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Occasional Contributor
Posts: 7
Registered: ‎04-09-2018

Bad Coma? Or Focus issue?

[ Edited ]

Hello all/ anybody who can help! I'm having a problem with my 70-200 F2.8L IS II. 


I've rented and used many copies of this lens over the years and have never had an issue with it. Granted, the people over at Lens Rentals always tests and recalibrates their lenses on arrival. After a bit of luck at work and just the right amount of room in my budget, I was able to grab a copy for myself. At first, all seemed well, it was used, but not a single mark on it. Not even a bit of dust. And indeed, all through the range, the lens performed as expected. 

And that's when the trouble started. 

On day two with the lens, I went out to shoot some wild life and noticed I wasn't getting anything sharp at 200. No matter the aperture, everythign appeared to be slightly off. Heavy tripod, no wind, manual focus, fast shutter, 2.8 - 11, nothing sharp. No sense testing any more since the results aren't going to change. The images are in fact, sharp, but they're off. As though a second, very out of focus image is smudged across it. My guess, a slight stigmatism is going on. 

Anyway, I got a refund on the lens, sent it back, and picked up a new copy. First thing I did when I got the new (still used) copy of the lens, everything tested just as sharp as any good copy I've used. Fast forward a few days, that issue cropped up again. Same exact thing. Slightly off. Everything from at least 125mm-200mm clearly shows the problem. Though it's a gradient from not terrible to crippling at 200mm. Sometimes it's not particularly present. But it usually is there in full force. 

Perhaps that it comes and goes could be a symptom of the ambient temperature of Michigan currently being somewhere between the Arctic and Pluto. 

The lens works fine belwee 100mm with literally no issues, sharp as a razor and very much matches my 24-70l IS II.
The image of the nest, looking closely, you can see the image is actually very sharp, but there appears to be the effect of petroluem jelly being smeared across the front element. It's very obnoxious. This has always been my dream lens. :/ 

The image of the thread right below should show the stygmatism I was referring to. That's at the sharpest possible focus. Going in either direction on the focus ring from here will either result in the highlights becoming bokeh balls or just shifts the "focus" back further.

I would like to make sure everybody knows that this is in now way a back or front focus problem and no amount of MFA will fix this. It's not a camera issue as I've tested it with almost a dozen different cameras at this point. One thing I've noticed with both this lens and the first one I got was the front bit of the barrel is a bit loose, but that pretty much does nothing to the image. And searching all over the internet shows that it is pretty common, I've noticed other people post about this here and in other forums and the answers are never found, but I their description is similar to my issue, but poorly described. I followed up with a couple of different people on another site and their problems were never fully solved, they just either returned the lens, sold it was broken, or sent it in and got it fixed.

I tend to fall on the hardware engineering side of things and have read/ watched a lot about lens calibrations in the past and the stigmatism here seems to fall in line with an off-kilter calibration. But since it's noticeable as you zoom past 100mm and not really an issue until around 125mm, perhaps it's something entirely? Maybe somebody could help me? Bad Coma

Issues.

Honored Contributor
Posts: 6,149
Registered: ‎08-13-2015

Re: Bad Coma? Or Focus issue?

I once had a similar problem with the same model.  My lens was loose, and could not focus accurately.  I could shake the camera/lens combo and hear a click. As it turned out, my lens was missing the rubber ring that goes around the lens mount.

----------------------------------------------------------------------------------------------------------------------------------------------------------

"I don't rent software. I use Photoshop CS6, ACR 9.8 and Lightroom 6.8 ."
Occasional Contributor
Posts: 7
Registered: ‎04-09-2018

Re: Bad Coma? Or Focus issue?

Oh man, I wish that was the case. Unfortunately(or not?) The seal is perfectly in place and it mounts firmly and without issue to the camera body.
VIP
Posts: 8,911
Registered: ‎12-07-2012

Re: Bad Coma? Or Focus issue?

I have around 40 lenses currently.  I have had over a hundred or so.   I have had both versions of the ef 70-200mm f2.8L.  Neither exhibited this either.   Now I know it makes little difference to you but I have never had or seen this problem.

But to get to your porblem, I would send the lens to Canon for a C&C. Today ! There is really no other way to make sure it is good.

What bothers me is you said it works sometime? The lens does this on several cameras?  The lens do not do it at 125mm or less FL?  OK, last question.  Are you the only person to test it or have others seen the same results with the same rig?

A lot less stuff for 2018 but still a lot of Canon stuff. Along with, a lot of other stuff.
Respected Contributor
Posts: 1,892
Registered: ‎02-26-2015

Re: Bad Coma? Or Focus issue?


@Chip_Ormwrote:

Hello all/ anybody who can help! I'm having a problem with my 70-200 F2.8L IS II. 


I've rented and used many copies of this lens over the years and have never had an issue with it. Granted, the people over at Lens Rentals always tests and recalibrates their lenses on arrival. After a bit of luck at work and just the right amount of room in my budget, I was able to grab a copy for myself. At first, all seemed well, it was used, but not a single mark on it. Not even a bit of dust. And indeed, all through the range, the lens performed as expected. 

