Delboy_Hog

17 hours ago, pete_l said:

Just by eyeballing the left side, there appears to be 6 separate "dithers". Between them they make up about 1/14th of the frame. Normally a dither would be 2 or 3 px per frame.

I would suspect that if the polar alignment wasn't pretty good, there would be some field rotation which is tricky for a stacker to account for, since it is only looking for uniform X,Y displacements across the field. Not ones that vary due to curvature.
How long are you allowing the mount to "settle" back into its tracking after each dither?

Thanks for this Pete, that's really helpful.  I'll definitely be going for much smaller dithers next time around.

Your suspicion about my polar alignment could be spot on too.  I guess field rotation over that kind of time-frame would explain why the individual subs had no trailing, but the final product wasn't spot on...  I'm interested in this - if there had been field rotation, that would be reflected in the "angle" column of DSS, is that right?  I noticed there were some differences in the figures in that column when the frames were stacked.  Probably only about half a degree over the time period these frames were taken in - would that be enough to give the stacking a hard time, do you think?

The Synguider appears to be pretty good at continuing where it left off, once you 'resume' from its previous calibration run, so I've only been allowing a few seconds.  But then I hit restart on the intervalometer, which gives it a few more seconds to settle I suppose.  It always feels quite time-consuming at the time, but I've no doubt it's worth it for the noise reduction it brings. 

Thanks again!

Derek

I don't know what's causing the problem...although I think it might be the images rather than the stacking.  Either way, I'd be **really** grateful for your help!

Short version of the question: 

How can a series of seemingly ok individual photos without any obvious signs of trailing, come out of DSS in such a calamitous mess!?

Longer version:

I've been trying to capture as much of the Veil nebula as possible in a single frame, with the Canon 6d, Skywatcher ED80, HEQ5.  5 min subs at ISO 1600, guided by a Skywatcher Synguider.  Utterly fabulous patch of the sky, I always think!

All of the individual light frames look reasonable (albeit to my admittedly un-trained eye) - example frame below.  But stacking them results in something that looks like one of those hidden / 3d image things that make you feel a bit sick if you look at them for too long!!  On the plus side, the calibration frames seem to be evening out the illumination across the field of view, and got rid of the dust-bunnies!

My guesstimate of what's going wrong:

1) I gather the 6d is not a great match for the ED80 because the chip isn't fully (evenly?) illuminated.  I may have to accept that the corners will always be ropey, and be prepared to crop significantly?  Can flats do anything about the star shapes, or are they all about the illumination across the field of view?

2) To compound that, in my over-zealous attempt at dithering, I attempted to manually dither the frames (stop the autoguider, tap the arrow on the handset to move the field of view slightly, restart the guider, start the next frame), but I wonder if some of the movements I made were too big.  I read that only the tiniest of movements is required, so have the bigger movements made it harder for DSS to stack those streaky corner stars?  (e.g. if it's trying to stack a seriously sausagey corner star from 1 frame with a non-corner, non-streaky corner star from a different frame, it's going to struggle?

Example of the light frames:

And the images: straight out of DSS, no processing...

Lights and calibration frames - check out those corners!!

Light frames only, and took the lowest scoring frames out of the stack...about the best of a bad bunch - though the corners (especially the bottom left) are still a mess...still, I could probably process a crop of this?

Last one - a hideous attempt at using Kappa Sigma process on the light frames - it appears to have focused on aligning the stars in the corner, rather than in the middle....appears to have worked on the satellite trails though!!

Some bonus questions for any DSS experts out there:

1) I gather the "Kappa-Sigma" setting in DSS is the best approach to remove satellite trails - is that Kappa Sigma or Median Kappa Sigma?

2) And is that just on the light frames, or do you apply that approach to the calibration frames as well?

3) And do people just use the default settings when you choose one of these, or do you change the Kappa figure or the number of iterations? 

Many thanks for any light you can shed on all of this for me! 

Derek

Been practising the set up and polar alignment of my Star Adventurer through the short nights in the hopes I can get started on some proper imaging now that the nights are getting a little longer.

