sharkmelley

9 hours ago, vlaiv said:

I want to address one more misconception.

We have read previously in this thread - in one other quote from various posts on other forums - that drizzle does not perform interpolation.

Yes, of course drizzle is performing interpolation to drop the input pixels onto the output grid.  But for Bayer Drizzle the original raw pixels need no demosaicing and hence the usual interpolation during demosaicing is not required.  This means that bayer drizzled one-shot-colour data will give the same image sharpness as drizzled RGB data from a mono camera.

A full spectrum mod will allow you to do astrophotograpy and terrestrial infra-red photography.  For terrestrial IR photography you may want to use a specialised IR filter. For astrophotography you will want to use a UV/IR blocking filter to prevent IR diluting the colours.  Also, IR often comes to focus in a different plane to the visual spectrum which could lead to star bloat unless a UV/IR blocking filter is used.

1 hour ago, vlaiv said:

First time I've seen it like that. I saw regular square grid at an angle due to rotation and use of bilinear interpolation, but never this warped

The same for me - I've never seen an example this warped either.

11 hours ago, vlaiv said:

By the way - I love this strange pattern in the image and can't even begin to fathom what it could be.

A "warped grid" like that is often an indication of geometric transformations during star alignment.

10 hours ago, Clarkey said:

The overall reflection just looks too big for a reflection of this type? It's nearly 1/3 of the frame.

That gives us something to work with. 1/3 of the 1600mm sensor is approx 6mm.  Your scope is f/4.  The total extra distance travelled by the reflected rays is therefore 6x4=24mm.  The distance between the two surfaces causing it would be half this i.e. 12mm

It is likely to be a reflection between the camera (sensor or front window) and filter.  If so, the distance between the 2 glass surfaces causing the problem can be calculated by halving the distance calculated by the dust donut calculator: Dust Donut Calculator

Mark

It is quite common that when shooting in moonlight, stray light causes an obvious central circle which flats will not remove.  However, I've no idea about the cause of the vertical bands.

Mark

If you look carefully, there are quite a few stars with similar halos but they are dimmer and not so obvious.  The halos are most likely caused by internal reflections within the filter.

Mark

I believe the AffinityPhoto 32-bit mode works similarly to Photoshop's 32-bit mode.  Photoshop assumes a 32-bit file is linear.  It will therefore display the 32-bit image using a linear (i.e. gamma=1.0) ICC profile.  This means the brightness displayed on the screen is proportional to the pixel values in the image.  As soon as you change the mode to 16-bit the relevant colour space gamma is applied (e.g. gamma=2.2 for AdobeRGB).  In other words, when you change the mode to 16-bits the pixel values are non-linearly transformed.  You can easily see this by comparing the pixel values before and after.  However, the image displayed on the screen looks identical because the non-linear ICC profile knows how to transform the non-linear pixel values into the correct screen brightness.

Mark

6 minutes ago, vlaiv said:

Then it would appear that @Adam J was right to imply that it is effect of central obstruction - it is modulation that shows as pattern here since individual rings are blurred by seeing?

The individual rings are too finely spaced to be resolved by the sensor but the modulated pattern has a wider spacing which can be resolved.

Mark

The central obstruction causes a periodic modulation of the Airy rings:

Obstructed optics and rings around stars - Beginning Deep Sky Imaging - Cloudy Nights

Mark 

18 minutes ago, Cornelius Varley said:

The OP wanted to know why their photos rotated over a period of time and how to avoid it in future. If image rotation is turned off the camera will display all images in landscape.

Yes, that is the answer to the question raised by the OP.  But for the avoidance of any doubt, changing the "image rotation" flag in the camera menu makes no difference at all to the layout of the raw data file saved by the camera (unlike the JPG saved by the camera).  The only difference in the raw file is the "rotation" flag in the EXIF header.  Some astro-software (including DSS) respects this value, other astro-software (e.g. PixInsight) ignores it.

Mark

The raw file format is completely unchanged by the rotation to portrait.  This can easily be verified by RawDigger, for instance, where the image width (in the raw file EXIF) is greater than the image height even in Portrait mode.  The only thing that changes in the raw file is a "rotation" flag in EXIF header.   DSS might be choosing to respect this flag under certain circumstances (or maybe under all circumstances).

