ollypenrice

1 hour ago, Louis D said:

@DaveG64 Are you asking about a field derotator?  They're normally used with alt-az mounted scopes.  If you're using a RA-Dec aligned mount, you shouldn't need one.

The built-in rotator is there for framing purposes.  If you're alt-az mounted, it could still be used for this purpose, with the derotator following it somewhere in the rest of the focuser chain.

Ah yes, perhaps the OP is talking about a field de-rotator for long exposure alt-az imaging? I would just say 'Don't.' Don't throw money at de-rotators or wedges, just buy a proper equatorial mount. I'm not sure that there is any guiding sytem for alt-az de-rotated mounts, at least for amateurs.

Olly

Preprocessing, APP. Post processing, a bit in Pixinsight and a lot in Photoshop. I also use Registar, particularly for composite (multi-scope) images. I consider StarXterminator and NoiseXterminator to be absolutely essential.

Olly

One scope cannot do everything and a good beginner visual setup is likely to be totally different from a good beginner photographic one.  Narrow down your objectives and priorities.

Olly

So it looks as if the camera itself is very slightly vignetted. I've never tried this experiment so I don't know how my cameras would behave. To be honest, I don't see it mattering because the variation is minor and  this vignetting will find its way into the final flats (shot through the optics) anyway.

By the way, you posted some ABE-processed images earlier. What we see in them is a common ABE fault which regularly affects galaxy images. ABE puts background sky markers too close to the galaxy (or roundish nebula in your case) and treats faint outer glow as background sky. When applied, it lowers the pixel values close to the object and creates a dark region around it. I only use ABE when there is really no workable way to identify background sky anywhere in the image, as often happens in very deep stacks.

Olly

I've no experience of motorized rotators but find myself wondering why you might want one. I only ever shoot with the chip sides parallel with RA and Dec, so that's a choice between landscape and portrait.  Why do I do this?  Because, if I want to go back at some later stage and add more data, I can do so very easily.  I discovered that reproducing an arbitrary angle is a bit of a nightmare. I find that this hardly ever has any consequences for framing and it avoids complications with flats and makes troubleshooting easier. (Guiding, tilt adjustment, etc.)

Olly

I moved from Derbyshire to a deliberately-chosen dark site in the part of France identified as the best by professional astronomers' site-surveys going back to the thirties. I wouldn't know where to start, really, in making a comparison. In Derbyshire I never saw M101 at all.  Here I see it in a budget finderscope. I could never see the Rosette, with or without filter. Here I can see it either way in anything between binoculars and a 20 inch. I've seen the Gegenshein, naked eye, here but, on the other hand, I've never seen M33 unaided.

While both visual and photographic astronomy are outstanding, here, they both take second place to the simple fact of living under an unpolluted sky. Even if we're just driving back from a restaurant, or I'm nipping out to fetch some firewood, the night is night, it's dark and starry. It feels like the difference between breathing exhaust fumes and oxygen.

Olly

Fascinating stuff. The Samyang-RASA is a demon pairing for combining widefield and high res. Do you combine them in a starless state? I tend to do this then apply Samyang-only stars for consistency.

Olly

Lovely clean result.

Olly

9 hours ago, Icesheet said:

The depth the RASA has achieved in this image is amazing. Given it's a significant crop, the level of detail is very good too, but I wonder if you plan to use the TEC140 data you have here? Whilst I appreciate the depth the RASA has achieved I'm more drawn to the level of detail in TEC image,but why compromise when you can have the best of both worlds? Give the people what the want @ollypenrice!

OK, thanks for the encouragement! I tried again to exploit the TEC data in the inner galaxy and came up with the image below. To my surprise it was easy to upsample the RASA image to the scale needed for the TEC resolution to show.

Full size is here: https://ollypenrice.smugmug.com/Other/Galaxies/i-psSP6gB/A

Olly

4 hours ago, Icesheet said:

The depth the RASA has achieved in this image is amazing. Given it's a significant crop, the level of detail is very good too, but I wonder if you plan to use the TEC140 data you have here? Whilst I appreciate the depth the RASA has achieved I'm more drawn to the level of detail in TEC image,but why compromise when you can have the best of both worlds? Give the people what the want @ollypenrice!

