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  #1  
Old 22-10-2018, 01:27 PM
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Camelopardalis (Dunk)
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When is RAW really RAW?

Iíve been using my ZWO 1600 mono for a couple of years now and thereís no going back but once my rig has been setup and is imaging away, it requires very little attention (usually!).

This leaves me with not a lot to do on those nights out at a dark site. As a result, Iíve been experimenting with a couple of entry-level cameras I have to hand.

Of course, this led my mind down a bit of a rabbit hole when it comes to the data I get from my cameras...

Canon 1100D - this is a classic IMO, inexpensive and no frills, and Iíve astro modded it as from the factory (almost?) all consumer cameras are weak outside the visual wavelengths of light, including the valuable Ha band. This camera has the ancient Digic 4 chip (most recent Canon camera have the Digic 8), and saves its data in the CR2 RAW format that is well supported in most astro software.

Fujifilm X-A3 - I bought this as a point and shoot mostly for daytime, but the curiosity got the better of me of course This camera has much more recent Sony sensor with the standard Bayer array, unlike the rest of the X-series cameras. Regardless, the Fujifilm RAF RAW format is much less well supported, although support exists in DCRAW and Adobe Camera RAW. Interestingly, this camera seems to have a much less aggressive near-IR cut-off, and Ha emission targets show up reasonably well, for an unmodded camera.

Both cameras have been superseded by more recent models (many times, in the case of the 1100D!), with updated sensors and/or on-camera processing engines. The 1100D is always used with long exposure noise reduction off, and the X-A3 with Noise Reduction set to -2, which is the lowest value, there is no option for off.

Which leads me to question...when is RAW, RAW?

While I appreciate these are black boxes, and weíll never truly know, advancements in sensor and on-camera processors donít always give better results.

Take Sony and Nikon cameras for example. Both appear to feature spatial filtering algorithms to remove stray pixels before the data is written to the RAW files, examples being the infamous Sony ďstar eaterĒ, although from reading Cloudy Nights, even some Nikonís (including the D5300, with a similar sensor to my X-A3) appear to do some funky things to the stars.

Similarly we can question the uniquitous Canon processing, after all, skeptics might say they are likely to be employing comparable techniques to remain competitive. With the later and later revisions of the Digic processors, perhaps there is a case that the algorithms Canon are using are becoming more sophisticated, but just not as intrusive as the Sony and Nikon?

Iíll post a few example images shortly, but if anyone has any insights or would like to share some raw data or analysis, by all means post or get in touch.

Iím also curious about the spectral response of these cameras, but thatís another ball game...
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  #2  
Old 22-10-2018, 02:35 PM
glend (Glen)
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Dunk, I have a Nikon D5300 and would agree that it gathers Ha wavelength much better than my old cooled Canon 450D, which I believe had the Digic 3 processor. I have not noticed any strange star processing by the D5300, but then again it is mainly used for wide field shooting with my little Astro-tech ED60.
I do feel that modern DSLRs produce a significant amount of internal heat due to the processor activity. Some of these cameras have multiple internal processors with no way of shedding heat. Sensors alone don't produce much heat but it's the processors that heat up the camera. I would like to see a stripped down DSLR, with cooling, but I guess I am dreaming.
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  #3  
Old 22-10-2018, 06:10 PM
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Camelopardalis (Dunk)
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Glen, I think that raises another important point. If the noise reduction isn’t too intrusive, then it might go largely unnoticed in widefield. I’ve seen reports on CN that it can give rise to green stars, but I don’t own one myself.

Another good point regarding thermal behaviour too. The shrinking of many camera models could result in worse than expected performance, if one model is unwittingly assumed to perform similar to another with the same sensor.

A good example of this is the Canon 200D - potentially the same sensor as its more pricey brethren, such as the 80D, which comes in a larger case, so may be more tolerant to long exposures. Then let’s introduce the 1500D, again (possibly) the same sensor, but being cheaper it has a more lowly Digic 4+. How much does this affect the image quality for astrophotography? It’d be interesting to compare dark frames from such models under the same conditions.
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  #4  
Old 22-10-2018, 06:14 PM
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RickS (Rick)
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Quote:
Originally Posted by glend View Post
I would like to see a stripped down DSLR, with cooling, but I guess I am dreaming.
I think that ZWO make them
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  #5  
Old 23-10-2018, 01:53 AM
glend (Glen)
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Quote:
Originally Posted by Camelopardalis View Post
Glen, I think that raises another important point. If the noise reduction isn’t too intrusive, then it might go largely unnoticed in widefield. I’ve seen reports on CN that it can give rise to green stars, but I don’t own one myself.
Dunk, I am pretty sure I have noise reduction turned off on my D5300, but I will check that. As a matter of practice I always turn noise reduction off in my DSLRs, It was certainly never used in the Canon. Of course I shoot darks and bias frames. I think I picked up the D5300 setup programming off CN.

Here is one:

https://www.cloudynights.com/topic/5...0-ap-settings/


Rick makes a good point, when using a DSLR we have to go through the setup menu and turn off all of these sub-routines that some programmer thought were a good idea and which generate processor activity (hence heat and maybe unwanted AP outcomes).

My venerable ASI1600MM-C has the Olympus OM-10 (Panasonic made) sensor, in its mono form, has very little in terms of software control (and programming interference) other than shutter, download, etc functions; and that is all we need. If DSLRs came with an AP mode, which turned off all the internal gingerbread programming, that would be ideal, but doubtful as a sales success with the public. People have come to expect all that gingerbread, and imho it is one of the things that continue to make DSLRs expensive. The version 1 ASI1600 is pretty much the digital equivalent to my old Pentax KX film camera.

Last edited by glend; 23-10-2018 at 07:22 AM.
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  #6  
Old 23-10-2018, 02:23 AM
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What is 'really raw' ?
Canon CR2 and Nikon NEF are actually a sort of modified TIFF files.
And astro modding is not needed anymore for more modern cameras. I have an EOS 6 NOT modded (original version, the Mk2 and the just released Mk3, actually called EOS R) and can make perfect photos of Halpha red nebulas.
When I stack CR2's with DSS or Siril, I can open the resulting TIFF with Adobe RAW and do all the fine tuning as if it were a CR2.
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  #7  
Old 23-10-2018, 05:26 PM
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LewisM
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Quote:
Originally Posted by RickS View Post
I think that ZWO make them
I thought that was pretty much what the ZWO CMOS cameras were too
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