Our Beautiful Universe - Photos and Videos

[Andy Resnick]

Beautiful. May I download that to use as my background on my phone and laptop?

Thanks! Certainly! (thanks for asking first :) )

 

[Andy Resnick]

Beautiful !
Can I ask what is mygnifying of this image?

Thanks!

Regarding magnification, 800mm provides about 16X magnification, using the convention that a 50mm lens is matched to the field of view of a naked eye.

 

[bruha]

Thank you

 

[bruha]

Made by my friend (half professional photographer)':

The brightest star is Deneb from the constellation Cygnus, and to the left of it the Pelican Nebula and North America can be seen.
...
Technique: Sony A7, Samyang 135/2, SW Star Adventurer, UHC Astronomik filter
Exposure: 150x40sec
Post-processing: AstroPixelProcessor, PixInsight, Photoshop

 

[collinsmark]

NGC 281, the Pac-Man Nebula, captured from my back patio from late Oct through the first part of Nov, 2022. The nebula is found in the constellation Cassiopeia, and is about 9,200-9,500 light-years away (sources vary).

Its common name is the "Pac-Man" nebula, presumably due to the fact that, at a glance, it sort of looks like the 1980 video arcade game character, "Pac-Man." (Tilt you head and blur your eyes, if it helps.)

It obviously wasn't always called the "Pac-Man" nebula; it was discovered by American astronomer Edward Emerson Barnard (most famous for Barnard's Star, the star with the highest proper motion in the night sky) in 1883. It just goes to show that the common names of astronomical objects are not set in stone, and can evolve over time. (Edit: Even today, the nebula is frequently called "Pacman," without the hyphen.)

Looking at NGC 281 in more detail, there are features within the nebulosity that the brain might interpret as facial features, such as a human eye (upper-center), and maybe an ear. Also a mouth & chin, perhaps? Cheekbones?

Equipment:
Meade 10" LX200-ACF fork mounted on an equatorial wedge.
Starlight Instruments FTF2008BCR focuser modified for electronic focusing.
Off-axis guider (OAG) with ZWO ASI174MM-mini guide camera.
Baader 3.5-4 nm Ultra-Narrowband filter set.
ZWO ASI6200MM-Pro main camera.

In the 1980 video game, Pac-Man was chased by ghosts.

Software:
Nighttime Imaging "N" Astronomy (N.I.N.A.)
PHD2 guiding (of course)
PixInsight
Topaz Labs Sharpen AI

My back patio is called the Shady Crypt Observatory.

Integration:
Bortle class 7 (maybe 8 ) skies
All subframes binned 3×3
SHO mapping
SII: 78×10 min = 13.0 hrs
Hα: 75×10 min = 12.5 hrs
Oiii: 67×10 min = 11.17 hrs
Total integration time: 36.67 hours

 

[Borg]

Looking at NGC 281 in more detail, there are features within the nebulosity that the brain might interpret as facial features, such as a human eye (upper-center), and maybe an ear. Also a mouth & chin, perhaps? Cheekbones?

That's what I saw first. Like something out of a sci-fi movie. Beautiful pictures as always.

 

[Ibix]

Looking at NGC 281 in more detail, there are features within the nebulosity that the brain might interpret as facial features, such as a human eye (upper-center), and maybe an ear. Also a mouth & chin, perhaps? Cheekbones?

I see that but, to me, the whole thing kinda looks like a blue version of the Eye of Sauron.

 

[collinsmark]

It's Mars season again!

Here's my latest Mars image from the back patio:

Mars. Midpoint timestamp: 2022-11-30 08:51.0 UT.

Mars is at its closest approach right now. So if you if you want to get a good look at Mars, now is the time. Any time this week is good (see more below about the occultation event), but now is a good time.

Mars reaches opposition on December 7th (or the morning of December 8th, depending on your location)

If you're wondering why closest approach doesn't quite align with opposition, it's because Earth's and Mars' orbits are elliptical and are not exactly on the same plane.

