Macro Photography - Part 4: Understanding reproduction ratios and magnification

Reproduction ratios are used in understanding the magnification power of equipment.  The rectangles represent the size of a full frame sensor, measuring 36 mm across and 24 mm down.

A reproduction ratio is a pair of numbers used to express how much magnification a lens or macro setup is capable of providing.  The information can be used to determine how much you can magnify your subject by.  Most zooms are capable of 1:5 reproduction ratios, which isn't much.  Many 60 mm macro lenses allow reproduction ratios of 1:2.  This is fine for flowers and subjects the size of large coins.  True macro lenses have 1:1 capability.  This can be increased by using equipment such as lens reversal, extension tubes, bellows, or specialized macro equipment designed to give higher reproduction ratios.

In the format x:y, a RR is read as x to y.  The x is the the size of the model/image and the y is the size of the actual subject.  The units of measure must be the same.  In the above image, the top left frame shows a RR of 1:2 where the image on the camera's sensor is 6 mm and the actual subject is 12 mm.  This can be expressed as 6:12, but is reduced to its lowest values, in this case, 1:2.  If the values don't work out perfectly, a decimal is used with one of the two figures in the RR being 1.  So, if the beetle was 15 mm and the image on the sensor was 6 mm the RR would be 6/15 = 2/5 or 1:2.5.

Most of the time a RR is stated in a 1:x format for reductions and a x:1 format for enlargements.  Sometimes the x is a decimal, such as 1:2.5 or 3.7:1.  RRs don't always round nicely to whole numbers as you saw above.

Magnification is simply calculated as a percent.  The first (top) number is divided by the second (bottom) number and multiplied by 100.  There is little need for enormous accuracy; rounding the percent to the nearest whole number is enough.

Sometimes magnification is represented as a single number without determining percent.  In that case, the same math is done as above but there is no multiplication by 100.  The answer has an x after it.  In the last panel above, the 4:1 RR could also be 400% or 4x.  Most microscope work is done with these values.

How do you know how large the actual subject is on your sensor?  The answer is easy enough.  You can do it roughly on the camera's rear display simply by measuring the size of the subject against the size of the sensor.  Full frame sensors measure 36x24 mm.  Crop sensor cameras measure 24x16 mm, unless you use a Canon camera with a cropped sensor (22.5x15 cm) or a four-thirds camera (18x12 mm).

The reverse is also true.  Let's say you have an aphid measuring 3 mm.  To capture it full frame, you would need a 36/3 = 12:1 RR.  Giving a little extra space to work would mean a RR of 10:1 should be adequate.  Your 3 mm subject would appear to be 30 mm across on your full frame sensor.

Thanks for reading.

Eric Svendsen     www.ericspix.com

Comments

Post a Comment

Popular posts from this blog

Harjit Bahia - Science teacher and colleague from Garibaldi died August 2, 2024

Image
You will be missed Mr. Bahia.  You made a difference and we are sad you are gone. I keep in loose contact with my fellow retired teachers from Garibaldi Secondary School.  I talked with my long-time friend, Mike Lynch, today, and discovered that Hargit died over the summer.  Unbeknownst to him, he had an underlying heart condition and passed away after working out on his treadmill.  The date was August 2, 2024. I was shocked to hear this.  He was only 49 years old, turning 50 some 3 months later.  It was a shock to everyone, for he was loved by all who knew him.  As a teacher, Mr. Bahia was kind and fun.  He contributed to students in many ways and was always available to help those in need.   For myself, I knew him as a fellow science teacher and taught in the adjoining room to him.  He was always available to help, share ideas, and work together.  Easy to approach, I found that I could talk to him about anything and appreciat...
Read more

I found a black widow spider in a plant pot today

Image
The spider I found is a western black widow spider, one of three species of black widow that occur in North America.  The fact that this one has another red patch on the back of its abdomen above the spinnerettes tells us that it is an immature individual. The one thing that people know about black widow spiders is that they are extremely poisonous.  Their venom is something like 15x more toxic than that of a rattlesnake.  The saving grace is that there is very little venom injected from a black widow bite than what a rattlesnake can deliver.   The good news is that black widow bites seldom lead to death.  You are more likely to suffer nausea, muscle pain, and swelling around the bite.  Symptoms usually last only 12 hours or so.  Death may be a result in people with compromised immune systems or in the very young or the elderly.   In 2018, it was reported that there were 1015 cases of people bitten by black widows.  Of those, there ...
Read more

Mountain Bluebird - out of the blue.

Image
Mountain Bluebird photographed near Princeton, BC. While camping at a resort near Princeton, BC, I had a chance to visit a wildlife refuge that was nearby.  There are about 5 km of trails there and it took me two days to cover them all.  That may sound like an unreasonably slow rate of progression, but I took several hundred images during my time there and did a fair amount of step retracing.  The end result was the opportunity to get some great hiking in and see three bird species I have never encountered before. On the first day, I saw and photographed a pygmy nuthatch.  I have seen the white-breasted and red-breasted varieties but never this species.  The second day caught me completely off guard, as within the span of 30 seconds I saw the other two, a Bullock's oriole and a mountain bluebird.  It was a stunning discovery, for me anyway, and I can still feel the thrill of the moment thinking back on it.  Many of you may think this a bit odd, t...
Read more