Checking Your Camera for Front Focus or Back Focus.

I have been asked about this several times so I decided to write an article on it.  I hope someone out there finds this helpful.

Have you ever noticed that your camera’s focus seems a bit off when shooting at large apertures?  I’m not talking about a completely blurry photo here.  I’m talking about a situation where there is sharp focus in the photo, but its just in front of or just behind the area you focused on.   An example would be like when you focus on your subject’s eyes and their nose is more in focus or maybe their ears are more in focus.  If you are noticing this issue consistently happening in your photos, then perhaps you have a front focus or back focus issue.  This article will show you how to test your camera and lenses for front/back focus problems. 

First, what is front focus and back focus.  It’s pretty straight forward really.  When the auto focus on your camera focuses the lens, it establishes a focal plane in front of your camera.  Anything on this focus plane will be in focus.  Depending on the aperture setting of your lens and the distance from the camera,  there will be a “Depth of Field” where objects in front of the focal plane and behind the focal plane will also appear to be in focus.   This Depth of Field increases as the aperture on the lens get smaller in diameter.  For those new to aperture, the larger the f number the smaller the aperture and vice versa.

At larger aperture values, since the depth of field is increased, any slight variance between the actual focal plane of the camera and the camera’s autofocus. will probably not even be noticeable since both will fall within the “Depth of Field” area.  But, when you lower the aperture value and increase the size of the aperture opening, the Depth of Field decreases.   This decrease in the Depth of Field can be pretty dramatic for lenses that will allow aperture settings of 2.8 or 1.4, or anything else in that range.   With a razor thin Depth of Field, a variance between the camera’s autofocus and the actual focal plane can be very noticeable indeed.  If you were taking a portrait shot of Aunt Betty’s daughter and you are certain you were focusing right on her forward eye but when you checked the photo in the computer and her nose is more in focus, well perhaps you have a problem.

Most front and back focusing problems are usually human error.  If we are using a wide open aperture and we are handholding the camera, just breathing or rocking back and forth can throw off your focal plane.  Let’s say you are using your nice brand new 85mm f 1.4 portrait lens and you are doing a tight head shot with the lens wide open from about 7 feet away.  Sounds reasonable right?  Well, at that distance on a crop sensor camera your total depth of field is only a little over an inch.  So if you breathe to hard and move the camera even slightly forward or back you can throw the whole thing out of focus.  In that case the front or back focus would be due to human error and not the camera/lens combo.  The same would hold true if your subject moved slightly from the time you focused to the time you took the shot.  A lot of us engage in the practice of using the center focusing point on the camera to achieve focus lock then recompose the shot.  All this movement of the camera can lead to some forward or backward movement which could throw your focus off its mark.

But you think you hold the camera steady as any tripod and you’re still experiencing this problem?  Or maybe you use a tripod and you are experiencing some issues.  Or perhaps you just are curious and you want to waste an afternoon testing your lenses…   Well you’re in luck because I’m going to show you a fast and easy way to check your lenses for front and back focus issues.

There are many methods to do this.  You can download charts from the internet.  You can shoot down at a 45 degree angle at lines of text laid out flat on a table.  You can even purchase a commercially made lens calibration checker.  But, you can do nearly the same thing using a few AA batteries and a flat surface.   To do the battery test method you will need the following:  A tripod (or beanbag), 5 AA batteries, a flat surface, and some daylight.  That’s it.  So gather up your materials and let’s get started. 

Before we start, just a word of warning.  The tripod is not a suggestion  it’s a requirement.  For this test to be valid you will have to be absolutely certain that your camera does not move during the testing and the only way to be 100% sure of that is to use a tripod, and a sturdy one at that.  Using a flimsy tripod that wobbles or shakes under the weight of your camera will be useless.   Using something like a beanbag or sand bag could be an acceptable alternative but it’s still not 100% certain.  If you try to hold your camera steady on the table by hand, well… , good luck because your testing will probably show you have front and or back focus issues even if you really don’t have any issues at all.  Use a Tripod.  Enough said on that.  And while I’m at it, this testing should be performed in daylight.  Daylight is easy to find so this should be no problem  :)  Tungsten and fluorescent  light have different color temperatures than daylight so you may see some strange results that would not be there if you did the test in daylight.  Ok, so you got it right?  Tripod and daylight.  Ok good, now onto the testing.