The Moon will occult Mars on the evening of Dec. 7th or morning of Dec. 8th, depending on your location, for much of the Northern Hemisphere. So mark you calendar for that!
https://www.scientificamerican.com/article/on-december-7-the-moon-will-photobomb-mars/

Image details:

Equipment:
Meade 10" LX200-ACF fork mounted on an equatorial wedge.
Explore Scientific 1.25" 3x Focal Extender
ZWO ASI585MC camera

Software:
FireCapture (for acquisition)
AutoStakkert! (for lucky imaging processing and stacking
RegiStax (for wavelet sharpening)
PixInsight (for miscellaneous image processing)
WinJupos (for derotation and additional stacking of sharpened images)

Acquisition:
Exposure time per frame: about 9 milliseconds.
Eight separate, 2 minute videos were taken.
Seeing: Nothing to write home about.

 

[DennisN]

Mars is at its closest approach right now. So if you if you want to get a good look at Mars, now is the time. Any time this week is good (see more below about the occultation event), but now is a good time.

Thanks for the advice!

I would have a go at looking or even try photographing it (even though I expect it to be just a pretty small dot with my equipment). But the skies here go in fifty shades of grey, and they've done so for quite a while. And the forecast looks crappy too.

By the way, I've currently got a 3x teleconverter on the way to me. I don't know how it will perform, but we'll see.

 

[bruha]

Hi, beautiful mage (what is magnification?)

 

[bruha]

(unfortunately very bad weather nowadays here in BOHMERWALD)

 

[collinsmark]

Hi, beautiful mage (what is magnification?)

Magnification is not well defined when a sensor or film plane is used (i.e., photography). Sort of. Allow me to explain.

Magnification is well defined with a telescope/lens and an eyepiece, where everything is purely optical from start to finish. But when the eyepiece is replaced with a sensor, things are not so clear.

That said, we can do some back-of-the-envelope hand-waving, and say that if you have a 35 mm camera (36×24 mm sensor or film plane), then a lens with a focal length of 50 mm gives "standard" magnification, because it approximates the perspective of the human eye. Sort of.

So with a 36×24 mm sensor, a lens with a focal length of 100 mm is kind of like 2X magnification (sort of). A 200 mm lens is like 4X (sort of).

But if your sensor size is smaller, you'll also need a smaller focal length lens for the same equivalent "magnification." For example, if you had a 18×12 mm sensor, then a 25 mm lens is standard and a 50 mm lens is 2X. (Sort of.)

------

My setup:

The manufacture claims that my telescope model has a native focal length of 2540 mm, but I've characterized it myself, and it's closer to 2880 mm.

The Explore Scientific 3X focal extender brought the effective focal length to around 8640 mm.

So optically, that would bring the equivalent "magnification" (so to speak) of about 173X above that of a 50 mm lens. But I wasn't using a 36×24 mm sensor, so we're not finished yet.

The ZWO ASI585MC sensor has a pixel size of 2.9 micrometers (per pixel), and I cropped the image to 768×650 pixels before posting to PF. That makes the effective, cropped image size of 2.23×1.89 mm on the sensor plane.

So my cropping alone had an effective 36/2.33 = 15.45X of "magnification."

So, in a certain sense, the image posted here on PF corresponds to around 172.8×15.45 = 2670X magnification, sort of.

 

[bruha]

Thank you very much for detail explanation -I overaly understadt and give me sense. (At least seems me that image respond to this magnification). I was trying Mars as well but not quite succesfull.
Thank you and lot of succes

 

[bruha]

This is my Mars...

 

[collinsmark]

IC 1795 (also designated as NGC 896), the Fish Head Nebula (sometimes called the Fishhead Nebula), in the constellation Cassiopeia, caught from my back patio in November, 2022.

The Fish Head about 6000 light-years away, roughly.

When examining or studying images of IC 1795, it is customary to listen to the Fish Heads music in the background. Here is a link to the music.

"Fish Heads," by Barnes and Barnes (first released in 1978), to be listed to in the background.

Equipment:
Meade 10" LX200-ACF fork mounted on an equatorial wedge.
Starlight Instruments FTF2008BCR focuser modified for electronic focusing.
Off-axis guider (OAG) with ZWO ASI174MM-mini guide camera.
Baader 3.5-4 nm Ultra-Narrowband filter set.
ZWO ASI6200MM-Pro main camera.

