Home

Please support mflenses.com if you need any graphic related work order it from us, click on above banner to order!
SearchSearch MemberlistMemberlist RegisterRegister ProfileProfile Log in to check your private messagesLog in to check your private messages Log inLog in

chromatic abberation in water?
Post new topic   Reply to topic
Home   Manual Focus Lenses
View previous topic :: View next topic  


PostPosted: Tue Dec 06, 2011 3:57 am    Post subject: chromatic abberation in water? Reply with quote
I didn't know you got CA in water!


100% crop -


In this case I don't think the CA harms the shot too badly. It's a family snapshot anyway Razz they're quite forgiving of mediocre pictures.

Shot with my Super Takumar 135/3.5, wide open. I've got a couple of 135/2.8 lenses but the Tak is much sharper, great value for the money.

1/30s is tricky handheld, I laid the camera on my lap and used liveview to compose/focus.


PostPosted: Tue Dec 06, 2011 4:31 am    Post subject: Reply with quote
This is longitudinal chromatic aberration (some people dispute this term and call it bokeh fringing). It's purple in front of the focal plane and green behind. Here, the purple on the eyelashes indicates you backfocused this shot. It's actually helpful to check focus precision Smile


PostPosted: Tue Dec 06, 2011 6:21 am    Post subject: Reply with quote
CA in water is very common. Yours is not so bad. I've been able to clean up rather severe water CA using the CA removal routine in Paint Shop Pro. In this one respect, PSP is vastly superior to Photo Shop.


PostPosted: Tue Dec 06, 2011 8:24 am    Post subject: Reply with quote
The CA has nothing to do with the water, but everything with the strong (overexposed) highlights. Strong highlights like the sun reflected of water or any shiny surface can make CA very apparent.

I don't agree with Laurentiu that the sample photo was backfocused. It looks to me like the focus is spot on, although it's a bit hard to judge because the lack of detail. I believe that purple fringing is a category of CA of its own, so you can't say that the image was backfocused just because you see purple CA.

By the way, there is purple/magenta fringing on the inside of the highlights in the background. I think this has to do with spherochromatism (if I'm not mistaken).


PostPosted: Tue Dec 06, 2011 9:01 am    Post subject: Reply with quote
AhamB wrote:
The CA has nothing to do with the water, but everything with the strong (overexposed) highlights. Strong highlights like the sun reflected of water or any shiny surface can make CA very apparent.
I don't agree with Laurentiu that the sample photo was backfocused. It looks to me like the focus is spot on, although it's a bit hard to judge because the lack of detail. I believe that purple fringing is a category of CA of its own, so you can't say that the image was backfocused just because you see purple CA.
By the way, there is purple/magenta fringing on the inside of the highlights in the background. I think this has to do with spherochromatism (if I'm not mistaken).


+1
Spherochromatism is related to spherical aberration when this happens in different ways at different wavelenghts.
It is quite common in superfast lenses. In this case the lens is not superfast and not even fast, so it's obviously a problem of generic optical qualtiy. In all fairness, the Super-Takumar 3.5/135 does not have a great reputation. I used to have the SMC version which is significantly better.
I would suggest you to try a Jupiter-37AM. You can find one very cheap and they are visibly superior to the Super Takumar.


PostPosted: Tue Dec 06, 2011 2:58 pm    Post subject: Reply with quote
cooltouch wrote:
CA in water is very common. Yours is not so bad. I've been able to clean up rather severe water CA using the CA removal routine in Paint Shop Pro. In this one respect, PSP is vastly superior to Photo Shop.


Michael: Can you say more about that? In my experience PS is very effective, so wondering what PSP does differently.


PostPosted: Tue Dec 06, 2011 5:13 pm    Post subject: Reply with quote
AhamB wrote:

I don't agree with Laurentiu that the sample photo was backfocused. It looks to me like the focus is spot on, although it's a bit hard to judge because the lack of detail. I believe that purple fringing is a category of CA of its own, so you can't say that the image was backfocused just because you see purple CA.


That is not purple fringing though. You can easily confuse purple fringing with the purple part of LoCA and I did it too sometimes, but the fact that the water fringing is green shows that here this is LoCA. With PF, the water fringing would be purple too. In fact, the easiest way to generate PF is to shoot reflections on water - that's how photozone usually demonstrates the effect.

I shoot a lot of portraits with thin aperture and I can tell you that the focus here is not spot on on the nearest eye, but is probably on the other eye, either on it or on its corner. Not a big miss but a noticeable one at 100% crop.

LoCA goes away when stopping down the aperture, so if fuzzywuzzy would take a series of shots with his lens at different f-stops, you would see this.

LoCA can be very annoying when shooting head only portraits because if the focus is not spot on, the reflections in eyes will be either purple or green - purple is usually more noticeable. On the other hand, it's a clear indicator of how spot on the focus is and it can even help you with focusing if you watch for it in the viewfinder.


PostPosted: Tue Dec 06, 2011 5:17 pm    Post subject: Reply with quote
One more thing - this effect is present in all Pentax lenses - from Takumars to FA. I see it better controlled in DA designs, but those I used are not very fast either, so it may just be a side effect of that. Russian lenses don't have this, I agree. But most super-fast lenses will have it to a larger or lesser extent. The Tak 50/1.4, FA 50/1.4, FA 100-300/4.7-5.8 all have it for example. The Nokton 58/1.4 has it to much less extent than the FA 50/1.4. Cosina 55/1.2 has it too.


PostPosted: Tue Dec 06, 2011 8:51 pm    Post subject: Reply with quote
woodrim wrote:
cooltouch wrote:
CA in water is very common. Yours is not so bad. I've been able to clean up rather severe water CA using the CA removal routine in Paint Shop Pro. In this one respect, PSP is vastly superior to Photo Shop.


Michael: Can you say more about that? In my experience PS is very effective, so wondering what PSP does differently.


I can't recall specifically the routine that PS uses, but I do recall using it with disappointing results. Perhaps I just wasn't using its settings to the best of their ability. PSP allows you to center in on the exact color you want to correct for and draw a "box" around it. You can have up to 10 separate boxes per image. I should note that drawing the box around a bit of CA tells the program what colors to correct, not that one specific spot to correct. So if I draw a box around a rather pronounced bit of purple fringing, for example, all the purple fringing of that hue will be removed from the image.


PostPosted: Tue Dec 06, 2011 11:39 pm    Post subject: Reply with quote
Just adding a link to an older thread on the topic of CA - I just updated it to include a correction:

http://forum.mflenses.com/chromatic-aberrations-terminology-t34838.html

Here's water fringing from the Pentax FA 100-300/4.7-5.8:



Notice the green behind the focal plane and the purple in front.


PostPosted: Wed Dec 07, 2011 2:07 am    Post subject: Reply with quote
Here are some examples of what I can do with PSP v9.01. Not water, but rather pronounced purple fringing. I have had similar good luck removing green and magenta fringing also.

I took this photo at the San Antonio Airshow, 2009. F22 Raptor. Shot it with my Canon XS (1000D) and an EF 75-300 II zoom lens. The EF 75-300 does not have a very good reputation but I found its sharpness to be quite good. However, it did display quite a bit of CA, especially when shooting in poor lighting conditions. Unfortunately because of the way the show was set up, I was having to shoot into the sun with almost every shot, so the lighting conditions were exceptionally poor for most of the show. This particular photo was better than most. Even so, contrast was soft and even focus was off a bit mostly because of the airspeed of the F22. But as you can see, the photo also has LOTS of purple CA.



Here is a 100% crop of some of the wing surfaces of the F22, showing the extent of the CA.



And here's the same crop after passing it through PSP v9.01's chromatic aberration removal tool.



Not so bad, eh? I paid about $10 for an original copy of v9.0 from an eBay seller and then went to the PSP Users Group forums where I was able track down both the 9.01 and 9.01.1 (required for the English version of PSP9) patches. I've just looked around at Corel's site for these patches and they don't appear to be available anymore. But I have copies, so if you need them, I can email them to you.


PostPosted: Fri Dec 09, 2011 11:09 am    Post subject: Reply with quote
Laurentiu Cristofor wrote:
I can tell you that the focus here is not spot on on the nearest eye, but is probably on the other eye, either on it or on its corner. Not a big miss but a noticeable one at 100% crop.

I don't see that... Look at the cap that the boy is wearing: at the depth where the other eye would be, the cap is less sharp. If you look at the left corner of the boy's mouth, that looks sharp too. Also: look at the locks of hair on the boy's forehead: they get less sharp in the direction of the other eye (where you claim the best focus is).


PostPosted: Fri Dec 09, 2011 7:58 pm    Post subject: Reply with quote
AhamB wrote:
Laurentiu Cristofor wrote:
I can tell you that the focus here is not spot on on the nearest eye, but is probably on the other eye, either on it or on its corner. Not a big miss but a noticeable one at 100% crop.

I don't see that... Look at the cap that the boy is wearing: at the depth where the other eye would be, the cap is less sharp. If you look at the left corner of the boy's mouth, that looks sharp too. Also: look at the locks of hair on the boy's forehead: they get less sharp in the direction of the other eye (where you claim the best focus is).


I might be wrong - it's hard to tell when the face is underexposed and the skin has little detail but noise - but to me the farther part of his goggles looks in focus, not the nearest one, and I find the farther eye to have more detail in the lashes than the closer one. I don't see much detail in the cap or the hair locks to begin with.

Anyway, if I'm wrong, then the purple fringing on the nose bridge would indeed have to be PF.


PostPosted: Sat Dec 10, 2011 4:06 pm    Post subject: Reply with quote
Laurentiu Cristofor wrote:
I might be wrong - it's hard to tell when the face is underexposed and the skin has little detail but noise - but to me the farther part of his goggles looks in focus, not the nearest one, and I find the farther eye to have more detail in the lashes than the closer one. I don't see much detail in the cap or the hair locks to begin with.

I think the farther eyelashes look sharper because they are not swamped by noise. I agree though -- it's hard to judge because of the underexposure.


PostPosted: Tue Dec 13, 2011 5:33 pm    Post subject: Reply with quote
Here's some CA actually due to water: http://www.atoptics.co.uk/fz706.htm Wink
Post new topic   Reply to topic
Home   Manual Focus Lenses
Page 1 of 1