wimvb

9 hours ago, almcl said:

Just as you say, Wim.  I wonder if all I would do using the Tri-B mask would be to collimate out the camera tilt which is sometimes quite large according to ASTAP (I mis-typed above - it's ASTAP I use for SQM and tilt).

I found a thread on Cloudy Nights (here) which referenced a Tri-Bahtinov grabber on Github (here) which, although a bit quirky, seems to give understandable results.  

Here's what it made of image 5 in the sequence above:

 

I haven't worked out yet how to relate the channels to collimation screws (there is an assist diagram available but not sure how it works yet). Also not sure if I want to collimate for tilt at set-up every time (= lost imaging time) or whether 'close enough' is sufficient?

Perhaps something to have a play with during the next two months of Astro twilight?

I'll check those links. My scope is already in storage because I want to avoid birch pollen. Regarding orientation, if you rotate the mask such that the inner grid aligns with the collimation screws, the diffraction spikes are aligned with the screws. In the end, you'll probably need to test which is which anyway.

8 hours ago, Vroobel said:

Am I right if I assume that any sensor tilt adjustment makes sense only if the camera is permanently attached to a rest of the setup and is never touched, particularly never rotated? Of course, I don't mean a case when the sensor isn't parallel to a flange and it 'accidentally' passed a QC which hopefully doesn't happen to more expensive cameras. 

Everything with two surfaces can have tilt. In theory you'd first make sure that the camera itself doesn't have tilt. The link in @almcl's latest post is a thread here on sgl about a cheap rig and laser for that. ZWO cameras have a tilt adjutment plate. Second is tilt in the focuser. Then misalignment in the optical system. If you think about this too much, your brain will hurt.

@almcl your findings and concerns are as mine. Judging from image 2, I would say that collimation is good, and the concentre/cheshire method of collimation may be just as accurate as tri-Bahtinov collimation. It has the added advantage (for the former) that it can be done at any time, so won't interfere with observing or imaging time. The advantage of the tri-Bahtinov is that it is easy to do with imaging gear in place. This makes it an easier method to check collimation during imaging or during a season. No need to remove the camera, so no need to retake flats.

From what I've read/seen so far, I understand that the principle behind the tri-Bahtinov mask is that collimation (tilted mirror) results in a tilted focal plane, which spreads best focus for a star in different directions. But so, in a way, does tilt in the focuser or camera. So I wonder if it's even possible to distinguish one from the other. I will test more when astro darkness returns in August. Atm my telescope is in summer storage.

On 13/04/2024 at 00:13, vlaiv said:

Also, having trouble figuring out how the scope attaches to dovetail or how it's mounted to the mount itself.

On 13/04/2024 at 00:57, Sunshine said:

And how exactly is the OTA fitted to the mount, ghost clamps?

By PhotoShop, merge mode additive. A very solid connection comprised of several layers.

On 13/04/2024 at 00:41, John said:

No self respecting astronomer wears a rucksack when observing either 😁

They don’t??? 🫣

@almcl With perfect collimation, if you defocus, the central spike of the 11 and 1 o'clock patterns move towards each other, and the 3 o'clock central spike moves up. The 5, 7 and 9 o'clock patterns are the same as those that differ by 6 hours (opposite of the central star). If the 3 o'clock spike moves up, so does the 9 o'clock spike. A tri Bahtinov mask produces three ordinary Bahtinov patterns. The idea is that with miscollimation, the three patterns are focused at different focuser positions. Collimation equalises the focus positions. It's like a three legged stool, where you want the seat to be absolutely level.

What I found in my second test was that I could move focus position quite a distance before I could see a clear shifting of the central spike. That is why I questioned its applicability. Otoh, it may very well be that the coupler between the focus motor and the focuser shaft has come loose during the winter, causing some play in the focuser. The large temperature fluctuations that we've experienced during winter, can do that.

I just put my gear in summer storage until mid August (no astro darkness left after the coming full moon), but I plan to do some more tests when I set up again. I will have to check collimation then anyway, so I will be doing a side by side comparison (barlowed laser/cheshire vs tri-Bahtinov mask) then.

59 minutes ago, geeklee said:

Interesting approach for Ha combination you've listed above, I will try and keep a note of this to try myself - thanks for sharing.

Thank you, Lee. I got the idea from Seti Astro on youtube. I didn't remember the exact steps, so I "winged it". Normally I would emphasize the H-alpha regions a bit more, but this time I went for subtle.

On 16/04/2024 at 19:02, astrolix said:

I've already done that, but the asiair simply uses the EAF SDK compiled file, that's why you can't connect another focuser like a MyFocuserPro2 one or Moonlite one.

So the ASIAIR doesn't accept any other focusers than ZWO's own?

