Micro Nikkor 55mm 3.5 + tube

I am planning to buy a Micro Nikkor 55mm 3.5 to scan my negatives. With my setup I will have to use extend tubes to achieve 1:1.
With the extend tube, will I loose sharpness in the corner ?

I have a APS-C btw

I have the 2,8 55 its a very fine lens regarding centre sharpness. Corner sharpness depnds on the sample you have. You should not exceed 1:2, otherwise you loose sharpness. But from there to infinity, sharpness is very good. If centering is good, corner sharpness is also good. Contrast is slightly less than at modern lenses, but this is feasonable with lightroom. Only drawback is the missing lens profile in Lightromm as it has quite visible corner fall off and corner shift to green. But it is distortion free. If you should succeed creating an own profile for Lightroom, please let me know.
Regards, Gerhard

Take the 2,8. I talked about use for full format. If APS-c the issues should be gone. This lens has the highest center resolution of all my Nikon lenses.

Thanks for all the information.
I can have the 3.5 for half the price of the 2.8. In your opinion, is it worth it to go for the 2.8 ?

I have no experience with te 3,5 / 55, but it is older than the 2,8, so there should likely be improvements. Used 2,8/55 mm are a lot around. Possible flaws can be: Oily aperture blades, sticky aperture blades, aperture ring with worn out dents, decentering. Best is to buy it used, test it and sell it again if a non visible flaw should occure.

when you say “you should not exceed 1:2”, do you mean with or without the extension tube? do you even need the extension tube with an APS-C camera?

1:2, when used with a full format camera. This is the full extension of the helical mount without any additional extension tube.