Comet Neowise and Venus

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offering local "hands-on" observing
(visual and imaging) sessions and instruction
viewing and imaging from Rabbit Valley Observatory
a dark sky location on the mesa just west of Taos, NM


Rosette Nebulae (NGC 2237-39) and imbedded open star cluster (NGC 2244) -- compare data and process
Monoceros Constellation
Rosette Rosette
A more neutral rendering of the Rosette using the same exact data set; click the above image to go back to the original. Note that both of the renderings on this page amplify the very dim emission nebular dust surrounded the main cluster and nebulosity, this a tribute to the quality and sensitivity of the outstanding ZWOASI2400MC Pro camera.
A slightly redder (but not TOO red or orange, as typifies this object's rendering) -- and perhaps more accurate, but certainly more "traditional" -- rendering of the central star cluster and associated emission nebulosity. Further, this image also shows the great diversity of nebular nuance -- a testimonial, I think, to the attention to detail permitting the data to always remain in a16 bit format throughout the process, thereby displaying far greater dynamic range in the end result. Interestingly, this very different rendering compared to the image to the left is accomplished by a simple minor adjustment layer in Photoshop -- suggesting that color is, in fact, rather subjective; click the above image to go back to the original.

Image obtained March 02-03, 2022 through RVO's Explore Scientific’s 127mm ES127ED APO refractor resulting in an 952mm f/7.5 optical system and incorporating a HOTECH field flattener -- and employing RVO's new ZWOASI2400MC Pro Sony CMOS-chipped premium one shot color astronomical camera -- 19 of 20 carefully selected and stacked 240-second color light frames combined with multiple dark, flat and bias calibration frames shot at a Gain setting of 240 / Offset = 50 and using Astro Photography Tool image-acquisition software -- totaling 76 minutes effective luminance; this data used to create the above image. The optics were driven by the Hypertuned Losmandy G-11 mount equipped with Ovision's precision RA worm gear, guided with a ZWO ASI 120MM Monochrome CCD camera through a 60mm guidescope using PhD2 guiding software and post-processed with ASIStudio, DeepSkyStacker, CCDStack2, and Photoshop CS6 s/w.

Photographer's note: It is instructive to compare the image above, taken with the superior Explore Scientific apochromatic 127mm refractor (3 optical elements, virtually no false color fringing) and shot with the new ZWOASI full-framed camera with my older previous effort of this well-known object, linked here. The previous image of this very object although beautiful and quite colorful, was captured with a high quality but nevertheless a 2 optical element Williams' Optics Megrez achromatic refractor, and with a uncooled Canon 450XSi, modified for deep-sky use. The difference in the detail (especially noting the stars' lack of significant fringing coloration (halos around stars) and general resolution is extraordinary, due in part to the larger objective lens -- 127mm vs. 80mm -- but also due to the optical type (apochromatic vs. achromatic). Click this link for a discussion of telescopic lens optics. Also, in the case of the original shot, the computer post-processing steps necessary to end up with an acceptable shot was very extensive. The Rosette image as above required no such rigor in post-processing -- the photographs straight out of the camera were really quite good (although dim, process linked here), requiring really only calibration and stacking; followed by only some minor Photoshop adjustments and mild sharpening. Frankly, after calibration, there was virtually no sharpening or noise reduction needed in post-processing. The new image also displays much less "noise" -- that is because the camera is cooled to far below ambient, rendering it more sensitive and noise-free. Click on this text for a link to the steps involved with the acquisition and post-processing of this image. For another astrophotographer's ongoing adventure with this object, please click this linked text.

Below is a new astrophotography compilation log feature, recently developed here on this website, and inspired by the book The Astrophotography Manual, by Chris Woodhouse -- highly recommended and linked here.

Specific Data for the Rosette Nebulae and imbedded open star cluster
Subject Name -- Rosette Nebulae and Clusters Catalog Name -- NGC 2237-39 and NGC 2244 RA 06h 31' 56" DEC +04°56' 35' Time Rise -- 02:42PM Transit -- 08:59PM Time Set -- 03:16AM
Observing Location -- Rabbit Valley Observatory, El Prado NM 87529

