Lack of sharpness at f1.8 on Canon 50mm STM

SD19194 wrote:

This only hit me the other day after reviewing many older photos and then doing a ton of practice shots. My Canon 50mm STM (newer model) simply isn't sharp at f1.8. So many times in the past I've gone down to this aperture hoping to get those crisp shots and have had to delete the photos thinking something must have went wrong whether it were camera shake or subject movement or the wrong shutter speed, etc. Now I'm starting to think I just have a rather lackluster lens that advertises f1.8 but really is best suited for f2.5 or 2.8. Has anyone ever heard anything with this lens with regards to this issue? Or is it at all possible I've been doing something wrong all along when going down to this aperture? It should be noted that when I go to 2.5 or bigger, things are almost always fine.

Also, the test shots I've done at f1.8 have been with a timer with the camera on a table to completely rule out hand shake. I also changed the AF point (red dots) to just one red dot in the middle for the test shots. Still, the photos lacked super sharpness in the middle.

I think that what you are seeing is probably normal for that lens - it simply isn't sharp at f/1.8 and reaches it peak sharpness at f/5.6.

Have a look at the resolution table in the middle of this page from the review on Optical Limits: https://www.opticallimits.com/canon_eos_ff/905-canon_50_18stm?start=1

This isn't an unusual behaviour for a lens of this type. Even better quality lenses don't normally reach their sharpest point until 2-3 stops wide open. Reserve f/1.8 for when you really need it and then put up with the lower sharpness. Otherwise, shoot at narrower apertures. If you want a lens that is significantly sharper at f/1.8, then you are going to have to spend a lot more money for something like the Sigma Art 50mm f/1.4.

SD19194 wrote:

Thanks. Just strange how it’s made as an f1.8 lens yet it’s barely usable at that aperture. Then again at 1:20 in this review video there are no comments on issues with sharpness at 1.8 and the middle does seem to be very sharp(?)

https://youtu.be/x_7raMVLPeE

You say use 1.8 for when I really need it but if it’s never going to be sharp then when would I ever need to?

An example would be if you need to shoot in very low light and the only way to get the shot is to use f/1.8.  Whenever I travel I have two small, fast primes in my camera bag for exactly these situations.

The other point is that, unless you are going to crop your image very severely or you are going to make very large (e.g. 20"x30"} prints, then the sharpness at f/1.8 may well be fine for a lot of your photography.

A couple of things come to mind with my limited experience:

• Copy variations. I had the pre-STM version and it was more than sharp enough for me. Unfortunately I shot some photos at a restaurant and it being so small I left it on the **** table and only realised a few weeks later
• The specs for PDAF focussing are something like within 1 DOF - ah I found that I documented a post from some time back:

Canon spec is to focus with in one depth of field for standard lenses and with in 1/3 depth of field for lenses faster than F/2.8. All Canon cameras focus with the lens wide open regardless of what aperture you have the camera set at.
Here's a post by RD Kirk that explains it:
(quote)
"If the camera places the actual focused plane within the depth of focus range, the intended focused plane of the subject should "look sharp" on a 6x9-inch print from a distance of 10 inches. In "high precision mode" the intended plane of focus should "look sharp" on about an 11x14-inch print at 10 inches (extrapolating from the standard size given by Canon for normal mode).
This standard is important to understand. If you use high precision mode and view the image on a monitor at 100 percent of the original pixel resolution, do not expect the actual plane of focus to coincide with the intended plane of focus. It's not necessarily going to do that--it's only designed to get close enough to "look sharp" at the standard final display enlargement size and viewing distance. If it does that much, then it's doing its job as designed.
If you're operating at normal AF precision, the camera will happily settle for any point within the depth of focus range (and not necessarily the same place every time--randomness within limits is what "tolerance" means in this context).
If you need optimum sharpness at greater than the standard final display sizes and viewing distances, then yes, you'll have to focus manually. However, a lot of focusing problems are caused by users not realizing that even autofocus requires learning certain techniques, some similar to the techniques of using a manual split-image rangefinder.
(end of Quote)

• Have you tried a focus test with contrast detection/live view to see whether it is the PDAF or the lens that is the issue?

