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Thread: Do I have this right (macro calculations) ?

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    Former Username : Wetpixels Dazz1's Avatar
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    Do I have this right (macro calculations) ?

    I read up on macro lenses etc, and they talk about achieving 1:1 ratio or better. I also read about alternatives, such as zoom lenses, with macro facility included, that only get to 1:2 ratio.

    So, I was wondering what the 18-55mm kit lens I already have can do, so I photographed a ruler, and at closest focus at 55mm focal length, I get 57mm of the ruler across the image. Given that the APS-C sensor in Canon is 22.3 mm, this is about 1:2.5 ratio, isn't it?

    So does this also mean I would not achieve much, in terms of macro ability, by using one of these zoom lens that give 1:2.

    Or is my thinking all screwed up on this?
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    Quote Originally Posted by wetpixels View Post
    So does this also mean I would not achieve much, in terms of macro ability, by using one of these zoom lens that give 1:2.
    Exactly. That's why you should save your pennies for a dedicated macro lens, IF that's the way you want your photography to go. There would be no point in simply getting a zoom with close focus ability because you already have that in your kit lens ... or near enough.

    With a true 1:1 macro you can even add extension tubes or a teleconverter and get images larger than life size i.e. 2:1 or larger with only a small drop off in lens speed (maybe 1 stop). That won't matter so much if you use a flash attachment as well, as many dedicated macro shooters often do.
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    A royal pain in the bum! arthurking83's Avatar
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    Quote Originally Posted by wetpixels View Post
    ....... and at closest focus at 55mm focal length, I get 57mm of the ruler across the image. Given that the APS-C sensor in Canon is 22.3 mm, this is about 1:2.5 ratio, isn't it?

    ......
    Technically that's correct, but looking at Canon's own specs on this lens, it says 0.34x magnification .. which works out to 1:2.94 as a ratio.

    So! I dunno if you did something wrong, or if Canon have been ultra conservative with their specs.
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    Quote Originally Posted by arthurking83 View Post
    Technically that's correct, but looking at Canon's own specs on this lens, it says 0.34x magnification .. which works out to 1:2.94 as a ratio.

    So! I dunno if you did something wrong, or if Canon have been ultra conservative with their specs.

    OK, so here's the photo. That appears to be 57mm of ruler stretching across the frame (ok not quite square, but at least 56mm). Unless the sensor size of 22.3mm is incorrect...

    Last edited by Dazz1; 30-06-2013 at 8:00pm.

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    A royal pain in the bum! arthurking83's Avatar
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    Well .... there'ya go!

    Specs say that the Canon sensor is 22.3mm wide, so .....

    You have about a 1:2 reproduction ratio.

    Going by Canon's specs for the lens, at 0.34 magnification, you should be seeing 65mm on the ruler at minimum focus distance(MFD), and the fact that you're squared up perfectly doesn't account for an almost 10mm discrepancy .. a mil or two, maybe .. but not as much as Canon specs say it should be.

    As long as you're happy with the images the lens provides a6t close focus .. you have yourself a fairly capable close up lens there.

    Back onto one of your original questions: As for getting another lens to achieve 1:2 reproduction .. considering this lens gives you close to that already, don't waste your money.... unless this other lens also provides other possibilities for you.
    (eg. a longer focal length range, or faster aperture or whatever).

    But having that ability to get down to 1:1 with a proper macro lens is also a huge bonus to have at your disposal. For that, Tamron's 90/2.8 macro lens is awesome value for money and can be found cheaply. Doubles up nicely as a portrait lens.

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    Quote Originally Posted by arthurking83 View Post
    Well .... there'ya go!

    Specs say that the Canon sensor is 22.3mm wide, so .....

    You have about a 1:2 reproduction ratio.

    Going by Canon's specs for the lens, at 0.34 magnification, you should be seeing 65mm on the ruler at minimum focus distance(MFD), and the fact that you're squared up perfectly doesn't account for an almost 10mm discrepancy .. a mil or two, maybe .. but not as much as Canon specs say it should be.

