Canon 85mm Front + Back focus problem

I have a Canon 85mm 1.8 purchased from a certain auction site some months ago. Since getting it i have been unhappy with the focus results.

I have tried adjusting technique whilst hand holding and also been through the moire and ruler tests to attempt an adjustment.

Today i tried the battery test with 5AAs at 45 degrees to the camera on tripod 2 second timer centre spot focus.

At around 1 metre i had to dial in -20 ( the max ) on my 5D3 and -10 on my 5D2 to get it spot on, it then performed perfectly even off the camera at that distance.

I them aim it into another room at a wall clock about 4 meters away and now its front focusing and i have to return it to zero on both cameras to get it in focus.

This has left my head hurting and not sure what to do with it ( bar throwing it in a bin )

Is it possible for a lens to both front and back focus depending on the distance if so is this a mechanical fault that can be repaired does anyone know ?

thank you
Andrew

North East and Yorkshire Wedding Photography by Andrew Davies

andrewdaviesphotography wrote:

I have a Canon 85mm 1.8 purchased from a certain auction site some months ago. Since getting it i have been unhappy with the focus results.

I have tried adjusting technique whilst hand holding and also been through the moire and ruler tests to attempt an adjustment.

Today i tried the battery test with 5AAs at 45 degrees to the camera on tripod 2 second timer centre spot focus.

At around 1 metre i had to dial in -20 ( the max ) on my 5D3 and -10 on my 5D2 to get it spot on, it then performed perfectly even off the camera at that distance.

I them aim it into another room at a wall clock about 4 meters away and now its front focusing and i have to return it to zero on both cameras to get it in focus.

This has left my head hurting and not sure what to do with it ( bar throwing it in a bin )

Is it possible for a lens to both front and back focus depending on the distance if so is this a mechanical fault that can be repaired does anyone know ?

thank you
Andrew

North East and Yorkshire Wedding Photography by Andrew Davies

This sounds like what's known as Focus Shift.

My 50 f1.4 does this. Drives me nuts. It's common for that lens but not heard about the 85 f1.8 doing it.

Subject distance and aperture setting are tied up with focus shift issues you'll find.

andrewdaviesphotography wrote:

I have a Canon 85mm 1.8 purchased from a certain auction site some months ago. Since getting it i have been unhappy with the focus results.

I have tried adjusting technique whilst hand holding and also been through the moire and ruler tests to attempt an adjustment.

Today i tried the battery test with 5AAs at 45 degrees to the camera on tripod 2 second timer centre spot focus.

At around 1 metre i had to dial in -20 ( the max ) on my 5D3 and -10 on my 5D2 to get it spot on, it then performed perfectly even off the camera at that distance.

I them aim it into another room at a wall clock about 4 meters away and now its front focusing and i have to return it to zero on both cameras to get it in focus.

This has left my head hurting and not sure what to do with it ( bar throwing it in a bin )

Is it possible for a lens to both front and back focus depending on the distance if so is this a mechanical fault that can be repaired does anyone know ?

thank you
Andrew

North East and Yorkshire Wedding Photography by Andrew Davies

I think you got a dud.  Local craigslist sales are the only way I deal unless some auction was incredible and for some old legacy lens and not a commodity lens.