You will have to position 5 AA batteries on a diagonal at approximately 45 degrees to the sight line of the camera.  Check out the photo below.

 Position the batteries as shown in the photo.  Make sure that you have some nice text facing the camera to focus on .  Next, you will need to set your camera to use only the center focus point.  All DSLR cameras have focus points.  Some more than others.  But they all have the ability to select an individual focus point.  Read your owner’s manual to learn how to set your camera to use only the center focus point and leave it that way for the duration of the testing.  If you skip this step you may as well just not do the testing.  Once again, this is not a suggestion.  Center point focusing is a must.  If you are doing this in daylight (and you should be) the camera’s ISO setting shouldn’t be a problem.  You can probably leave it set to 100 or so but if need be, set the ISO high enough so you can have a shutter speed of at least 1/125th second or faster.  Remember we are trying to eliminate any possible camera shake issues here.  Next, make sure the lens you want to test is mounted to the camera.  Set the aperture setting to as wide open as the lens will allow (the smallest f number).  Remember from above, this will limit the Depth of Field so it will be easier for you to see any problems with focusing.

Once you are all set you are ready.  With the camera on the tripod, frame the shot as you see in the photo below.

 You want to be far enough away from the batteries so you are just a bit further away than the lens’ minimum focusing distance.  If you are too close the lens won’t be able to focus.  But you also want to be close enough that the batteries  mostly fill the frame.  This may take some trial and error to get the positioning right but  one or two tries should be enough.   Once you have this set up, you will want to focus your camera on the center battery.  To minimize the chance of camera shake you will probably want to use the camera’s short self timer mode (yep, get the manual out again).   Focus the camera and push the shutter button, wait a few seconds, the timer will do its thing, and the camera will take a photo.  Take a few photos to make sure you are getting consistent results then pop out the memory card and open the files in your photo processing program.

This photo shows what correct focus looks like.

 When focusing on the center battery it should look like this.  Center battery in focus and the rest out of focus to some degree.  If your photo looks like this you are good.  Time to break down the testing setup or time to test another lens.

This photo shows back focus.

The center battery was the point of focus but the camera focused behind the focusing point

This photo shows front focus.

 The center battery was the point of focus but the camera focused in front of the focusing point

If nothing is in focus, well I’ll address that at the end of the article.                       

If you have either front or back focus you either have a problem with the lens (bad but not so bad), a problem with the camera (bad but not the worst), or a problem with both camera and the lens (Yep, really bad stuff here).  If you have more than one lens you should try this with all your lenses.  If only one lens is causing a problem then more than likely you probably have a problem with just the lens.  If all your lenses are causing a problem then more than likely your camera’s sensor is not aligned properly.

So what do you do?  Some cameras have the ability to perform micro focusing  adjustments in the camera software.  Cameras like the Canon 1DIII, 1DIV,1DsMkIII, 5D, 7D, Nikon D3, D3x, D300, D700, Sony A900, and Pentax K20D, K-7, K-5 have the ability to calibrate the focus for up to 20 individual lenses by using the in camera software.  This is not a complete list so check your camera’s manual.  If you camera does not support this feature then you really have no alternative other than sending your camera back to the manufacturer to be calibrated.  Contact the manufacturer to see if you need to send the lenses in as well.  Some require that you send in the lenses so they can set the  calibration for each lens you will be using.

(As noted in the comments below, here are a few things you should also consider:
(1) A camera/body pair nicely focusing at the tested distance may still behave slightly off at another distance.
(2) For the zoom lenses one should either choose the mid focal length or the most used focal length for testing. In a problematic condition, you may have good focus at, say, 24mm and back or front focus at 90mm.)