Longitude -- 105° 37' 38.59" W

Latitude -- 36° 25' 11.54" N Altitude -- 2095 meters Date -- 03-02-2022 Beginning set-up time -- ~6:45PM MST Imaging Start Time -- 7:44PM MST
Weather Temperature F -- ~36°F at start Wind -- negligible        
Conditions -- Very clear Seeing -- Excellent -- Bortle 3-4 Transparency -- Excellent Cloud Cover -- none Moon Phase -- 29.5 days (new)    
Telescope Optics -- ES127ED Aperture -- 127mm FL -- 952mm Reducer -- none Imaging FL -- 952mm Focal Ratio -- f/7.5  
Imaging Camera -- ZWOASI2400MC Pro (full-frame OSC)
Sony back-illuminated IMX410 full frame format14-bit ADC CMOS sensor -- 24MP
Pitch in microns -- 5.94 square W (px) -- 6072 H (px) -- 4042   Well Capacity -- 100ke
Read noise -- 1.1e to 6.4e
Guider Camera and software -- ZWOASI120MM / PhD2 Guidescope -- 240mm f/4 Pitch -- 3.75 microns square W (px) -- 1280px H (px) -- 960px Guide Rate -- .5 sidereal RMS error total -- 1.21 arc-seconds / guide exposures of 3 seconds
Imaging Camera Details and Calculation Exposure time -- 240 seconds
Gain set -- 240
Offset -- 50
Number of Light Exposures -- 20
Binning 1X1 Camera cooled to ~10°F during exposure Filter -- none Imaging Resolution -- 1.287 arc-sec per px -- per Polar alignment error via PhD2 -- 10.2'
Imaging Software Acquisition -- APT Calibration -- APT & DSS 19L, 22D, 20F, 20B frames used Initial conversion -- ASIStudio & CCDStack2 Post-Processing -- PSCS6 Sharpening -- Topaz Labs' DeNoise AI
General Comments and details -- See log #2 , 2022

Used Bahtinov mask, was perfect "close" per get-go, will try auto-focus next time / electric focuser is Rigel's nSTEP


  Cooled to a lower temp this time (10 degrees F), camera had no trouble attaining this temperature   Guiding error less than imaging resolution -- should suggest tight images Need to develop a folder of dark and hot pixel frames for the guider, as well as hone in on the focus

Observing Notes (to myself and titrated (leaving out much of the guiding details and post-processing verbiage, believe it or not!):

I started up the AstroPhotographyTool program and aimed up on a star from a mount position west of the pier.  I lined up and focused on first-magnitude Betelgeuse, which was also relatively near to the subject object, NGC2244, the Rosette Nebulae and associated cluster.  One thing I MUST do is get the green laser and finder ‘scope aimed up well, and also aimed up well with the main ‘scope.  The right-angle illuminated finder is very nice -- the green laser pointer needs to be brighter.  I ordered and received same, with more power.

After centering the target star by using the main imaging camera with APT, I set off a sequence of short exposure images in the center and focus “plan” accessed in the plan section of the program.  Such images are not saved unless you ask APT to.

Centering at 16X setting on the mount was quick, focusing not as much.  At first I tried the auto-focus, but failed to understand how to set it up.  So, I installed the Bahtinov mask.  I switched between “Focus Aid” and “Bahtinov Aid.”  Amazingly, the focus was “close” from the get-go, so I didn’t adjust it at all.  I scrutinized some of the initial images –- they looked great.  I calibrated the NGC-MAX (digital setting circles), and pushed the mount to the subject object. My set-up doesn't automatically find objects -- I have to do that myself!

I took some images for centering purposes, but they looked weird, very off. 

Bahnitov masked image
single image Rosette
I forgot to take the focusing mask off! Note the lurking nebula behind the stars.
Even initially stretched (enhanced), the large nebula is barely visible.

This was the result of forgetting to take the mask off!  You could see the Bahtinov rendering of stars throughout the centering image.  Once I removed the mask, everything was fine.  Note nebula (faint) as well –- that’s how it looks at the time of imaging, even with intense stretching.

Now it was time to “test” the mount movement with PhD2, using the “on camera” toggle as previously discussed, and switching over to .5 sidereal.  It worked perfectly and calibrated itself quickly, per my previous successful results.  I used the new multi-star function as well.  For now the guiding situation is resolved!

PhD2 calibration

Guider calibration graph -- looks like the mount axes are little out of orthogonal (exactly 90 degrees)

mount drift
Numeric representation of the auto-guiding session
Numeric representation of the mount's polar alignment accuracy

These graphs and charts are just a small part of the output rendered by the excellent PhD2 auto-guiding program -- and it's FREE! Entire books are written on auto-guiding and the interpretation of such output. Many more books are written on the post-processing of such "data." All that's far too much to cover here; suffice it to say that nowadays the reality that the mount sort-of automatically guides itself into achieving sub-pixel accuracy is frankly astounding, and is a significant reason why modern-day amateur astrophotographers are able to produce such stunning images! Good thing -- I didn't do all that well in math class-- and guiding is all about engineering and math. Post-processing as below is all about art -- and I didn't do all that well in art class, either!

After some testing, I decided on 240-second subs, and set up a new “plan” in the program for same.  I set the gain at 240, as the previous 160 setting did not render a view of the nebula, even with quite a bit of stretching.  Per on-line instructions I set the offset to 50 as well.

During the imaging session, I clicked back and forth between acquired images in APT and PhD2 guiding.  I was generally pleased with the output on both screens, although the nebula was quite dim, and not exactly centered perfectly.  Above (right) is what those sub frames coming out were looking like.  I wasn’t at all sure I could draw out much nebulosity in the final picture.

