Using a Canon SX70 HS camera with a Raynox DCR-150 Macro Adapter to take Measurements (1 of 3)

            Whenever possible when I'm photographing an insect that I've not seen before, I try to get an estimate of its length, in the hope that it might facilitate the identification process.  I used to do this just by holding a ruler in its general vicinity (but in the same plane) and then including the subject and the ruler in the same shot.  For obvious reason, this didn't always work!

However, now that I use my macro adapter for most of my insect photography it struck me that a better way of doing this would be to essentially calibrate the camera lens and adapter combination so that for a selected camera focal length, I'd be able determine the width of the shot in the plane of the subject.  Then provided that the subject was perpendicular to the line of sight, then it's absolute length could be calculated by determining the ratio of its width to the width of the photo from a computer screen.   (This process is illustrated in Photo 3.)  

The reason this should work is that with the adapter fitted, the depth-of-field is generally so narrow that for any given focal length the subject is always going to be the same distance from the camera (which has to be manually focused).  

The first part of the calibration procedure involved photographing a ruler (with 0.5mm divisions), perpendicular to the line of sight, over an appropriate range of camera focal lengths.  In all 34 shots were taken spanning the range from 15mm to 247mm.  A selection of these images is included in Photo 1.

More text to follow with Photo 2.

Taken on: June 8, 2021

Tags:

Canon

PowerShot

superzoom

bridge

camera

Raynox DCR-150 Macro Snap-on Adapter

Raynox

Macro

Lens

calibration

focal length

width of view

measurement « less

Sets appears in: • Raynox DCR-150 Macro Adapter Calibration

Camera: Canon PowerShot SX70 HS, f/6.3, 1/80 sec, 19.5mm, ISO 800 (more info) (hide info)

Camera:	Canon PowerShot SX70 HS
Aperture:	f/6.3
Exposure Time:	0.013 sec (1/80)
Focal Length:	19.5mm
ISO:	800
Exposure Bias:	-2/3 EV
Flash:	No Flash
Exposure Program:	Aperture-priority AE
Exposure Mode:	Auto
Metering Mode:	Spot
White Balance:	Manual
Color Space:	sRGB
Software:	Adobe Photoshop Elements 5.0 (20060914.r.77) Windows
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