Lightning and Star "Flaring" at f/2.8

[Alex Elmore]

In April of this year, I purchased a used Canon 17-55mm f/2.8 IS USM lens. This is now the fastest lens I own, and the fastest I’ve ever had. Thanks to the slow spring, I didn’t get to test it as much as I wanted, but was very happy with the quality of the photos it produced when I was able to use it. In July, I finally got to test it out at its fastest. I was impressed with the low-light capabilities that f/2.8 has to offer. However, I noticed a couple flaws that, while not very noticable, show up if you look closely at light sources in the photo. I have no idea how to describe it other than some sort of flaring, and I’m not having much luck finding anything about it online. The attached images are extremely cropped examples of this effect. In the first image below (ISO 200, 31mm, f/2.8, 7.2sec), you’ll notice the lightning flaring/blurring to the left, and the street lights look oblong/elliptical. The second and third images are from the same photo (ISO 3200, 17mm, f/2.8, 9.4sec); the second being from the right side of the photo, and the third image being from the left side of the photo. The flaring is noticed here as well, and the flare direction seems to depend on which side of the photo the object is on. Is this a common effect when shooting at wide apertures? If so, what is it called and is there a way around it (other than not shooting at f2.8)?

FYI, I double checked my focus when I noticed this in real time, and I made sure the image stabilizer was off.

 

[Rick Schmidt]

Alex-- Generally, the sharpest part of the lens is toward the center, and it will show distortions near the edges. I would go to the next f-stop, and double your time. That would give you the same exposure as the above examples. You could also double your ISO speed at f/4 or 3.5, which ever one your lens has, and keep the same time exposure. Lightning will also drift with the wind in a time exposure. Does this help?

 

[Alex Elmore]

Thanks for the reply, Rick. It does help. Since I usually shoot at wide angles, I am familiar with various types of distortion that creep in around the edges of the frame, but this one was new to me. I have been meaning to play around with various seeings with this lens to see how it changes things, but have yet to have the time to do so. I just wanted to make sure this was a common effect at wider apertures and not an issue with the glass.

 

[Greg Campbell]

What you're seeing is perfectly 'normal' if rather unwelcome.
Here's a good write-up of the assorted aberrations found in most lenses.
https://www.lonelyspeck.com/a-pract...rations-and-the-lonely-speck-aberration-test/

Some of the modern Rokinon / Samyang lenses hold sharpness to the edge and corners even when wide open.
The same site has a number of lens reviews and comparisons.

 

[Alex Elmore]

Here's a good write-up of the assorted aberrations found in most lenses.

That is a great write up. Thanks for sharing!