Plastic Fantastic 50mm - Too Soft when Wide Open?

Bstanley

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Joined
Mar 1, 2001
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This past weekend my wife was performing in an indoor choir performance at church - Great I figure an excuse to take pictures - indeed a perfect venue for using my fastest lens - the Canon 50mm f1.8 II.

While waiting for the show to start I was taking test shots to see what speed/aperature settings were possible in the available light - and I noticed that the closer to f1.8 I got the softer the pictures got, now admittedly I was making this determination by looking at the not so hi-res 2.5" LCD on my Rebel XS, but when the aperture was set to f4 everything was as sharp as a tack, when set to f1.8 everything was blurred...I really looked at the entire picture to make sure that it wasn't a Depth of Field thing. I tried manually focusing until a particular focus dot blinked, snapped a picture and then looked at the face that had been focused on - f1.8 blur, f4 sharp.

I'm going to set up some sort of more tightly controlled test this weekend. Set the camera on a tripod, use a camera release etc and take a series of shots to check if what I was seeing is actually related to the lens or not.

Has anyone used Canon's little f1.8 50mm enough to say - yes indeed "that's just the way it goes with a $100 lens you silly man", or maybe this particular lens needs some help?
 


I have this lens, and haven't had that issue wide open, though it does focus slower while wide open in a low light setting. I would do a focus test with it. Given that you've already pixel peeped, I assume that it was blurry across the whole picture, and none of the parts were in focus. That suggests a focusing issue to me.

But hey, it's a $100 lens - what do you want?;)
 
Has anyone used Canon's little f1.8 50mm enough to say - yes indeed "that's just the way it goes with a $100 lens you silly man", or maybe this particular lens needs some help?

Even at less than $100 this lens is pretty sharp and even wide open at least *some part* of the image should be in focus. It could be the lens or it could be the camera. I had a focusing issue with my Xsi (that was apparent when using the 50 wide open) and Canon quickly corrected it.
 
Yes, it is comparitively soft wide open, as most leneses are (although the higher end glass tend to perform better than average wide open). One reason for buying such fast glass is not just so you can shoot wide open, but so that you can shoot a stop down, which would still be pretty wide, and get sharp results.
 


This past weekend my wife was performing in an indoor choir performance at church - Great I figure an excuse to take pictures - indeed a perfect venue for using my fastest lens - the Canon 50mm f1.8 II.

While waiting for the show to start I was taking test shots to see what speed/aperature settings were possible in the available light - and I noticed that the closer to f1.8 I got the softer the pictures got, now admittedly I was making this determination by looking at the not so hi-res 2.5" LCD on my Rebel XS, but when the aperature was set to f4 everything was as sharp as a tack, when set to f1.8 everything was blurred...I really looked at the entire picture to make sure that it wasn't a Depth of Field thing. I tried manually focusing until a particular focus dot blinked, snapped a picture and then looked at the face that had been focused on - f1.8 blur, f4 sharp.

I'm going to set up some sort of more tightly controlled test this weekend. Set the camera on a tripod, use a camera release etc and take a series of shots to check if what I was seeing is actually related to the lens or not.

Has anyone used Canon's little f1.8 50mm enough to say - yes indeed "that's just the way it goes with a $100 lens you silly man", or maybe this particular lens needs some help?

Can you post the pictures you took in the church so I can see how much "blur" you are talking about?

In general, almost every lens is worse wide open than when stopped down a few F-stops. This is especially true for most large aperture lenses
 
Thanks cpbjgc, I'll use the process and targets from the Focus Test link you posted this weekend as my test.

VVFF, I didn't include any pictures because in all honesty it's certainly possible that the problem is the 'nut behind the wheel' or button in this case, and it's also possible that reviewing the pictures on the small LCD (even zooming in) was part of the problem. I haven't even had time to review the pictures on a bigger screen yet. I'll include some of the 'Focus Test' pictures one way or the other after the weekend.

bob - that's my concern I guess, that either the camera or the lens has something a bit wrong. After the 'Focus Test' this weekend I should know.
 
I got some nice images at Disney with this lens and my XSi playing around with depth of field. Both of these were wide open (f/1.8)

MickeyPost.jpg


VenusMickey.jpg
 
100% crops

F1.8
f1_8%20crop.jpg


F2.2
f2_2%20crop.jpg


F3.5
f3_5%20crop.jpg


Looks to me like something is not right at wide open...
 
I've got the 50mm f/1.8 II and use it often. I've never had any issues with it that were not user error. However, from the focus test you posted, maybe you have a bad copy or something is a bit wonky. Those are not the type of results I have seen with that lens on my Rebel G, Rebel XT or 50D.
 
Looks to me like something is not right at wide open...

You should look at the sharpness in the center of the frame, that's where it will be evident if something is wrong. Even though this lens isn't a good performer wide open, it should still be decent in the dead center. Have to remember that it's only a $100 lens, I don't even use my 50/1.4 wide open unless absolutely necessary because it simply isn't very good away from the center until f/1.7.
 
Most lenses have a "sweet spot" aperture at which the lens produces its sharpest images. The "sweet spot" falls somewhere in betwen the maximum and minimum apertures. A lens is usually not perfectly sharp at its widest aperture. Even items that are in focus may not be completely crisp. Lenses produce noticeably sharper image a few stops down from their maximum aperture. The images Bstanley posted show exactly what I've described. It's not a problem with the lens, it's just a characteristic inherant in all lenses. The 50mm f/1.8 lens is a decent performer for its price. You can't expect it to perform as well as a $2300 pro lens with nano-coating or L-glass, etc..