Software:
Nighttime Imaging 'N' Astronomy (N.I.N.A.)
PHD2 guiding (of course)
PixInsight
Topaz Labs Sharpen AI

Integration:
Bortle class 7 (maybe 8 ) skies
All subframes binned 3×3
SHO mapping
SII: 78×10 min = 13.33 hrs
Hα: 65×10 min = 10.83 hrs
Oiii: 80×10 min = 14.83 hrs
Total integration time: 39.00 hours

 

[DennisN]

An amazing photo:

Orion, the Moon, and Earth in one photo (NASA)

Source: https://arstechnica.com/science/202...d-the-moon-returns-an-instantly-iconic-photo/

 

[DennisN]

And a movie clip with an eclipse of the Moon and Earth (!) here:

Orion views an eclipse of the Moon and Earth

(Nov. 28): On flight day 13, Orion continues to distance itself from Earth and the Moon, looking back on our home planet and lunar neighbor as the two begin to eclipse in this video taken at 10:34 a.m. CST.

Link to video clip: here (NASA Johnson)

 

[Andy Resnick]

The weather has been uncooperative lately, so I'm posting this (hopefully) intermediate image:

That's a composite image of Neptune, taken from 10/22 (bottom) through 12/4. As you can see, Neptune was moving apparently retrograde and was nearly switching direction by 12/4, here at 200%:

One piece of data I can extract from the image is the rate of change of angular position, when I had consecutive nights of viewing:

From this data, I could generate the apparent angular position as a function of time. I don't know if I have enough information here to deduce Neptune's orbital parameters- it seems to be that I should be able to at least approximate it, especially in earth-centered coordinates. If anyone knows how to analyze this data, I would be interested in learning!

Interestingly, all four planets I have been imaging (Neptune, Uranus, Jupiter, Mars) are, or until recently were, moving (apparently) retrograde. We'll see how Uranus's image turns out...

Another piece of information we could obtain from Neptune's image: initially, Neptune appears to move in a straight line, but then deviates as it approaches switching over from retrograde to prograde motion. I don't really understand the out-of-plane motion, but it appears to be a universal feature- check out this person's images.

 

[Devin-M]

 

[russ_watters]

Acquisition:
Exposure time per frame: about 9 milliseconds.
Eight separate, 2 minute videos were taken.
Seeing: Nothing to write home about.

Great pic! So, are you stacking like 50,000 frames to get that?

I have comparable equipment but your results are better and I'm trying to figure out why...

 

[bruha]

Hello, it is very interesting -but you made graph just from four points? -which ones from 17 positions on your image?

 

[collinsmark]

Great pic! So, are you stacking like 50,000 frames to get that?

I have comparable equipment but your results are better and I'm trying to figure out why...

My frame-rate was a bit lower than expected (I still haven't figured that out), at only around 26 FPS. It might be ZWO's driver for the ASI585MC is not playing nicely with FireCapture (maybe the camera is debayering prior to USB transfer?) Anyway, I was expecting about 3x the FPS. To make matters worse, FireCapture would crash on most region of interest (ROI) settings I tried. So, long story short, until I get things figured out, frame-rate was only 26 FPS.

So, 26 FPS times 16 minutes \approx 25,000 frames. But only 70% of the frames were stacked (per lucky imaging parameter), making a total of approximately 17,500 frames stacked.

Exposure time per frame was set at around ~9ms. This is done to reduce atmospheric seeing. The idea is to keep the exposure time short, to get a quick shapshot of the target, before the seeing has a chance to cause motion blur.

Then just get lots and lots of frames, and let the Central Limit Theorem take care of the read noise.

Significant sharpening is required for this method in post processing. That is normal and expected. The information is in there, it just needs appropriate sharpening algorithms to coax it out.

(Edit: and WinJUPOS was used as an intermediate step. AutoStakkert! was used to produce 8 separate images. Each of those images were sharpened separately with RegiStax (actually, first the colors were separated, and then each color was sharpened separately, then recombined into an RGB image after RegiStax sharpening). The same parameters were used for all 8 images. Then, those 8 sharpened images were de-rotated and combined in WinJUPOS.)

 

[Andy Resnick]

Hello, it is very interesting -but you made graph just from four points? -which ones from 17 positions on your image?

I only used data points generated when I imaged on consecutive nights (images 24 hours apart) to reduce the ambiguity about when the angular velocity was measured. Yes, I could synthesize more data points since I know the dates I acquired the images, but I have limited time to goof around.

 

[bruha]

Thanks its clear

 

[russ_watters]

So, 26 FPS times 16 minutes \approx 25,000 frames. But only 70% of the frames were stacked (per lucky imaging parameter), making a total of approximately 17,500 frames stacked.

Exposure time per frame was set at around ~9ms. This is done to reduce atmospheric seeing. The idea is to keep the exposure time short, to get a quick shapshot of the target, before the seeing has a chance to cause motion blur.

Whelp, that was easy enough, thanks! This is one of my best ever, using what is a fairly new camera for me, a QHY290C. 20,000 frames, 75% stacked; that's about 5x more than I've typically used and it seems to make a big difference. It also greatly simplifies the processing to use a color camera that captures so fast. I'm getting a whopping 126 fps at 6ms exposure. Seeing was just mediocre, 3/5.

I'm using a similar but simplified workflow: FireCap -> AutoStakkert -> Registax (wavelets, rgb align) -> Photoshop (color adjustment, blur, unsharp mask). I'm sure there's more in there if I can pull out of it.

 

[bruha]

Excelent
What is your telescope gear?

 

[russ_watters]

Excelent
What is your telescope gear?

Thanks! Celestron C11 and QHY 290C (color) camera.

 

[bruha]

Very good gear Thanks too

 

[DennisN]

New impressive eye candy from JWST:
(and I think it was interesting to read the comments in the article from various scientists of the PEARLS team)

Webb Glimpses Field of Extragalactic PEARLS, Studded With Galactic Diamonds

NASA’s James Webb Space Telescope has captured one of the first medium-deep wide-field images of the cosmos, featuring a region of the sky known as the North Ecliptic Pole. The image, which accompanies a paper published in the Astronomical Journal, is from the Prime Extragalactic Areas for Reionization and Lensing Science (PEARLS) GTO program. [...]

Article: Webb Glimpses Field of Extragalactic PEARLS, Studded With Galactic Diamonds (NASA blog, December 14, 2022)

Photo:

A swath of sky measuring 2% of the area covered by the full moon was imaged with Webb’s Near-Infrared Camera (NIRCam) in eight filters and with Hubble’s Advanced Camera for Surveys (ACS) and Wide-Field Camera 3 (WFC3) in three filters that together span the 0.25 – 5-micron wavelength range. [...]"

Photo source: here.
Other photo versions (low to high resolution) are available here.

 

[collinsmark]

The Heart Nebula (IC-1805, SH 2-190) core, taken from my back patio in late-November and December, 2022.

The image here is just of the center/core of the heart nebula, since the entire nebula is too big (angular wise) for my Meade to capture the whole thing. If you were to see the entire nebula, it has the shape between that of a Valentine heart and the tell-tale human variety that you would carefully stash under your floorboards, "I felt that I must scream or die! — and now — again! — hark! louder! louder! louder! louder! —"

Here's a crop of the full image.

Equipment:
Meade 10" LX200-ACF fork mounted on an equatorial wedge.
Starlight Instruments FTF2008BCR focuser modified for electronic focusing.
Off-axis guider (OAG) with ZWO ASI174MM-mini guide camera.
Baader 3.5-4 nm Ultra-Narrowband filter set.
ZWO ASI6200MM-Pro main camera.

Software:
Nighttime Imaging 'N' Astronomy (N.I.N.A.)
PHD2 guiding (of course)
PixInsight (with RC-Astro PixInsight plugins)
GIMP

Integration:
Bortle class 7 (maybe 8 ) skies
All subframes binned 3×3
SHO mapping
SII: 75×10 min = 12.50 hrs
Hα: 67×10 min = 11.17 hrs
Oiii: 75×10 min = 12.50 hrs
Total integration time: 36.17 hours

 

[timmdeeg]

What a wonderful image!!! Congratulations.

 

[collinsmark]

Portion of the California Nebula (NGC 1499) observed from my back patio in San Diego, California; December, 2022.

The California Nebula (NGC 1499) can be seen in the constellation Perseus, not too far from Taurus. Its large angular size makes it one of the bigger emission nebula in the night sky (from our perspective). For an emission nebula, it has a low surface brightness (being so spread out).

NGC 1499 is roughly around 100 light-years across and about 1000 to 1500 light-years away (sources vary). The image shown here is only a small section of the California Nebula.

Equipment:
Meade 10" LX200-ACF fork mounted on an equatorial wedge.
Starlight Instruments FTF2008BCR focuser modified for electronic focusing.
Off-axis guider (OAG) with ZWO ASI174MM-mini guide camera.
Baader 3.5-4 nm Ultra-Narrowband filter set.
ZWO ASI6200MM-Pro main camera.

The California is difficult to see visually.

Software:
Nighttime Imaging 'N' Astronomy (N.I.N.A.)
PHD2 guiding
PixInsight (with RC-Astro PixInsight plugins)
Topaz Labs Sharpen AI

The California is filled with gas and dust. Some of it's ionized.

Integration:
Bortle class 7 (maybe 8 ) skies
All subframes binned 3×3
SHO mapping
SII: 55×10 min = 9.17 hrs
Hα: 80×10 min = 13.33 hrs
Oiii: 66×10 min = 11.00 hrs
Total integration time: 33.5 hours

 

[Devin-M]

Casper the Friendly Ghost Nebula (Messier 78 / NGC 2068)

Details:

Meade 2175mm f/14.5 Maksutov Cassegrain with Nikon D800 on Star Watcher 2i equatorial mount
17x stacked 90 second exposures @ 6400iso + 19 dark calibration frames + 5 flat calibration frames
RAW NEF files converted to 16bit TIFs in RawDigger
Stacking in Starry Sky Stacker
Final Histogram Stretch in Adobe Lightroom

 

[Devin-M]

Central Core of Andromeda Galaxy - distance: 2.5 million light years
(All the individual visible stars are foreground stars within the Milky Way)
Meade 2175mm f/14.5 Maksutov Cassegrain with Nikon D800 on Star Watcher 2i equatorial mount

 

[bruha]

Hi, it s amazing image, . Can I ask what is magnification?
thanks and lot of succes

 

[Devin-M]

Well, if we treat a 50mm DSLR lens as 1 magnification then the 2175mm telescope would be 2175mm/50mm=43.5x magnification. On a 35mm wide sensor camera, a 50mm lens has a 40 degree field of view so the 2175mm telescope has a roughly 0.91 degree field of view.

 

[bruha]

Ok, thanks.

 

[Devin-M]

That was the simple answer…

…However, that’s assuming you’re focusing at infinity and fixed distance from the subject like a star or nebula. If you factor minimum focus distance and being able to move the camera closer to the subject, among Nikon lenses, the 105mm macro lens will give you better magnification than my 2175mm telescope. Thats because the 105mm has a closer minimum focus distance so you can bring the camera closer to the subject while being in focus, and when you do that you can make an in focus object appear larger on the sensor with the Nikon 105mm lens than you can with, say, a 2175mm telescope. The 105mm won’t have more magnification than the 2175mm telescope when the in focus subject is the same distance from both cameras, however. At the minimum focus distance, the 105mm Nikon lens can achieve 1:1 reproduction ratio meaning a 1cm object will have a 1cm image of itself projected onto the image sensor. But suppose we could transport the 105mm and 2175mm lenses to an exoplanet and put each camera at the minimum focus distance from the surface, in that case the 105mm lens will provide more detail. At my 2175mm telescope’s minimum focus distance it will have ~20.7x more detail than the 105mm if they are both the same distance from the subject, but the 105mm’s minimum focus distance is much less than 1/20th the 2175mm’s minimum focus distance, hence the 105mm can provide more detail on close subjects.

 

[Devin-M]

Center (RA, Dec): (83.801, -5.462)
Center (RA, hms): 05h 35m 12.151s
Center (Dec, dms): -05° 27' 42.583"
Size: 51.8 x 34.5 arcmin
Radius: 0.518 deg
Pixel scale: 3.88 arcsec/pixel
Orientation: Up is 88.2 degrees E of N
Equipment: Meade 2175mm f/14.5 Maksutov Cassegrain with Nikon D800 on Star Watcher 2i equatorial mount
Exposures: 137x 30seconds, 1600iso + 19 darks, 40 flats, 20 bias
Software: Stacking: Siril, Histogram Stretch: Lightroom

 

[Devin-M]

New Technique:

Previous Technique (same data):

I realized the way I've been processing my data for years has been degrading the photos so I've been reprocessing some of my old shoots with the new technique. I'd never been able to get really accurate color before, for example in this photo I'd never been able to show the faint blue stars in the outer fringes of the Andromeda galaxy. The mistake I'd been making was converting my RAW NEF files from my Nikon D800 DSLR into 16 bit TIFs with Adobe Lightroom before stacking (my old stacking software couldn't read the RAW files). What I didn't realize is that conversion process adds noise to the RAW files resulting in incorrect colors after stacking. Now I use Siril on MacOSX to do the stacking, as it is able to stack directly from the RAW files resulting in much better color in the final image, and it outputs to a 32 bit FITs file. Next I use Siril to convert the 32 bit FITS to 32 bit TIF, then I use Adobe Lightroom to do the final histogram stretch.

Equipment: Nikon 300mm f/4.5 with Nikon D800 on Star Watcher 2i equatorial mount
Exposures: 59x 117seconds, 800iso + 56 darks, 28 flats, 30 bias
Software: Stacking: Siril, Histogram Stretch: Lightroom

Center (RA, Dec):	(10.681, 41.262)
Center (RA, hms):	00h 42m 43.419s
Center (Dec, dms):	+41° 15' 44.071"
Size:	2.47 x 1.65 deg
Radius:	1.485 deg
Pixel scale:	11.1 arcsec/pixel

 

[Drakkith]

I was hoping to get a good image of Thor's Helmet (NGC 2359) tonight to show off, but due to flexure issues I couldn't do any guiding, so I called it a night soon after starting a headed in out of the cold to eat some hot tortilla soup. So here's a picture from the ESO instead:

I don't know when I'll break out the telescope next. It's become such a huge source of frustration that I sometimes think about getting rid of it all.

 

[timmdeeg]

That's a wonderful nebula, I put it on my to do list.

Frustration, yes well known. Within the last month's we had 2 to 3 times clear sky only and at these occasions when I was ready with alignment dew issues started and I had to give up.

I don't know what "flexure issues" means, is this a mechanical problem?

 

[Drakkith]

I don't know what "flexure issues" means, is this a mechanical problem?

Flexure occurs when imaging with one telescope and guiding with another telescope that is typically attached to the first. There is a slight amount of flex in each telescope and its mountings and attachments, which is different between the two telescopes. One flexes more than the other basically. So when guiding this difference in flex makes the imaging telescope shift off target slightly even though the guide scope stays locked on its guide star.

Long story short, things flex and it makes blurry images.

 

[collinsmark]

I don't know when I'll break out the telescope next. It's become such a huge source of frustration that I sometimes think about getting rid of it all.

I can appreciate/empathize with the frustration.

I started with astrophotography about 15 years ago. I kept up with it for about a year, with only limited instances of success. Then I gave it up for awhile, sort of. It was just so much work and effort, just to have things dashed by vibration or tracking or flexure or dew or unexplainable gradients or god-knows-what.

Rare instance of something I would call a "success," from back in 2008.

While I stopped setting up the telescope regularly, it was always in the back of my mind. It was at about the same time I discovered Physics Forums. And at that period of my life I found that working through problems in physics (helping students with homework sort of stuff) was as gratifying, if not more-so, than mucking with the telescope and the dew and all the layers of failure and frustration.

But the telescope was always there in the background (literally). I was always keeping an eye on new developments in backyard astronomy technology (e.g., the rise of lower noise CMOS sensors), as well as ways to improve my techniques. As the years progressed, it became apparent that a good chunk of my gear (e.g., old Meade camera) became obsolete. But I kept studying astrophotography none-the-less, even if I wasn't actually doing it physically.

