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Magnifyers: |
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rhysrkid Senior Member Joined: 14 Nov 2003 No. of posts: 98  View other posts by rhysrkid |
Posted: 22 Aug 2005 Can anyone enlighten me on the use of magnifyer filters - dont really know much about them. What effect do they have on depth of field, working distance and image quality? I use a 105mm 1:1 macro with my digi SLR which is great but sometimes feel it would be good to have a little more working distance. Am I on the right track? Any recommendations? Cheers guys Rhys |
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Wolfgang Wuster Senior Member Joined: 23 Apr 2003 No. of posts: 326  View other posts by Wolfgang Wuster |
Posted: 22 Aug 2005 Basically, they allow you to move closer to your subject, and therefore it fills the frame more. As you move closer, you inevtiably loose depthof field. Image quality - bolting an extra piece of glass in front of your lens will inevitably lead to some slight loss, but if you choose a good make and keep it clean and scratch free, it should not be noticeable. An alternative choice is an extension ring, which you fit between the lens and the camera body, and which has the same effect. Differences are (i) you don't get an extra piece of glass in front of your lens, hence no loss of quality; but (ii) you have to take the entire lens off the camera to fit it(possibility of dust getting in, bad for digi-SLRs); and (iii) you loose some light (i.e. f-stops) unless you use a flash. Cheers, Wolfgang Wolfgang Wüster School of Biological Sciences, University of Wales, Bangor http://sbsweb.bangor.ac.uk/~bss166/ |
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rhysrkid Senior Member Joined: 14 Nov 2003 No. of posts: 98 View other posts by rhysrkid |
Posted: 22 Aug 2005 Thanks Wolfgang - I hadn't realised that they simply allowed you to get closer - not really what I had in mind. Rhys |
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Wolfgang Wuster Senior Member Joined: 23 Apr 2003 No. of posts: 326 View other posts by Wolfgang Wuster |
Posted: 22 Aug 2005 If you want something that allows you greater magnification at the same distance, or more distance at the same magnification, then you will need a teleconverter. These go between the lens and the camera, but instead of allowing you to go closer, they make your lens "longer" - i.e., if you use a 1.4 X teleconverter with a 100mm macro, then you will in effect have a 140 m macro, if you use a 2x a 200 mm macro, etc. However, you again loose quite a bit of light with a teleconverter, and I suspect that image quality may also suffer slightly. Note that these aren't as cheap as magnifying filters or extension rings, since they contain quite a bit of optical glass themselves. On the other hand, they are a lot cheaper than actually buying a 200 mm macro.... Cheers, Wolfgang Wolfgang Wüster School of Biological Sciences, University of Wales, Bangor http://sbsweb.bangor.ac.uk/~bss166/ |
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rhysrkid Senior Member Joined: 14 Nov 2003 No. of posts: 98 View other posts by rhysrkid |
Posted: 22 Aug 2005 Wolfgang, Thank you very much - sounds like what I'm after! Cheers Rhys P.S. Gemma - good forum idea!! Rhys |
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-LAF Senior Member Joined: 03 Apr 2003 No. of posts: 317 View other posts by -LAF |
Posted: 23 Aug 2005 A quick note on image qaulity with teleconvertors. They work by cropping the image coming from the lens, then magnifying this cropped area over the image sensor. As a result there is a loss in quality directly relational to the convertor factor. So, a 1.4x convertor reduces a lenses linear resolving capability by about 30%, whereas a 2x convertor will reduce linear resolution by 50%. These figures assume the teleconvertor is optically perfect, which in reallity, none are. More expensive TCs DO perform better than cheap ones but by far the biggest factor influencing final image quality is the quality of the original lense. Prime lenses do markedly better with TCs than zooms for this reason, while 1.4x convertors tend to give noticeably superior results to 2x ones. Rhys, I'm not sure what system you use but in case it's Canon it's probably worth pointing out that Canons own 1.4x and 2x only work with a few Canon lenses, and no lenses by other manufacturers. In which case, the best bet is something like Kenko Pro TCs, that work with everything but EF-S lenses. As for light drop off, this is easy to calcuate: 1.4x convertor = 1 stop light loss 2x convertor = 2 stops light loss So if you're not using flash, it helps to start with a fast lens (another reason primes are useful!). Lee. Lee Fairclough |
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Paul Williams Member Joined: 18 Aug 2005 No. of posts: 35 View other posts by Paul Williams |
Posted: 17 Nov 2005 I use both a 2x and a 1.5x on my canon 100mm macro and have to say the 1.5x is acceptable but the 2x is poor in terms of image quality so dont tend to use it much at all |
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