Focus-Stacking with the Raynox-250
5 months ago
If you want maximum magnification and resolution with the Raynox-250, you have to go to maximum optical zoom on the camera (150.5 mm for the SX30/40 and 215 mm for the SX50) with the focus at infinity. For my SX30, the calculated magnification under these conditions is (150.5 mm / 125 mm) = 1.204. I measured 1.174 and calculated the line-pair resolution as approximately 0.004 mm (4 microns) on the subject.
The following Photo shows a horizontal scale with gradations every 0.1 mm. My SX30 was aimed slightly downwards at a glancing angle of approximately 12 degrees, so the distance of the lines from the camera increases by almost 0.1 mm (only about 2% less). You can see that the depth-of-field is only about 0.2 mm and there is already some blur at the front and back of that range.
A) Focus by Using the Camera's Manual Focus
Here is a stacked image of 20 photos covering a range of about 3.5 mm, which isn't really enough.
The first photo of the series was taken with infinite focus, capturing the 5.9 mm line. The remaining photos were taken by adjusting the camera's manual focus closer as finely as I could manage. Blur is evident on the 5.2 and 5.3 and 5.8 mm lines. As the focus gets farther and farther from infinity, it becomes increasingly difficult to manage. Near the close end of the range, the focus jumped from 4 mm to 3 mm. All this is to illustrate that using the camera's focus is difficult and it won't allow you to stack very many images.
B) Focus by Macro Rails
The shallow depth-of-field means that, if you want to focus stack images at this magnification, you should probably take photos approximately every 0.1 mm to allow for some overlap of the photos where they are sharp.
When I asked my wife for macro rails for Christmas, I had not yet heard of focus-stacking. I was concerned only about the difficulty of trying to move the whole tripod by fractions of a millimetre to get a single shot. Even if I had heard about focus-stacking, I would not have asked for the expensive lead-screw type of macro rails.
B1) Method 1: Using a dial on the Lead-Screw Knob
The following site shows an example of the lead-screw type of macro rail:
It costs $375 for a single stage (motion in one direction only) and delivers 1.06 mm of travel per full revolution of the knob.
The following site describes how to mount a calibrated disc on the knob of the lead-screw:
I tried this method with my rack-and-pinion type macro rails, which deliver approximately 30 mm of travel per full revolution of the knob. That means, in order to get the 0.1 mm travel that I am seeking, the knob has to be turned 1.2 degrees. I tried all this, but decide that it was too imprecise to use with my rack-and-pinion macro rails.
B2) Method 2: Vernier Scale
Photo 3 shows a Vernier scale mounted on the macro rail. I sawed the Vernier scale of a cheap plastic set of Vernier callipers that I bought from Canadian Tire for $1.00.
The scale can supposedly be read to 0.05 mm, but my error in reading it was +/ 0.05 mm. So, in moving the Camera from A to a location B, 0.1 mm farther along, you could have an error of +/- 0.1 mm from the readings at A and B. In practice, it might not be that bad, but I decided that that the Vernier scale did not give enough precision.
B3: Method 3: Push-Screw
This is my variation on Method 1, above. Photo 4 shows my macro rails.
Each rail came with plates screwed onto both ends, like the one in the upper left of the photo. I removed the plate on the back end and replaced it with a larger, slightly thicker one and tapped an 8-32 screw-hole into it. Turning the screw causes it to push against the base of macro rail, so that the macro rail itself moves backwards.
The thread pitch is 1/32" = 0.79375 mm, so 1/8 turn delivers 0.0992 mm of travel, or very close to 0.1 mm. There is still some error in judging 1/8 turn, but I think it is acceptable. Photo 5 shows the results of photo-stacking 31 shots, with the 30 intermediate rail movements made by turning the screw 1/8 turn each time, using a stubby screwdriver. (My next project will be to add some sort of knob onto the screw.)
Regardless of the focusing method, the perspective appears wrong in both Photo 2 and Photo 5. There is a hint of this even in single photos, such as Photo 1. Photo 6 is my attempt to correct the perspective of Photo 5 using PhotoShop Elements 9.
Photo 7 shows the grooves of an LP from an angle of approximately 45 degrees. The image is from 21 stacked photos using the push-screw method, with the blurred portions cropped away: