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Magnification and Working Distance

Determining Magnification:

The easiest way to calculate your magnification is to take a picture of a ruler. That's it, you can do all kinds of math etc. (and most of it will be wrong because of lens design - more on that below) or take a picture of a ruler and compare it to your sensor size. So, first you need to determine your sensor size which is available on numerous websites.

Keep in mind that magnification does not change when sensor size changes. So, you will have the same magnification on a "Full Frame Sensor" as you will on a "Crop Sensor". That's where the term "Crop Sensor" comes from, it "crops" the image. So you will have less of it. Once you have your sensor size either the length or width, you just divide what it says on the ruler into the sensor size. For instance if you have a full frame Canon your sensor width is 36 mm. If your ruler shows 18 you divide 36/18 and you get 2.0 magnification. If your ruler says 36 and you have a full frame sensor you have 36/36 or 1:1 magnification. So, in a nutshell if your ruler number is larger than your sensor, you already know you are not at 1:1 or higher magnification.

Working Distance:

Working Distance is the distance from the end of the lens to the subject. Many times you will see the distance to the film plane quoted and your camera may even have a mark on it showing exactly where it is. I have yet to find a lens where I can measure from the subject to the film plane and dial in the focus. So, kind of useless I think.

What is useful is the distance from the end of the lens barrel to the subject. The reason I say lens barrel is some have a recessed lens like the Canon 50mm Macro lens. It is about an inch or so behind the end of the lens. Knowing that distance really doesn't do me much good either. However what is good to know is how close the end of my lens barrel needs to be to the subject.

When you change the distance to the subject you are also changing the magnification. Some macro options actually go in the opposite direction if you move to far away from the subject. In other words if you are not close enough you could end up with more magnification without your macro option!

Angle of View:

If you look at a 100mm lens and a 180mm macro lens they have one thing in common, they both can generate 1:1 magnification. However, they do it at two different differences because the angle of view is different. The 180mm has a narrower angle of view so the user is further away. What is important here is to remember the narrower the field of view the easier it is to get camera movement which is the number one reason for failed macro images.  So when you make your lens purchasing decision keep that in mind.  

 

The Test:

The chart below is an simple test, not super scientific as I am photographing a ruler, I don't have all kinds of laser measurement devices. It is to provide an idea of what you can expect. For instance I have read on numerous websites that if you reverse a 50mm lens you will get 1:1 magnification. The fact is I tried it on three different 50mm lenses and I didn't get it or anything close to 1:1, so don't buy into it unless you do your own test. The three 50mm lenses tested were also not even close to each other.

The distances to the subject has been rounded a little but they are close. As for reading the image it is close as well but where do you actually read the line. I know the lighting was poor as I had to keep moving things, but this is not about that it is just about magnification. What was photographed is a cheap plastic ruler with a machinist's SS ruler in 100ths of a inch placed on top of it and held in place by alligator clips. I set the camera on a tripod and used Canon's live view, I focused the lens (depending upon the test) as close as it could go and then I moved the ruler towards the lens and when it was in focus I took the shot. The exposure was done with the automatic Tv function (Shutter Speed). The images were saved in RAW (for reference), and Small JPG, the Small JPGs were later batch shrunk to fit in this table. The original small JPGs can be viewed by clicking on the image in the table. No post processing of any kind was done. So it should also present a decent view of out of the camera quality.

 
Lens Distance Image - Magnification
(click on Image for a larger view)
100mm Macro 15 cm - 6 inches

1:1 Magnification with a 100mm Macro
36mm - 1:1 Magnification - perhaps a little more

100mm Macro 31 cm - 12 inches
112mm - 1:32 Magnification
100mm Macro
with
1.4X Tele-Converter
15 cm - 6 inches 1.4 Tele Converter Magnification with 100mm Macro
25mm - 1.4:1 Magnification
100mm Macro
with
1.4X Tele-Converter
31 cm - 12 inches 1.4 Tele Converter Magnification with 100mm Macro
71mm - 1:51 Magnification
100mm Macro
with
1.7X Tele-Converter
15 cm - 6 inches 1.7 Tele Converter Magnification with 100mm Macro
22mm - 1.6:1 Magnification
100mm Macro
with
1.7X Tele-Converter
31 cm - 12 inches 1.7 Tele Converter Magnification with 100mm Macro
49mm - 1:73 Magnification
100mm Macro
with
2X Tele-Converter
15 cm - 6 inches 2X Tele Converter Magnification with 100mm Macro
18mm 1.9:1 Magnification
100mm Macro
with
2X Tele-Converter
31 cm - 12 inches 2X Tele Converter Magnification with 100mm Macro
48mm 1:75 Magnification
100mm Macro
with
65mm Extension Tubes
120 cm - 5 Inches
close as possible
Magnification of 100mm Macro and 65mm extension tubes
18mm 2:1 Magnification
100mm Macro
with
65mm Extension Tubes
180 cm - 7 Inches
far away as possible
Magnification of 100mm Macro and 65mm extension tubes
57mm 1:63
100mm Macro
with
Canon 250 Close up lens
85 cm - 3.5 inches 100mm Macro and Canon 250 Close Up Lens
22mm - 1.6:1 Magnification
100mm Macro
with
Canon 250 Close up lens
15 cm - 6 inches 100mm Macro and Canon 250 Close Up Lens
56mm - 1:65 Magnification
28mm  Lens Reverse Mounted 60cm - 2.5 inches 28mm Lens Reversed for Macro
18mm - 2:1 Magnification
50mm  Lens Reverse Mounted

I tried three different 50mm lenses and each performed differently but none were close to 1:1 - they actually performed very differently

100cm - 4.25 inches 50mm Lens Reversed for Macro
53cm - 1:63 Magnification
43-70mm Zoom Mounted Backwards and set at 43mm 70cm - 2.75 inches 43-70mm Zoom Reversed for Macro at 43mm
27cm - 1.3:1 Magnification
43-70mm Zoom Mounted Backwards and set at 70mm 220cm - 9 inches 43-70mm Zoom Reversed for Macro at 70mm
120 cm - 1:3 Magnification


 

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