To continue Lou Jost request, today's post presents the resolving power of the Sigma APO MACRO 180mm f/2.8EX DG OS HSM lens at a 1:2 close-up working distance of 16 inches.
I photographed my resolution chart (described in my June 9th post under LVF) at an effective aperture of f/4.2, and apertures f/5.6, F/8, f/11, f/16, and f/22. I did f/16 and f/22 out of curiosity as to how much diffraction sets in.
Note - I used my Nikon D500 camera with this lens. Nikon cameras records "effective aperture" when the lens is close-up at large aperture openings, f/2.8. In my case, when the lens is set at f/2.8, the camera reports an effective aperture of f/4.2 for a 1:2 photo. Canon and Sony cameras will report an aperture of 2.8 and not report the affect of light loss within the lens at these close-up settings (although, the exposure will be correct for the loss of light).
I am particularly interested in a 1:2 photograph because my Nikkor 300mm f/4E PF lens with the Nikon 17E II teleconverter, attached to my Nikon D500 camera, takes 1:2 photos at 48 inches working distance.
Since I cannot kneel on the ground, I am hoping that the Nikkor 300mm lens + 17E II teleconverter, will produce as good 1:2 photos at a working distance of 48 inches, as the Sigma 180mm lens does at a working distance of 16 inches. I rather shoot 1:2 photos at 48 inches than 16 inches.
Now, to continue with the resolving power of the Sigma 180mm lens.
This is a photo of the computer generated resolution chart that was used for the 1:2 photographs:
To clarify what part of the chart is showing in the following 1:2 photographs, I have identified sections of the chart as 2nd and 3rd circular bars:
The portion of the resolution chart photographed at 1:2, is the 2nd circular bars as shown here:
I will be showing crops of the 1:2 photos which will show the smallest 3rd circular bars:
Some dimensions are shown in these two photos but are not shown on the actual print used to photographed the 1:2 photos. The above resolution chart photos are the computer generated photos, not the printed photo used to take the 1:2 photographs (the chart was printed on glossy photo paper with an Epson R3000 printer). The smallest bars and white spaces between these bars in the 3rd circular bars photo, (no. 6 on right side) have a thickness equal to the diameter of the average human hair, 0.004 inches or 0.1 mm.
PLEASE NOTE
The following photographs are of the printed chart which is not as elegant as the computer generated chart shown above; the ink pattern is shown and the edges of the bars are jagged, not straight, and the colored inks used to make black are seen (magenta, cyan, and yellow). Also, the edges of the bars at 1:2 will not be tack sharp in the following CROPPED PHOTOGRAPHS because the ink spots are 0.0002 inches (0.005mm) in diameter. Any of these extremely small ink spots on the edges will appear blurry, even for this sharp lens. Also, to repeat, the average width of the smallest printed bars is 0.004 inches or 0.1mm.
The Nikon D500 camera was mounted on a tripod, and the lens was manually focused using live view. A Nikon MC-36 cable release was used to release the shutter. The shutter was released several seconds after I removed my fingers off the lens to reduce vibrations. At 1:2, the front of the lens was 16 inches from the chart.
Here is the photo taken at an effective aperture of f/4.2 (f/2.8 for Canon and Sony cameras):
The physical size of the photographed chart in this photo is approximately 1.8 inches by 1.2 inches (2 times the size of the D500 camera sensor).
To get a closer view, I cropped the 5624x3754px photo to 512x512 pixels:
The printer used colored ink to make black, thus the colored ink spots in the jagged bars and numbers (cyan, yellow and magenta ink spots). As stated before, the average printed width of the smallest bars is 0.004 inches (0.1mm) , the diameter of the average human hair.
Here is the photo taken at an aperture of f/5.6
I then cropped the f/5.6 photo to 512x512px:
Here is the photo taken at f/8:
I then cropped the f/8 photo to 512x512px:
Here is the photo at f/11:
I then cropped the f/11 photo to 512x512px:
Upon really close examination, the f/8 photo is some what sharper than the f/11 photo, possibly diffraction starting at f/11?
Here is the photo at f/16:
I then cropped the f/16 photo to 512x512px:
There definitely is the start of lens diffraction.
Here is the photo at f/22:
I then cropped the f/22 photo to 512x512px:
This photo show the affects of lens diffraction.
To see more clearly at what aperture diffraction starts, I croppped the 6 5524x3754 pixel photos to 256x256 pixels and combined the 6 cropped photos in one photo:
Comparing these six photos clearly shows that diffraction starts at f/11. This photo also shows that this lens takes sharp photos wide open at effective f/4.2 (f/2.8 for Canon and Sony cameras), and at f/5.6, and f/8.
My next post will show photos taken with the following combination: Nikon D500 camera with the Nikon 17E II teleconverter between the camera and the Nikkor 300mm f/4E PF lens.
This combination of photo equipment produces a 1:2 photo at a working distance of 48 inches. Here is a photo taken with this combination at 48 inches:
This is a photo of my Nikon D500 close-up chart I made with photoshop which is described in the April 25th post under the username LVF. The center red rectangle marked 1:1 is the physical size of the D500 camera sensor, 0.925x0.618 inches. This photo was taken at 48 inches from in-front of the Nikkor 300mm lens to the close-up chart.
I am hoping the results will show this combination is as good at a working distance of 48 inches as the Sigma 180mm lens is at a working distance of 16 inches.
Leon