Ok, now what about that issue of nothing being in focus.  If nothing is in focus, it’s just possible that your lens is not sharp wide open.  If the center battery is more in focus than the rest then it is possible that all is well but your lens just isn’t sharp wide open.  If this is a cheaper lens then it’s possible that this is the best the lens can do.  If it’s a more expensive lens you may want to return the lens for another copy or try another copy of the same lens to see if there is any improvement.  If you think your lens is bad you should send it in for repair. 

This entry was posted in Beginners Guides, Photoshop Tips and tagged , , , , , , , , , , , , . Bookmark the permalink.

50 Responses to Checking Your Camera for Front Focus or Back Focus.

  1. Melissa says:

    Great job covering this topic. I thought that I had a back or front focusing problem with my 24-70 lens then I realized it was just me. ;)

  2. Bulent says:

    Thank you for preparing this informative and easy to follow guide which is sure to help many beginners. You may perhaps consider adding a sentence or two on the below points: (1) A camera/body pair nicely focusing at the tested distance may still behave slightly off at another distance. (2) For the zoom lenses one should either choose the mid focal length or the most used focal length for testing. In a problematic condition, you may have good focus at, say, 24mm and back or front focus at 90mm.

  3. great tutorial…thank you for sharing this!

  4. Glen says:

    It would be nice to have some idea how far apart the batteries should be, along with a schematic drawing to show the position of the camera in relation to the batteries.

  5. Glen says:

    It would be nice to have some idea how far apart the batteries should be spaced, plus a schematic drawing showing the position of the camera in relation to the batteries.

  6. Glen says:

    it would be nice to have some idea of the spacing between the batteries, along with a schematic drawing showing the relative position of the camera to the batteries.

    • Scott says:

      Glen, the spacing is shown in the first photo. the space between the batteries is about one battery width. the camera should be set up directly in front of the center battery. The line of batteries should be at a 45 degree angle to the sightline of the camera. I hope that helps.

  7. Jon Pierson says:

    Hi,

    I just wanted to thank you for taking the trouble to explain theses issues. I would love to buy a Canon 70-200 EF f2.8L II USM but I’m checking third party lens reviews and came across these terms. Thanks to you, I now know what they mean.

    Regards,

    Jon

  8. Rania says:

    A friend turned me on to this site! Thanks for such great info! I hope this will help me solve some of my issues!

  9. Pingback: D7000 Focus issues - Page 15

  10. I have the 70-200mm 2.8 IS mark i – reknowned for being “soft” wide open but I have been having trouble with it being sharp at all!

    I wanted to test that it wasnt back-forward focussing so this was very useful-way easier than the charts etc that Ive heard about before.

    Still cant decide if it is just “not sharp” or focussing wrongly?!

    anyone care to look at the 4 photos I took and see if you think you know what it is?

    I invested in the 2.8 IS for weddings that I have coming up this year and need good results from it. Am currently considering selling it for the 135 L and 85 1.8 combo

    Thanks all

  11. sorry forgot to hit the notification by email button

  12. Pingback: Canon 7D and 400mm 5.6 lens photo problems advice please. - Page 2 - Wild About Britain

  13. Lukas says:

    Hi,

    First of all thank you for the detailed explanation it is more than perfect. I just made the same test with my lenses as I recently purchased a 35mm 1.8G lens for my D5100 and have been noticing the subject is not always in focus.
    My results are slightly different to what you are describing. Basically the battery in the middle is in focus which is great, but the one behind it is more in focus than the one in front of it. Is there a place I could email you my result images (obviously if this is OK with you) and let me know what you think about it? Feel free to email me if you prefer.

    Many thanks,
    Lukas

    • Scott says:

      Hi Lucas,
      Instead of emailing the photos, why not just join the forum and post them there? I’ll be more than happy to look at them for you. You can get to the forum by going to the front page of the blog and clicking the forum button on the menu or just go to http://www.cameralightlens.com/forum. Sign up should take about a minute.

