Understanding macro lenses - DPChallenge Forums

04/13/2005 07:59:36 PM · #1

Hi, can somebody can explain the magnification factor? I often see number like 1:1 or 2:1 or even 5:1 magnification factor and while I think I know what it mean I surely don't know how to read it in a way to understand the impact of it in real life. Thanks.

Message edited by author 2005-04-13 19:59:47.

TooCool

Canon EOS-300D Rebel

Canon EF 50mm f/1.8 II

04/13/2005 08:02:03 PM · #2

Originally posted by nicklevy:

The way I understand it, 1:1 means the image on the film plane is the exact same size as the object in real life. Once you turn that into an 8x10 you have a close up of the object. 2:1 is twice the size on the image plane as the actual object, etc.

04/13/2005 08:03:47 PM · #3

Originally posted by TooCool:

So by what you say should I consider a ratio of 2:1 better than 1:1 without exception?

TooCool

Canon EOS-300D Rebel

Canon EF 50mm f/1.8 II

04/13/2005 08:08:45 PM · #4

Originally posted by nicklevy:

So by what you say should I consider a ratio of 2:1 better than 1:1 without exception?

If you are judging solely by magnification... I suppose it would depend on what small objects you are attempting to photograph.

Message edited by author 2005-04-13 20:09:27.

Canon RF 24-70mm f/2.8 L IS

04/13/2005 08:11:04 PM · #5

Thanks a lot TooCool. Before this moment I thought that 2:1 meant that the lense is able to achieve an image half the real size on the film plane. That helps a lot.

kirbic

Canon EOS R5

04/13/2005 08:11:46 PM · #6

Right... in addition to what TC posted, when you consider how large an object will be when printed, you also need to consider the sensor size. On your cam, the sensor is about 7.2mm wide by 5.3mm high, so an object that's 7mm long will fill the frame lengthwise at 1:1 magnification. Print that at 8x10, and you have an object close to 8 inches long.
Now consider a DSLR, with a sensor 22mm wide. That same object, at the same 1:1 magnification, will only fill 1/3 of the frame width. Now when you print at 8x10, the object will be only 2.7 inches wide!
So magnification is a bit misleading in today's photography landscape, where sensor sizes vary so greatly. Of greater importance is the minimum field of view (FoV). A horizontal FoV of 25mm, blown up to 8x10 inches, will mean an object 1 inch long becomes 8 inches long on the print, and that remains true no matter what camera is used. The FoV is also easily measured by the user, just shoot a finely-graduated ruler at your closest focus.

Message edited by author 2005-04-13 20:21:30.

Canon RF 24-70mm f/2.8 L IS

04/13/2005 08:21:22 PM · #7

Thanks Kirbic. I'll be upgrading to 350D maybe in the next few days and I want a macro lens and all the technical data I can get the better will be my choice (not sure if this sentence make sense but in my french-people-trying-to-write-in-english mind it do :-) ) Does that mean that I should look for FOV (focal length) and closest focusing distance rather than magnification factor?

kirbic

Canon EOS R5

04/13/2005 08:25:59 PM · #8

Originally posted by nicklevy:

Well, if you are looking to compare lenses for the same camera, then of course, the higher the magnification, the smaller the FoV will be (for the same sensor size). Any good macro lens will go to 1:1. Very few go higher without accessories, the notable exception is the Canon MP-E65 which goes all the way to 5:1, but is useless for non-macro photography (does not focus further away than a few inches).
There are other ways to achieve macro-type magnifications than with a didicated macro lens, but all are compromises. A really good maco lens can also serve as a great short telephoto and portrait lens. For reasonable money, there are none better or more flexible than the Canon 100/2.8 Macro USM.

Mattel Barbie Photo Designer Digital Camera

04/13/2005 09:01:30 PM · #9

The lens I'm looking at for both landscape and macro is the sigma 70-300mm APO wich can focus at 91cm, with a FOV of 8.2 degrees. They rate the magnification factor at 1:2. Is there any math formulas I can use to calculate the size of objects on prints? Also, does the crop factor in DSLR affect the magnification ratio?

nsbca7

04/13/2005 09:11:10 PM · #10

Originally posted by nicklevy:

1:2 is only half the magnification of 1:1

LEONJR

Fujifilm FinePix S3 Pro

04/13/2005 09:15:34 PM · #11

that would explain those macro filters to right?

kirbic

Canon EOS R5

Canon RF 24-70mm f/2.8 L IS

04/13/2005 09:39:44 PM · #12

Originally posted by nicklevy:

I ran some calculations, the 8.2Â° is the diagonal FoV, for a full 35mm film frame (approx 36x24mm). For a 1.6 crop cam, the horizontal FoV is about 71.4mm at the minumum focus distance. That relates to about 1:3.25, not the 1:2 that Sigma gives, so I'm not sure how they get that figure. In any case, count on a 2.8-inch object filling the frame at highest magnification. You could add an extension tube to further reduce the minimum focus distance.
Macro work at 300mm will require a monopod at the very least, and lighting will be tricky at those long working distances.
To calculate how large an object will apear on a print:

Dp= (Wp/Ws)*Wo*M

Where:

Dp = The dimension of the object on the print (what you're solving for)
Wp = The width of the print
Ws = The width of the sensor
Do = The dimension of the object in real life
M = Magnification

Example:

Dp = ?
Wp = 8 inches, or 200mm (remember you can't mix units!
Ws = 22.2mm (for 350D)
Do = 10mm
M = 1:2 = 0.5

Dp = (200/22.2)*10*0.5 = 45mm

So the object, which was about the size of a dime, will appear on the print as an object about 1.8 inches across.

Edit: correct typos and terminology (focus distance, not focal length)

Message edited by author 2005-04-14 22:02:10.