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noob lens questions : infinity focus distance and what is macro

Discussion in 'Open Discussion' started by squeegee, Jan 26, 2010.

  1. squeegee

    squeegee Mu-43 Veteran

    403
    Jan 26, 2010
    okay so I have 2 noob lens questions :

    1) how do I calculate how far is the closest object is at infinity focus? So as an example, I have the oly 17mm prime, if I were to focus at infinity, what's the closest object that would actually be in sharp focus?

    2) What is a macro lens? I've read the google results and I'm still confused. It's easy to say "it's 1:1 size" but I don't understand what the difference between a macro and telephoto lens is. 2 examples :

    a) if I get a 200mm lens, and I point it at something "close by" like say some thing in the same room as me, won't I get a life-size (1:1) image of that item anyways? Or conversely if I used a macro lens and just walked away from an item, it won't be 1:1 anymore, it'll be smaller, like any other lens...

    b) if I get a 50mm macro lens, and I get a 50mm prime (or a zoom lens set to 50mm) and I take a picture of something, what's the difference in the picture I actually get? (Sure I could just try it, but that would entail me buying a bunch of lenses I don't understand.)

    Hey I did say these were noob question okay...
     
  2. pxpaulx

    pxpaulx Mu-43 All-Pro

    Jan 19, 2010
    Midwest
    Paul
    1:1 macro, as basic as I can describe it, means the lens can focus so close that what is projected onto the sensor is the actual size of the framed imaged. Say for the purpose of example that a penny is the size of the sensor. With a true 1:1 macro lens, the image you will be able to capture of the penny will take up the entire frame - it will be actual life size as it related to the actual real life size of the sensor...in this case the frame is the sensor, prior to digital it would have been the size of the film.

    If a macro lens is designated 1:2 (or 1:3, 1:4), then the image of the penny within the frame will only be half as big (or 1/3 or 1/4 and so on...though beyond 1:2 I dont think a company would even bother to specify). some people only consider 1:1 lenses true macro (unlike lenses such as the bigger zooms from sigma/tamron, say the 70-300mm lenses that say they have macro capability, but they are not true 1:1 macro).

    Finally, there are true 1:1 macros at different focal lengths. Pentax for instance has 35mm, 50mm and 100mm macros. The difference here is how close you have to put the subject to the lens in order to achieve the 1:1 size on the sensor (in the case of my 50mm macro, it is about 1 inch away - fine for plants and static objects, but not as good for bugs or moving subjects).

    As far as your first question, there are probably calculators online (there are for depth of field so I assume this can also be calculated), but cant be of any help!
     
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  3. Alan Wolf

    Alan Wolf Mu-43 Regular

    66
    Jan 20, 2010
    Berkeley, CA
    close in focus distances

    I’ll take a stab at the first question, but am going to just give the idea; using the D of field tables will give you specifics.

    Okay, first you need to know that depth of field means “from what distance to what distance will objects appear in focus.” There are several variables involved, and I am listing them in no particular order. The first is focal length of the lens—the shorter the focal length (wider the lens) the greater the depth of field. Second is the aperture—the smaller the aperture (which means a bigger number), the greater the depth of field. So, for a given lens, say a 20mm lens, there will be more depth of field at f11 than there will be at f4.

    Third is the image size. This always meant film size, but now also means sensor size. The smaller the sensor (or image size) the greater the depth of field. This is one reason that compact point and shoot cameras (with really small sensors) have almost everything in focus.

    Fourth is the distance that the object is from the image plane. The further away, the greater the depth of filed. This relates very much to your macro question, because at macro distances, there is VERY little depth of field—it can be hard to get both of a fly’s eyes in focus.

    If you have any older cameras around, lenses used to illustrate all of this right on the lens barrel. There was a distance scale, that showed how far away what you were focussed on was, and then a series of marks that represented how wide the field of focus was at variable apertures. A trick photographers used to use (and still do) was to set their focus ahead of time, based on where the markRon their lens said that infinity would still be in focus at the aperture they were shooting at—this sounds confusing, but is very simple. (Called hyperfocal distance.)

    For an m4/3 camera, with a 20mm lens at f8, the hyperfocal distance is 11 feet, at which setting, everything from about 5 feet to infinity is in focus. The web site that allows you to figure this out (since many lenses no longer have the scales on them, and also, the scales would only be valid for use with the image size that the lens was originally intended for):

    http://www.dofmaster.com/dofjs.html
     
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  4. Streetshooter

    Streetshooter Administrator Emeritus

    Dec 15, 2009
    Phila, Pa USA
    Very nice explanation.
    The dof program is available as an app for the iPhone.
    If you can't find your camera listed, m4/3 uses a
    COC, Circle of Confusion, of .015...
    Enter that and your lens focal length and your good to go.
     