    • Kate says:

      For Lukas – I have the same issue! I have posted pictures on the forum http://www.cameralightlens.com/forum/viewtopic.php?f=18&t=3133&p=19542#p19542

      I also get the battery behind more in focus than the one in front! – Can anyone tell us whether this is how it is supposed to be or is there a problem!! Lukas, did you post your pics to the forum so I can have a look and see if it looks the same issue as I have? Thanks

      • Lukas says:

        Hi Kate,

        Haven’t had the time yet will do so this weekend. Let you know once they are posted. Been terribly busy at work.

        • Paul says:

          It sounds normal – there is generally more depth of field behind the point of focus than in front of it. As long as you know it and expect it, you can either cater for it, or actively use in your photographs by moving the depth of field to where you want it to be, rather than the ‘default’ – i.e. around the point of focus.

  14. Kate says:

    Hi – I have a Sony A37 and thought I had a focusing issue, especially with the 50mm f1.8 lens I purchased – I have done your test and am going to try and post the pictures on the forum as comments would be greatly appreicated – however is there a chance my camera could have top/bottom focusing issues rather than back/front? I’ve done a couple of tests, this one and one with a ruler on a table and when I use the centre focusing point the clearest part of the photo seems to be just below! Is this an issue that could be fixed by manufacturer calibration? Thanks

  15. Pingback: ‘Please Don’t Buy an SLR if You’ll Only Use the Kit Lens’ — The Brooks Review

  16. John says:

    My 50mm f/1.8G requires different AF adjustments for different focus distances to get sharp images. I’ve been shooting batteries/books/star chart to show that it always front focuses.

    Close focus is ok at +6
    Medium focus is ok at +16

    Is this something you’ve experienced?

  17. Chris says:

    on ebay I found an interesting device for checking AF cameras, simply type the focusing lens jig in the search ebay

  18. Pingback: Is the 70-200 f2.8 Mk II L IS USM all that?

  19. Victoria Kaufman says:

    Thanks so much for sharing your focus test with us all. I have had my D7000 for nearly a year now and I have been miserable, I felt as if I may as well pack in photography, I have been a professional news photographer for 30 years and have shot every subject under the sun. I am now an addicted bird photographer but nothing has been sharp and I thought I had just lost the plot!!!!I did the test and now my 80-400mm is pin sharp on -6.
    It still seems crazy that Nikon DOesnt HIGHLIGHT this problem!! I am mad as a snake about it, if I was still working for a newspaper I would have been fired by now????vicky

  20. Els says:

    Hi, thanks for sharing this very useful information with us. I am using a nikon d5200. When I did the test at f2.8, focal length 50mm and shooting distance about 1 feet, the focus was very sharp. However, when I increase the shooting distance to about 1 metre or more, it starts to backfocus to one battery behind or worse, two batteries behind. And the back focus occurs across different apertures, f2.8, f3.5, f4. However, it was really sharp when the shooting distance was only 1 feet.
    Could you advise what could be the reason for that? Thks.

    • Scott says:

      Every zoom lens has the potential to do this. Its because there are lots of parts moving inside the lens. I’m always amazed how the lens designers manage to pull off what they do with the lens optics. The FF/BF test should be done at the focal length you use the most. If you’re not happy with your lens’ performance you should send it into the manufacturer for service/repair.

  21. Yehuda says:

    I have a question about the batteries I should use: Are rechargeables OK or I have to Alkalines?
    Thanks,
    Yehuda

    • Scott says:

      Any type of battery is ok. actually you could use anything you want to as long as each item is small and identical. The point really isn’t the battery. Batteries were only used because they are a great size, they have some graphics/writing on them so you can see focus sharpness and they are so very common. But you could use shot glasses, dice, or anything that’s a similar size that you can arrange in the same pattern.

  22. Lukas says:

    Haha! Your comment made my day. How about a Duracell !

  23. Chris says:

    Thanks Scott I have the 7D and need to look at the focus users setting and understand them more I think before I start playing with micro calibration etc.

    I use Sigma Lens and have been pretty happy with them

    • Scott says:

      Sigma makes some really nice lenses. I have a few and I’m very happy with them all. Their new line of lenses really look impressive.