Then, finally, a couple years ago I bit the bullet and made some equipment upgrades, thrusting me deep down the astrophotography rabbit hole. And a result, like many before me, it's overtaken my life and I can't get out.

The telescope, the camera and I have become bounded by a fortified garrison of dovetail adapters & plates, mounting rings, field flatteners, reducers (a.k.a., telekompressors), dew straps, and T-thread adapters (M42, M48 and more). Mentally speaking, stacking techniques, image processing algorithms and the Central Limit Theorem lord over my existence. There is no escape. Thanks to all the studying, however, at least I know where I am.

The upside is my astrophotos have shown some limited signs of improvement.

A little bit better image from late 2021.

I don't know what "flexure issues" means, is this a mechanical problem?

Yes, flexure is a mechanical problem. It means that due to gravity*, the guide camera system gets pulled slightly differently than the main camera system. This causes unwanted drift in the main image, as both systems track across the sky (to counteract the Earth's rotation).

*(while it's usually due to gravity, it can also be caused by improper cable management.)

It's the reason I try to avoid guidescopes when possible, and use off-axis guiders (OAGs) instead. This is particularly true for me when imaging with long focal length setups.

 

[timmdeeg]

Thanks for explaining flexure. If I understand it correctly it isn't a problem of the mount driving system but of a non rigid connection between the autoguiding camera and the telescope. Its hard to imagine though, my StarAid Revolution is fixed on the tubus by screws such that no relative motion is possible due to gravity.

I started in 1998 deep sky visual observing always thinking that I can watch the nicest astro images any time. It needed a particular experience to convince myself to start astrophotography. That happened just one year ago. And I had a hard time to learn all these details to do it and to process the pictures. But now its almost an obsession.

 

[collinsmark]

Thanks for explaining flexure. If I understand it correctly it isn't a problem of the mount driving system but of a non rigid connection between the autoguiding camera and the telescope. Its hard to imagine though, my StarAid Revolution is fixed on the tubus by screws such that no relative motion is possible due to gravity.

Flexure isn't necessarily just a issue with the guide camera to telescope connection (although that could be one potential cause). It could be any differential flexing. Another example could be slight sag caused by the weight of the comparatively heavy main camera with respect to the optical tube assembly (OTA), without a corresponding sag on the guidescope and guide camera system. Another potential cause is having USB cables (or any cables) dangling down causing torque on whichever cameras they're connected to. With long focal length systems, it doesn't take much.

 

[timmdeeg]

Flexure isn't necessarily just a issue with the guide camera to telescope connection (although that could be one potential cause). It could be any differential flexing. Another example could be slight sag caused by the weight of the comparatively heavy main camera with respect to the optical tube assembly (OTA), without a corresponding sag on the guidescope and guide camera system. Another potential cause is having USB cables (or any cables) dangling down causing torque on whichever cameras they're connected to. With long focal length systems, it doesn't take much.

ah I see, multiple possible reasons. Then it might be not trivial to detect the origin of flexure. Thanks!

 

[Devin-M]

Isn’t flexure not a problem after the images are stacked? I thought the registration stage where each image is adjusted for X, Y and rotation differences during the stacking process would take care of it. I don’t use guiding and consequently during a 2 hour imaging campaign I expect some field drift but that doesn’t seem to significantly affect the final output in my experience.

https://free-astro.org/index.php?title=Image_registration

“Registration is the process of aligning a set of images so that they can be used as if taken from the same point of view, in astronomy this applies to aligning images in order to be able to stack them.”

 

[Drakkith]

Isn’t flexure not a problem after the images are stacked?

Flexure blurs individual exposures (at least for me it does) so stacking does nothing to help.

 

[Drakkith]

It's the reason I try to avoid guidescopes when possible, and use off-axis guiders (OAGs) instead. This is particularly true for me when imaging with long focal length setups.

Indeed. I was using a 2000 mm focal length OTA as my imaging scope last night. My much shorter focal length refractor doesn't seem to suffer from flexure as far as I can tell. I actually made sure to get an OAG when I last upgraded my camera to a new Atik ccd, but the OAG requires a specific Atik guide camera. Which I didn't find out about until I got it in and tried to attach my Orion guide camera.