Can a Panasonic 100-300 lens back/front focus be corrected?

Sorry if this is the wrong forum to ask this - could not find a "lens" forum

I have a 100-300 II on a G9 which, at 300mm is not too sharp. I did some preliminary tests and it APPEARS the auto-focus may not be "on". Is this something that can be "fixed" in the lens - or do I just have a bad copy. Bought it used on eBay - visually seems to be if fine condition. At shorter zooms it is, AFAIK - good. Just a bit disappointing to see such poor long-end performance - especially after seeing this vid

Ideas?

alanvee wrote:

Sorry if this is the wrong forum to ask this - could not find a "lens" forum

I have a 100-300 II on a G9 which, at 300mm is not too sharp. I did some preliminary tests and it APPEARS the auto-focus may not be "on". Is this something that can be "fixed" in the lens - or do I just have a bad copy. Bought it used on eBay - visually seems to be if fine condition. At shorter zooms it is, AFAIK - good. Just a bit disappointing to see such poor long-end performance - especially after seeing this vid

Ideas?

the 100-300 is not the strongest performer at 300 mm to begin with. However, I am sure sample variation can be at play, or just simply an issue with the lens. However, the 100 to 300 on a Panasonic body cannot front or back focus. It uses contrast to find a point of focus, it doesn’t understand distance so it can’t front or back focus.

ive Owned several 100 to 300 lenses, and they’re all a bit soft at 300 mm, but at the price point I’ve been fine with them.

If you can post some examples, we could comment on whether it’s similar or different from what is normally seen

alanvee wrote:

Sorry if this is the wrong forum to ask this - could not find a "lens" forum

I have a 100-300 II on a G9 which, at 300mm is not too sharp. I did some preliminary tests and it APPEARS the auto-focus may not be "on". Is this something that can be "fixed" in the lens - or do I just have a bad copy. Bought it used on eBay - visually seems to be if fine condition. At shorter zooms it is, AFAIK - good. Just a bit disappointing to see such poor long-end performance - especially after seeing this vid

Ideas?

To eliminate focus as a variable, you should test with manual focus and see if that gives you better results.

You can eliminate stabilization and camera shake as a factor by disabling stabilization and doing a sharpness test with the lens on a tripod (or some stationary surface) and using a timer to activate the shutter. You can also use e-shutter to eliminate shutter shock as a variable. Another thing to keep in mind is decentering and field curvature (the focus may not be the same across the frame).

Also, MFT lenses focus wide open and then stop down to take the picture (unless you use the Constant Preview mode). The focus may shift during this process, causing a front or back focus situation. Some lenses are more susceptible to this (for example 25mm f/1.7 have been reported). If you are shooting wide open this should not be a factor however.

https://photographylife.com/what-is-focus-shift#focus-shift-and-fast-aperture-lenses

There are a lot of variables that can cause poor performance at 300mm (not that the 100-300mm has a high reputation for performance in the long end).