SD19194 wrote:

AnthonyL wrote:

A couple of things come to mind with my limited experience:

• Copy variations. I had the pre-STM version and it was more than sharp enough for me. Unfortunately I shot some photos at a restaurant and it being so small I left it on the **** table and only realised a few weeks later
• The specs for PDAF focussing are something like within 1 DOF - ah I found that I documented a post from some time back:

Canon spec is to focus with in one depth of field for standard lenses and with in 1/3 depth of field for lenses faster than F/2.8. All Canon cameras focus with the lens wide open regardless of what aperture you have the camera set at.
Here's a post by RD Kirk that explains it:
(quote)
"If the camera places the actual focused plane within the depth of focus range, the intended focused plane of the subject should "look sharp" on a 6x9-inch print from a distance of 10 inches. In "high precision mode" the intended plane of focus should "look sharp" on about an 11x14-inch print at 10 inches (extrapolating from the standard size given by Canon for normal mode).
This standard is important to understand. If you use high precision mode and view the image on a monitor at 100 percent of the original pixel resolution, do not expect the actual plane of focus to coincide with the intended plane of focus. It's not necessarily going to do that--it's only designed to get close enough to "look sharp" at the standard final display enlargement size and viewing distance. If it does that much, then it's doing its job as designed.
If you're operating at normal AF precision, the camera will happily settle for any point within the depth of focus range (and not necessarily the same place every time--randomness within limits is what "tolerance" means in this context).
If you need optimum sharpness at greater than the standard final display sizes and viewing distances, then yes, you'll have to focus manually. However, a lot of focusing problems are caused by users not realizing that even autofocus requires learning certain techniques, some similar to the techniques of using a manual split-image rangefinder.
(end of Quote)

• Have you tried a focus test with contrast detection/live view to see whether it is the PDAF or the lens that is the issue?

Unfortunately I wouldn’t have the first clue how to do this

What camera do you have?  Does it have a live view screen on the back?  If so look up the instructions to shoot with live view, its focussing is more accurate than what you have been doing.

SD19194 wrote:

I have a Canon Rebel T7

You can download the manual from Canon's Support site. Canon also have a Learning Centre site which may be of use. There are also many videos and explanations of enabling and using Live View focussing.

My posts are based on the fact that, and in the absence of any example, you may see the lack of sharpness you may expect because you are not getting exact focus. If you are getting exact focus it is still possible/probable that the budget lens is not as sharp as you might like, or as a more expensive lens would be. So the first thing is to ensure you are properly focussed which Live view focussing will enable you to do.

Note that on many sites, including Canon, the Rebel T7 is more commonly known as the 2000D. Yes, it's annoying.

https://www.canon.co.uk/support/consumer_products/product_ranges/cameras/eos/ (or choose your country when you search for Canon support)

https://www.usa.canon.com/learning

https://asia.canon/en/support/8200044900

and no doubt other sites/sources are available.

Best to upload an example once you've got a photo via Live View focussing if you are still not happy.  There could be other things that people could suggest is the cause of the problem.

SD19194 wrote:

This only hit me the other day after reviewing many older photos and then doing a ton of practice shots. My Canon 50mm STM (newer model) simply isn't sharp at f1.8. So many times in the past I've gone down to this aperture hoping to get those crisp shots and have had to delete the photos thinking something must have went wrong whether it were camera shake or subject movement or the wrong shutter speed, etc. Now I'm starting to think I just have a rather lackluster lens that advertises f1.8 but really is best suited for f2.5 or 2.8. Has anyone ever heard anything with this lens with regards to this issue? Or is it at all possible I've been doing something wrong all along when going down to this aperture? It should be noted that when I go to 2.5 or bigger, things are almost always fine.

Also, the test shots I've done at f1.8 have been with a timer with the camera on a table to completely rule out hand shake. I also changed the AF point (red dots) to just one red dot in the middle for the test shots. Still, the photos lacked super sharpness in the middle.

Well, 50/1.8 STM is the most basic, cheap, optically simple lens. Can we then expect it to be super sharp wide opened? I guess the answer is obvious.

Stop it down to f/2.2 and things improve significantly while still maintaining shallow DoF and a strong bokeh.

SD19194 wrote:

Canon_Guy wrote:

SD19194 wrote:

This only hit me the other day after reviewing many older photos and then doing a ton of practice shots. My Canon 50mm STM (newer model) simply isn't sharp at f1.8. So many times in the past I've gone down to this aperture hoping to get those crisp shots and have had to delete the photos thinking something must have went wrong whether it were camera shake or subject movement or the wrong shutter speed, etc. Now I'm starting to think I just have a rather lackluster lens that advertises f1.8 but really is best suited for f2.5 or 2.8. Has anyone ever heard anything with this lens with regards to this issue? Or is it at all possible I've been doing something wrong all along when going down to this aperture? It should be noted that when I go to 2.5 or bigger, things are almost always fine.

Also, the test shots I've done at f1.8 have been with a timer with the camera on a table to completely rule out hand shake. I also changed the AF point (red dots) to just one red dot in the middle for the test shots. Still, the photos lacked super sharpness in the middle.