    As long as you're happy with the images the lens provides a6t close focus .. you have yourself a fairly capable close up lens there.

    Back onto one of your original questions: As for getting another lens to achieve 1:2 reproduction .. considering this lens gives you close to that already, don't waste your money.... unless this other lens also provides other possibilities for you.
    (eg. a longer focal length range, or faster aperture or whatever).

    But having that ability to get down to 1:1 with a proper macro lens is also a huge bonus to have at your disposal. For that, Tamron's 90/2.8 macro lens is awesome value for money and can be found cheaply. Doubles up nicely as a portrait lens.
    Thanks Arthur. Once again, advice appreciated.

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    Ausphotography Veteran Speedway's Avatar
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    Simply put at 1:1 you could close in till you get 22.3 mm of the ruler in focus at 100%. That's approximately 2.5 times more Magnification which is quite a lot on the finished subject.
    Cheers Keith
    Last edited by Speedway; 01-07-2013 at 2:40pm.
    Keith

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    Arch-Σigmoid Ausphotography Regular ameerat42's Avatar
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    Quote Originally Posted by wetpixels View Post

    ...So does this also mean I would not achieve much, in terms of macro ability, by using one of these zoom lens that give 1:2.

    Or is my thinking all screwed up on this?...
    1. So does this also mean...: Yes, if that extra magnificence doesn't matter to you.
    2. Or is my thinking...: Nope! Quite right. It's all simple geometry.

    Only Q is: how well does your present gear work? Good IQ, etc? Don't do all that much macro? etc...
    Am.
    Last edited by ameerat42; 01-07-2013 at 3:22pm.
    CC, Image editing OK.

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    Quote Originally Posted by Speedway View Post
    Simply put at 1:1 you could close in till you get 22.3 mm of the ruler in focus at 100%. That's approximately 2.5 times more Magnification which is quite a lot on the finished subject.
    Cheers Keith
    Yep, thanks, confirms my calcs looking at it another way.

    - - - Updated - - -

    Quote Originally Posted by ameerat42 View Post
    1. So does this also mean...: Yes, if that extra magnificence doesn't matter to you.
    2. Or is my thinking...: Nope! Quite right. It's all simple geometry.

    Only Q is: how well does your present gear work? Good IQ, etc? Don't do all that much macro? etc...
    Am.

    Macro is one of my main interests, so I will eventually want to upgrade something so my Canon can get at least as close as the Fuji, and hopefully with better IQ. However, like all my decisions, I will probably agonise over what is the most cost effective way. I want to be sure I won't be just as happy with extension tubes, or reversing rings, etc, before I buy a much more expensive dedicated macro lens (but as I think you pointed out elsewhere, this could also double as a portrait lens - not that I plan to do many portraits).

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    I started out with the reverse adaptor and a set of old screw on macro filters, then got a cheep set of extension tubes but with both these and the reverse ring you have no adjustments possible I then got a set of AF macro tubes off E Bay and these still get used with my 90mm Tamron to get in even closer.
    Cheers
    Keith.

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    Quote Originally Posted by Speedway View Post
    I started out with the reverse adaptor and a set of old screw on macro filters, then got a cheep set of extension tubes but with both these and the reverse ring you have no adjustments possible I then got a set of AF macro tubes off E Bay and these still get used with my 90mm Tamron to get in even closer.
    Cheers
    Keith.
    I have been looking at the extension tubes that have electrical contacts. They say they allow AF to work, but do they also allow aperture to be set?

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    Arch-Σigmoid Ausphotography Regular ameerat42's Avatar
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    So the answer is, "If serious, then a macro lens."
    In the distant - and at the time very DIM - past, I had extension bellows and a lens reversing ring.
    You could get about 10:1, but all light was extinguished after about 6:1. Also DOF was a fraction of a mm.
    Or, you could go JGKnights way.
    Am.

