Distortion question

[seabass]

I'm playing around with my Canon S120. These pictures were all taken in aperture priority mode, 100mm equiv. zoom, ISO 100, f/8, exposure -1/3 stop.


Scaled down, cropped image.


100% size, cropped image.

You can see the distortion on the tips of the anemone (which is less noticeable when scaled down). BTW, what is this distortion called? Is this from the processor creating the JPEG? I haven't played around with shooting in RAW format yet; would this be a non-issue when shooting in RAW?


With Clownfish just for fun.

[farkwar]

Fringing like that is normally called chromatic aberration.

 

Its usually green or purple though.

 

It being the same or similar color, my best guess would be poor quality lens or lens out of alignment on a quality lens.

 

It doesnt look like jpg induced. Its probably more visible on your raw.

[doppelganger]

It is indeed chromatic aberration. I happens when the lens isn't able to focus certain colors to the same spot.

 

It would still be an issue shooting raw but the raw file will allow for more post processing options in which you could more easily remove/reduce it.

[seabass]

Thank you both. So I'm assuming that it's just a shortcoming of my compact point and shoot, as opposed to it being defective.

 

I get this with my purple tipped green BTA as well, but not so much with other colors. I'll play around with it some, to see if I can reduce it any. I guess I'll try post processing fixes, using the manual focus, as well as a shorter zoom. For me, it's a little disappointing but still not that big of an issue, as I scale down most of the images for the web.

[daletu]

Your best bet to reduce CA is to stop down the aperture which means increase the f-stop number. Also, sometimes use zoom in middle range will reduce it a little, because most lenses design it's best performance in the middle zoom. Your best option will be shooting in RAW and then fix it in Photoshop or Lightroom, they can be easily fixed in both programs.

[doppelganger]

CA can also be an issue in some of the most expensive slr lenses. Some lenses control it better than others but it's just a fact of life most the time when it comes to contrasty areas in photography. There's 2 different types of CA as well so it can get more complicated but yeah a point and shoot lens isn't particularly ideal for getting super sharp, distortion free images. Still a nice shot none the less!

[seabass]

I've done a few searches on chromatic aberration, and have been playing around with my camera a little more. I can even see the color fringing on the LCD panel before I take the shot (and it's present throughout the zoom range of the lens).

 

After seeing a visual description of CA, I started thinking that it might just be from the front glass of my 40 breeder that I'm shooting through (which isn't exactly low iron, or high clarity). So I took some test shots of items out of the water to see if I can notice any color fringing; and the shots looked good to me.

 

So do you suppose that the color fringing is just from the glass? Does that even make sense? Also, I have to say that I'm not taking the shots with the lens perfectly parallel to the glass.

 

Any thoughts on this?

[seabass]

So after a little more research, I'm thinking that (at least part of) the problem might be shooting through the glass at an angle. Being able to see the CA on the LCD panel will allow me to judge the color fringing at different angles (without actually taking any pictures). The camera can magnify the focus point, on the screen, by up to 4× during manual focus (making it fairly easy to see). I'll post an update when I have some more time to play with it.

[seabass]

So just experimenting with the CA, without trying to get a good picture (dirty glass, no tripod, autofocus, white balance not set right, etc), it looks like the fringing was mostly due to taking the pictures at an angle. This tank is on the floor, so in order to take a picture with a tripod it had to be angled down. Plus that seemed like a natural viewing angle, and my camera's LCD panel doesn't tilt, so parallel wasn't exactly a natural shooting angle.

Cropped image, not scaled down.

[daletu]

So just experimenting with the CA, without trying to get a good picture (dirty glass, no tripod, autofocus, white balance not set right, etc), it looks like the fringing was mostly due to taking the pictures at an angle. This tank is on the floor, so in order to take a picture with a tripod it had to be angled down. Plus that seemed like a natural viewing angle, and my camera's LCD panel doesn't tilt, so parallel wasn't exactly a natural shooting angle.

Cropped image, not scaled down.

 

I think this looks fine to me. So this picture is taken with an angle and not parallel to the tank glass? If it is, then note on the camera settings... zoom and aperture. This might be the sweet spot of your camera because I don't see much CA at all.

[daletu]

Ah I see, so this image is not in an angle, I see what you mean now. Yes. Taking image at an angle will create fringing or distortion.

[seabass]

Yeah, the first set was taken at an angle. The one above was pretty close to parallel.

 

I took another with a more proper white balance, set on a box, with shutter delay, and manual focus.

 

 

Thanks everyone. I'm glad that got worked out.

[daletu]

This one has a little bit CA, you should take note of the previous photo's camera settings. I think that's your lens/camera's sweet spot.

[seabass]

You're right, I didn't even notice it at first. I might play around with it some more later on, but it's not nearly as bad as the first set that I took; so I'm feeling better about the whole thing. I appreciate everyone's input. It looks like I'll be able to get some decent pics out of this camera after all.

[4x5]

Those little S series Canons are really cool and are capable of taking great shots. CA is something that happens (even with $2000 lenses) and especially when it comes to underwater imagery. Shoot in RAW (it is so much better than jpeg can dream of being) and if you have lightroom you'll be able to remove it pretty easily.

 

If you struggle to see the CA when the image is zoomed out to full screen size then I'd not stress over it, you're not going to print it or look at it at that size very often.

 

BTW; try stick the lens up against the glass. It makes a big difference especially with handling reflections.

[Veng]

I'm a little late to the thread, but shooting perpendicular to the glass (and I mean exactly 90 degrees, not 80m 85m or 89 degrees) makes a huge difference. The problems will get exponentially worse as you come off 90 degrees, just try taking a shot through the glass at about 45 or even 30 degrees and you'll understand. It's one of the nightmares of trying to take pictures of fish tanks is the restrictions on what angle you can shoot at.

[seabass]

Cool. It's just funny that, after shooting tank pics for over a decade, I've never noticed it before. Although I understand why. My pictures (from my cheap cameras) were never clear enough to consider using them not scaled down. Now I have a camera that's good enough to notice what's actually happening.

 

I've seen where people have recommended shooting straight at the glass, but I guess that I thought it would just distort the shape slightly (like how your eye sees it). I even owned a bow front aquarium and never directly noticed it before (or at least never put two and two together). Bow front tanks distort how your eye sees it, but never thought about how a complex lens would see it.

 

It might be interesting to go back and look at some of my old originals, to see what they look like. For the sake of this thread, I'll see if I can find one to post that shows the CA in the photo.