I kept going anyway.  I heard Tawny, our Australian Cattle dog, barking to make sure I was OK (right!) –- and later in the session I heard the “howling” or “yipping,” maybe of multiple coyotes!  This kind of stuff really makes the imaging session (mostly looking at the computer screen, and switching back and forth between programs) tolerable, even enjoyable!

I finished up the light frames, covered the scope, aimed it downward, and clicked onto the already-developed dark plan, making sure both the Gain and Offset settings matched the L frames.  I watched several of the dark images appear before I crawled out of the observatory and locked up for the night.

The next morning (03-03-22) I opened up and, to my satisfaction, all the darks had been shot and were fine.  I ran the “CCD Flats Aid” –- it worked perfectly and created and exported a nice flats plan. To accomplish this, I aimed the telescope at a lit wall, and put on the diffuser.  I needed to use the amount of exposures to match (in this case 20), at least, the light plan, which I did.

As to the bias frames, I covered the telescope and chose .000001 as the exposure (S/B zero, which didn’t work).  APT created a nice set of bias frames, so I unhooked everything, shut down and took the saved images on the laptop inside (with the laptop in hand, since I need the programs on it to calibrate and pre-post-process the images)!

After reviewing one or two of the satisfactory light frames in ASI .fits viewer, I waited and rested a day before actually calibrating, stacking, and processing the final image.


Post-processing details:

(It has become clear that I need a rather linear and specific routine for the steps of post-processing, mostly due to complexity and forgetfulness):

1 –- Organize images by types (L, D, F, B) after shooting and saving.

2 -- Bring images into DSS, and per the parameters for M45 or Rosette (M45 is log #11, 2021, Rosette is log #2, 2022) -- go through the steps and produce final calibrated and stacked image.  Save as both .fits and .tif.

3 –- Open .tif (16bit) image in CCDStack2.  First, deconvolve (must be done before any stretching -- 
“Deconvolution is an early-stage process, most appropriately applied to the linear data before any other (non-linear) changes have been made to it.” –- from PixInsight tips
if needed, then -- follow program’s instructions (starting on page 43 in tutorial, generally).

  1. Normalize background
  2. Make color adjustments, DDP checked “auto scale”
  3. Play with Background, Maximum and Gamma settings.
  4. Test with “Balancing White Points” routine.
  5. Readjust color, then (likely) increase saturation.  Make sure background isn’t “too” black.
  6. “Save as” scaled .tif.  It is a 16bit image, which can now be . . . 
  7. Checked in Windows PS Elements -- if OK, save and open in PSCS6 on the Mac or (new Rosette routine below) . . .
  8. Carefully sharpen with new NI sharpening tool in PS Elements on the Windows machine.
  9. At this point, create “starless image” with StarNetv2.
  10. Now, transfer both the scaled image and the starless image into the Mac and open in CS6, 16bit .tif format.
  11. Open and adjust starless image to bring out nebulosity, etc.  “Save as” unique, adjusted image, saving all adjustment layers, etc. for later duplication.
  12. Create per links below a star-only image.  This is accomplished by opening the original imported image with nebulosity and stars, choosing “image drop-down,” select source (the original combined imported image, now opened), selecting the target (the starless image adjusted and copied!) with settings blend=subtract, offset=1 (rendering a black background).  This will create a combined image minus nebulosity image equaling a star-only image.  Then duplicate the adjustment layers in this star-only image (to equalize the look of the stars vs. the look of the starless nebulosity image).  Flatten this image and “save as” a new flattened star image.
  13.  Open both the starless adjusted image with adjustment layers and the star-only adjusted, flattened image.
  14. Copy and paste the star-only adjusted flattened image using “Duplicate layer,” (name it), choose destination (the starless image).  This creates the stars-only image added to the nebulosity image.  Once pasted, play with the star-only layer “layers, choose screen or linear dodge” (no reduction)  -- and your choice in the “drop-down menu, opacity, fill” -- all this concerning the star layer), then, when satisfied with combined image, move onto another adjustment layer if desired, as below.  If above the pasted star layer, this new adjustment layer(s) will effect the entire image.
  15. If spotting is needed, spot on final background layer, creating a new adjustment layer and thereby preserving all other layers.  Also, this technique allows for multiple spotting sessions.  Refer to M45 spotted layered image.

4 -- Working now with this combined 16bit .tif file in PSCS6, final adjust levels, color balance, vibrance, etc.  Save unflattened master image with layers.
5 -- Save original master (use layered approach) 16bit .tif; then create all renamed flattened high-res full-sized versions, various also renamed small web copies for internet, and high-res .jpg copies for printing, etc.  Make sure to save all steps so you can go back and tweak if necessary.


[copyright Rabbit Valley Observatory/Willis Greiner, 2022 -- all rights reserved]


visual observing sessions
imaging sessions
image post-processing
"The Imperative of Night" narrative
contact us


(all content copyright 2015-2022 Willis Greiner Photography, all rights reserved)