topic Re: Curious Double Image in BG in EOS DSLR & Mirrorless Cameras

Curious Double Image in BG

jblooo — Wed, 14 Aug 2019 22:54:30 GMT

My wife has been using her Rebel T7i and Canon 70-300 IS USM lens. Over the last couple days she's been very disappointed to see that her images have a strange Double-blur diagonal lines effect in the background. And nowhere in the image is razor sharp.

See attached. A closeup of the bouble line bachground image is inset. (Autofocus, 300mm, 1/320th, f/6.3, ISO400 if that helps)

I have not been able to duplicate the problem but would like to help her prevent it in the future. She lost several hours on a beatiful day today and I like to help keep her interested.

Anyone seen this before? I'm not even sure where to start.

Thanks in advance for any thoughts.

joe

Re: Curious Double Image in BG

Waddizzle — Wed, 14 Aug 2019 23:36:10 GMT

“See attached. A closeup of the bouble line bachground image is inset. (Autofocus, 300mm, 1/320th, f/6.3, ISO400 if that helps)”

That is an unusual artifact. I never seen exactly that, but I seen “ugly bokeh” that was most likely a result of the Image Stabilization having a tug-of-war with the auto focus tracking in AI Servo mode.

Which autofocus mode and autofocus point did she use? Canon’s DPP software can tell you. What was her setting on the shooting mode dial? Again, DPP can tell you.

For that focal length, my shutter speed would have been at least 1/640. That follows the rule of thumb that says use a minimum shutter speed of at least 1/FL, which is 1 / (Focal Length). But that is the rule of thumb for full frame sensor camera bodies. For an APS-C sensor I think the rule of thumb should be at least 1/2*FL, which is twice the focal length, 1/1280 or faster. For fast moving critters like rabbits, you may want to go even faster than that!

As for the strange artifacting, turn off Image Stabilization if the lens has it. The camera has noise reduction settings that can degrade image quality when shooting wildlife, which is actually a very demanding shooting scenario. I doubt if they are making a difference for the artifacting. A cheap lens filter could cause it, though.

For stationary subjects, you can use One Shot focusing mode. Use AI Servo for moving subjects. Always use the center AF point for focusing in One Shot mode because it is the most accurate. For AI Servo focusing, enable all of the AF points, but you can tell the camera to always start with the center AF point.

Re: Curious Double Image in BG

jblooo — Wed, 14 Aug 2019 23:57:13 GMT

Waddizzle,

All good suggestions. Glad to hear I'm not the only one who thought it strange looking.

AI Servo AF, Zone AF, Program AE but she changed to AV later. The focal length and focal point changed throughout the day, but the artifacts remained fairly consistent.

I like your comment about the cheap filter. It does have a UV filter, and a fairly old one at that. That will be my first investment.

Excellent starting place. Thank you.

I'll keep you updated.

Re: Curious Double Image in BG

cicopo — Thu, 15 Aug 2019 03:33:14 GMT

Looks like camera shake to me. Too slow a shutter speed for the stationary target.

Re: Curious Double Image in BG

ebiggs1 — Thu, 15 Aug 2019 16:35:36 GMT

First off I believe it is lens aberration and just the limits of the ability of the lens. If you have everything absolutely correct you may reduce but I bet if you critically examine all your shots with that lens you will see it more or less. It will appear more on things like grass or tree branches. That type stuff.

If you have any filter attached remove it and don't ever use it again. Try to keep from using the most open f stops. Also avoid the most closed f stops. Stay in the middle range. When you are at the 300mm side of the lens try to keep the SS above 1/500. Avoid extreme crops trying to enlarge the subject.

As distance increases lens resolution decreases. That is true for any tele lens not just the low end ones. That lens is never going to take photos like you see in magazines and other pro things. But there is a fellow here on the forum that gets amazing results form it so maybe he will see this and offer some suggestions

Re: Curious Double Image in BG

ebiggs1 — Thu, 15 Aug 2019 17:16:59 GMT

Oh, BTW, one other thought, the aberration will always be worse at the corners of the photo. Most lenses even the cheap ones are best at their center. It looks to me that your your lens is astigmatic. It could be misaligned. To reduce it, do try to shoot with smaller apertures.

Re: Curious Double Image in BG

jblooo — Sat, 17 Aug 2019 12:34:03 GMT

Here is what I eventually found for anyone looking at this n the future.

The UV filter was not a "Cheap" one, but I bought a new one anyway because it seemed logical.

When I went to replace it I noticed that the old one had some sort of film on the INSIDE of it I couldn't see from the outside. My GUESS is that this was causing reflections between the lens and filter. I cleaned the inside and haven't seen the distortion since. See attached.

I've always said that what is wrong with my photography can't be fixed by buying better equipement. This wasn't what I meant, but it fits this situation.

Thank you all for the help.

Re: Curious Double Image in BG

ebiggs1 — Sat, 17 Aug 2019 15:17:49 GMT

The type of aberration I suggested won't show in a photo like the heron. It is possible that the filter was at fault. Let's hope so and not your lens.

Re: Curious Double Image in BG

jblooo — Mon, 19 Aug 2019 16:51:17 GMT

OK. Latest update.

After MUCH more testing and disappointing shoot days,.. It appears the Canon 17-300 lens works fine on my 7D, but is consistantly soft on my wife's T7i.

I have no idea why but am tired of spending time on this.

My newest Tamron lens works perfectly for us on BOTH Cameras. I guess I just lost my beloved Tamron.

Re: Curious Double Image in BG

ebiggs1 — Tue, 20 Aug 2019 15:31:11 GMT

Any problem or the lack of will show up more on the higher resolution camera. OK on the 18mp camera but soft on the 24mp camera. This is to be expected. The good gets better and the worst gets worse.

Re: Curious Double Image in BG

RobertTheFat — Tue, 20 Aug 2019 15:47:53 GMT

@jblooo wrote:
OK. Latest update.

After MUCH more testing and disappointing shoot days,.. It appears the Canon 17-300 lens works fine on my 7D, but is consistantly soft on my wife's T7i.

I have no idea why but am tired of spending time on this.

My newest Tamron lens works perfectly for us on BOTH Cameras. I guess I just lost my beloved Tamron.

If you haven't done so already, check to see if you have any autofocus microadjustment set for the Canon lens on your 7D. That could explain why the lens works well on the 7D but not on your wife's T7i.

But if that is what's going on, it doesn't really solve your problem, since the T7i lacks AFMA. You'd still have to give your wife the Tamron (or replace her T7i with, say, an 80D).

When my wife and I got married (50+ years ago), I had a Nikon F-2 and she had a cheap Sears-Roebuck camera. Her camera soon gave out, so I asked her what sort of camera she wanted to replace it. Her answer was immediate: "One that can use your lenses!"