Mark

There's nothing wrong with a 40% CO.  My Tak Epsilon has a 44% CO.  Ritchey Chretiens are near 50% and some imaging Dall Kirkhams are well over 50%.

Mark

When I use my full spectrum Z6 with an IR/UV filter I find that if I choose an in-camera white balance of K* with colour temperature set to 4500K and G-M set to G4.5 then it works quite well for daylight shots.

However when I process astro-images I calibrate and stack raw data.  Colour temperature plays no direct role for me.

Mark 

Was this a full spectrum mod (removing all filters) or an H-alpha mod (which leaves one of the 2 original filters in the camera or replaces it with a IR/UV filter).  If it's full spectrum you will want to use it with an IR/UV filter to prevent IR reaching the sensor.

Mark

It's quite normal to these these large scale background patterns in H-alpha.  See here for instance in a long Cloudy Nights thread discussing this very point:

https://www.cloudynights.com/topic/661685-word-of-warning-asi294mc-pro-and-opt-triad-and-nb/?p=9458529

Mark

17 minutes ago, Shimrod said:

You seemed quite sceptical of the R series for long exposure photography earlier in the thread, what changed your mind? Or is it a specific difference between the older 'R' and the newer R5 & R6 which is the issue?

The issue is raw data filtering on the R5 and R6 that was noticed by Bill Claff's tests on the PhotonsToPhotos site.  The question is whether or not this filtering damages small tightly-focused stars.  From the evidence I've seen in long exposure dark frames, I doubt if stars are affected but it would be nice to know for sure.   The EOS R does not have this filtering.

Mark

You definitely have a strong left/right tilt.  The stars in the central column are looking quite reasonable.  It's possible you have a spacing issue as well.

Mark

That's an excellent write-up. 

Thanks!

Mark

Did you come to a decision on this?  I recently bought the Canon EOS R for astrophotography and I'm very pleased with the results.   I will certainly be using it in preference to my Sony A7S and Nikon Z6.

Mark

1 hour ago, Shimrod said:

My understanding of the Sony issue is that it is a hot pixel removal process rather than noise reduction which is removing stars.

It's a question of semantics.  The Sony issue is well understood because of detailed investigation and it only affects pixels with outlying values - which of course is a type of visible noise.  With these types of algorithm the problem comes when tightly focused stars are damaged along with the rest of the noise.  The problem is that we don't yet know the effect of the R5/R6 raw data filtering on stars.  From the reviews we know it probably doesn't affect untracked images with slightly trailed stars but the Sony raw data filtering didn't cause any issues for these types of images either.

Mark

1 hour ago, Shimrod said:

A quick search seems to indicate it is not a problem in the real world - noise reduction is applied mostly on short exposures and up to ISO 640. I 've  no experience of the 'R' series, but these user reviews for astro seem don't seem to flag any issues.

dpreview

petapixel

Sorry, I can't take those reviews seriously.  Marco Nero (DPReview) is shooting untracked JPG images.  Brent Hall (PetaPixel) is also shooting untracked and has star trails.   Those reviews don't help us understand if accurately tracked long exposure astrophotography with good quality optics will have problems similar to the well known Sony star eater issues.

Mark

There are one or two DPReview threads relating to "noise reduction" on the R5 and R6, from the work done by Bill Claff.  For example here:

https://www.dpreview.com/forums/post/64403868

The Fourier transform of the raw data certainly shows that internal camera processing of the raw data is taking place but it's impossible to say whether or not it is a deliberate attempt at noise reduction.  It's unusual to see such processing on short exposures.   I have seen some of these raw files and I've confirmed what Bill is seeing.   However, it is not possible to extrapolate from these results what would be the effect on astrophotography.  For that we would need to see some raw long exposure dark frames and some astro long exposure raws containing very tightly focused stars with no trailing.

Mark

7 hours ago, MarsG76 said:

Are you sure that the canon software doesn't apply a stretch to the totally raw data before exporting as CR2???

Yes, I'm absolutely certain that the CR2 file contains linear raw data.

Mark