Front Focusing 300 f2.8?

[JamGrey]

Hey guys

I recently bought a Nikkor 300 f2.8 af-i. Lens was in immaculate condition. There was actually more sign of use after I got it for one day than when I bought it. I have this slight suspicion that it is front focusing though. I am still new to shooting so just wanted to get a second opinion before i start testing where to set the fine tune (D700). Majority of shots were fine (but they were far so big DOF), but i did notice that at f2.8 at closer distances, the focus wasnt always spot on. Im also new to forum, so if no pics come up, or they not right resoltion, just hold, i did something wrong and will sort them.







The pics of the cat were shot in Single dynamic AF focusing on the eye. Dog Running was continous dynamic AF just focusing somewhere on his head. The bird was Continous auto area. My suspicions stem mostly from the dog running as you can see from the grass that the DOF is in front of the dog aswell as the cats eyes are not 100% in focus.

Any thoughts? Like I said, I am still new so i could just have missied focus or am being padantic.

James

[Forgiss - Sean Nel]

I think micro adjustment is your best bet

[Chris F]

James we are about to start playing with adjusting the focal distance of lenses via the camera, ie on camera micro adjustment.

There are many threads on the topic. In essence a piece of paper is place at 45 degree to the plane of the camera, with numbers or lines or patterns on the paper. You focus on the MID POINT and fire away ... the lines/patterns/numbers then show if the lens is front or back focussing.


seems simple enough ... now to see how we can chase our own tails trying this ....

[Andre v]

http://regex.info/blog/photo-tech/focus-chart

One of the better methods i have found and used with success

[Francois Loubser]

Ditto Andre, the site and chart worked for me.

[Chris F]

Andre we have actually downloaded that numberset, and I am busy making the rig.

[Andre v]

Its a bit of a pain to get it done, but well worth it.
Make sure to also check your lens with TC's attached as well.

[Henk Coetzee]

I've struggled to get good results with the 45 degree focus chart. What has worked for me is setting the camera up parallel to a flat contrasty surface and testing the focus adjustment in increments of 2 units from one end of the scale to the other (for me this was -10,-8,-6,...+6,+8,+10), finding the best zone and then going in in detail to get to the best focus point. I've made marginal improvements in 2 lenses so far this way.

[visagieh]

paper is place at 45 degree to the plane of the camera

This is not the correct way to calibrate long lenses, The focal plane needs to be at line of sight of the lens, 90 degrees straight up. Phone OPD and ask if they still have the kit to calibrate.

A easy DIY is say put 7 batteries on a platform at some angle. Focus on the middle one, adjust accordingly.

[Forgiss - Sean Nel]

This is not the correct way to calibrate long lenses, The focal plane needs to be at line of sight of the lens, 90 degrees straight up. Phone OPD and ask if they still have the kit to calibrate.

A easy DIY is say put 7 batteries on a platform at some angle. Focus on the middle one, adjust accordingly.

Same principle... the only difference is that there is a much better and solid target to lock focus on for the AF. You can use a large unit like the one ODP has in the rentals (to test lenses) or a smaller unit like the lenscal (good investment for manual work) or... you can go all out and get yourself FoCal - full software (PC Only!!!) that can give you an amazing amount of information about your lens at all ranges.

[visagieh]

I just have to add, callebrate with and without your TC's if you have any and use them. Mine goes - and the other +.

On Nikon it recognise the different Lens combo setups.

O, and more than one test.

[Forgiss - Sean Nel]

I just have to add, callebrate with and without your TC's if you have any and use them. Mine goes - and the other +.

On Nikon it recognise the different Lens combo setups.

O, and more that one test.

Yep, have to +1 all the above.

Finally, my Canon 5DmkIII also recognizes the differences of a lens with and without a TC

[Andre v]

I've struggled to get good results with the 45 degree focus chart. What has worked for me is setting the camera up parallel to a flat contrasty surface and testing the focus adjustment in increments of 2 units from one end of the scale to the other (for me this was -10,-8,-6,...+6,+8,+10), finding the best zone and then going in in detail to get to the best focus point. I've made marginal improvements in 2 lenses so far this way.

Henk what distances are you working at. You should use a minimum of 50x focal length.

[Ken]

Yep, have to +1 all the above.

Finally, my Canon 5DmkIII also recognizes the differences of a lens with and without a TC

Sean, I see the latest 5DmkIII firmware upgrade caters for mkIII extenders. If you have not upgraded yet then it may be relevant to redo.
Firmware Version 1.1.3 incorporates the following improvements and fixes.

1. Supports the single focal length EF40mm f/2.8 STM lens that is to be released at the end of June, 2012.
2. Fixes a phenomenon in which an image may become underexposed when using the Auto Lighting Optimizer for continuous Auto Exposure Bracketing (AEB) shooting.
3. Fixes a phenomenon in which the backlight of the LCD monitor may not turn off depending on the camera settings and timing.
4. Fixes a phenomenon in which the camera’s power may not turn on when a super-telephoto lens*1) is mounted to the camera with an extender*2).
5. - EF 300mm F2.8L IS II USM / EF 400mm F2.8L IS II USM
6. - Extender EF 1.4X III / Extender EF 2X III

[Henk Coetzee]

Henk what distances are you working at. You should use a minimum of 50x focal length.

Trying to get to that. I was working with a 70 and a 100 when I did the last measurements. This meant 3.5 and 5 metres which was just about possible.

[Robbie A]

Henk what distances are you working at. You should use a minimum of 50x focal length.

So are you saying that with a 500 mm lens you should be using 25m?

[Andre v]

Yes, 25M sounds right.

edit : there was another link regarding this i will try find. Its on one of the forums and has about 10 pages of commentary. I will see if i can find it and paste a link here

[visagieh]

So are you saying that with a 500 mm lens you should be using 25m?

Well 2m wont work, the lens cannot focus that short. But yep about that range. Thats why there are products like Lens Align Pro, with that massive 4 foot ruler. Ask ODP.

[Chris F]

okaaayyyyy .....

the last time Grant and I packed out "props" in the cul du sac for testing cameras the neighbours just laughed at us .... I can just see myself standing on the neighbours driveway, accross the road, trying to focus on some calibration device inside my garage ....


but if thats what it takes ....


THANKS for all the info, might just rethink the rig we are busy building.

[Richard Sloman]

Once you have determined that the lens is front or back focussing, what can be done to remedy this? Is it something on the camera or is this something the pro's have to calibrate?