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08/05/2009 08:00:01 AM · #1 |
I'm not so good with the understanding of how different lens' work - never been on a course etc. Does anyone have any links which would explain say... the difference between a 70-300mm lens and a 18-200mm lens.
Or... if anyone has any time to spare....I'm wanting to buy as good as I can get macro lens, with possible the choice of having a telephoto lens too.
If I bought the 18-200mm, and I already own a 18-55mm canon lens - surely I would only get the same macro capability on the 18-200mm? Am I right? :S
If I wanted a good macro lens (better than my 18-55mm) would I have to go lower than the 18mm?
Again - not so good with the technicals - so apologies for sounding like d'oh!
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08/05/2009 08:20:50 AM · #2 |
Macro capability actually has nothing to do with the focal length.
When speaking of macro, we are speaking of the actual reproduction ratio or ratio of the size of the object in real life to how large it appears on your sensor. Generally people will say true macro only starts where you reach 1:1, meaning what is depicted on your sensor is the same size as the actual object.
What a larger focal length (the 200 in the 18-200) will do is give you more "reach" or distance to the subject. What that means is you can achieve 1:1 from farther away. The 18-200, however, does not have a terribly high maximum magnification ratio, at only .24x. A reasonable macro lens is the Canon EF-S 60mm f/2.8. You will have to get pretty close to your subject though. Another option is to get a cheap 50mm 1.8 and use extension rings, though you will lose infinity focus, which means you will only be able to focus up close and not at objects in the distance.
As far as talking about "going lower than 18mm," 18mm is actually a wide angle focal length, and 200 a telephoto focal length. What this means is that the single 18-200 lens covers the range between the two, giving you great flexibility for a wide variety of situations. There are some optical drawbacks due to this huge range, but it is a great all around lens.
I would recommend you check out the virtual camera for some general info. It's a flash based simulator of camera operation that is great for learning. I think there might be some other ones that are similar.
Does that explain things a bit or make them more confusing?
ETA: Your 18-55 actually has a higher magnification ratio, at .3x, so it will produce a more magnified version than the 18-200. You could also get the Canon 500D Close Up lens which you can screw onto the end of your lens like a filter, but I wasn't very impressed with the performance of closeup filters (I haven't personally used the Canon version, however).
Regarding the difference between the 70-300 and the 18-200; The 70-300 will give a higher magnification over a distance. The minimum focusing distance is longer (meaning, your subject has to be further from the focal plane (your camera's sensor) to achieve focus) but given the same distance from the focal plane, if the 70-300 is fully zoomed (to 300mm), the subject will appear larger than how it would appear on the 18-200 fully zoomed (at 200mm). On the wide (low number) side of things, the 18-200 will be significantly wider, meaning you will be able to fit more things into the frame given the distance to subject.
These are pretty crude explanations, so somebody else might be able to explain things better.
Message edited by author 2009-08-05 08:44:55. |
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08/05/2009 08:53:25 AM · #3 |
I'd go with the 100mm Canon Macro, f/2.8
I love it, and it can also double as a telephoto (especially on your XSi, as it'll actually be more like 160mm rather than 100mm -- meaning that you will be able to "zoom" further...).
It's around $600 new, but it's my best lens (though I only have four lenses, but that's besides the point). ;) |
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08/05/2009 08:53:26 AM · #4 |
| Perhaps this illustrated explanation can help. I can ran across a really good explanation a while back, but I don't appear to have it bookmarked. |
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08/05/2009 10:19:36 AM · #5 |
Originally posted by spiritualspatula:
ETA: Your 18-55 actually has a higher magnification ratio, at .3x, so it will produce a more magnified version than the 18-200. You could also get the Canon 500D Close Up lens which you can screw onto the end of your lens like a filter, but I wasn't very impressed with the performance of closeup filters (I haven't personally used the Canon version, however). |
Bryan Peterson (author of Understanding Exposure) also has a book on closeup photography. He's a Nikon guy and swears by the Canon 500D. I've yet to actually try it myself however.
Message edited by author 2009-08-05 10:20:31. |
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08/06/2009 04:14:34 PM · #6 |
Wow, thanks for all the help guys - you've all been FAB, and special thanks to spiritualspatula :)
I bought myself a Sigma 70-300mm (APO) today! I pick it up Friday! Yay! |
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