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  5. squeegee

    squeegee Mu-43 Veteran

    403
    Jan 26, 2010
    okay so let me try to re-iterate then...

    With a 4/3rds sensor... if want to take a picture of something that's 18×13.5 mm (4/3rds sensor size), I'm capable of putting the camera close enough that the item fills my entire picture, and the lens is good enough to focus at that distance.

    So if that's true, wouldn't it mean that a Macro lens is the same as any other lens but has the ability to focus really close? (because technically speaking, I can take a picture of a 18x13.5 item with my 17mm lens, it's just out of focus).

    Now if that's true. If you had a choice between say a 50mm regular lens, and a 50mm macro lens, why wouldn't some one just always buy the macro (other than say maybe the price). Does allowing it to focus so short affect it's normal / longer focus abilities or other properties?
     
  6. squeegee

    squeegee Mu-43 Veteran

    403
    Jan 26, 2010
    okay I kind of under stand DOF and that the smaller the aperature the longer DOF and I have read and kind of understand the concept of hyperfocus distance too. But, what I'm trying to do is kind of backwards from that.

    As an example, with the DOF calculator web link, if I put in my 17mm lens at f4. If I put in a subject distance of 4.9 metres, I notice the far limit of the DOF becomes infinity (where as 4.8 does not). So I guess for the answer to 17mm+f4, my answer is roughly 5 metres. I was just wondering if there was an easier way to come up with that number, I guess it's not too bad just putting in distances till I see it go to infinity. (I have no real world application, just back ground knowledge I was wondering about how far infinity is for different lenses like 17mm v.s. 50mm v.s. 200mm etc at a given reasonable F number the lenses support.)

    Thanks everyone for the answers, it's making a little more sense now.
     
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  7. pxpaulx

    pxpaulx Mu-43 All-Pro

    Jan 19, 2010
    Midwest
    Paul
    That is pretty much right in a nutshell. given the 4/3 sensor size of 18x13.5, an item that is actually that size in real life will fill the 4/3 sensor frame.

    With a non-macro lens, you'll usually hear people discuss its close focus ability. I wouldn't categorize a macro as 'good enough' to get close to the subject, it is simply designed to do this. With a macro, the lens is designed so the front element and interior glass adjust a significant amount (by extending away from the camera body). The focal length of the lens also determines whether macro can be achieved. A wide angle lens simply can't be a macro because the field of view is too extreme. For example, my 10-17mm fisheye lens can focus on a subject that is less than 1/4" of an inch away from the front lens element. But, because it is such an extremely wide angle, even right in front of the lens the subject hardly starts to fill the frame (since the fisheye is 180 degree field of view at the widest end).

    Macro lenses still have infinity focus, and can be used in standard ways as well (my 50mm macro makes a decent portrait lens as well, lacking extreme shallow depth of field at portrait lengths due to the F2.8 max aperture). They are just specially designed to be able to get right upto the subject. With a longer focal length (say 100mm vs 50mm) you can be (somewhat) farther away from the subject. Macro lenses are usually a slower max F-stop (2.8 is pretty standard), which limits their low light ability, and the ability to achieve a shallow depth of field for portraits is also diminished.
     
  8. Amin Sabet

    Amin Sabet Administrator

    Apr 10, 2009
    Boston, MA (USA)
    For me, macro photography is about showing things in a photograph that are too small to appreciate with the naked eye. People sometimes call any close up photography "macro", but that doesn't really make sense because a long focal length macro lens will get you into that small world from a greater working distance than will a short focal length macro lens.

    This is the reason why macro is defined based on 1:1 or greater magnification ratio, but that too is a very limited way to conceptualize the idea of being able to appreciate very small things because magnification ratio is directly dependent on sensor size.

    Say, for example that we have an insect which is 35mm in width and take a picture of it with a Nikon D700 where the bug occupies the whole frame. That will be 1:1.

    Now say that you take a picture of the same 35mm bug using a lens on a Four Thirds (or Micro Four Thirds) camera such that the bug occupies the entire frame. You are now shooting at 1:2 but still getting into the same very small world that you got using 1:1 on the D700.

    1:2 is plenty of magnification for a lens which I would use for "macro" on a :43: body.
     
  9. pxpaulx

    pxpaulx Mu-43 All-Pro

    Jan 19, 2010
    Midwest
    Paul
    Actually, I believe the 1:1 image on the 4/3 sensor, as related to full frame 1:1 macro shot, would actually be 1:0.25 (since the 4/3 sensor is about 1/4 the size of a FF sensor). A 1:1 macro lens will always project a 1:1 image onto the sensor - the only variable is the sensor size itself. Since the registration distance of a lens doesn't vary (i.e. if you have a nikon macro mounted via adapter on the m4/3 camera, it is still the same registration distance, and will still display a 1:1 image onto the sensor - the sensor is just smaller, therefore the 1:1 image will be smaller than on the 24x36mm full frame sensor).