Additionally, at f/1.8 the widest aperture the depth of field is EXTREMELY shallow. In the pictures bstanley posted, the test chart is not perpendicular to the camera. Therefore, the left side of the page is at a different focal plane than the right side. Therefore, the entire text wouldn't be equally sharp.
 
To me it looks like its front focusing just a tiny bit. You could send it to canon and have them see if there is any problem. However, I have heard these lenses are fairly soft wide open. Doesn't look out of the realm of possibility to me. I can't really comment since I don't have one.
 
I have heard these lenses are fairly soft wide open.

If the amount of what I'll call 'blur' at f1.8 is typical for this lens (ie my copy is not unusual) then frankly it becomes less useful to me - part of why I bought it was the expectation that I could take very low light pictures with it.

But if I need to close it down to f3.5 to get a clear picture I might as well use the kit lens in low light anyway - especially since the kit lens is also image stablized.

the test chart is not perpendicular to the camera... the left side of the page is at a different focal plane than the right side.

The page is oriented as it is supposed to be to run a Focus Test. It is at a 45 degree angle top to bottom with respect to the focal plane. The left and right side of the image are in the same plane - the top and the bottom are not.

Doesn't matter in any case - both sides are the same - out of focus at f1.8 and in focus at f3.5.

it looks like its front focusing just a tiny bit

I agree. Pretty clear at f3.5, but it is still in focus where it was supposed to be focused so I wouldn't send it back for that.
 
I think that you did the focus testing correctly. There should be a much clearer focus than what you've got. It should be a very narrow band, but it should still be very clear, and, clearly, it's not. :-)

I haven't done that focus test with mine, but might be able to next weekend, as I'm heading to the "World" this week.

Also, the 50mm primes are the most commonly made lenses over the history of SLR's, and as such, generally are very good lenses for very low dollars (relatively).

If you can get ahold of someone else's lens, you could check your camera's focusing ability, and compare the focus test to yours.

Good luck,

Boris
 
Keep in mind that the closer you are to the subject, the shallower the depth of field will be. For everyday images with subjects several feet away, the depth of field will be greater and the apparent sharpness will improve. It can also be further improved with sharpening in processing. Rarely do people view or print images equal to a 100% crop. Even if you don't shoot at 1.8, the lens is very useable at f/2.8. At wider apertures the differences between the numbers don't appear to be much, but in terms of light, you're doubling the light with each stop of light. f/2.8 emits double the light as f/4 and half as much as f/2. Also, the kit lens you reference may be more blurry at f/3.5 than the 50mm would be at the same aperture. Also, the kit lens likely isn't f/3.5 throughout the focal range. What is its max aperture at 50mm? Let's say, for the sake of arguement, that it's f/5.6 at 50mm. Well, it's not going to be its sharpest at f/5.6. If you want it sharp, you'll need to stop it down to f/8 or f/11 (16 times less light than f/2.8).

Try comparing 100% crops of the target from the 50mm and your kit lens, both at the kit lens' largest aperture at 50mm.
 
So here is the Kit Lens (the 18-55mm f3.5-f5.6 IS v2) at 48mm at f5.6, quite tidy - perfectly acceptable - although the camera definitely front focuses a touch.

It looks like send the 50mm back to Canon time to me, unless someone has one they want to try the focus test on to demonstrate that what I've seen is normal.

Kit%20at%2048mm%20f5_6.jpg
 
It looks like send the 50mm back to Canon time to me, unless someone has one they want to try the focus test on to demonstrate that what I've seen is normal.

I still recommend you look at how the 50mm performs in the dead center before deciding to send it back. Have a look at the SLRgear review of this lens (specifically the blur index chart).. it simply isn't sharp anywhere outside the center at f/1.8, or even f/2.0. At f/2.8 you should have a pretty decent sized area of reasonable sharpness in the center.
 
In my experience the 50mm f/1.8 has proven to be somewhat sharper, even wide open at a short distance, than the 18-55 kit lens. If I have time this weekend I'll do a focus test with both lenses.
 
Code brings up a good point about lenses being less sharp around the edges vs dead center. The problem is less prevalent with cropped sensors, because they only receive light from the center-most portion of the lens elements where it's sharpest, but the problem still does exist. Bstanley, do you have a filter, eg a "protective" filter, on the lens? That sometimes exacerbates the problem around the edge of the frame (less so in the center).

Bstanley's posted image of the test target using the 18-55 kit lens at 48mm & f/5.6 leads me to question my belief that lenses performed better a few stops down from their maximum aperture at a given focal length. In other words, the 18-55 may reach it's aperture "sweet spot" as you approach f/8, regardless of the focal length. So, even though f/5.6 may be the largest aperture it can use at 50mm, it's still relatively sharp at that aperture, because it's a little over a stop down from the lens' overall max of f/3.5 (only available around 18mm). That would mean that there's no real "fair" way to compare these lenses. Ideally, you'd want to use the kit lens' largest aperture, f/3.5, but then you'd be photographing at 18mm, not 50mm, and a 100% crop would be different.

Oh, well. It sounds like you're not happy with the lens, and that's all that matters.
 
I took the lens to the dealer where I bought it, they basically shrugged and suggested that they send it to their Canon rep for testing. I said fine and off it went.

Here are 'real world' samples that prompted the testing. These are 100% crops from roughly the center of the picture. I was approx 50 feet away, seated and hand holding the camera with my elbows on the pew in front of me.

First at f1.8 (not acceptable to me)

1to1%20%20Crop%20f1_8.jpg



Now at f2.8 (fine with me)

1to1%20%20Crop%20f2_8.jpg




Again - another try at f1.8 (not acceptable)

1to1%20%20Crop%20f1_8%20v2.jpg
 













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