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IFN, M81, M82 with Sony A7S


sharkmelley

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This is my first light with the modded Sony A7S on the Tak Epsilon 180ED so I thought I'd be a bit adventurous.  It's 4 hours of total integration time taken over 2 nights here in Kent using 90 second exposures at ISO 2000.  A Baader IR/UV filter was used.

My sky registered SQM 20.8 so its not really dark enough to do justice to the Integrated Flux Nebula and there were some tough gradients to remove.  I'm still not completely happy with the result but I ran out of time.

There's a bright patch at the top edge, left of centre which might be a light leak - I need to investigate this further.

post-19658-0-20896700-1432251888.jpg

Larger version here:

http://www.markshelley.co.uk/Astronomy/2015/ifn20150518.jpg

Mark

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The IFN is showing very well thanks to the fast aperture of the Epsilon but why 90s exposures? with such dark sky as yours I'd do as least 300s with the fast aperture. The SQM at 20. something is a stuff of dreams for me even with the clouds eventually disappear.

A.G

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Really nice result, a few sat trails have survived the stacking though, not sure how with that many exposures I'd have thought they would be taken out.

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I selected ISO 2000 because that is the lowest ISO with the ultra-low read noise then selected 90sec subs to not burn out the galaxy cores. Longer subs would not bring out fainter detail because the read noise is already swamped by skyglow at 90 sec.

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Very nice, you've done well not to bloat the stars by keeping sub length down yet the galxies are really nicely detailed..

Anychance of getting to see a full size image and if possible 1 single sub for curiosity.. :)

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Anychance of getting to see a full size image and if possible 1 single sub for curiosity.. :)

I don't have a full size image as yet - I binned this 2x2 during processing to better control the noise.   I'm going to do a full reprocess when I get a bit more time.

Here's a Dropbox link to one of the 90sec subs (in Sony ARW format):

https://www.dropbox.com/s/dg7ybabowcz226m/DSC00040.ARW?dl=0

The "star eater" effects are quite noticeable in a single sub.

Here are some stats on the noise components in that 90sec sub, per pixel:

Skyglow noise:  23e

Thermal noise: 2e

Read noise 1.4e

You can see that I could easily use much shorter subs and still the skyglow noise would be the dominant noise source.

It makes for a very versatile imaging setup :smiley:

Mark

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As with the Sony A7S Needle Galaxy image recently posted, this one strikes me as being very weak in the red channel. The Ha jets in the Cigar are not showing well despite the fact that you have, indeed, captured a good deal of IFN - which is actually fainter. So well done the blue and green channels but I think the red is some difficulty.

Olly

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...A PS to my post above. Could the Visible Spectrum filter be tighter on the Sony than on the other cameras widely used? If so, will we be seeing modded Sonys with the deep red end opened up a bit?

Olly

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The Op said the camera was modded, what the specifics or the mod are I don't know but I can't imagine any astronomer would modify a camera but leave a filter that blocks Ha in place unless it was welded to the sensor (and some would have a go at that anyway!).

There is red colour in the stars though so it could well be just the Ha response is too low.

I'm curious to see how these cameras will do on emission nebulae.

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The Op said the camera was modded, what the specifics or the mod are I don't know but I can't imagine any astronomer would modify a camera but leave a filter that blocks Ha in place unless it was welded to the sensor (and some would have a go at that anyway!).

There is red colour in the stars though so it could well be just the Ha response is too low.

I'm curious to see how these cameras will do on emission nebulae.

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Sorry, my mistake. I missed the 'modded' bit in the original post.

The Milky Way is rising so it will soon be full of testable emission nebulae.This has to be a really interesting chip, though. The IFN is terribly faint yet there is is.

Olly

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My own impression from the two images I have done (the other was M51) is that the H-alpha is still on the weak side - even though the camera is modded.  I'm trying to think of a way of testing this.  On the other hand it could be something to do with my processing!

It's always possible to shoot some separate data with an H-alpha filter and add it in.

Mark

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Interesting to see. I once did this with the same scope, though with a Baader modded 5D MKII at ISO 1600 and a total integration time of 12 hours 20 min (5 min. subs) at a 21.5 magn/arcsec sky.

How is the quality of the stars in the corners of your full frame image? Tight and symmetrical compared corner to corner? The collimation of the e-180 is very rigid, though I find it difficult to get tight stars across the entire FOV. My suspects are slight sensor tilt and play in the bayonet mount (although I adjusted this to be very tight).

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How is the quality of the stars in the corners of your full frame image? Tight and symmetrical compared corner to corner? The collimation of the e-180 is very rigid, though I find it difficult to get tight stars across the entire FOV. My suspects are slight sensor tilt and play in the bayonet mount (although I adjusted this to be very tight).

I'm reasonably happy with the stars but I might have a little more fine adjustment to do.  My main issue with that camera is heavy vignetting in the extreme corners.  There's a single sub here - tell me what you think:

https://www.dropbox....C00040.ARW?dl=0

Mark

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Stars seem to be allright; elongation in the corners is symmetrical from the center. I did a quick peek though. I'll have a better look this evening and make a comparison with one of my raw files (sampled to the same image scale).

I suppose you use a traditional T-ring (M42). Unfortunately I don't see Sony mentioned in Takahashi's list of wide T-rings.

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I have made a comparison of the two images, resampled to the same image scale. Yours is on top. You'll notice peculiar comma shaped stars in the lower right hand corner of my image. Vignetting is more severe in your image, though I guess it won't be much of an issue when you use flats.

ifn_shelley.jpg

ifn_toet.jpg

Also a side by side comparison concerning colours (single subs). Yours is on the left. I think the reds are definitely there in M82's burst.

ifn_shelley_toet.jpg

Mine is almost over-exposed (@ ISO 1600, 5 min. exposure time), though I managed to get some colours back in my final version.

m81_m82_140325_1000.jpg       

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