# Softness and center-frame coma issue with Canon EF 100-400mm lens?



## jrista (Mar 19, 2013)

I seem to have an issue with my EF 100-400mm lens. I just took it out to shoot Double-Crested Cormorants and some other birds the other day, first time since early February. The last time I used the lens, it was for pretty close up shots of smaller birds, such as Juncos and Chickadees, in my yard. When it came to the Chickadees, I did not see anything wrong at first with the shots. Yesterday, while photographing the Cormorants, it seemed the 7D AF locked on pretty well, even though the subjects were only filling 1/4 to 1/3 of the frame most of the time. I spent a few hours photographing, and went home with a couple CF cards full of photos. When I got home, it seemed as though 100% of the shots were soft and/or slightly out of focus. I've been using this lens with it's current AFMA setting for months, and it seemed to work at that setting before. To my knowledge, the lens has been sitting on a tripod, attached to my camera, in the same place since the middle of February...it hasn't been dropped or anything like that. 

So far, out of quite a number of photos, I have yet to see one that I would call sharp or properly focused. Most of the shots seem to have the focal plane a few inches behind the subject, even though the 7D in AI Servo appeared to have locked onto the subject and tracked it while I held the AF button down (I use rear-button AF as taught by Art Morris.) The Camera is a 7D, no teleconverters used, and it was mounted on a GT3532LS tripod with the Jobu Pro 2. IS was in Mode 2, and was always active and stabilized before any shots were taken (so I don't think the issue is blurring caused by mid-exposure actuation of the lens' stabilization element group.) In addition to the softness and OOF issue, ALL of the highlights, even in the center of the frame, seem to have a coma-like shape. All of them are "stretched" towards the upper right corner of the frame.






(Not the best photo of the bunch...it just has a lot of spot highlights that demonstrate the problem well. Small highlight on the end of the bill, another in its eye, several on its wing feathers. The whole image overall appears soft. Focal plane looks to be slightly behind the bird, despite the fact that I was using center-point only AF in with rear-button AF, and it was right on the bird (LR doesn't show AF points, sadly, and I a

Since getting home, I've run the lens through FoCal, as well as a manual AFMA procedure, and I keep ending up at the same setting: -5. I've tested a bunch of shots indoors on well-lit objects, including those with very fine details (I have a calendar with extremely fine lines). Things look pretty sharp, however a numeral six right at the center of the frame also appears to have a slight lower left to upper right "blur":

NOTE: Click images to view them full size, to actually see the 100% pixel peeping view. 




(I used AF with -5 AFMA. The diagonal blur appears when using live view contrast-detect AF as well...pretty much identical.)


I am beginning to wonder if the Junco and Chickadee photos from a couple months ago might even have some problems. Based on this 100% crop of an unprocessed Chickadee photo, I now see that the same lower left to upper right blur and coma-like highlight shape. There also appears to be some soft fringing around the beak and the top of it's head. The feather detail does not look as sharp as I thought it was...certainly not as sharp as I would have expected for how close the subject was, and the fact that AI Servo AF seemed to instantly nail it right on the birds eye. I rarely look at my photos at 100% like this...I usually process and sharpen at the "Fit" setting in Lightroom. At 100%, it definitely appears as though shots from over a month ago have the same problem as the shots today. I am guessing the issue is just more pronounced with more distant subjects like the cormorants (which had to be at least 8-10 times farther away).





(Shot from a few feet away, almost at the MFD of the lens. IS was off in most of these shots, with the camera mounted on a tripod with a gymbal head.) 

It is also possible that I've just become spoiled. I have rented several of Canon's new Mark II telephoto and supertelephoto lenses. The sharpness on those is quite stunning, and certainly puts the piddly little old 100-400mm lens to shame in every way. However, that said, I do believe the funky coma-like highlight halos and stretching seem to just be wrong to me, and I do not remember seeing them in my photos from a number of months ago. Do I need to send in my lens for repair? If I do need to send it in, is it best to send the camera body with it for proper alignment, or will AFMA cover that? Thanks for any insight!


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## Mt Spokane Photography (Mar 19, 2013)

The photos do not look as good as the lens can do, but at or near mfd, most lenses have issues.
Any zoom is going to have coma problems, even good primes have trouble with coma. Its just that astronomers are the ones who see it most.

Did you have a polarizing filter on the duck photo? Bright reflections can be too much for a sensor to handle and cause blooming.

Here is a ~ 8-10 ft shot with my 100-400. Its not up to a big white, but for the difference in cost and weight, I can live with it.

It would not hurt to have canon touch up your lens, one of the elements might have slipped a little.


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## jrista (Mar 19, 2013)

Mt Spokane Photography said:


> The photos do not look as good as the lens can do, but at or near mfd, most lenses have issues.
> Any zoom is going to have coma problems, even good primes have trouble with coma. Its just that astronomers are the ones who see it most.
> 
> Did you have a polarizing filter on the duck photo? Bright reflections can be too much for a sensor to handle and cause blooming.
> ...



No polarizing filter, or any other filters of any kind. I shoot bear lens as every filter impacts IQ in some way. 

The Cormorants and Shovelers were probably 30-50 feet away most of the time, however I have a bunch of shots of Coots and Shovelers within 10 feet, and they too had the issue. The Cormorant crop is dead center of the lens, where IQ should be at the highest and aberrations (such as CA and coma) should be at their lowest. The calendar 6 shot was from maybe 12 feet away, and again was dead center of the lens. The Chickadee was only a few feet away...not exactly at MFD, I had some leeway, but it was pretty close (the bird itself was at least 70% of the frame), and it was mostly center (slightly shifted towards the top edge). 

I've NEVER seen coma at the center of a lens before, and I don't ever remember it being on this lens in the past. I just can't figure out if it is the lens. I dropped the 7D a few feet back in October or early November, but it landed in sand. That scratched up the top LCD a little, but otherwise the hit did not seem to be particularly hard. Given the fact that the 7D is built fairly ruggedly, I haven't imagine that could affect it like this...but I guess it's possible the IR cut and OLPF shifted.

I recently remembered that I apparently bumped my tripod a few months back as well, and damaged it beyond repair. I didn't even notice it until I got home...it is possible I damaged the lens at the same time, as the 7D with the 100-400 was mounted on the tripod that day...


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## jrista (Mar 20, 2013)

Sent it in for repair, along with my 7D to get them calibrated. Hopefully it won't cost too much, and my lens will come back at peak performance.


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