2. Making your own DoF table
The easiest way to create one is to use a spreadsheet so it can do the math for you. A table should be created for each focal length that you use so yes it's tedious, but only has to be done once. Before starting, find the closest focusing distance for your lens and decide what aperture(s) you'll use and subject distances you'll shoot at. Each aperture needs three rows:
The DoF table for a 100mm macro lens.
- The first shows the total DoF value in inches taken from the online calculator at http://www.dofmaster.com/dofjs.html.
- The second multiplies that value by 25.4 to convert it to millimeters.
- The third multiplies the second row value by two-thirds (0.66) for the step-size in millimeters to allow enough overlap for the stacking process.
After opening the calculator page:
- Use the camera dropdown box to find and select your brand and model which sets the sensor size. If it isn't listed, find a model with a similar sensor in your brand.
- Choose the subject distance measuring unit you want to use - I prefer inches.
- Use the lens focal length dropdown box to find and select it.
- Use the f-stop dropdown box to find and select it.
- Enter the subject distance.
- The Total depth-of-field is displayed on the right of the screen so use it and ignore the Near and Far limit distances. Enter it in the first row of the spreadsheet and the other two rows should fill in.
- Repeat steps 5 and 6 for each additional distance.
- If you want to include another aperture in the table, setup three more rows, go to step 4 and again repeat steps 5 and 6 for each distance.
Congratulations, you've finished making your table so save and print it. To use it, all you have to do now is:
- Focus on the closest required element.
- Measure the approximate distance from it to the camera's focal plane.
- Find that distance in the table for the required step size.
- Repeat the 'move and shoot' using the same step size every time until the required distance has been covered.
I'm a Canon shooter but brand plays no part in making or using a DoF table. For any given focal length, Canon, Nikon, Sigma, Tamron or any other all have the same DoF so other factors will determine your lens selection.
- Canon T3i 18 MP camera with APS-C sensor 22.2 x 14.8 mm. I got it used after being highly recommended for what and how I shoot. Its vari-angle display makes using live-view easy for framing and focusing so I never use the viewfinder.
- Canon 100mm f2.8 non-L version macro lens.
- Sigma 18-250mm f3.5-6.3 DC zoom lens for general purpose and some close-up work.
- This extreme lens made me a Canon shooter. The MP-E 65mm f2.8 super-macro lens (1-5X life size) isn't a normal macro lens but once you get used to its operation and capabilities, it really can open up whole new worlds. Section 5 is dedicated to it - Its table and usage are in sections 5.2 and 5.3. I got it used so it too was much more affordable.
- Cognisys Stackshot motorized focusing rail. This is the 'icing on the cake' as it does the very small steps required for the MP-E and eliminates ALL of the frustrations involved with a manual rail.
- Photoshop CS5 to do the stacking and any post processing as I already had it.
3.1 Canon 100mm macro
Its closest focusing distance is 12 inches where it produces a life-size image. Most things aren't that small, so I opted for 2 inch increments up to 24 inches and then 3 inches up to 48 inches - most of my shooting is in the 12-24 inch range. I did many tests when I got this lens and for me, f11 gives the best results after stacking but do your own tests and if need be, make a table for your own shooting requirements.
3.2 Sigma 18-250 zoom
Because of my studio's layout I have to be less than five feet from the subject. If it's too big to shoot with my 100mm macro, then I use this set at 35mm, 50mm or 80mm to get closer.
Its closest focusing distance is 13.8 inches where it produces a one-third life size image. I used a 4 inch increment over a distance range of 12-32 inches. I don't use it often so didn't test it as much as the other lenses and I also use it at f11.
4 A butterfly example using the 100mm and its table
Note: Butterfly's scales don't all have clearly defined edges so there will be areas that aren't 'tack sharp' - blame mother nature, not me.
- I turned the Blue Clipper butterfly so its wings were at about 45 degrees to the camera to ensure there was a significant depth to shoot. The width of the whole butterfly is about three and a half inches
- I setup the shot and focused on the closest element, the bottom of the right wing by the body - excuse the clamp that holds it in place.
- I measured the distance from there to the camera's focal plane and it was about 17" which isn't in the table. At that distance, the lens provides just over a one-third life size image.
- The table shows the step size at 16 inches is 3.52mm and 4.69mm at 18 inches, a difference of 1.17mm. I find focus isn't linear so I add one-third of the difference or 0.40mm, not one-half, to the smaller value to get 3.92 mm and use it - that's only about one-sixth of an inch.
The closest in the series showing the right wing's scales by the body.
The furthest in the series showing the antenna on the left.