And that's when the trouble started. 

On day two with the lens, I went out to shoot some wild life and noticed I wasn't getting anything sharp at 200. No matter the aperture, everythign appeared to be slightly off. Heavy tripod, no wind, manual focus, fast shutter, 2.8 - 11, nothing sharp. No sense testing any more since the results aren't going to change. The images are in fact, sharp, but they're off. As though a second, very out of focus image is smudged across it. My guess, a slight stigmatism is going on. 

Anyway, I got a refund on the lens, sent it back, and picked up a new copy. First thing I did when I got the new (still used) copy of the lens, everything tested just as sharp as any good copy I've used. Fast forward a few days, that issue cropped up again. Same exact thing. Slightly off. Everything from at least 125mm-200mm clearly shows the problem. Though it's a gradient from not terrible to crippling at 200mm. Sometimes it's not particularly present. But it usually is there in full force. 

Perhaps that it comes and goes could be a symptom of the ambient temperature of Michigan currently being somewhere between the Arctic and Pluto. 

The lens works fine belwee 100mm with literally no issues, sharp as a razor and very much matches my 24-70l IS II.
The image of the nest, looking closely, you can see the image is actually very sharp, but there appears to be the effect of petroluem jelly being smeared across the front element. It's very obnoxious. This has always been my dream lens. :/ 

The image of the thread right below should show the stygmatism I was referring to. That's at the sharpest possible focus. Going in either direction on the focus ring from here will either result in the highlights becoming bokeh balls or just shifts the "focus" back further.

I would like to make sure everybody knows that this is in now way a back or front focus problem and no amount of MFA will fix this. It's not a camera issue as I've tested it with almost a dozen different cameras at this point. One thing I've noticed with both this lens and the first one I got was the front bit of the barrel is a bit loose, but that pretty much does nothing to the image. And searching all over the internet shows that it is pretty common, I've noticed other people post about this here and in other forums and the answers are never found, but I their description is similar to my issue, but poorly described. I followed up with a couple of different people on another site and their problems were never fully solved, they just either returned the lens, sold it was broken, or sent it in and got it fixed.

I tend to fall on the hardware engineering side of things and have read/ watched a lot about lens calibrations in the past and the stigmatism here seems to fall in line with an off-kilter calibration. But since it's noticeable as you zoom past 100mm and not really an issue until around 125mm, perhaps it's something entirely? Maybe somebody could help me? Bad Coma

Issues.


In the thread photo I expect you are at or close to the Minimum Focus Distance of the lens.

 

In the nest photos, there are just out of focus branches in the foreground. 

 

I see nothing that looks out of the ordinary. Remember with a long wide aperture lens you have a very shallow depth of field, objects in front of and behind the plane of focus will be blurry. 

VIP
Posts: 8,911
Registered: ‎12-07-2012

Re: Bad Coma? Or Focus issue?

"I see nothing that looks out of the ordinary."

 

I agree.  I suspected operator error.

A lot less stuff for 2018 but still a lot of Canon stuff. Along with, a lot of other stuff.
Esteemed Contributor
Posts: 4,186
Registered: ‎06-25-2014

Re: Bad Coma? Or Focus issue?


@ebiggs1wrote:

"I see nothing that looks out of the ordinary."

 

I agree.  I suspected operator error.


Something clearly doesn't look right, but there are still two potentially important data items that I haven't managed to extract from the verbiage:

a)  What camera is being used?

b)  How much magnification has been applied to what we're seeing?

In particular, at least something in the bird's nest picture should be sharper than it is, UNLESS we're looking at a very small portion of the original image.

Bob
Boston, Massachusetts USA
VIP
Posts: 8,911
Registered: ‎12-07-2012

Re: Bad Coma? Or Focus issue?

"I suspected operator error."

 

Since two lenses, in a row, the OP has tried exhibited the same flaw, especially from one of the best made lenses in the world, I suspect he is doing something wrong.

A lot less stuff for 2018 but still a lot of Canon stuff. Along with, a lot of other stuff.
Esteemed Contributor
Posts: 3,394
Registered: ‎06-11-2013

Re: Bad Coma? Or Focus issue?

It's much easier to detect coma when you photograph a point-source.

 

E.g. take a steel ball-bearing and reflect a light (e.g. a flashlight) off of it.  The reflection on a mirror-like curved surface tends to reduce the light down to something which is nearly a point source.  You can use this to test for coma.  (preferably with a dark background).  

 

The lens should be on tripod to avoid camera motion being confused for optical issues.  Turn off the image stabilization.

 

Take several test images with the reflection in the center... as well as near each side & corner.

 

 

Tim Campbell
5D III, 5D IV, 60Da
Occasional Contributor
Posts: 7
Registered: ‎04-09-2018

Re: Bad Coma? Or Focus issue?

There are no out of focus branches in the forground. I'm about 6 yards away. 

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