Difference between lenses

[ibr4him]

Hi,

At1z recommends the "Canon EF 50mm f/1.8 II" lens for its book scanner but my T2i came with "Canon EF-S 18-55mm f/3.5-5.6 IS" lens. I wonder whats the difference between the two lenses. Would the results be better or worse if I use the default lens compared to what at1z recommends?

I'd appreciate any help. Thanks!

[lexicographer]

Your lens has had very good reviews (see for example http://www.photozone.de/canon-eos/181-canon-ef-s-18-55mm-f35-56-is-test-report--review); the major problem I see is that is simply not a fast lens. This means that you will need a lot of lighting; personally I was not contented with the results, but that may be a matter of taste. You can set ISO to 400 or 800, but that will increase the noise in your scans. If you can get enough light with ISO 400, you should try. If you photograph RAW, the Canon-software even corrects the vignetting (afaik; I have never tried it myself).
Myself, I use the EF 50mm f/1.4 USM which is even faster than the 1.8-lens of atiz, but unfortunately it is also pricier. Hope this helps.

[bnz]

Speed on the side of taking a sequence of pictures subsequently is also a problem. I have the cheap 50mm lens and if I go too quick, a get an error. From my experience, boosing up the ISO value is not a problem with capturing book pages. In my tests I went up to 1600 and it didn't cause any noticeable noise in the results. Obviously, it is different when I shoot something else than a book page.

Regarding the lens comparison: http://photo.tutsplus.com/tutorials/sho ... 50mm-lens/

Having written that. One reason that my ISO values don't cause much noise is actually the fact that I use a 50mm lens.

[Misty]

bnz, the article actually says the opposite of that - the 50mm lens is good at reducing noise because it allows you to use a low ISO. They provide examples of how noise increases when using a higher ISO.

For text, a higher ISO probably wouldn't cause a great problem, though I've found that it hurts readability on coloured pages. White pages with black text might work better. Illustrations will definitely benefit from the lowest ISO possible.

Lexico, while lens speed helps it's worth keeping in mind the sharpness. All lenses will be softer with their widest apertures. For example, DPReview notes that the f/1.8 50mm has very soft corners until you reach f/3.5, and reaches optimum sharpness at f/5.0, while they say that the f/1.4 50mm is also very soft wide open and has optimum results at f/5.6 - f/8. That said, it's still a bit better than the 18-55 which reaches optimum sharpness at f/8 - f/11. Perhaps the bigger benefit is the sharpness - in the same focal length range, both two 50mm lenses provide much better optimum sharpness than the zoom lens does.

The advantage to the zoom lens is that you can zoom in and out to fill as much of the image with page as possible. That's a big advantage if you're scanning books of a variety of sizes, since it allows you to fill the frame for any of your books without moving the camera. If you're scanning books that will all be essentially the same size, you will probably be able to set up your camera to get fairly optimal use of the frame size with the 50mm.

[russca]

Perhaps the bigger benefit is the sharpness - in the same focal length range, both two 50mm lenses provide much better optimum sharpness than the zoom lens does.

The advantage to the zoom lens is that you can zoom in and out to fill as much of the image with page as possible. That's a big advantage if you're scanning books of a variety of sizes, since it allows you to fill the frame for any of your books without moving the camera. If you're scanning books that will all be essentially the same size, you will probably be able to set up your camera to get fairly optimal use of the frame size with the 50mm.

Misty, what would be your recommentation then? Zoom lens? Sure books are gonna be of different sizes. I am thinking about buying Canon DSLR. Just don't know which lens to choose. I was leaning toward EF 50mm f/1.4 before reading this thread.

EF 50mm f/1.4 vs EF 50mm f/1.8 - the very first product review on that page.
http://www.amazon.com/Canon-Standard-Me ... 585&sr=8-5

[bnz]

Hm, yes, the general statement that low iso's yield sharper pictures is definately true for the usual cases. I thought that prime lenses at higher ISOs yield less grain than zoom lenses at high ISOs, but I may be mistaken here. However, with my tests, I really had the effect that I had sharper letters with ISO 400 and upwards. I can imagine two reasons for that: 1) my lighting was really bad. Even though I had three lamps in addition to the room lights, all of them weren't very powerful (40W) or 2) this might be something that is related to the live view when using the tethered connection. This is how I manually focused my lens. I am no expert here either.

