What focus tests should I do prior to taking it in?

[PaulWog]

I'm taking my 35mm 1.8G lens in for focus adjustment next week (Monday or Tuesday), since they aren't open on weekends. I've officially packed it up in a box (finally). I've been using it in liveview to suffice. Bit of a catch-22: when I have the free time to get it serviced I need to use the lens & can't be without it, and when I can do without the lens I don't have the free time to drive out to get it serviced.

What lens tests can I do prior to bringing the lens in to be fixed? I've done one test shooting the 35mm against a print-out at different distances from the wall in regular mode and in liveview mode. In liveview, it's crisp and sharp at all distances. Using regular focus, it's less and less focused the further I get from the wall (it seems to focus well at close distances, about 1-3 feet from the subject). The reason I ask is because I called the center, and I was told to give a description of the problem in a write-up when I drop the lens off. I would prefer to be as thorough as possible so that my problem is dealt with quickly (since I don't want to end up being put in the same category, mistakenly, as a guy who might simply not know how to focus his lens). Yes, I realize "Just take it in and don't worry!" is an answer.

 

[Josh66]

Do a google images search for 'focus test chart' and you'll get some ideas. You might be able to find a chart that you can print to scale.

If so, then in your description of the problem, you'd be able to say "it's back focusing by 2.5mm" - or whatever it actually is.

(since I don't want to end up being put in the same category, mistakenly, as a guy who might simply not know how to focus his lens).

I would also make sure, without a doubt, that you are not actually in that category, lol.

 

[PaulWog]

Do a google images search for 'focus test chart' and you'll get some ideas. You might be able to find a chart that you can print to scale.

If so, then in your description of the problem, you'd be able to say "it's back focusing by 2.5mm" - or whatever it actually is.

(since I don't want to end up being put in the same category, mistakenly, as a guy who might simply not know how to focus his lens).

I would also make sure, without a doubt, that you are not actually in that category, lol.

I'm not sure how to say "it's backfocussing by X", since it seems to backfocus worse as distance goes further. Focus is also somewhat inconsistent (when focused on the same spot, it will occasionally get a little closer to correct focus sometimes, but it's always off).

It absolutely doesn't focus correctly.

 

[TheLost]

If you can get your hands on a camera with AF fine tune ajustments (D7000 / D7100.. etc) you could use a program like FocusTune.

I hate to say it... but you may have better luck if you also send your body. Nikon has always wanted both when I've talked to them.

 

[Derrel]

First off, I would read this article and DO the tests suggested. Autofocus troubleshooting by Thom Hogan

Chances are, your camera and lens are both fine, but you're unaware that the AF brackets in the viewfinder are covering a larger and larger area as the distance increases, AND, very likely, the AF brackets are not actually accurately showing you the exact location the AF SENSORS are reading. With wide-angle lenses, as distance increases, the increased coverage and the slight discrepancy between the AF indicators and the ACTUAL AF "target" makes focusing wide-angle lenses sometimes a bit tricky.

We often see the same issue with exposure and wide-angles...

 

[PaulWog]

First off, I would read this article and DO the tests suggested. Autofocus troubleshooting by Thom Hogan

Chances are, your camera and lens are both fine, but you're unaware that the AF brackets in the viewfinder are covering a larger and larger area as the distance increases, AND, very likely, the AF brackets are not actually accurately showing you the exact location the AF SENSORS are reading. With wide-angle lenses, as distance increases, the increased coverage and the slight discrepancy between the AF indicators and the ACTUAL AF "target" makes focusing wide-angle lenses sometimes a bit tricky.

We often see the same issue with exposure and wide-angles...

Nah the lens definitely isn't fine.

Just looking for advice on specific tests I can do that might be useful to the repair depot so they know what the issue is immediately. I figure they'll probably figure it out though.

 

[PaulWog]

First off, I would read this article and DO the tests suggested. Autofocus troubleshooting by Thom Hogan

Chances are, your camera and lens are both fine, but you're unaware that the AF brackets in the viewfinder are covering a larger and larger area as the distance increases, AND, very likely, the AF brackets are not actually accurately showing you the exact location the AF SENSORS are reading. With wide-angle lenses, as distance increases, the increased coverage and the slight discrepancy between the AF indicators and the ACTUAL AF "target" makes focusing wide-angle lenses sometimes a bit tricky.

We often see the same issue with exposure and wide-angles...

Nah the lens definitely isn't fine.

Just looking for advice on specific tests I can do that might be useful to the repair depot so they know what the issue is immediately. That info is useful nevertheless though