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SX40, SX 50 vignetting, flat frames etc

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SX40, SX 50 vignetting, flat frames etc
« on: 11 / November / 2013, 11:09:30 »
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I have recently been shooting some VERY large panoramas with the SX40hs  ... yes 40hs.
In fact, they are too large to view in any image editor so I will split into multiple panos and then create a movie that pans along the individual panos.

The view is Liverpool, Merseyside and the region beyond.
However, I am shooting this from a location in Wales twenty miles away.
Some features are seen seventy miles away on an extremely clear day like yesterday.
For this, using a reasonably-sized rugged tripod and rotating platform the SX40hs is ideal and used at 840mm focal length.

For this unique panorama, there are few alternative options.
A DSLR with 800mm lens is impractical for many reasons :-

http://www.luminous-landscape.com/images-85/mr-800.jpg

There is however a major problem, the very bad vignetting at 840mm as shown in the image below.
I took that vignette shot by taping a piece of white paper over the TV screen, manually focusing to infinity and then zooming to 840mm.

Even after using Photoshop vignetting correction the panos created by Autopano exhibit dark bands at the join of each image.

So, the question is   ..............  does the SX50hs exhibit this vignetting  behaviour at 840mm ?


David

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Offline dvip

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Re: SX40, SX 50 vignetting, flat frames etc
« Reply #1 on: 11 / November / 2013, 15:25:10 »
Hi David,

You can do vignetting correction using RawTherappee:

http://rawtherapee.com/downloads

I do this from time to time with my SX40HS. You can create a PP3 file (profile) and from there on it does it automatically.
Love the SX40SH + chdk DNG.
What I like best about the cam is the F2.7 lens and the IS which helps big time in low light.

Some nice pano examples here:

http://www.flickr.com/photos/mikedie1/

Nice bokeh:

Danbo on the edge

I hope this helps.


Re: SX40, SX 50 vignetting, flat frames etc
« Reply #2 on: 11 / November / 2013, 18:46:40 »

You can do vignetting correction using RawTherappee:

Thanks, I will check that out.

I have just made a first attempt at http://www.panos.at/howto/vignetting/  , and even though it needs a bit of tweaking, apart from correcting vignetting it reveals features not visible in the original image.

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Love the SX40SH + chdk DNG.

All the images taken yesterday included DNG, some were taken with an R72 IR-passing filter.
The CHDK colour matrix is not very accurate, what correction values do you apply ?

Quote
Some nice pano examples here:

http://www.flickr.com/photos/mikedie1/

They are very good.

Quote
Nice bokeh:

Danbo on the edge

I have never heard of that technique, very interesting.

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Re: SX40, SX 50 vignetting, flat frames etc
« Reply #3 on: 11 / November / 2013, 19:06:44 »
>The CHDK colour matrix is not very accurate, what correction
>values do you apply ?

I create my own... lower  the green channel a little :)
You can try the dcp file (SX50HS) found here or play with COLORMATRIX1:

http://chdk.setepontos.com/index.php?topic=9247.0



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Offline blackhole

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Re: SX40, SX 50 vignetting, flat frames etc
« Reply #4 on: 12 / November / 2013, 12:18:27 »
@Microfunguy
To remove vignetting is preferable to use flat frames, option 'Vignetting correction' in the various tools for postprocessing never give the best result. Another advantage of using a flat frames is to removing shadows caused by the accumulation of dirt on the sensor and lens. Very important is to have a correctly exposed a flat frame because the underexposed flat frame will increase the noise in the image. Histogram graph with the proper exposed flat frame must be very close to the right edge. Attached is how it should look.
Very good flat frame can be done if you shooting a blue sky at sunset, about ten degrees east of the zenith. Good  flat frame can be used on all images with the same f / n.
The simplest way of using the flat frame is pasting the flat frame as a new layer and setting that layer to Overlay and then adjust the opacity of that layer until it looks well.

Re: SX40, SX 50 vignetting, flat frames etc
« Reply #5 on: 12 / November / 2013, 13:02:50 »
Thanks for that.

Not sure what a 'flat frame' is but maybe I took one earlier today when I photographed the clear blue at the 840mm setting.

I will convert to 16-bit greyscale, expand histogramme to cover full range, Gaussian blur to remove banding and then invert and save as 16-bit tif.

That will be used as a mask together with a separate brightness/contrast layer.

As no SX50hs users have responded as to whether that camera has significant vignetting   ... I decided to buy one.

I may convert the SX40hs to full spectrum.



David
« Last Edit: 12 / November / 2013, 13:10:14 by Microfunguy »

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Offline dvip

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Re: SX40, SX 50 vignetting, flat frames etc
« Reply #6 on: 12 / November / 2013, 18:08:20 »
David, you can also try an lcp profile to use with RawTherapee and others:
 
http://chdk.setepontos.com/index.php?topic=10455.msg103321#msg103321

Or create your own lcp profile:

http://www.adobe.com/support/downloads/detail.jsp?ftpID=5490


Re: SX40, SX 50 vignetting, flat frames etc
« Reply #7 on: 13 / November / 2013, 11:41:05 »
David, you can also try an lcp profile to use with RawTherapee and others:

I have installed RawTherapee and loaded the lens profile (which is only for 50mm setting).

The vignetting correction produces the usual problem of distinctive annular bands all over the image but particularly over large areas of grey sky.

The SX40hs is quite simply not suitable for this application.
I guess large panoramas at the 840mm setting is a bit specialised.

I look forward to receiving the SX50hs.
However, the images I took some days ago were during extremely clear visibility so I need to correct them somehow.


David


Re: SX40, SX 50 vignetting, flat frames etc
« Reply #8 on: 13 / November / 2013, 11:52:55 »
To remove vignetting is preferable to use flat frames

Do I convert my blue sky flat-frame to grey scale and invert before adding to a new layer ?

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Offline blackhole

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Re: SX40, SX 50 vignetting, flat frames etc
« Reply #9 on: 13 / November / 2013, 15:35:43 »
You can try but it is not necessary.
Your flat frame can also be used on this way

 

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