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-   -   17mm lens corrections (https://e-group.uk.net/forum/showthread.php?t=46682)

MikeOxon 25th November 2017 11:22 AM

17mm lens corrections
 
One aspect of Olympus lens design that surprises me is their reliance on software corrections. I recently replaced my elderly 17mm f/2.8 with the f/1.8 version, mainly because the old lens was slow and hesitant to focus, and the extra light-gathering capacity is very useful indoors.

I use AfterShot Pro3 (ASP3) for raw image conversion and was surprised to see that the images from the f/1.8 looked a lot worse than those from the f/2.8.

Investigating further, I realised that, although ASP3 lists the 17mm f/1.8 amongst its compatible lenses, it does not actually have any lens correction data. The images it displays have considerable barrel distortion and colour fringing in the corners :eek:. (there are correction data for the f/2.8 and the displayed images look free of these faults)

I've explored further, with several other raw converters, and have concluded that the 'true' raw images, produced by both these lenses on the sensor are, indeed, rather poor, in terms of distortion.

The conversions applied by OV3 and other 'Olympus-aware' raw converters clearly amount to much more than de-mosaicing the image. (and the in-camera JPEGs are also 'corrected')

It surprises me that Olympus don't produce lenses with better corrections in the first place. Correcting optical defects by means of software must, inevitably, introduce errors from causes such as pixel interpolation, when the image is digitally manipulated. Perhaps this explains why I have seen mixed reviews of these lenses over the years.

MJ224 25th November 2017 11:09 PM

Re: 17mm lens corrections
 
Interesting post.............

My level of photography is way below that, I just look at the result in an art/composition/colours way.

Personally I don't mind the shot not being technically perfect, as long as the subject works.........

Perfection only came twice in my book, exwife and JC........

However, your points are interesting. Old Pentax days were far from perfect, but seemed to work well enough..............:confused:

Phill D 26th November 2017 07:16 AM

Re: 17mm lens corrections
 
I agree Mark it is an interesting post and like you it's way beyond my knowledge level. However, Mike how about posting some of the images to illustrate the point further. It would certainly be interesting to see the differences electronics are making visually.

pdk42 26th November 2017 10:30 AM

Re: 17mm lens corrections
 
Software correction, at least of distortion, is pretty common these days and is a practice followed by many companies. It leads to some slight loss of resolution in the corners but TBH I'm OK with it mostly (and I can be pretty picky!).

As per the m43 standard, lens distortion correction parameters are stored in the lens and passed to the EXIF of raw files. Many raw converters will automatically apply the corrections (and in fact you can't turn them off). ASP is one of the few that don't do this. LR certainly just applies them so you can't actually see the uncorrected results.

CA correction is similarly stored in the lens, but I don't think this is part of the standard and it is not applied to raw files by programs like LR. However, in-camera JPEGs will have CA correction applied. Cleaning up CA in post processing is very simple and effective though and so long as the fringing doesn't exceed a few pixels it won't be visible.

As to the 17/1.8 - it's a frustrating lens IMHO. The size, weight, focal length, max f-stop etc are all great but the IQ is not as good as it ought to be. The Sony 35mm f2.8 FE for Sony FF is no bigger and it's significantly better optically. I'm sure the new 17/1.2 will be stellar but it's much bigger and heavier. I really must try the Panasonic 15/1.7 since most people say it's better optically. But - it's 15mm and not 17mm.

Greytop 26th November 2017 10:39 AM

Re: 17mm lens corrections
 
Interesting post.
The more in depth reviews online do illude to the software correction, some lenses are effected more than others.
The RAW converter I use (Capture One) automatically corrects for any distortion with inbuilt lens profiles. The neat thing is you can disable it and see the distortion if you want to.
I suspect the issue may be (and I'm no expert) the relative compactness of these very small but still relatively fast lenses. I would suspect the new f/1.2 primes require much less attention in this area, looking at the older 4/3rds legacy lenses which didn't require correction we can see that they are also larger (with a longer flange distance too of course).

The bottom line is that even with varying degrees of distortion correction most of the MFT lenses are excellent performers. The 17 f/1.8 is possibly the exception needing a little stopping down sharpen up across the frame.

MikeOxon 26th November 2017 11:41 AM

Re: 17mm lens corrections
 
Many thanks to all who have replied and am glad you found this an interesting post.

As MJ244 said, a lot has changed since film days. Back then the picture was 'made' by the lens and the film, while the camera body's main jobs were to be light-tight and to hold the lens at the right distance from the film.

PDK42 has pointed out that corrections are part of the 4/3 system and it is clear that 'system' is a key word here. I've realised that micro4/3 actually represents a radical shift from the old way of doing things - every component in the system works together to produce the final image.

I guess that Nikon and other traditional cameras saw digital as simply replacing the film by a sensor and, otherwise, carried on much as before.

The flip side of the 'system concept' is that we have to stay within it for optimum results. I have already noticed that OV3 does a much better job on raw images than ASP - I just wish OV3 wasn't so S-L-O-W, such that it's virtually impossible to make adjustments because their effects take so long to appear.

As Phil D suggested, I'll put up some pics later to illustrate the points.