[Misty]

Misty, what would be your recommentation then? Zoom lens? Sure books are gonna be of different sizes. I am thinking about buying Canon DSLR. Just don't know which lens to choose. I was leaning toward EF 50mm f/1.4 before reading this thread.

EF 50mm f/1.4 vs EF 50mm f/1.8 - the very first product review on that page.
http://www.amazon.com/Canon-Standard-Me ... 585&sr=8-5

I've found that zoom lenses are fine in most cases, but that depends on what level of quality you're looking for.

How much variation in size are you talking about? A few centimetres difference (like small paperbacks vs 6x9"), or much greater (small paperbacks vs A3)? The greater the variation in size, the more advantage you get from a zoom lens. Lens sharpness won't help you so much if you've cut your resolution in half by heavy cropping.

Are you imaging pure-text books you intend to run through Scan Tailor, or are there illustrations or historical book pages you'd like to retain the exact appearance of? The slight sharpness difference between a zoom and a prime will not affect Scan Tailor output nearly so much.

Hm, yes, the general statement that low iso's yield sharper pictures is definately true for the usual cases. I thought that prime lenses at higher ISOs yield less grain than zoom lenses at high ISOs, but I may be mistaken here. However, with my tests, I really had the effect that I had sharper letters with ISO 400 and upwards. I can imagine two reasons for that: 1) my lighting was really bad. Even though I had three lamps in addition to the room lights, all of them weren't very powerful (40W) or 2) this might be something that is related to the live view when using the tethered connection. This is how I manually focused my lens. I am no expert here either.

I believe you're mistaken. There should not be a difference in grain, just in sharpness and in other aberrations such as geometric distortions.

Are you letting the camera select the shutter speed? My guess would be that going to ISO 400 increased the shutter speed, which can help improve sharpness. At lower ISOs, the shutter speed was probably slow enough that you were getting a slight amount of tripod wobble softening the images. If that's the case, you could improve quality by using more lights or by securing your camera more thoroughly so that it won't wobble at all.

[russca]

I've found that zoom lenses are fine in most cases, but that depends on what level of quality you're looking for.

How much variation in size are you talking about? A few centimetres difference (like small paperbacks vs 6x9"), or much greater (small paperbacks vs A3)? The greater the variation in size, the more advantage you get from a zoom lens. Lens sharpness won't help you so much if you've cut your resolution in half by heavy cropping.

Are you imaging pure-text books you intend to run through Scan Tailor, or are there illustrations or historical book pages you'd like to retain the exact appearance of? The slight sharpness difference between a zoom and a prime will not affect Scan Tailor output nearly so much.

I am not sure about variation, but I expect most of the books to be around A4. I am planning to build a scanner with a cradle slightly bigger than A3 [15x18] just in case. And I think Scan Tailor is the only option I have right now. From your reply it looks like zoom lenses are the way to go in my case. Could you recommend a good one?

Forgot to add: My desired scan resolution is 400 dpi, the lowest - 300 dpi.

[Misty]

I'm afraid I'm not a Canon shooter, so I don't have any specific recommendations I can give you. I'm not familiar enough with the options. That said, for Scan Tailor purposes, you would probably be fine with just the kit zoom (the 18-55 that comes with the camera).

However, if you're shooting only text with no illustrations I think a DSLR might be overdoing it. I recommend a DSLR or a mirrorless large-sensor camera for books where quality imaging of illustrations, or of the original appearance of the book page, is important. A cheaper compact camera should be able to give you roughly comparable results for pure-text pages processed through Scan Tailor.

[russca]

However, if you're shooting only text with no illustrations I think a DSLR might be overdoing it. I recommend a DSLR or a mirrorless large-sensor camera for books where quality imaging of illustrations, or of the original appearance of the book page, is important. A cheaper compact camera should be able to give you roughly comparable results for pure-text pages processed through Scan Tailor.

That might be the way to go for me. I can get 2 Canon G12's for the price of one Canon DSLR.