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Severe CA/Purple Fringing Canon 70d

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Fabienne R Riccoboni
Severe CA/Purple Fringing Canon 70d
on Jul 7, 2015 at 2:42:54 am

Hi! I'm new to photography and need some help. I recently purchased a Canon 70d and I was pleased with its overall performance except for a few things that have definitely frustrated me.

1) I've been noticing that out of a large batch of cr2 files I always have a few corrupted ones once i've copied them over onto my computer. But the strange thing is is that after about a day the corrupt file suddenly is completely fine and "magically" uncorrupted. All photos were on a SANDISK 32 GB sd and the computer I use is an iMac. Also, I just purchased this camera about 2 months ago. Is it the camera, the sd card, or the computer thats causing the trouble? Is there any way to figure out which is?

2) I recently took some shots at a concert and noticed that a bunch of the pictures had severe purple fringing. Originally I thought it was just the purple light on the stage that made the fringing effect, but when I zoomed in on the picture it didn't seem to be the case. Some examples are in the link below: https://www.dropbox.com/sh/r5d5s8v8rzbtfe7/AACq0btZFNyUIBTUNLYYwEG6a?dl=0

Can someone please help me understand whats going on? Should I return the 70d?

Thank you.


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Blaise Douros
Re: Severe CA/Purple Fringing Canon 70d
on Jul 7, 2015 at 4:13:38 pm

I can't help you with the corrupted files, but I can tell you that there's nothing wrong with your camera that's causing the purple fringing. I pulled down one of your images and looked at the EXIF info--the one I looked at had you at 1/125, f5.6, ISO 4000, with the EF-S 55-250.

So your number one problem is that you were shooting in low light. I can follow your thought process--fast shutter speed of 1/125 in order to freeze motion, ISO 4000 to support that exposure, f5.6 because that's as wide as your lens goes. And that's your problem--the EF-S 55-250 is just not anywhere near fast enough to use in a low-light situation. You would need a f2.8 lens at the very least, to get a few extra stops of light.

See, what's happening is that at ISO 4000, the sensor gets super noisy, and the dynamic range is lowered. If you zoom in on the images, you can see a ton of luma grain (the little black dots). The other effect of this is that super-saturated colors, like the colors coming from the purple light, start clipping and bleeding because the sensor is struggling to capture enough light.

At lower ISOs, the sensor won't have trouble with those super saturated colors, because it has more dynamic range--but as you squeeze it upwards, you'll get lower and lower image quality.

This is true for almost any camera except for the Sony A7S, because Sony sacrifices goats and kittens to Satan on a weekly basis to support the black magic that runs their newest sensors.

So: is your camera broken? No. But there are a couple things you need to do if you're planning to do a lot of low-light shooting, especially at high speeds:

1) Invest in better lenses. The faster the lens, the less you have to crank that ISO up. If you just can't afford it, consider renting them for these gigs where you know there's going to be a lot of low-light.

2) Invest in off-camera flashes--pushing more light into the scene means you can afford to use lower ISOs. Using flash is nerve-wracking if you don't know what you're doing. Go to Strobist.com, grab some popcorn, and read like the wind. David Hobby explains how to use off-camera flashes better than just about anyone. There are some really inexpensive speedlights out there by Yongnuo; they're not the greatest quality, but at 80 bucks, who cares? Buy five of them and rotate one in when another one fails.

3) If none of this sounds appealing, and you NEED to shoot a lot of low-light, then consider returning the Canon and looking at the Sony A7S. I hate to tell you to get out of a system you've invested in, but you do need the right tools for the right job. I've been a loyal Canon user for a long time, but right now Sony is that sexy little redhead waving at me from her convertible, and texting me that I should really come over and check out what she's wearing...


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Fabienne R Riccoboni
Re: Severe CA/Purple Fringing Canon 70d
on Jul 19, 2015 at 2:47:28 am

Sorry for the extremely late response.

Thank you for your reply! I've been looking into better quality lenses as you advised and am currently looking at purchasing the Tamron 15-30 VC. I like shooting at wide angles so I think this lens would suit me the best. Do you have some other lenses you could recommend?

Strobist.com was very helpful and informative. I definitely will consider buying a few off-camera flashes. Thank you!

As a student, I unfortunately have a very tight budget but I will definitely consider the A7S sometime in the future. I was very impressed with the iq which looks much better than that of the GH4. And the flat image style is absolutely amazing.

Thanks again!!


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Warren Eig
Re: Severe CA/Purple Fringing Canon 70d
on Jul 19, 2015 at 5:06:57 pm

How are you copying the files to the Mac. There have been some issue with cheap card readers causing corruption -- I've experienced it. Also, years ago when I bought a Canon 5D there was a firmware incompatibility with my Lexar cards (I know you have Sandisk), but a quick call to them and they swapped my cards with ones with newer firmware and I never had corrupt files again.

Obviously there are a million different reasons why these things happen. This is just my experience.

Warren Eig
O 310-470-0905


email: warren@babyboompictures.com
website: http://www.BabyBoomPictures.com


REEL: http://www.babyboompictures.com/BabyBoomPictures/Reels.html


For Camera Accessories - Monitors and Batteries
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Fabienne R Riccoboni
Re: Severe CA/Purple Fringing Canon 70d
on Jul 20, 2015 at 7:44:01 pm

Thank you for your response!

I'm just pulling them over straight from the card itself. Now that I think about it though I have noticed some glitches in different videos I've taken on these exact cards. I thought the corruption happened after I pulled them off, but now I'm not so sure...

Are there any better cards I can buy?


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