  This is just what tried to do and have done many times before, but I haven't yet managed to make it work this time. In fact, scaled to fit the RASA image, there is not all that much more resolution in the TEC than the RASA. If I were to rescale in the other direction, making the RASA image larger, I'd be lifting the noise in the RASA and it's already on the ragged edge of the possible stretch. It doesn't help that the TEC field of view stops short of the upper spiral arm.

If I can come up with any new ways of making the composite I'll give them a try.

The obvious solution would be a RASA 14.... If the people would like to give Olly one, he'd be most willing to accept it! 👌

Olly

Edit: there is another problem, too. The TEC's resolution requires dynamic range, ie contrasts within the central spiral arms. In the ultra-deep RASA image a lot of the lower dynamic range has been used by the faint outer streams so the dark stuff in the central spiral is brighter and can't be as contrasty. I'd be in danger of having the tidal streams brighter than the dark regions between the bright spiral and, in reality, they are not.

You should be able to get far more of the long tidal tail to show, though it will run out of the frame on this crop, I think. It will be there in the data. If you have Photoshop,  just go to Image-Adjustments-Equalize and it should leap out. You can't just use that as a processing technique but it will show what you have in the data.

Olly

You wouldn't go far wrong with this, on the astrophotography side.  https://www.firstlightoptics.com/books/making-every-photon-count-steve-richards.html

Like most things in life, DSLR photography is best approached by thinking things through from the basics. There are really not so many of those and this is, for me, the big one:

Understanding F stops and light cones. https://www.dpreview.com/forums/post/63155522 When a lens is wide open it lets in more light and therefore shortens exposure time, freezing fast action, but the steep light cone has a shallow depth of field meaning only selected parts of the image can be in focus. This can be good or bad, depending on the photographer's intentions. A stopped down lens has a greater depth of field but lets in less light and, therefore, needs longer exposure - which can introduce motion blur.

If you were to go out with a basic DSLR and experiment with this single set of related parameters, and really get the feel for them and how they play out, you'd be self-educating very effectively, I think, and would have a grounding for further learning.

For land and sky photography, check out the free Sequator software.  https://www.startools.org/links--tutorials/free-image-stacking-solutions/sequator

On image processing and U-tube tutorials, the instant you hear the presenter say, 'I just play with the sliders till I like what I see,' turn them off and never go back to them! 

Most astrophotographers are autodidacts and the best ones are the best because they seek to understand before they act.

Olly

Just for info, an all-new RASA 8 image has gone much deeper than this.

Olly

A deep dive with Paul Kummer (capture and pre-processing.) This had 9 hours in the RASA 8, equivalent to about 40 hours in a fast refractor of comparable focal length. After 3 hours we were going well but 9 hours brought out more structure and, of particular interest, the uppermost spiral arm winding anticlockwise in this orientation. This arm is a new one to me and was an exciting find in the processing.

Edit: please scroll down for a version using TEC140 data to enhance the core.

This is a close crop and is presented at one-to-one here: https://ollypenrice.smugmug.com/Other/Galaxies/i-sgC3bGn/A

Olly

Fascinating extensions.

Olly

The spring is a lean time for short focal lengths but mosaics in the Coma-Virgo cluster can be fun. Sooo many galaxies!  Once the southern Milky Way starts to come up in early summer you can't go wrong. We're at Lat 44 and you'll be south of that but, even here, we get four hours of darkness in June. You can work through the year.  I'd look at the Eagle and Swan, Sagittarius triplet, The Great Sagittarius Star Cloud, Rho Ophiuchus...

Olly

I denoise in a Photoshop top layer with the original underneath. This lets me erase, wholly or partially, any areas adversely affected by the NR. Often it's only needed on the faint stuff so it's easy to select and erase the bright stuff or just erase it by eye.

I sharpen in the same way, though I sharpen the bottom layer and selectively erase the unsharpened top layer.

Olly

My small object imaging was initially done with an ODK 14 (2.6M FL) and then with a TEC 140 (1M FL.) Image scales were about 0.6"PP for the ODK and 0.9"PP for the TEC. I'm pretty satisfied that both were, in truth, oversampled, the ODK massively so. Alas, the ODK's camera would not bin satisfactorily so we were stuck with the oversampling. On the whole, I preferred the TEC.

https://www.astrobin.com/335042/?nc=&nce=

https://www.astrobin.com/full/tak87a/0/

I would say this: don't expect any kind of radical transformation in your high res imaging over what you can do with the Esprit 100 and a modern, small pixel CMOS camera. There will be more detail to come, but it may be a lot less than you think and your guide RMS will need to be no more than half of your image scale in arcsecs per pixel. Presumably you already know your guide RMS or can easily find out what it is.

