Article: The Automatic Lens Correction Conundrum

Foreword: This is a in-depth article on how unavoidable automatic lens corrections applied in Adobe Lightroom, Adobe Photoshop, Adobe Camera Raw and Adobe RAW Converter can negatively affect your astrophotography with certain micro four thirds cameras and lenses. I have experienced this using an Olympus OM-D EM-5 Mark ii with Olympus Zuiko M. 12-40 f/2.8 PRO lens and using an Olympus OM-D EM-10 Mark ii with the old Olympus Zuiko M. 14-42 f/3.5-5.6 r ii lens.

The article you are about to read is long (2000+ words) but it should read quite easily. At the end, I give you some solutions to either deal with the problem or remove it completely from your astro photography.

Have an happy reading.

Introduction

All lenses are prone to introduce some sort of geometrical distortion in your image, regardless how optically good they are. In particular, among all lenses, wide angles and ultra wide angles are, together with fisheye, the ones that introduce the greater distortions. 

Among full frame, APS-C, micro four thirds and compact cameras, micro four thirds and compact camera lenses are those that probably benefit most from software correction of the geometrical distortion and, in fact, the raw files those cameras produce embed information (metadata) that most commercial editing software use to automatically apply the proper corrections for lens distortion and lateral chromatic aberration.  

Adobe certainly is the world leader company when it comes to photo editing software, thanks to Photoshop and Lightroom. Adobe Camera Raw, ACR, the Adobe RAW file developer module, reads those metadata and automatically applies the proper lens correction.
You can verify this by opening a raw file in Adobe Photoshop: ACR will be launched and at the bottom of the Lens Corrections tab you will see a message like “Built-in profile applied…” . By clicking on the info balloon icon next to it, a pop up will let you know which kind of corrections have been applied: distortions and chromatic aberration or chromatic aberration only.

Photo 1: The image shows how to obtain info on the lens correction applied in Adobe Camera Raw.

Photo 1: The image shows how to obtain info on the lens correction applied in Adobe Camera Raw.

The only exception is if you took the photo with a manual lens: in this case no correction is applied because camera body and lens do not communicate. For the camera body, in fact, it is like you are shooting without a lens and no lens correction information are then embedded in the RAW file.

Why should you care about this? I admit it: 99% of the times this automatic lens correction is as good as gold, as it improves the quality of the image and spares you from install and apply the proper lens profile or to do the correction manually by yourself.

The tricky part of this automatic lens correction procedure is that in many commercial software, and for sure with Adobe Photoshop and Ligthroom, there is no way to turn it off. And this bad, in particular if:

1)    You shoot in RAW because YOU want to decide how to develop the image without a middle man taking over some aspects of this developing process;
2)    You own a fisheye and you want to have full control over the lens distortions because, well, distortions are the nice and funny reasons why you probably own a fisheye lens;
3)    You do astrophotography.

While point 1 is rather extreme, the other points are much more commons, in particular when it comes to do some star trails, as micro four thirds gears are fully capable to do quality night photography. Plus, star trails photography is the kind of astrophotography that requires the least fancy equipment of all: a tripod and a reasonable wide and fast lens (f/4 or wider) and you are good to go. Virtually everybody could do it.

The problem with automatic lens correction and astrophotography

They say an image is worth a hundred words: the photo below shows what the lens correction does to your star trail photo.

Photo2: Star trails obtained stacking and blending 100 frames (edited with Adobe Lightroom CC) in Adobe Phoshop CC.

Photo2: Star trails obtained stacking and blending 100 frames (edited with Adobe Lightroom CC) in Adobe Phoshop CC.

For this image, I stacked and blended with the lighten mode 100 photos taken with my Olympus OM-D EM-5 Mark ii and Olympus Zuiko M. 12-40 f/2.8 PRO lens. The original RAW files were previously developed in Adobe Lightroom CC 2015 and then exported as layers directly in Adobe Photoshop CC 2015.

What you can see on the image is a sort of symmetric checked pattern all over the image, particularly in the sky. 

In photo3 you see the same pattern from stacking and blending (lighten mode) only 10 frames and it is not fainter than in the previous image.

Photo3: A star trails from using only the first 10 frames from the 100 ones used previously in Photo2.

Photo3: A star trails from using only the first 10 frames from the 100 ones used previously in Photo2.

Is this coming from my particular way to blend the frames together? Not really: the image below is the star trail created with the software StarStax, starting from 10 frames, previously exported as tiff from Adobe Lightroom CC 2015.

Photo4: Star trails from StarStax software.

Photo4: Star trails from StarStax software.

Is this a problem of my lens? Not really. Below you can see a photo obtained by stacking and blending (lighten mode) 10 photos of a white wall taken with an Olympus OM-D EM-10 Mark ii with the Olympus Zuiko M. 14-42 f/3.5-5.6 R ii kit lens. The camera was on a tripod and all photos were edited to boost contrast and clarity before stacking them. While it is faint, the unwanted checked pattern is definitely visible in the final image.

Photo5: Stack of 10 frames blended in Lighten mode in Adobe Photoshop CC: the pattern is evident.

Photo5: Stack of 10 frames blended in Lighten mode in Adobe Photoshop CC: the pattern is evident.

Note that for both camera/lens combinations mentioned so far, the automatic (and unavoidable) lens correction is for both distortion and chromatic aberration.
Obviously, such pattern is not visible on the single frames, as you can see from the photo below.

Photo6: Single frames show no pattern.

Photo6: Single frames show no pattern.

Should we really blame automatic lens correction for this?

I have several clues pointing to automatic lens correction as the responsible for the appearance of this pattern, or, at least, to blame the way the lens correction and the lighten blending mode work together. In fact, lighten and difference blending modes are, as far as I could see, the only modes producing a pattern on the flatten image. 

So, here are my clues:
1) In the photo below, you can see a star trails I have done with an Olympus OM-D EM-10 camera mounting a Samyang 7.5 f/3.5 MFT fisheye lens. The photo does not show any pattern and the lens is fully manual, so no information for lens correction is embedded in the RAW files. 

Photo7: A star trails I did some time ago with an Olympus OM-D EM-10 and a fully manual Samyang fisheye lens: no pattern is visible in the image. 

Photo7: A star trails I did some time ago with an Olympus OM-D EM-10 and a fully manual Samyang fisheye lens: no pattern is visible in the image. 

2) The photo below is a star trails done combining in Affinity Photo then photos taken with my Olympus Zuiko M. 12-40 f/2.8 PRO lens: the RAW filed do embed lens correction parameters, but this program ignore those metadata and the final image shows no pattern.

Photo8: A star trails done with Affinity Photo software (Mac OS X only): no pattern is visible in the image.

Photo8: A star trails done with Affinity Photo software (Mac OS X only): no pattern is visible in the image.

In the same way, the star trail below, which was obtained by combining ten tiff files created by developing the RAW files in Rawtherapee, does not show any pattern. Rawtherapee, as Affinity Photo, ignores metadata for the lens correction and no pattern is present in the final image.

Photo 9: A star trails done with Rawtherapee software ): no pattern is visible in the image.

Photo 9: A star trails done with Rawtherapee software ): no pattern is visible in the image.

3)  I found a discussion in here where a guy solved the problem by avoid editing, and lens correcting, the RAW files before stack them to produce the star trails. He was not using a m43 camera, hence he could, and did, switch the lens correction off.

I think it is safe to conclude that the problem is, indeed, due to the automatic lens correction for distortions (correction for the only chromatic aberration is fine) automatically applied when importing the RAW files into Adobe Lightroom or Adobe Camera Raw (and probably other commercial software as well).

Multi frame noise reduction: no more the magical wonder it used to be

This is a technique consisting in combining and average a number of photos taken without moving the camera between exposures and using high ISO speeds. This allows to greatly reduce from the final image the random noise due the high ISO settings while boosting the details.

This technique is widely used in astrophotography and I use it in 90% of my night photography and, with my Olympus OM-D EM-5 Mark ii + Olympus Zuiko M. 12-40 f/2.8 PRO lens, A pattern similar to that seen for the star trails appears on the final image. Bummer!

Two ways to live with problem minimizing its negative effects on your photos

You have two options to make the unwanted pattern the most unnoticeable as possible:

Edit only the final image

In the photo below I have created my star trails by combining 240 unedited raw file and then carefully develop the resulting tiff. I was able to reduce the visibility of the pattern, but if you look carefully, it is still there. Besides, tiff editing is much less flexible than RAW developing, particularly when it comes to recover highlights and shadows and reduce noise. Therefore it is not an ideal solution.

Use the despeckle filter

I am not sure what the origin of the pattern is, but I thought that, maybe, changing even so slightly the images before stacking them could get rid of it. I tried to apply a Gaussian blur to the images in Photoshop and to use the moire and noise brush in Lightroom but that didn’t work. 
What it worked quite well was to apply the Photoshop Despeckle filter on each layer in the stack and only then blend those layers in Lighten mode and flatten the image. The pattern is not gone for good and if you have many frames to combine, it may better to divide the job in groups: do a star trail every 50 or so images, each one threated with the Despeckle filter and then combine the partial star trails into the final one, applying once again the desplecke filter on each partial star trails.

Below is the final image from 240 frames using this method: the unwanted pattern is practically unnoticeable and it will probably not show up in any print.

Photo10: My final image using my despeckled method shows no pattern in the final image from stacking and blending 240 edited frames.

Photo10: My final image using my despeckled method shows no pattern in the final image from stacking and blending 240 edited frames.

The problem with this method is that it is a tedious, time consuming, job to do, and you probably will need a fairly powerful computer if you are planning on doing many star trails. To help you out, I have put together this script for Photoshop to apply the despeckle filter on each layer in the active document. Copy it and save it as .jsx file.

var doc = activeDocument;
for(var a =0;a<doc.layers.length;a++){
doc.activeLayer = doc.layers[a];
doc.activeLayer.applyDespeckle();
}  
To execute it, go to File->Script->Browse and select your script.

Two ways to avoid the problem entirely + bonus

As far as I know, there are only two ways (and one bonus for Olympus OM-D users) to avoid dealing with the problem:

1)    Shoot with manual lenses, for which no lens correction parameters are embedded in the RAW file;

2)    Use a different RAW converter/editor such as Rawtherapee (multiplatform and free), Affinity Photo (Mac OS only and commercial) and so on.

In particular, i found that for me Rawtherapee is THE solution, as this software is, at the time of this article, freeware and multi-platform and has the ability to batch convert RAW files into TIFF 16-bits, which can then be imported in Adobe Lightroom and Photoshop and edited as usual. Apparently, while are not exactly the same things, RAW and TIFF files both allows to recover highlights and boost shadows and so on.

3)    If you have any Olympus OM-D camera (except for the EM-5), you are better off using the Live Composite mode. Here are a couple of interesting links: 1, 2 I'd like to thank the Edwin van Keulen for the tip.

Conclusions

I successfully do astrophotography with my compact camera Sony RX100 Mk ii and never had this kind of problem despite an automatic lens correction is applied to the RAW files, I suspect the pattern appears only with certain cameras and certain lenses.

However it is, Is this really a true problem for mirrorless and micro four thirds users?

I think it is, in particular when camera manufacturers are working to create a PRO line of bodies and lenses targeting enthusiast and professional photographers.
Some Pros have already moved away from DSLR and embraced the mirrorless world, in particular for landscaping, as mirrorless cameras and lenses are, undoubtedly, less bulky and heavy than their DSLR counterparts. 

Furthermore, to want to record a decent star trails is not really stretching the limits of your m43 gears: those cameras and lenses are perfectly capable of doing this and much more, but they are getting crippled by this unavoidable automatic lens correction Adobe (and others) uses in their software and it is a real shame.

What is really needed here is that Adobe (and the others) modifies their camera raw software to apply the correction by default while providing the photographer with a way to disable it, if needed. 

Unfortunately, users are complaining about automatic lens correction on websites and forums (even the Adobe forum) since 2013 but nothing has changed so far: maybe it is time that camera manufacturers with the ambition to target pro photographers, like Olympus and Panasonic, will acknowledge the problem and use their leverage to make the world leader company in photo editing software give back to the photographer the power to apply or not apply lens correction.