Mike

Otto 26th November 2017 01:04 PM

Re: 17mm lens corrections
 
DxO Photolab has full lens (and body) corrections built-in. There's an easy one-click way to see 'before' and 'after'. To be honest I can hardly tell the difference between my mFT 12-50 and FT 12-60 lenses, the corrections are that good.

Meanwhile I just developed a film exposed in my OM-1n, my first film for several years. Nice to see it still works perfectly, and no software correction is necessary!

MikeOxon 26th November 2017 01:48 PM

Re: 17mm lens corrections
 
Thanks, Otto, it looks as though the 17mm is a rather extreme example.

Some of the cheaper Olympus lenses are amazing. I have the MFT 12-50mm and find it an amazingly versatile travel lens that is weather resistant as well - it's survived trips to Borneo and New Zealand, with plenty of rain in both places.

I also have the 40-150mm (the cheap one) and it provides amazing optical quality for the price. The plastic mount is a bit off-putting and I did have to have the contacts replaced (under warranty) but, otherwise, it's an excellent lens.

Otto 26th November 2017 01:56 PM

Re: 17mm lens corrections
 
I have both those lenses and yes, they are remarkable performers.

If you want to send me a raw file from your 17/1.8 I can run it through DxO and send it back, so you can see the results and compare with your own software. I can PM you an e-mail address or you could use Dropbox or similar.

MikeOxon 26th November 2017 03:57 PM

Re: 17mm lens corrections
 
2 Attachment(s)
This is my first attempt at posting images so, here goes...

I've taken screen shots of the same images, taken with the 17mm f/1.8 lens on my E-M1 Mk ii, as diplayed by two different raw converters.

After Shot Pro does not have built in conversion data for the 17mm f/1.8 and the image can be seen to have pronounced barrel distortion.

Olympus Viewer 3 has the lens data built and largely corrects the barrel distortion.

ASP-OV3Compare-1.jpg

It's not just the distortion that is different. When I view files at 1:1 size on the two programs, there is far less image noise and better sharpness in the case of OV3, when compared with ASP - both at their default settings.

ASP-OV3Compare-2.jpg

Otto 26th November 2017 04:23 PM

Re: 17mm lens corrections
 
On that evidence OV3 does a much better job!

pdk42 26th November 2017 04:34 PM

Re: 17mm lens corrections
 
Quote:

Originally Posted by MikeOxon (Post 433871)
This is my first attempt at posting images so, here goes...

I've taken screen shots of the same images, taken with the 17mm f/1.8 lens on my E-M1 Mk ii, as diplayed by two different raw converters.

After Shot Pro does not have built in conversion data for the 17mm f/1.8 and the image can be seen to have pronounced barrel distortion.

Olympus Viewer 3 has the lens data built and largely corrects the barrel distortion.

ASP-OV3Compare-1.jpg

It's not just the distortion that is different. When I view files at 1:1 size on the two programs, there is far less image noise and better sharpness in the case of OV3, when compared with ASP - both at their default settings.

ASP-OV3Compare-2.jpg

I gave up with ASP several years ago. I was big fan of Bibble 5 but Corel's acquisition was a disaster. The lack of updates for new cameras finally convinced me to change but TBH, the quality of the output compared to other raw converters isn't good. I'm using LR now and sort of like it, but I do find it slow and I wish I wasn't paying Adobe 10/month for the privilege.

I'm playing with ON1 Photo Raw and the moment and that looks quite good. I might swap.

MikeOxon 26th November 2017 04:40 PM

Re: 17mm lens corrections
 
I can only agree, Richard. My all-time favourite raw-converter was Pixmantec Raw-shooter - fast and good - but Adobe bought the company and it disappeared.

I find LightRoom is over-blown and, in a comparative test of various products, I liked the features in ASP best but, sadly, it's not looking too good on ORF files. Actually, I find the out-of-camera JPEGs so good nowadays that I rarely need the raw files anyway.

Greytop 26th November 2017 04:46 PM

Re: 17mm lens corrections
 
I find Capture One Pro excellent with ORF files, I've used it for years. It's great with Fuji X-Trans and Pentax in my experience too.
You can trial it for 30 days without purchasing (as with many other converters).
https://www.phaseone.com/en/Products...ighlights.aspx

AMc 27th November 2017 10:02 AM

Re: 17mm lens corrections
 
Quote:

Originally Posted by MikeOxon (Post 433854)
I have already noticed that OV3 does a much better job on raw images than ASP - I just wish OV3 wasn't so S-L-O-W, such that it's virtually impossible to make adjustments because their effects take so long to appear.

FWIW I use OV3 very occasionally mainly I'm in the standalone version of Lightroom and once in a while GIMP if I want layers.
An update a few months ago seemed noticeably quicker and the release notes mentioned adding GPU acceleration.
I've just had a dig around and found the setting (Cntl+K on Windows or click on the cog in the top right corner to open settings>Graphics Processing Unit)
This tells me that I can't enable GPU acceleration as mine is only 1GB and it wants 2GB
I'm fairly sure it did work at one point

My main gripe with OV3 is the speed at which it works, but I could forgive it quite a lot of performance issues if the documentation available was better.
The help file describes the way functions work but there's no indication of a workflow or even why you might choose to apply a certain editing option or what the sliders are for.
Why would you use the "RAW development" editor instead of choosing "Edit" which offers more functions and AFAIK all the same RAW ones? It's mysterious!


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