300 F4 L IS USM - not sharp

I recently purchased a used 300 f4 L, older lens I know but what I could afford.. After using for a couple of months I felt it wasn't nearly as sharp as my 70-200f4 (non IS) from which Ive gotten some beautiful and insanely sharp images. I made a test comparison from a print on the wall from both lenses, with and without a 1.4 TC. I found that the 70-200 was very much sharper than the 300 - even with the TC on it was sharper by a big amount.

So, my question is, is it normal fro the 300 to be so much less sharp than the 70-200? I thought a prime would be much better, even an older L like this one.

2nd question - does Canon still service this lens? Can it be made sharper? I'm currently using it on a 50D, with maybe a 7D Mk 1 in the offing.

I'd appreciate any input, thanks. Hoping I haven't made a big mistake buying this lens.

It would be unusual for the 300mm f/4L to be much worse than the 70-200mm f/4L. The non-IS 70-200/4 is impressively sharp, and could have the edge over the prime wide open. But they should be very close, not a dramatic difference, especially on a crop body where the 70-200's worst performing areas (corners) are cropped out. Have you checked the 300 for front and back focusing issues? Could it possibly just need a little micro-adjustment?

Because there are so many factors, fairly rigorous, controlled testing is necessary to see if a lens is really not performing properly, or if it's a motion issue, AF adjustment issue, etc: Tripod, mirror lockup, remote, no-filters, clean lenses, focus in live view, IS off, etc. The 300mm f/4L IS USM is one of those early IS lenses that does not automatically detect a tripod, so if you're shooting with a tripod, or even a monopod, you might check to be sure that IS isn't causing issues.

FWIW, I'm actually not super impressed with my 300mm f/4L IS either. I too was used to new, excellent zooms, and I expected the prime to be just that much sharper, and it really isn't. Sharpness is not noticeably different from the 70-300L @ 300mm that I used to use for wildlife. I only changed lenses because the 300 can autofocus with a 1.4x TC on it, and the 70-300 couldn't.

Thanks for your input, absplastic

I did the comparison test on a tripod with MLU, f8 and the same distance for both lenses, same subject. I haven't micro-adjusted'd yet, but will do that today (if I can figure out how it's done) If the sharpness wasn't so noticeably different it wouldn't bother me, it is an older lens, after all. And I bought it for the same reason as you, with the 1.4 TC it would be quite versatile.

I have looked carefully at my images to see if there's front- or back-focusing, but it's hard to see, given the subject matter and distance (herons on a busy background sort of thing.) More testing needed, I think

I have a 100mm non-L Macro as well as the 70-200, and I'm used to both lenses being so sharp, even on my cranky old 50D, maybe it's spoiled me, lol.

I used to have the Canon 300 F4 L IS and the reason that I bought it was it's sharpness. Mine was to replace a good copy of the 100-400 L IS (Mk1). My 300 could be cropped to equal or exceed the 100-400 despite being 100mm shorter.
Later on I bought a Canon 300 F2.8 L IS and though better it certainly did not make my F4 look shabby.
Not perfect but I have attached and un-edited image for reference, it's just scaled for web.

If your 300 F4 (either version) is not decently sharp then there is something wrong somewhere. I have been told that the older (non IS version) is sharper than the IS model that I had, though I cannot confirm this.

I used to say my 300L F4 IS is so sharp I had to carry bandaids in my camera bag. I owned that lens since 2006 and it produced thousands of tack sharp images. The only reason it is resting now is because I purchased the 100-400 II. It should be just as sharp or sharper than your version of the 70-200. The 70-200 2.8 V1 was the model that was known to be soft.

Canon still lists it on their site so they have to service it.

7D with no MFA.

The one thing you have not mentioned is whether it has a filter or not. If you purchased it with a filter and have not tried it without the filter yet, that very well could be the problem.

Nogo wrote in post #17698047
The one thing you have not mentioned is whether it has a filter or not. If you purchased it with a filter and have not tried it without the filter yet, that very well could be the problem.

I had a B+W filter on the shot I posted and it was on the lens for every shot I took since 2006. Good point because a low quality filter can cause issues.

greyswan wrote in post #17696293
2nd question - does Canon still service this lens?

Most certainly. In fact, it is a current lens.....there is nothing newer so far as the 300 f4 models are concerned. Canon should be servicing this lens for many years to come.

Thanks to all who replied. Nogo, I didn't have a filter on - never use one, so that came off asap. Thanks, Digital and Johnf3f for the photos, great examples of sharpness. I MFA'd it this weekend, with some improvement, but I suspect it's going to the Canon doctor soon.

If I'm not sure and it does not seem right Canon service is the place to go to eliminate potential issues. I have a new 70-200 2.8 II that needed + 15 at 200mm while it was good at 70mm. It was brand new and it turned out there was a mis-calibrated board.

I would suggest to try tripod and Live View, just to remove the AF and micro-adjusting from the equation.

If you have not micro-adjusted a lens with questionable performance, there is no point for discussion...

Digital, I will be sending it in to Canon definitely - MaksiM1 I did adjust, and tested on a tripod in live view at 200% with remote shooting from my computer, I used the term MFA (micro-focus adjustment) with IS turned off.

Or you have extremely sharp 70-200 same as mine. I measured sharpness of my lenses in FoCal and it shows that my 70-200/4 non IS is a bit sharper than 400/2.8 L IS, which is known as one of the sharpest lenses in Canon. BTW both lenses are very sharp.

yes, my 70 200 is razor sharp - that's a lens I will never sell, lol! And I hadn't considered that point mkkaczy.

When I was shooing for my 70-200 F4 the local mom and pop shop was a huge supporter of the the non IS lens.