Canon 28-80mm f/3.5-5.6

[lennon33x]

Just curious if anyone has ever experienced this.

I scored a 28-80mm Canon EF on the cheap about a month ago. It's fast and produces sharp pictures about 90% of the time. Randomly, I'll get a subject that is soft and requires more post-processing sharpening that I'd like. It's totally random, and not something that I can't overcome. Just curious if there is anything that one would do (i.e. light mods, etc.) or if anyone has experienced this.

Thanks

 

[eswebster]

are the soft pictures always at the same focal length or varied across the zoom range?

 

[Derrel]

Maybe it does not focus reliably????? Sometimes slower lenses like that are not the most-reliable focusing devices. I have a small,light, plastic-y, cheap Nikkor zoom of the same basic specification....28mm to 80mm f/3.5~5.6, the old AF-D model....it must weigh like 7 ounces...it's got a plastic-y mount...it's reeeeeeealy cheezy...but when it hits focus right, the pics are surprisingly good at f/8. Buuuuuut, since it's a maximum of f/5.6, at times the AF is not all that hot...

 

[lennon33x]

As far as the focal lengths, I'll have to check LR

Derrel, as far as speed is concerned, it's unbelievably fast. It's just weird that it occurs randomly. I'll also check my apertures and see. This is the first model of the lens, and it's build reliably better than the EFS 18-55 I sold. I hated that thing. The CA was abhorrent for me.

For whatever reason, I never thought to compare.

 

[Derrel]

As far as the focal lengths, I'll have to check LR

Derrel, as far as speed is concerned, it's unbelievably fast. It's just weird that it occurs randomly. I'll also check my apertures and see. This is the first model of the lens, and it's build reliably better than the EFS 18-55 I sold. I hated that thing. The CA was abhorrent for me.

For whatever reason, I never thought to compare.

Well, although it might be counter-intuitive, ultra-fast focusing is often more of a curse than a blessing on low-spec lenses...many lower-spec lenses have fairly short focusing travel arcs, AKA "short throw"...that allows them to focus quickly...but the problem is that with small maximum apertures the difference between SPOT-ON focus and OUT-of-focus, which is the way phase detect systems determine focus point, is not all that much...

Combine a short throw, and a smallish max aperture, and many low-spec'd lenses focus fast, but not with the highest repeatability. The aperture is a critical aspect: at f/2.8 the difference between IN focus and OUT of focus is pretty clearly delineated, at least for a modern AF sensor system. But, the difference between IN and OUT at f/5.6 is much more of a gray area. So, random mis-focusing is not all that surprising...my 28-80 is similar--focuses fast, normally, but...does not "Hit focus" properly the way I would like....but then...it's a cheapie...

 

[lennon33x]

Well, although it might be counter-intuitive, ultra-fast focusing is often more of a curse than a blessing on low-spec lenses...many lower-spec lenses have fairly short focusing travel arcs, AKA "short throw"...that allows them to focus quickly...but the problem is that with small maximum apertures the difference between SPOT-ON focus and OUT-of-focus, which is the way phase detect systems determine focus point, is not all that much...

Combine a short throw, and a smallish max aperture, and many low-spec'd lenses focus fast, but not with the highest repeatability. The aperture is a critical aspect: at f/2.8 the difference between IN focus and OUT of focus is pretty clearly delineated, at least for a modern AF sensor system. But, the difference between IN and OUT at f/5.6 is much more of a gray area. So, random mis-focusing is not all that surprising...my 28-80 is similar--focuses fast, normally, but...does not "Hit focus" properly the way I would like....but then...it's a cheapie...

So I checked in LR, and this is what I found. The shot that was in question was 72mm f/5.6. I then looked at other shots...I was shooting mostly, that day, around 35mm and between f/3.5 and 5.6. Very crisp pictures. I was framing shots on the fly (my 16 month old twins running around the park), and there is a good chance that she stepped just outside the DoF. I checked other images that I shot, that I framed and really focused on, and even at 70-80mm, they were pretty sharp. I have had it happen before though with a framed shot. It may be that in low lighting that it just isn't as sharp. I guess it's the nuances of really knowing your equipment. Obviously, having a higher quality reliable lens (24-105mm L), would produce sharper pictures. It was the randomness of occurrences that made me question what was happening.

 

[lennon33x]

Let me also mention that I use back-button focusing. I absolutely love it, however, am starting to learn some of its limitations (i.e. moving targets). It works great for swings because I can control when the image is in focus, vs having the camera take FOREVER sometimes to tell me something I can already see. I may just have to tweak how I take shots when it comes to my kiddos running around. Here's the picture in question: