Help correcting blue chromatic aberration

Hi All,

I took a set of photos using a borrowed Vivitar Auto Telephoto 200mm the other day. I am pleased with some of them but they are showing a blue aberration along some lines. Not sure if it is my fault or the lens's. This is an example:

[IMG]http://i40.tinypic.com/20aufle.jpg[/IMG]
Larger version here: http://i40.tinypic.com/20aufle.jpg

I was shooting in RAW+. Does anyone know if the Pentax Digital Camera Utility can correct this? Or can it be done after the jpg conversion?

Any help would be amazing.

Lightroom is good at removing such stuff

Hi Smeggy. Thanks for the advice. I don't have lightroom sadly.

I was hoping to do this without having to buy any additional software. Do you think it is possible? Maybe if the Pentax DCU wont do it then I could convert to jpg and try to use GIMP?

Or maybe I just need to stump up the £100 for lightroom. Is it worth it do you think? I don't have photoshop either. Do I need that to take advantage of lightroom?

Telephoto lenses are prone to chromatic aberrations and this is what you are seeing. Using a more suitable lens will help and, if you wish, there are tools for correction in most RAW converters. I haven't used the Pentax one very much, rather using Adobe ACR, but I think there is something in there to do the job.

You would probably be better using the £100 to invest in a more modern, digital friendly lens.

At or around that price point, avoid the Tamron 70-300, since that would be very much a case of out of the frying pan into the fire.

The Pentax 50-200mm would be a good option, perhaps buying one of the many second hand ones available from SRS and others.

Hi Guys,

Thanks for all the advice. I actually am planning to take more photos of this type soon (portraits of singers taken from balcony at the back of a poorly lit church) so a new lens might be the best solution.

John - do you think the 50-200 would outperform the vivitar 200 prime at the long end? Just because I think for this purpose I would be using it only at the 200 end and wide open aperture (as much as possible).

I haven't compared the two side by side, but the Pentax lens does perform well and is specifically designed for digital use. At the second hand prices being asked, it's definitely worth having.

The Pentax 55-300mm is better, but then it is also rather more expensive.

Eddy, have a look at the PPG link, you can do specific searches for images taken with various Pentax gear and you can also get the EXIF on each image so you can see what the camera settings were and what focal length was used in the case of zooms.
That will give you an idea of what a particular lens can do.

eddyc if you want to rescue these images there is a very basic and simple solution to CA's, that doesn't require pro software, simply adjust the hue/saturation and remove/reduce blues.

This was done in Elements in seconds, I don't use Gimp but I'm sure it will have colour adjust.




You may have an image where there are blues elsewhere in the image you want to keep, in such cases use the select tool to highlight the specific area you with to reduces the blues in.

Hope this helps.

Secondly I would start doing some tests with your set up to see when the CA's are coming out so you can avoid them. e.g My DA 100mm Macro gives CA's around F2.8, but it disappears stopping down to F5.6 +.

Wow dodge. That looks amazing! I think I'll give it a solid go in GIMP. I don't think I can afford to buy elements and a new lens (I'd rather not try to afford either!).

Cheers for the link to the PPG fatspider. I'll have a look through that before I buy anything new. Good resource.

Thanks a lot for all the help. I'll post back if I manage to work out how to do it in GIMP!

You could also check out "darktable" which I believe is the shareware/freeware version of lightroom. I have no experience of it myself.

K.

Lightroom at it's new price is incredible value for money. It's not just a photo processing package it's major value comes from the cataloguing and management of your photo collection.

You can keyword your photos and create smart collections which are automatically updated as you keyword new photos. these collections can then be used for slideshows

I also make use of the star rating facility, again you can crate smart collections based upon ratings.

Lightroom has graduated filters and an adjustment brush,which is the modern equivalent and dodging and burning in a darkroom. but allows lot of parameters to be locally applied to an image.

Lightroom 4 now adds geotagging by showing google maps within. Very simply just drag your images or multiselected images from the filmstrip at the bottom to the location on the map.


No you don't need photoshop unless you plan on making women look strange and fake fro magazine covers . Photoshop is a graphics editing tool and used for far more than photographs too.

Lightroom is designed for photographers.

It would be silly to spend the £100 on a single lens in comparison. You can remove the CA from an infinite number of lenses in lightroom.

I've only just touched the surface on the power of lightroom. Amazing program. And now at a great price

Ok I downloaded the lightroom trial and started having a play. I am really happy with the results so far:

[IMG]http://i42.tinypic.com/978ktj.jpg[/IMG]

This was done by turning the blue saturation down to -100 and turning the exposure, contrast and highlights down a little. I then put the shadows, whites, clarity and vibrance up. Not really sure what those all mean but it seems to have done the trick. Thanks for all the help!

I also downloaded a free piece of software called RawTherapee which is supposed to be pretty good but not as full featured. I think I will probably end up buying lightroom but I would be interested in testing out how well the free one can stand up to Adobe. I'm all for supporting open source. I think it is similar to darktable but can be installed on windows. I would have to dual boot ubuntu or something for darktable. Does look good though.