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A7S, Antares, Astrofarm, Astro Pixel Processor

sharkmelley

By sharkmelley
in Imaging - Deep Sky

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sharkmelley

sharkmelley

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This mosaic of the Antares and Rho Ophiuchi region was taken on my recent visit to Astrofarm in France using the the usual Sony A7S and Takahashi Epsilon combination.  It's an 8 piece mosaic, each piece comprising 20 x 30sec at ISO 10000.  It was shot over 2 nights: 23/24 May.  To assemble the mosaic I used a trial version of the new Astro Pixel Processor software and followed the (silent) mosaic tutorial video here: https://www.astropixelprocessor.com/video-tutorials/.  I'm really impressed with the result: it automatically positioned and assembled the 8 pieces seamlessly and with the stars perfectly aligned!  It's the easiest mosaic ever.

As an added bonus, you might be able to find comet 71P/Clark hidden away in the image as an exercise for the reader :) 

antares_2017_05_23_small.thumb.jpg.b4612914cdbb3e8de60bd9af7d574512.jpg

Large version can be found here http://www.markshelley.co.uk/Astronomy/2017/antares_2017_05_23_large.jpg

Mark

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davew

davew

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Oh wow Mark. You've gone beyond superlatives with this one !

Just as a matter of interest, how much " Work " did APP have to do ? Did the edge brightness match well on each panel ? How much distortion, if any, did the scope introduce ?

Dave.

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sharkmelley

sharkmelley

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Thanks very much to all of you for your very kind comments.  As you can guess, I am very pleased with this result.  I reckon it's in the top 3 of all the astro-images I've ever taken.  I've tried but failed to capture this in the UK (in Kent) because it's always sitting in the "murky part" of the sky.  In France the extra few degrees of altitude and the darker sky made it viable.  I'd love to try it in Spain or the Canaries :)

Here are a few replies to some of the points raised.

5 hours ago, davew said:

Just as a matter of interest, how much " Work " did APP have to do ? Did the edge brightness match well on each panel ? How much distortion, if any, did the scope introduce ?

 

Firstly a disclaimer: I have no connection with APP whatsoever - I simply downloaded the 30 day trial version but so far I'm very impressed with the mosaic functionality. The scope doesn't introduce a lot of distortion but there's still a fair amount of correction to do before stars line up perfectly from panel to panel.   APP seems to do exactly what I need and seems to do exactly what I would have coded myself if I had the time.  Simply dump all the mosaic pieces into the APP and it performs star matching to work out what piece goes where.  On the other hand PTGui failed abysmally - I had to set lots of manual control points to get the right panel in the right place and even then I still ended up with double stars without a lot of further manual work.  PixInsight mosaics are also manually intensive to get registered well, at least in my experience.  For this image I performed a basic background subtraction on each mosaic piece before feeding them into APP but the brightness differences were quite obvious with the  blending option disabled.  With blending switched on, the brightness of each panel was adjusted so well I couldn't work out where the joins were.

 

5 hours ago, StargeezerTim said:

The image is so smooth at iso 10000! I must look into that Sony...

The Sony A7S is very definitely a consumer camera rather than a scientific instrument.  That said, it has the lowest read noise and highest quantum efficiency (QE) of any consumer camera at the present time.  I think it also has the lowest dark current (thermal noise) per unit area of sensor but figures for this are difficult to obtain (I calculate my own).  I strongly recommend ISO 10000 because the read noise is around 1 electron (RMS) and because it overcomes issues such as coloured concentric banding that sometimes appear in calibrated light frames.  Don't be tempted by the more expensive A7SII - it uses the same sensor but the IBIS (image stabilisation) means there is less internal copper plating to conduct the heat away.

1 hour ago, peter shah said:

a real stunner....I've yet to use my A7s on my scope...think I might give it a go after seeing this

I definitely think you should give the A7S a try on the AG12.  On the Tak Epsilon (focal length 500mm) I reckon the pixel size is slightly larger than the ideal.  On the AG12 I think it could be a perfect marriage.  F3.8 is also very fast - you will still be in the zone where the skyfog noise (rather than read noise or thermal noise) is the only limitation.  I use a Sony E-mount to Canon lens adaptor.  Once that is fitted on the A7s you can use all the standard Canon T-rings etc.

Mark

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davew

davew

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49 minutes ago, sharkmelley said:

 

Firstly a disclaimer: I have no connection with APP whatsoever - I simply downloaded the 30 day trial version but so far I'm very impressed with the mosaic functionality. The scope doesn't introduce a lot of distortion but there's still a fair amount of correction to do before stars line up perfectly from panel to panel.   APP seems to do exactly what I need and seems to do exactly what I would have coded myself if I had the time.  Simply dump all the mosaic pieces into the APP and it performs star matching to work out what piece goes where.  On the other hand PTGui failed abysmally - I had to set lots of manual control points to get the right panel in the right place and even then I still ended up with double stars without a lot of further manual work.  PixInsight mosaics are also manually intensive to get registered well, at least in my experience.  For this image I performed a basic background subtraction on each mosaic piece before feeding them into APP but the brightness differences were quite obvious with the  blending option disabled.  With blending switched on, the brightness of each panel was adjusted so well I couldn't work out where the joins were.

 

 

 

It was mainly the edge blending that intrigued me. PTGui was comprehensively re written a few years ago and was supposed to be a step up from the original PanoTools. Maybe it's just a daylight programme now ? I know ICE is quite good but APP is certainly something to further investigate. 

Cheers for the answer.

Dave.

 

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sharkmelley

sharkmelley

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8 hours ago, davew said:

It was mainly the edge blending that intrigued me. PTGui was comprehensively re written a few years ago and was supposed to be a step up from the original PanoTools. Maybe it's just a daylight programme now ? I know ICE is quite good but APP is certainly something to further investigate. 

Cheers for the answer.

Dave.

 

I would like to understand the APP mosaic algorithm a bit better but it certainly seems to be working very well.  The data was acquired with  a 1/3 overlap of all the mosaic panes.

Mark

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Mabula

Mabula

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On 23-6-2017 at 07:37, sharkmelley said:

I would like to understand the APP mosaic algorithm a bit better but it certainly seems to be working very well.  The data was acquired with  a 1/3 overlap of all the mosaic panes.

Mark

Hi Mark,

more explanation will come in the documentation and new video tutorials.

(In the meantime, if you have questions, feel free to post them on the APP forum)

My compliments for this 8 panel mosaic. It's simply stunning, I love it ;-) !

Kind regards,

Mabula

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