Recent experiences capturing the fine details in cleaned diatoms frustules left me frustrated. The effect of chromatic aberration from my achromatic objectives was having more than just an aesthetic effect with their red and cyan colored fringes, it was also affecting my ability to get the sharpness I was used to seeing.
In order to reduce the objectionable color fringing, I decided to convert the images to grayscale, hoping that would improve the sharpness as well. In the discussion that followed, Gekko correctly pointed out that the effect of the fringing would remain even after the color was eliminated, and so would not improve sharpness.
He went on to suggest that I try a green filter to counter the CA. Of course the resulting images would be colored green, but since the aspect of interest in this subject is its structure, and as it is predominately colorless, converting to grayscale would take care of the green.
As it happens, I have a filter in my astronomy kit that would be suitable for experimentation. It is a #56 green filter, rather a dark green, but at hand and that made it the choice for the job.
IMG_20160425_194142-600x808.jpg [ 92.9 KiB | Viewed 3684 times ]
I would shoot the same subject, with and without filter, using both the 40x and 100x oil. I shot for stacks, with the same number of images for both filtered and unfiltered - 7 each for the 40 and 8 each for the 100.
I then processed the stacks using identical parameters in CombineZP. I did all methods, and in each case the Pyramid Weighted Average produced the best image.
I resized the resulting images to 1024 on the long side, made adjustments to levels and applied unsharp mask using identical parameters. Below are the results, starting with the 40x
File comment: 40X Brightfield Natural Coloration
BF40Natural.jpg [ 150.03 KiB | Viewed 3700 times ]
File comment: 40x Green Filtered
Green40Natural.jpg [ 96.17 KiB | Viewed 3700 times ]
And now the same images converted to grayscale
File comment: 40x Brightfield coverted to Grayscale
BF40Gray.jpg [ 119.77 KiB | Viewed 3700 times ]
File comment: 40x Green Filtered converted to Grayscale
Green40Gray.jpg [ 91.36 KiB | Viewed 3700 times ]