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    Quote Originally Posted by ameerat42 View Post
    So the answer is, "If serious, then a macro lens."
    In the distant - and at the time very DIM - past, I had extension bellows and a lens reversing ring.
    You could get about 10:1, but all light was extinguished after about 6:1. Also DOF was a fraction of a mm.
    Or, you could go JGKnights way.
    Am.
    I presume you mean focus stacking?

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    Arch-Σigmoid Ausphotography Regular ameerat42's Avatar
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    Quote Originally Posted by wetpixels View Post
    I presume you mean focus stacking?
    Yes, but also look at his equipment. I think a bit of FS is inevitable, but not always called for.
    Am.

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    Quote Originally Posted by wetpixels View Post
    I have been looking at the extension tubes that have electrical contacts. They say they allow AF to work, but do they also allow aperture to be set?
    In a word yes they allow all lens functions to operate and are still very usable when you do get a dedicated macro lens.
    Cheers
    Keith.

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    Quote Originally Posted by Speedway View Post
    In a word yes they allow all lens functions to operate and are still very usable when you do get a dedicated macro lens.
    Cheers
    Keith.
    Seems like an easy way to start then. Thanks for the info.

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    Quote Originally Posted by wetpixels View Post
    Seems like an easy way to start then. Thanks for the info.
    Easy way yes1
    Good way .. no!

    Kit zoom lenses are not particularly ideal for use with extension tubes.
    You may have some luck getting some OK image detail from the centre of the lens, if the lens is particularly sharp to begin with.

    But (and I'm assuming that your lens is an EF-S specific lens, meaning that it has APS-C only coverage.
    If so, then as you push the lens further forward of the correct mounting plane, the image circle that the lens forms(onto the sensor) becomes smaller.
    Each and every lens is different, and only testing can provide the necessary data to know how well a lens works or not.

    The larger the image circle that the lens creates to begin with, the further forward you can push it from the mount.
    I can test something like a Nikon APS-C lens to see roughly where it cuts out too much of the image circle .. but of course this test is of no use to yourself.

    An EF type prime lens .. that is any prime lens made for full frame, is ideal for use on a set of extension tubes.
    Note too tho, that the shorter the focal length, the more effective that the extension tube becomes in terms of producing magnification from the lens.

    ie. a 35mm focal length, will provide more magnification than will a 90mm focal length with the same extension distance. And unless the shorter focal length is something extraordinary to begin with, the image quality from that short focal length is generally not as good as it will be from a longer focal length once extension tubes come into the equation.
    Either that or all my shorter focal length lenses are just simply complete duds(which I'm pretty sure is not the case).

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    Quote Originally Posted by arthurking83 View Post
    Easy way yes1
    Good way .. no!

    Kit zoom lenses are not particularly ideal for use with extension tubes.
    You may have some luck getting some OK image detail from the centre of the lens, if the lens is particularly sharp to begin with.

    But (and I'm assuming that your lens is an EF-S specific lens, meaning that it has APS-C only coverage.
    If so, then as you push the lens further forward of the correct mounting plane, the image circle that the lens forms(onto the sensor) becomes smaller.
    Each and every lens is different, and only testing can provide the necessary data to know how well a lens works or not.

    The larger the image circle that the lens creates to begin with, the further forward you can push it from the mount.
    I can test something like a Nikon APS-C lens to see roughly where it cuts out too much of the image circle .. but of course this test is of no use to yourself.

    An EF type prime lens .. that is any prime lens made for full frame, is ideal for use on a set of extension tubes.
    Note too tho, that the shorter the focal length, the more effective that the extension tube becomes in terms of producing magnification from the lens.

    ie. a 35mm focal length, will provide more magnification than will a 90mm focal length with the same extension distance. And unless the shorter focal length is something extraordinary to begin with, the image quality from that short focal length is generally not as good as it will be from a longer focal length once extension tubes come into the equation.
    Either that or all my shorter focal length lenses are just simply complete duds(which I'm pretty sure is not the case).
    Well, I have been told that a nice prime lens, maybe a 50mm f/1.8, should on my wishlist anyway. Someone also mentioned a prime/macro.

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