered in order of price range, not in quality - generally the three last categories can provide similarly good results.
FAQ
Should I use an autofocus or manual focus lens?
Using a manual focus lens will typically get you the same results at a much lower price compared to more modern auto-focus lenses. However, it might slow you down because you will want to check your focus between every time you set up or when you change the format, or something else about your scanning setup. Therefore, an autofocus lens can save time, particularly if you scan several formats.
Can I use a normal non-macro lens?
Yes, normal lenses can be used if you have the right length of extension tubes. However, the results can range from acceptable to terrible and we always recommend getting a lens actually designed to focus close. If you want to use normal photographic lenses, you will get the best results by stopping down as far as the lens will go, such as f/16 or f/22.