noob lens questions : infinity focus distance and what is macro

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!

 

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

 

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.

 

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.

 

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!

 

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.

 

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!

 

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.

 

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.

 

I was surprised how well the images lined up when I layered them. You were surprisingly close between the two shots.

 

a macro using the G1 and a Canon FD 50mm
macro lens and 1:1 adapter... simple weed