Focus Issues

[Steve's Girl]

For the last few months, I have been having focus problems with my camera and/or lens. I kept thinking it was user error, but now I'm thinking it is either a lens or camera issue. Below is a photo I recently took (it is straight out of the camera and needs to be cropped, etc. So, ignore the composition part)

I focused on my daughter's eyes. However, the eyes are soft and her sweater is in focus. It appears that it is a back focus issue. Is this likely a camera or a lens issue? I've tried focus charts in the past, but don't know how reliable the results are since you have to have the camera at the right angle, etc. Several of my WDW pictures have a similar issue. It appears to happen most often with my Tamron 28-75 lens. Maybe send the lens in to be calibrated?

 

[GrillMouster]

Well, it certainly looks like the focal plane is behind the eyes, but I can't say that it's a back-focus problem with the lens based on this one image. For one, you really should use a perfectly stationary camera & subject to test it out. If you don't like using a focus chart at 45 degrees, try photographing books on a shelf, where the spines are progressively slightly farther back as they are farther from the center book. In other words, a V pattern from a birds-eye perspective. Put the camera on a tripod, and aim it straight (90 degrees) at the spines, using single (not continuous), center point, and the timer function, focus on the center book and take the picture.

 

[Steve's Girl]

OK, here is a focus chart. It isn't that I don't necessarily like to use focus charts. I just don't know that I am using them correctly.

I used a tripod and wireless remote. I think the camera was about 45 degrees. Although I didn't have my protractor handy to verify that. The chart seems to back up what I have been experiencing in my photos - back focus.

 

[GrillMouster]

The size of the photo you posted makes it tough to judge whether the focal point -- the dark bar in the middle, the text superimposed on that bar, and the text to left and write of the bar-- are in sharpest focus. You'll need to view the image at 100% and probably even larger on your computer monitor to judge at what distance the lens is sharpest. The absolute sharpest point is supposed to be where you focused, the center bar (and the text to its left and right), but if it's slightly off, don't worry about it.

The good news is that the center bar appears to fall within the depth of field, that is, the range of acceptable focus. Remember that with depth of field, approximately one-third of it will fall in front of the focal plane (the point you focusd on) and approximately two-thirds will fall behind it. In other words, when you focus on the bar in the chart, the bar should NOT fall right in the center of the area that's in focus. In the image it looks to me like it's in okay focus up to 20mm, so if that area is supposed to be one-third, and the area behind the bar is supposed to be two-thirds, it should be in focus to about 40mm behind the bar. In the photo it appears to be in okay focus between 40 - 50 mm behind the bar. Again, these ratios are not exact, and I'm judging a small picture. You really need to look at the full sized image and judge where on the chart its' sharpest (compare the little horizontal lines on the side).

Another thing: it's common for zoom lenses to have different levels of front or back focus at different focal lengths. This makes is tough, even if your camera allows AF fine tuning. It's easier with prime lenses.

 

[EnnEss]

What type of AF is the camera using?

 

[Steve's Girl]

Af-s

 

[pjacobi]

You can't just point the dSLR in the general direction and just snap a picture!

You need to be conscience of focal point selected by the camera and evaluate if it is the correct focal point. If it is not correct, you need to change the focus mode or resort to manual focus. The focal point is especially important with wide apertures and telephoto lens.

Great photos don't just happen. It takes work and skills to make great photos.

Photography is about all the thought, efforts and skills that you put into the picture *before* you hit the shutter.


-Paul

 

[Steve's Girl]

You can't just point the dSLR in the general direction and just snap a picture!

You need to be conscience of focal point selected by the camera and evaluate if it is the correct focal point. If it is not correct, you need to change the focus mode or resort to manual focus. The focal point is especially important with wide apertures and telephoto lens.

Great photos don't just happen. It takes work and skills to make great photos.

Photography is about all the thought, efforts and skills that you put into the picture *before* you hit the shutter.


-Paul

Uhhh....thanks. I'm very aware of that. I carefully selected the focus point and made sure it was on my daughters eyes. I don't just point and shoot. In fact, I took the time to set the exposure manually on both the camera and strobe I was using. I did put a lot of thought and effort into this shot. I don't expect good photos to just happen. I do work at them. Sorry it didn't appear that way to you. I seem to be having a problem with this particular lens and was hoping to get some advice on how to evaluate whether or not a lens is focusing properly. But thanks for the critique of my photo.

 

[boBQuincy]

Focus issues are a pain to track down and another pain to get the manufacturer to acknowledge them. Part of the problem is we hear of so many focus issues that are not. Yours appears to be for real.

One problem with testing is that the focus spots are actually much larger than as shown in the viewfinder. To test my camera I set up a business card and set the distance so the card filled most of the center third of the frame. I let the camera focus on this and then set the lens (50mm f/1.8) to manual focus so it was not disturbed.

