Macro Photography: Sensor Format
1 Introduction
Choosing a sensor format for macro photography has significant implications for the photographic practice.
This article covers the topic from different perspectives so you can make an educated buying decision.
2 Reproduction Ratio and Sensor Format
The original definition of macro photography is based on the so-called reproduction ratio. It describes the relationship between the size of the subject in real life and its size on the film or digital sensor.
R: reproduction ratio, Image Size: on the sensor,Subject size: in real life
In the traditional sense, macro photography starts at a reproduction ratio of 1:1, also called a 1x magnification, meaning that a subject with a diameter of 1cm in the real world is reproduced on the film with a diameter of 1cm.
1 Dollar, diameter 25mm in real life.
1:1 reproduction on 35mm film.
The higher the ratio, the greater the magnification, for example 2:1 or 2x magnification means that the subject is imaged twice as big on the sensor as in real life.
1 Dollar, diameter 25mm in real life.
2:1 reproduction on 35mm film.
In digital photography, the classic definition is a bit problematic, as pixels are dimensionless.
A theoretical example: When viewed on the screen or when printed, one pixel from a 5 MP digital medium format camera and one pixel from a 5 MP smartphone camera will be the same size.
This has very specific implications when it comes to macro photography and the reproduction ratio. To illustrate that, I’ve captured the images below at 0.5x magnification with various camera-lens combinations.
0.5x Magnification - Different Sensor Formats
The same reproduction ratio with different sensor formats leads to different levels of perceived magnification on a screen or print of the same size.
3 Equivalent Reproduction Ratio
To meaningfully compare the reproduction ratio of different sensor formats in digital photography, an equivalent reproduction ratio has to be calculated.
The universally accepted standard is the 35mm-equivalent reproduction ratio.
Requ: equivalent reproduction ratio, R: reproduction ratio, CF: crop factor
4 Reproduction Ratio and Sensor Format Implications
1. Comparing two camera systems with different sensor formats both equipped with lenses of similar design which provide the same angle of view, the smaller format camera is generally able to focus closer than the larger format camera.
This effect scales linearly with sensor size.
2. Smaller sensor cameras can achieve very high reproduction ratios with relatively small lenses.
Nikkor 60mm 1:1 for 35mm and Zuiko Digital 35mm 2:1 for Four Thirds
3. Small sensor cameras can deliver ultra-high equivalent magnifications which are practically unobtainable with larger sensor cameras unless specialized equipment like macro bellows and extension tubes are used.
5 Depth of Field
Depth of field, or better, the lack thereof, is always of concern when it comes to close-ups in general and macro photography in specific.
The smaller the sensor, the more depth of field can be achieved at a given angle of view and subject distance with the same f-number.
f/5.6, f=72mm, 35mm Sensor
f/5.6, f=35mm, Four Thirds Sensor
This is a significant advantage in practice, as with a larger format camera you either need more light, higher ISO or advanced post production tricks, like focus stacking, to get the same results.
6 Image Quality Considerations
A small sensor potentially potentially delivers higher magnification and more depth of field in a smaller package.
The downside is that a larger imaging system is capable of better image quality, although the relationship is not linear and in terms of required image quality very often in favor of a smaller imaging system.
A camera system twice as small is not twice as bad in terms of image quality.
6.1 Sufficient Image Quality
The compact camera OM System TG-7 delivers a median resolution of 0.2 cycles/pixel at ISO 100. Up to 8x10 inch, this camera will deliver as much resolution as most commercial printers can print (150LW/inch).
As with bigger print sizes the viewing distance will increase, the effective resolving power of the compact camera at low ISO sensitivities is definitely sufficient.
Of course, the TG-7’s is not as sharp in the corners as a professional-grade Micro Four Thirds setup, but usually a macro subject is placed in the center of the frame.
On a side note, high-end industry-leading digital microscopes like the Leica Emspira 3 utilize a 12MP 1/2.3 inch sensor quite similar to the 12MP BSI sensor found in the OM System Tough TG-7.
6.2 The Cropping Fallacy
A common, albeit very problematic argument in favor of choosing a larger sensor for macro photography is as follows: On a larger sensor, you can crop the image and get the same equivalent reproduction ratio of the smaller sensor with comparable image quality as you have more resolution and bigger pixels to work with.
There are are two major oversights in this argument:
1. Pixels are dimensionless so how big they are on the sensor is irrelevant. Only the actual resolved details and tonal values relevant.
2. The ability to crop a digital image is almost never limited by pixel resolution, but by lens resolution. So although there still might be sufficient megapixels left after cropping, the lens’s resolving power will be exceeded at some point and the image quality then deteriorates significantly.
The following comparison of the macro shots from earlier were cropped so that they depict matching picture sections. Note the increase in detail from shot to shot.
[COMPARISON IMAGES]
To conclude: Cropping eliminates the image quality advantage of a larger imaging system.
6.3 ISO Performance
In many cases, you will use a tripod allowing for longer shutter speeds and low ISO settings.
In most other cases, when photographing very close to the subject, the camera casts a shadow on the subject. So flash is mandatory anyway.
Also, to achieve the same depth of field with a small sensor camera, a smaller f-number can be used which results in more light per unit area. As a result, a lower ISO setting will suffice.
In my experience, ISO performance is practically a non-factor.
If you still feel like ISO might be a show stopper, remember the film days when ISO 400 was considered fast and people got amazing macro shots nonetheless.
OM System TG-7 at ISO 400, no noise filter or noise reduction applied, out-of-camera JPEG.
7 Closing Remarks
All in all, it is fair to conclude that a smaller sensor camera is the sensible choice when high reproduction ratios are needed.
The truth is that when it comes to macro photography, how small you are willing to go sensor-wise depends mostly on the voice in your head and not on actual image quality requirements.
What really prevents you from getting good macro shots in practice is not having the right tool in terms of reproduction ratio and portability.
Taking the pocketable 11.1x magnification OM System TG-7 with an attached ring flash diffuser everywhere is effortless, while bringing the Nikon D800 with a macro bellows and a macro flash is not.
Pick the right tool for the job, don’t hesitate to go small.
Because the more you practice with a camera that you actually bring along, the better your macro photography skills will get and the better your photos will be.
Getting excellent results with the smallest conceivable setup is a testament to your skill as a photographer, while having a large setup just for the sake of it is overcompensation.