    Edit: regarding your example of shooting a bug. If the bug fills the frame on a FF sensor, using the same macro lens should result in, say, the bug's head filling the frame on a 4/3 sensor.
    When I get my K-m/43 adapter I will demonstrate this for the OP!
     
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  10. squeegee

    squeegee Mu-43 Veteran

    403
    Jan 26, 2010
    thanks for the replies, I think I have a grasp of macro concepts now.

    I've been passively thinking of getting a macro lens but I wanted to kind of understand how it would fit into my collection and I think this info helped.

    thanks.
     
  11. Amin Sabet

    Amin Sabet Administrator

    Apr 10, 2009
    Boston, MA (USA)
    Pxpaulx, I'm pretty sure that I have this right.

    In that case, the macro lens would be 1:1 on both cameras but the 4/3 camera would be taking us into a smaller world than the 35mm frame camera (assuming equal pixel counts for both sensors and a lens which could outresolve both sensors).

    Now let's say that you had a macro lens on a 35mm frame camera where the whole bug exactly fit the frame and the image of the bug was life size as projected onto the sensor (1:1) and wanted to find another lens for a 4/3 camera such that the whole bug exactly fit the 4/3 frame - the bug's image as projected onto the 4/3 sensor would now be half of life size, ie 1:2 magnification ratio.
     
  12. Alan Wolf

    Alan Wolf Mu-43 Regular

    66
    Jan 20, 2010
    Berkeley, CA
    close up lenses

    If you're curious about macro, the least expensive way to try it is with some close up filters. These will screw in front of your lens and allow it to focus closer. Okay quality—certainly good enough for you to get used to what's involved (generally tripods, possibly additional lights or reflectors, something to shield the breeze if you're outside) and see if this type of shooting appeals to you. It can be addicting, looking at things in so much detail. If you do buy a dedicated macro lens, the filters will still come in handy, as they are so easy to toss in a bag pocket and have with you.
     
  13. pxpaulx

    pxpaulx Mu-43 All-Pro

    Jan 19, 2010
    Midwest
    Paul
    1:1 Macro comparison 50mm lens aps-c vs 4/3

    I got my adapter today! So, I have taken a few photos (which will be posted in the adapted lenses thread and the weekend contest) but I remembered to compare my Pentax SMC F 50mm F2.8 Macro on APS-C with my Pentax K-x and 4/3 (well, m4/3) with my GF1. Here is the comparison:

    1:1 macro with the 50mm lens on the Pentax K-x:

    <a href="http://picasaweb.google.com/lh/photo/xwuej-ZM1KGAWu50qldzLA?feat=embedwebsite">http://lh5.ggpht.com/_HmFO4R4ztlk/S2SfxskGMpI/AAAAAAAABdA/kXdQG4BsDQ0/s800/IMGP0329.JPG" /></a>

    and 1:1 macro with the same 50mm lens adapted to the Panasonic GF1:

    <a href="http://picasaweb.google.com/lh/photo/PZKguuo4BvLjAbWDuqof4g?feat=embedwebsite">[img]http://lh4.ggpht.com/_HmFO4R4ztlk/S2SeKMprZJI/AAAAAAAABcQ/rko6S9Fp94s/s800/P1000192.JPG" /></a>

    Shots were both made with Pentax AF360-fgz flash off camera (to the left), wireless p-ttl with the Pentax K-x and wireless slave mode with the GF1.

    Hope that was helpful!
     
  14. spark

    spark Mu-43 Regular

    28
    Feb 8, 2010
    Toronto
    Here are those last 2 images in the previous post overlayed on each other. I scaled the GF1 image by ~0.8 because the GF1 has a crop factor of 2 and the Pentax (I assumed) a crop factor of 1.6 (i.e. 1.6/2 = 0.8).

    The orange outline shows that the GF1 can "see" less of the subject because the sensor is smaller even though the lens is shooting at 1:1.

    Note: They don't line up exactly because I didn't play with the perspective and the two cameras weren't in exactly the same position.
     

    Attached Files:

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  15. pxpaulx

    pxpaulx Mu-43 All-Pro

    Jan 19, 2010
    Midwest
    Paul
    Yeah they weren't exact since these were handheld (have to remember the lens is less than 1 inch from the subject!). Also, only Canon has the 1.6x crop factor, all other brand aps-c sensors are 1.5x.

    Like you said, both images are 1:1, only since the actual physical 4/3 sensor size is smaller, it 'appears' to get closer to the subject.
     
  16. spark

    spark Mu-43 Regular

    28
    Feb 8, 2010
    Toronto
    I was surprised how well the images lined up when I layered them. You were surprisingly close between the two shots. :thumbup:
     
  17. hodad66

    hodad66 Mu-43 Top Veteran

    806
    Jan 27, 2010
    Indialantic, Florida
    a macro using the G1 and a Canon FD 50mm
    macro lens and 1:1 adapter... simple weed

    4382471729_144ee0cce7_o.