I set up two more business cards on either side of the first, one in front and one behind (by about 1/4"), and took the shot. The card in front was the sharpest, confirming my suspicions.

Then I repeated the test from the beginning, two more times, and with another lens all three times again, and checked for consistency.

After all this if you still detect rear focus at least you have a lot of data to help convince the manufacturer (and yourself) that it is for real. Good luck!

 

[Steve's Girl]

Focus issues are a pain to track down and another pain to get the manufacturer to acknowledge them. Part of the problem is we hear of so many focus issues that are not. Yours appears to be for real.

One problem with testing is that the focus spots are actually much larger than as shown in the viewfinder. To test my camera I set up a business card and set the distance so the card filled most of the center third of the frame. I let the camera focus on this and then set the lens (50mm f/1.8) to manual focus so it was not disturbed.

I set up two more business cards on either side of the first, one in front and one behind (by about 1/4"), and took the shot. The card in front was the sharpest, confirming my suspicions.

Then I repeated the test from the beginning, two more times, and with another lens all three times again, and checked for consistency.

After all this if you still detect rear focus at least you have a lot of data to help convince the manufacturer (and yourself) that it is for real. Good luck!

Thanks boB - I'm going to try the business card thing. I zoomed in on the focus chart I used and the black focus line is not the sharpest area. The sharpest point is about 20mm behind he dark line.

I first started to suspect that it could be a lens issue when I was looking at my Beauty and the Beast pictures from our Oct trip to WDW. We got VIP seating, so I was hoping to get some good photos. They were all back-focused. I'm uploading them to smugmug now. I'll post a few samples later.

 

[pjacobi]

I carefully selected the focus point and made sure it was on my daughters eyes.

The focus could have locked on the hair, just to the left of the eye, the subject could have moved, or the camera could have been moved and the shot re-composed after focus was acquired. The depth of field is only a few inches it's very easy to get wrong. For portraits you need to use a high enough f/stop so that you have enough depth of field to cover nose, eyes, and hair all at slightly different focal points. You just didn't have enough light for this shot.

This is good example of when it is time to bring out an external flash unit.


-Paul

 

[Steve's Girl]

The focus could have locked on the hair, just to the left of the eye, the subject could have moved, or the camera could have been moved and the shot re-composed after focus was acquired. The depth of field is only a few inches it's very easy to get wrong. For portraits you need to use a high enough f/stop so that you have enough depth of field to cover nose, eyes, and hair all at slightly different focal points. You just didn't have enough light for this shot.

This is good example of when it is time to bring out an external flash unit.


-Paul

I used an Elinchrom studio strobe. I had plenty of light!

 

[wenrob]

The focus could have locked on the hair, just to the left of the eye, the subject could have moved, or the camera could have been moved and the shot re-composed after focus was acquired. The depth of field is only a few inches it's very easy to get wrong. For portraits you need to use a high enough f/stop so that you have enough depth of field to cover nose, eyes, and hair all at slightly different focal points. You just didn't have enough light for this shot.

This is good example of when it is time to bring out an external flash unit.


-Paul

Dude, what is up with you? It might be a little more helpful to ask if someone has tried something rather then assume that they haven't and are stupid. Is it at all hard to get that she may know her camera and lens and has narrowed it down? She's asking for ways to test her theory not how you think she should take the picture.

My apologies to Stevie'sgirl and the other DISer's here if I'm out of line. There are so many, kind, helpful people here that are so willing to go out of their way to help people learn. It bugs me when people are spoken to like they're idiots that just don't know better.

 

[pjacobi]

I used an Elinchrom studio strobe. I had plenty of light!

But not a large enough f/stop for the required depth of field to get the face in focus.

99% of all focus problems are caused by the photographer, not the equipment! Even if the lens has a focus bias, a good photographer would know how to compensate.

Does a golfer blame the clubs? Does the musican blame the instrument for a poor performance?

Would you rather I lie and say go buy a more expensive lens or camera and it will instantly solve all your problems?

Learn from you mistakes and try again.


-Paul

 

[Steve's Girl]

But not a large enough f/stop for the required depth of field to get the face in focus.

99% of all focus problems are caused by the photographer, not the equipment! Even if the lens has a focus bias, a good photographer would know how to compensate.

Does a golfer blame the clubs? Does the musican blame the instrument for a poor performance?

Would you rather I lie and say go buy a more expensive lens or camera and it will instantly solve all your problems?

Learn from you mistakes and try again.


-Paul

I am not asking if I should buy a new camera or lens. If you would even bother to read my posts, you would know that. I have taken hundreds of photos with this lens over the past few weeks at various apertures trying to evaluate this. I own several other lenses and have not had focus problems like this. I know how to use a lens with a large aperture. I have 1.4 and 1.8 lenses that I use regularly. With my other lenses, if I focus on the eyes, the eyes are sharp. But when you take 75 photos in a controlled setting of a stationary object and every one of them is back-focused, you have to start to suspect that the lens may have a focus issue. If the lens is not focusing properly, I want to send it in to have it calibrated. Why should I compensate for a lens that is not working properly? I've got enough to think about with exposure settings, lighting settings, etc. The last thing I want to have to add to the mix is to remember to focus in front of my subject to get the proper focus.

