Should I buy a 1:1 (life size) or a 1:2 (half life size) macro lens? That's a common question asked by many a beginning macro photographer. The problem: life size is the now standard spec for current macro lenses but old, half life size models from the beginning of the AF era (or even the MF era for that matter) can be had for a fraction of the cost of a modern macro.
So, how big is the difference? Well, look below to see.
As you can see, the difference between life and half life size is very noticeable indeed, with the life size quarter appearing to be about 4 times bigger than the half life size one. As for why the huge difference, it is thanks to the fact that the image is a 2 dimensional object and, by shrinking each axis by a factor of 2, you get a total shrinkage of a factor of 4 (½ x ½ = ¼).
Now, that's quite a loss but there's a clear way around the problem: cropping in Photoshop.
As you can see on the above picture, I could easily just crop the half life size image to be the equal of the life size one. Unfortunately, by doing this, I would be eliminating ¾ of the original image's resolution in the process, which presents another problem: can I afford to lose 75% of my pixels.
For 99% of people reading this, the answer is 'yes!'
Modern dSLR cameras have insane resolutions of at least 16Mp, which is way, way more than most people will ever need. Take it from someone who has been doing this since high school: you don't need massive pixel counts to get great prints. In high school, we were sometimes using 3Mp images (state of the art in the early 2000s) to fill 11x14 pages. Result: they looked great!
Don't print? No problem as all affordable computer and TV screens are 1920x1080 pixels in resolution, which translates to a measly 2Mp, which is half of the 4Mp you would get by cropping a 16Mp half life size image to the equivalent of a life size one. Bottom line: whether you show off your images on screen or on paper, you'll have plenty of resolution to send your audience members' jaws dropping to the floor provided you know how to shoot macro.
See also: Macro Photography Primer
My advice: save the cash, buy the 1:2 lens, and crop your pictures. After all, money doesn't grow on trees.
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