Olly

Lovely image.

Olly

Very stylish! They instantly reminded me of the beautiful Snow Hill Lane Bridge over the motorway, near Lancaster, UK.

I have 10x25 by Leica and find them super-useful - but I'd rather have 8x, for sure. Light binoculars can be quite jittery, lacking much anvil effect.

Olly

57 minutes ago, AstroRookie said:

@ollypenrice

Don't know if I could orientate the camera as you showed, I think my guide scope and camera would somewhere be in the way - I'll check. I have considered upgrading the focuser, but if that is not the problem then this is yet another "useless" upgrade, and a "30 days money back guarantee" is taking into account my location not really helpful 😉

@michael8554

Diff flex: that's interesting, as I have to say up to now I've always been imaging near the zenith and this is the first time I have been imaging at +- 40° altitude south (rosette nebula) - I'll have a look on how the cables and guide scope behave at that position

Thank you both!

AstroRookie

 

 

This change in orientation might also introduce tilt.

Olly

A small amount of matt black paint fully covering the scratch and of a soft, rounded shape, will entirely eliminate it as a cause.

13 minutes ago, AstroRookie said:

Hi Clarkey,

Maybe stupid question, but would that not be reflected in the graph of the guide software?

AstroRookie

No, the guide camera might be following the star perfectly but the imaging scope (or just its mirror) might be moving relative to the guidescope. An off axis guider removes this possibility by guiding on the imaging light cone itself. So called 'Mirror flop' has essentially the same consequences as flexure.

However, I'd put money on tilt, in your case. (Not a lot of money but a bit... ) From what I can see, the elongations all go the same way, meaning they are parallel with each other. Optical defects rarely produce this effect but tilt does. Since you see the same thing in two cameras, it is unlikely to be a tilted chip. (These are not uncommon and some cameras have chip tilt adjustment built in.) I would look for sag or slack in the focuser. Are all your attachments screw-fit rather than push fit? Screw fit is best. Are you placing your camera in this orientation, parallel with the counterweight bar? It's the best.

Tilt can spring up suddenly because some mechanical component becomes loose or a bearing breaks.

Olly

I would rather say that OIII is faint, rather than noisy. 

Russel Croman's Noise Xterminator is an order of magnitude better on astrophotos than any other NR routine I've tried. Because our RASA 8 data invites extreme stretching, I do often lift it well above the noise floor but StarXt sorts it out in an invisible or, in extreme cases, almost invisible manner. Here's a close crop pushed beyond its limit. Before Noise Xt...

After noise Xt...

Had I wanted to erase the brighter parts of the noise reduced image, feeling that the NR had damaged them, this would have been a ten second operation in Photoshop Layers but, really, are they damaged? Here I had the 'Preserve details' option in StarXt set to minimum. Alternatively, the noise reduced image could now be further sharpened.

Olly

12 minutes ago, AKB said:

NOW you tell me … !

See my post of last night’s session:

 

Ouch, and if you want to do this collision thing properly (!!!) do it with a RASA...

Phew.

Olly

I have three automated sheds based here and have developed some Golden Rules, the first of which is to accept that, if a thing can go wrong, it will. For this reason we have a 'No Possible Collision' rule. No telescope can ever stop in a position in which the roof can collide with it.  (A much more lavish remote hosting provider a few miles away has exactly the same rule and he is orders of magnitude ahead of me in IT savvy.)  A design using 'rolling roof and upper sides' makes this rule easier to comply with.

Another simple thing is to make as much of the gear inside as showerproof as possible. Despite the best efforts of the IT guys who are responsible for the sheds here, unwanted openings have happened several times. Simple shower protection of fixed items can save a lot of money.

Good UPS backup is essential but not so easy to assure because office UPS machines don't like the temperature extremes of observatories and tend to have a shortish life. You probably won't have our upper temp extremes, though.

Olly