This was a (cropped, but otherwise unprocessed) 7 min exposure of the tail of the Plough (Alkaid, Mizar / Alcor and Alioth), taken just a few days after the longest day - admittedly I'm only using an 85mm lens at the moment but I'm still delighted with the tracking capabilities of this little mount!  Check out M51, M101 and M63 all in frame!  Think I must have just cut of M106, which is a bit of a shame...

Getting some curious star shapes in the corners with this lens (could I ease that by stopping it down a bit, do you think?) but otherwise it's looking good for some seriously deep Cygnus time over the next couple of weeks!  7 minute exposures with anything approaching f1.4 is hugely exciting!

Star Adventurer

Canon 6d

Samyang 85mm f1.4 stopped down to about f2

ISO 100 (to prevent total over-exposure!)

1 x 7 minute exposure

Oh that's interesting - many thanks Freddie, I'll take a look!

Hi all,

A little while back, I took a sequence of photos of the sun, with the intention of doing a time-lapse.  Unfortunately, before my planned sequence of photos had finished, I had to move my mount and scope because the sun was about to go behind a tree (poor planning on my part, I know!).  The problem is that in moving it, I loosened the clutches on the HEQ5 mount, so the camera was (unbeknown to me at the time) rotated a few degrees out from where it had been previously.  When I've come to making the time-lapse, there's a 'jump-point' where the features on the sun's surface in the animation jump to a slightly different place.

To add to my problems, the features in Windows Photos and the various online tools that can rotate an image by just a few degrees, resize the image in doing so....so I can correct the angles so that the features appear in the same place throughout, but now the jump-point in the time-lapse is a significant re-sizing of the sun, which looks equally weird...

Has anyone made this mistake before, and does anyone know if / how it's possible to rotate a photo by just a few (probably 15 or so) degrees without re-sizing the object in the photo in doing so?

Many thanks for any light you can shed on this for me! ☀️ 

Derek

15 minutes ago, Anthonyexmouth said:

 ive only got the kit 18-55 and a canon 55-250. if i just used the lenses what range of targets would i have.

Having the star adventurer has actually given me a real kick of enjoyment recently from the wider-field (than most telescopes) images.  Andromeda will look lovely at 250mm (as well as shorter focal lengths, which might enable slightly longer subs) as will M45 I'd have thought, and even with relatively short exposures you'll be able to get some cracking images in and around Orion anywhere within your 55 - 250mm range.  At the lower ranges of that lens, you can get some interesting shots with 2 or more of the better known galaxies in.  At the 50 - 85mm range you'll get Andromeda and M33 in the field which is pretty spectacular to see, and you'll similarly get M51 and M101 in if you focus somewhere between the stars Alkaid and Mizar in the plough.

If in doubt, I'd recommend a quick peek in the images section of this forum, or the website "Astrobin", where you can see what other people with similar kit are imaging.  You also get a good idea of what kind of camera settings / exposure lengths etc that you'll need to think about using.

Hope that helps!

Great work Jonas.  An incredible amount of effort and dedication must have gone into this, and you've created a truly remarkable outcome, so congratulations and thanks for sharing! 

Dare I ask...what's your next project going to be?! 

dew heaters should be set to be literally just a tiny bit above ambient. the metal should not be warm to touch just used enough to 'take the edge off'.

I set mine very low and leave them going long before i go out. To the touch it feels like they are not working, but the lack of any dew tells a different story.

Ah, thank you, yes that makes sense.

Seems mad doesn't it... We have to wait for scopes to cool down to ambient to get best performance. And then we warm the front to keep dew off!

I think the mad part is that we're out in the dark in these cold damp conditions in the first place!

However, this does raise an interesting point, and while I guess the answer lies in the number of people who are pro-heated strips here, I curious - would having a source of heat not create that awful shimmer that you get from having anything warm in the line of sight? Or do the heated strips not get so toasty as to cause this problem?

I recently got an Astrozap dew shield for a birthday prezzie and it makes a huge difference, though, as has already been pointed out, spending a long period of time on the same object, especially if it's high in the sky, will probably still encounter dew problems.