Canon FES 17-85 MF softness

Hey folks,

I'll start off by saying that I bought the mentioned lens for £50 because of the stuck aperture problem. I reckoned I'd be able to fix it myself or give it a try.

I know that this ribbon cable issue can effect AF too, as it focus hunts at 85mm which you would expect as the ribbon cable gets moved internally.

An issue of softness has popped up throughout all of the image I took today in Manual Focus. I thought at first it was my technique however, in live view at 10x digizoom I manually focused on the part in 'red box near center' in the below picture, and in live view it was sharp.

I took the picture, and checked over the image and its just generally soft, with no point of focus even though, I did find MF in Live View.

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Looks like some of the Tulips in the back are in focus. You need to do a better test.

Thanks for the reply.


This is straight out the camera with no PP. I did do a little work in photoshop. Some sharpening using the High Pass Filter, and there was quite a dramatic result.

I am maybe getting far to used to using this Tamron Lens as its super, so everything else is going to look soft, especially @ 17mm and wide open.

I'll fix the stuck aperture problem, and stop it down to F8 to see where I go from there.

I think I'm just that used to getting fairly sharp results with the Tamron, however the subject matter and field of view are totally different.

I guess my inexperience with lenses is showing a bit :/

A good guideline for selecting apertures for shots with significant DOF is to set....

Aperture = Focal Length / 2

So for 17mm ideally you would be at around f/8-f/9, possibly more if you had close foreground detail to be kept sharp. I understand that you are unable to adjust the aperture with this lens, but that doesn't make the problem disappear.

Basically, no matter how great your DOF, the lens can still only focus precisely at a single distance at any one time. Anything closer or further away from that plane of focus is going to get progressively softer. The calculated DOF is simply a guideline to indicate the range within which the softness should still be acceptable when viewing at "normal" reproduction sizes - like a 12x8 print.

If you are at f/4 when you should be at f8 or more, and you are pixel peeping rather than examining at "normal" magnification then you are going to see problems. Also, from my own experience of this lens I would say that the wide end is its worst performing range, while at 85mm mine was really pretty good.

Add all that together and you have.....

- A lens used at its least capable focal length;
- A lens used wide open at that least capable focal length;
- An aperture which is inappropriate for the selected subject/scene.

If I may go on, you were at 400 ISO and 1/2500. Why? At 400 ISO with the 7D you're going to get some pixel level noise, which might be suppressed with NR, but NR will further soften the image. I can't think of any reason not to be at 1/640 and 100 ISO for this shot, given that you were stuck at f/4.

BUT, the flowers look to be quite well lit by sunshine, and maybe overexposed a little. Certainly your exposure settings are for conditions dimmer than full sunshine, so I suspect you might have clipped some pixels through overexposure, and that will have lost you details in the plants. Maybe 1/800 at f/4 and 100 ISO would have been better still.

So I'm not sure that your lens is a dud beyond the limitations imposed by the fixed aperture, and I'm afraid those will constrain the type of photos you will be able to take successfully.

Thanks for that reply tdodd. Very informative.

I have no explanation for why I used ISO400 other than I just had it set there from the day before, and I was just dying to try out the lens. I slipped it into Av mode and locked the wheel at the back so i made sure I wouldn't change the aperture.

I also dialing in -1 or EC. ISO400 was too high I know.

On viewing the RBG histogram I clipped the reds.

I've been shooting with the 70-300 for about 2-3 months now, so maybe I'll need to re-learn how to shoot with this lens.

On reading further into it, the 17mm wide open does produce bad results, but this is essentially the reason I wanted this focal length. I just hope it gets better stopped down, or i'll be sorely disappointed.