Well, 50/1.8 STM is the most basic, cheap, optically simple lens. Can we then expect it to be super sharp wide opened? I guess the answer is obvious.

What lens might you suggest that can go actually perform well and properly at f1.8 (or better)?

Well, the currently best of the best in close focal lengths is Sigma 40mm f/1.4. Wide opened it is very sharp with great contrast and no fringing. Focuses flawlessly on mirorrles cameras but I do not know how it would perform in focusing accuracy on your T7. Sigmas tends to suffer from focus inconsistency on Canon DSLRs.

Otherwise native Canon 50mm primes weren't Canon's shining spot. You have your nifty fifty with its optical design. Then there is an old EF 50/1.4 with quite big copy variation and still not great at f/1.4 - f/2. And then there is EF 50/1.2 which is portrait oriented with creamy bokeh and mild rendering up to f/2.0. That is it.

You can check and try the Tamron 45mm f/1.8. I do not know this lens personally but from the tests it looks very well. And it has image stabilisation which is quite rare and very useful. But again I have no idea how it will focus on T7.

Hello

to be expected at this price point

My old Canon 50mm f/1.4 super sharp but not at f/1.4

it really shines from f/2.8 and is über-sharp at f/5.6, same as a very expensive prime

That’s actually what you pay for when you reach for the expensive primes.. they are tack sharp directly from full opened

still, at f/1.4, I managed to shoot my most beautiful and dreamy portraits at night with air ballons filled with fire in the background … that would have been impossible to shoot at f/1.8

rgds, Gaul

SD19194 wrote:

gaul wrote:

Hello

to be expected at this price point

My old Canon 50mm f/1.4 super sharp but not at f/1.4

it really shines from f/2.8 and is über-sharp at f/5.6, same as a very expensive prime

That’s actually what you pay for when you reach for the expensive primes.. they are tack sharp directly from full opened

still, at f/1.4, I managed to shoot my most beautiful and dreamy portraits at night with air ballons filled with fire in the background … that would have been impossible to shoot at f/1.8

rgds, Gaul

Thanks for the reply. You lost me a bit here though. You said how your 50mm 1.4 was not super sharp at f1.4 but then later say (in bold) that at f1.4 you were able to shoot beautiful and dreamy portraits. Did you just mean you still got some great bokeh shots at 1.4 but they just weren't super sharp?

Yes, exactly

Getting a very sharp shoot is not always synonymous of a nice shoot.. important, but in low light, it's only part of the equation

Why you pay several times the price for an "L" prime over this "Nifty-Fifty" is just about that, getting a sharp shoot straight from the maximum aperture.

If you go to f/5.6 or f/8, the difference btw the 2 is minimal and does not matter

If you want sharp images at f/1.2 f/1.4 f/1.8 you need to go for the likes or Canon "L" or Sigma ART lenses

Take care and relax about your lens

Just know its normal use case and expected limitations... or upgrade it

Gaul

Absolute sharpness is generally something you do not want for a portrait. Generally a good portrait shot is a little soft. People usually don't want to see every freckle and skin blemish. For this reason, image processing software which has pre-sets for portraits and landscapes and so on softens the portrait pre-set just as it boosts the saturation on the landscape one.

More broadly, it is good photographic practice to respect the natural limitations of your equipment. It is normal for equipment to function best in the middle of its useful range, less well at the extremes. With lenses, it is normal to have less sharpness and more flare wide open - in fact it is very difficult  to make a lens which doesn't act like this, and although it can be done the result is heavy and expensive. Similarly, zoom lenses very seldom perform especially well at the limits of their zoom range.

Suppose you want to shoot at 35mm and you have two lenses, a 16-35 and a 24-70. Which lens should you use? Well, the 16-35 will do OK, but chances are that it will be a bit soft at 35mm and have some distortion. The 24-70 will be in its sweet spot.

For the same sort of reason, it should be your usual habit to shoot a stop or at least a half stop above wide open. Try to use f/8 on an f/6.3 lens; try to go for f/2 with an f/1.4 lens, and so on.

Note that some lenses are so beautifully made that you can ignore the normal rules. I habitually shoot a Canon 600/4 wide open at f/4 for example, I expect perfect sharpness at f/4, and get it. But it weighs 4 kilograms and cost $15,000.

Finally, there are times when you can't get the shot doing the "right" thing (e.g., shooting stopped down a little, not using outlandishly high ISOs). At these times, you do whatever it takes to get the shot.

cheap.  so a cheap crappy lens