I have said:
https://www.photomacrography.net/forum/ ... 928#236928JH wrote:I use a short empty tube with my Nikon 200mm on a FF Canon. This helps with the corners.
https://www.photomacrography.net/forum/ ... 928#236928JH wrote: In the few occasions when I used a short empty tube with a Nikon 200 mm the quality looked the same with and without the empty tube - even though the focus was not at infinity. At least in the centre of the picture you can probably be off by a few centimetres with a 200 mm tube lens before you see disturbing degradation with the Canon cameras I use.
To what extent is the help with the corners true, and how much does the use of an extension tube actually affect the image quality?
Here is a series of screen grabs, subject Euro, 1 cent, camera Canon 5D II FF, objective Mitutoyo MPlan apo 10x. I tried to have the crossing scratches in focus.
OBS! I wanted to show the exact same area of the subject so I used my Optiphot microscope. This means that there is approx. 5 cm distance between the back of the Mitutoyo and the front of the Nikkor. With less distance between the objective and the Nikkor the dark corners are smaler than what I show here.
When I use the Nikkor I have the lenses closer together, this makes the corner problem less severe, but you must find an empty tube that does not add to the vignetting. I use a cheap approx. 1 cm eBay tube.
#1 Nikkor 200mm at infinity - clearly problems with the corners OBS 5 cm distance between objective and tube lens.
#2 Extension tube 12mm tube. Better corners but still some problems here with 5cm distance. If you look at picture #3 you can see that you do not need an extension tube for this you can just change focus.
#2 Nikkor 200mm at closest focus.
#3 Nikkor 200mm at infinity with 36mm extension tube, little problems with corners, clearly degraded image quality.
If you already have a Nikkor 200 mm, wants to use a FF sensor and do not want to crop out the corners you could change focus from infinity or use a short extension tube. An extension tube or a closer focus makes the corners better but affects the image quality. The longer the extension tube the larger the effect on the image quality.
#4 Raynox DCR-150 as a reference. Still 5 cm between tube lens and objective.