I can clearly see that you view me as a stooge who does not know how to use my equipment. Your opinion has been noted. You no longer need to offer your "assistance".

 

[pjacobi]

I can clearly see that you view me as a stooge who does not know how to use my equipment.

I'm sorry but you misunderstand my comments.

In my opinion, the focus problem is due to the fundamentals of photography, not equipment failure.

I started photography over 30 years ago on a manual focus, manual exposure SLR film camera. One had to learn the fundamentals of photography just to get a decent shot. If the shot was out of focus or not exposed properly, it was obviously the fault of the photographer.

With today's auto focus and auto exposure cameras, it leads to a dependence on the equipment, rather than an understanding of the fundamentals of photography. In most cases, the camera does get it "right" much quicker than I could have ever focused manually and used a light meter. However, there are still some situations where the camera will get it "wrong" and it is up to the photographer to use knowledge of the fundamentals to override the camera settings.

That's why there are so many recommendations for Byran Peterson's book, "Understanding Exposure". It teaches the fundamentals that were overlooked by depending on the automatic settings.

In this particular example, even if the auto focus would have locked perfectly on the eyes, the short depth of field would have left the hair out of focus. Every strand of hair deserves to be clearly seen on such a pretty girl!

I believe that you were so distracted on getting the perfect Christmas tree "bokah" or blur, that you overlooked the depth of field requirement for portraits. This is a difficult shot that would require you to bracket the f/stop to get the perfect depth of field for the face *and* the best Christmas tree bokeh. The results would probably not have been visible on the tiny camera display, but judged only after looking full-screen on a larger monitor. That's tough to do when the subject won't sit still.

That's my opinion. I'm sorry that you took my comments personally.


-Paul

 

[maccagerl]

Does a golfer blame the clubs? Does the musican blame the instrument for a poor performance?

Yes, golf clubs can be defective and instruments can be out of tune.

Would you rather I lie and say go buy a more expensive lens or camera and it will instantly solve all your problems?

Learn from you mistakes and try again.


-Paul

The OP has never suggested that a more expensive camera/lens will solve all her problems- she is trying to troubleshoot a specific problem.

Good luck OP, I hope you can get this figured out!!

 

[Groucho]

Good grief. Obviously camera and lens focusing issues are a true problem and not one to be explained away by blaming the person behind the lens.

Steve's Girl, you may want to take a look at this focus chart... or even if you use the one you've got, it should give tips of usage. The important thing is to put it at approximately a 45' angle and get it so it fills the frame, set the camera to center focus point, and point it right at the middle of the focus chart. If the lettering is focused in front or back, then you've got a problem.

I had wondered if something was up with my camera for a while after some AF large-aperture shots were not as sharp as they should be (and MF ones were fine), and sure enough, it was off a little. I adjusted it in the custom menu (your camera may or may not have such an option) and when I didn't need the camera for a little while, sent it off to be adjusted. It's back and seems to be spot-on... though I'm hoping to have time to double-check it and my AF lenses before my trip, but I suspect I'm going to run out of time!

 

[Steve's Girl]

Groucho - thanks for posting the link to the Pentax chart.

I have used three focus charts now and this one was by far the best and easiest to interpret. It did confirm what I had been seeing on the other charts. The sharpest point is about 20mm behind the focus point. The focus point is definitely not sharp.

Sorry for the huge photo, it is just easier to see that way. I have e-mailed Tamron several images and they agree the lens is not focusing correctly and needs to be calibrated. So, I will be sending it in.

I am really glad I was able to figure this out. I have been so disappointed with my photos lately. And this time of year, since most of my photos are indoors, this lens is the one I use the most. So, I had basically put my camera away and haven't used it much since I was assuming that I just didn't know how to use it any more.

Below is a photo from Beauty and the Beast

I was so disappointed that every photo was back-focused. I originally intended to use my 70-200 2.8 lens for this show. That lens is spot on and very sharp. But we got VIP seating and were sitting in the second row. So, I used my 28-75 instead. I had been having problems with this lens, but had simply been assuming it was user error, so I was very careful with how I focused and tried to only take photos when the actors were not moving for a few seconds to try to avoid out of focus photos. But, that didn't help. That is one of my favorite shows at WDW. At this point, we don't have another trip planned. So, I'm not sure when I'll get to photograph it again. Whenever that is, hopefully next time will be an improvement.

 

[seashoreCM]

Try the focus chart tilted front to back on the left and again tilted front to back on the right etc. Maybe your camera has a subtle defect where there is a spot focus but it is not in the center of the frame.