  24. OjieLS says:

    Thanks for sharing this test… very useful indeed!

    So much so that i did it to test my newly acquired Sigma 17-50mm f2.8. Result is that i noticed some back focusing when on the 17mm focal range. Everything is fine on mid-focal range of 35mm and at 50mm.

    Should i need to have it calibrated?

    I used a D90 body by the way.

    Thanks!

    • Scott says:

      If the BFing bothers you perhaps you should have it looked at. If you bought it new it should be covered under warranty right? I think Sigma has some pretty long standard warranty times. But since you said it only BF at the widest focal length, perhaps you should take some photos with it and see how it performs in the real world. Shorter focal lengths always have greater Depth of Field so if you’re shooting landscapes you’re probably not shooting wide open and close up. If you’re lens is performing as you need it to then I’d just leave it alone.

  25. Incendiary says:

    used this test last night after getting frustrated with not getting a proper focus. Didn’t have a tripod but still managed to find that I’ve got a pretty severe back focus with my 50mm and a -17 seemed to mostly correct it on my d7000. I’ll be doing a better test with a tripod and my other lenses when I get home to see if it’s just the one lens (I hope) or if I’ll be sending the camera in.

    • Scott says:

      I’m glad the test helped you see a possible issue but I should warn you, shooting wide open and fairly close with just about any lens will give you a very thin Depth of Field so its very important that you use a tripod for these tests. your body movement just breathing will be enough to throw off the results.

  26. Michael says:

    Thanks for a nice web-site. Yesterday I did the the test with my D7100 and the 18-300mm DX lens. The test turned out quite ok, although at shorter focal distances such as 40 or below I noticed a very slight back-focus. When the focal distance was over 60mm and all the way up to 300mm I really did not notice any front- or back-focusing issues at all. My conclusion in my own case is not to mess with the AF fine tune becos there is always a possibility that the focus issues will start to occur at the longer focal distances such as 60mm or more. I guess that almost every lens can have some minor focusing issues at certain focal lengths depending on the distance to the object. Thanks again, Scott for a instructive web-site and I would be most delighted to hear your comment about my case.

  27. Michael says:

    Hi Scott, Just finished my second day of AF testing. And I am trying very hard to not become addicted to AF-testing (hahaha). Today was a beautiful day but instead og going out to take pictures I stayed indoors the whole day testing AF issues. My question/additional comment is: When you do an adjustment at one particular situation then how can you be sure that this particular adjustment will be ok for another situation. For example a zoom lets say at 60mm can have some minor focus issues but at the other end lets say at 150mm it is correctly focusing. So this means that the AF fine tuning you may have done may not be correct at all focal lengths. So I think we should be careful not to overdo it. I totally agree that if the lens is very clearly not focusing correctly in a number of different situations then AF-tuning is necessary. The point is: You can have a perfectly good lens attached to a perfectly good camera body, and STILL have focusing issues. Why? Because of the dreaded reality of manufacturing tolerances. There are millions of cameras + lenses; it would be impossible for all of them to be manufactured to focus exactly the same. Instead they are manufactured to perform within tolerance ranges.

    That’s what AF Fine Tuning is for: to adjust for small errors due to tolerances, if required.
    It’s NOT there to fix the lens if the lens is defective.

    • Scott says:

      I think you hit the nail on the head. There are tolerances lens to lens, I check my lenses to the focal length I use the most. Nothing will ever be perfect. We just have to accept the fact that there are manufacturer tolerances that we will have to deal with and work around

  28. Danny says:

    THANK YOU SCOTT!! This has helped me a lot!

  29. Pingback: Frustration! - Page 2

  30. Ali says:

    That was most helpful.
    I got my first prime lens, and after a few test shots with its widest aperture I became skeptical of a back-focusing issue not paying attention to the very shallow depth of field in lower f numbers.
    Your article helped me with the correct testing and I found out that lens was OK.

    Thank you very much Scott for the great article! :)

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>