A while ago, I designed a tri-Bahtinov mask to aid in the collimation of my Mak-Newt. I even cnc-ed the secions of the mask. Since my cnc machine is limited to a 30 x 18 cm work area, and the telescope has a 20 cm tube, I had to make 3 sections of the mask. Before I had an opportunity to assemble the sections, other things got in the way, and I forgot all about it. (I wasn't happy with the final outcome, so forgetting was quite easy, and age helps.)

A week or so ago, I came across the sections and finally glued them together. On a partially clear night, I put the mask on my MN190 and tested on Arcturus. For the first test, I only did a coarse focus and took RGB images. For the second test, I focused better and took an image with the L filter in place. Here are the results.

When I did the second test, I found the mask not that sensitive to defocus, so I wonder how sensitive it will be as a collimation tool. Does anyone here have experience of using such a mask for collimation?

Here is my design. Each third of the mask holds one section of the three zones, as described in this link. The mask is cnc-ed from 2 mm black acrylic. The slots are 4 mm wide and spaced 4 mm.

The sections are glued together with epoxy (butt jointed). I have since designed supports to make the joints more stable, but haven't yet cut those.

https://satakagi.github.io/tribahtinovWebApps/reports/improveSensitivity.html

Since astro darkness is all but gone up here, the moon is gaining, and clouds are obscuring it all, I have started to reprocess data from a few years back. Inspired by deep images posted here and in the deep field challenge, I've reworked my 2022 version of M51.

This is 15 hours of data, captured at f/5.3 with my SkyWatcher MN190 and ASI294MM camera.

Reprocessed, as always, in PixInsight. For H-alpha and red combination, I tried something new. I created an HaRR image with channel combination in PI, and colour calibrated that with the standard colour calibration process. Then I merged the red channel of this image with an RGB image. It took a bit of tweaking, but the result looks pleasing.

The original version, which was all about the Ha regions in this galaxy, is here:

2 hours ago, Vroobel said:

When I run a StarXterminator on it I found 63 galaxies.

Unfortunately, StarXTerminator doesn’t eliminate just stars.

@ollypenrice

There's a very thin "string of rubies" coming in from the right edge in your image. It's different in your two versions. Is this real signal, or maybe an artefact?

1 hour ago, ollypenrice said:

Managed to squeeze a bit more out of the Ha:

Olly

That's definitely more than "one drop". Very nice image.

1 hour ago, OK Apricot said:

Naturally I'm going to struggle to bring my whole rig inside to point it at the telly, it's got to be in the region of 60kg, don't fancy that with a bulging disc. Could I use the t-shirt and the street light? It's a bright light source albeit more "orangey" than white? 

Unless the telly is an antique, it may be easier to take it out to the scope.

Not completely unrelated; many years ago a colleague built his own large format camera around the lense from an airplane surveillance camera, a really massive piece of glass. The camera was so heavy that he mounted it on a truck to do nature photography. When he told me that, he sighed that it would be easier to keep the camera indoors, and take nature to the camera.

More related: a street light, even with t-shirts isn't good for flats. A street light is more of a point source than a flat surface.

1 hour ago, ONIKKINEN said:

Part of me is excited to see if new faint background galaxies emerge from the noise,

There is a limit to that, set by your sky darkness. Going past some 22+ Mag/arcsec2 just isn’t feasible. But yours is an excellent image as is.

No need for an OCAL, in my opinion. A cheshire for the secondary, and a barlowed laser (I use the cheap one that came with my scope), is all you need.

1 hour ago, ollypenrice said:

Well spotted.

Courtesy of my computer screen. It shows even the smallest irregularities even when my Galaxy Tab just shows pitch black.

1 hour ago, ollypenrice said:

There is certainly what looks like IFN in the top right.

Yes, It shows better in the image you posted on AstroBin, as does the red in the background.

1 hour ago, ollypenrice said:

The 255 hour image on AB does show some field Ha which you might pick up. Probably worth a look, though they said it was very faint.

Olly

Amazingly deep image, Olly. On my screen I definitely see a faint red background towards the right. (But also a very blue star, so can it be colour saturation?)

Holmberg IX, right next to M81, is an irregular sattelite galaxy, similar to the LMC. Many galaxies have sattelite galaxies. They are the remainders of past accretion events.

https://www.sciencenews.org/article/dwarf-galaxy-m81-astronomy-space

What you see around the single star is the diffraction caused by the mirror clips. To get rid of this, you'll need a mirror mask, a ring which you attach on top of the clips, and which covers them. This will decrease the effective aperture by about a cm, but that isn't necessarily a bad thing. You can 3D print your own mask, or buy one.

https://www.firstlightoptics.com/misc/backyard-universe-primary-mirror-mask-for-sky-watcher-250mm-newtonian-telescopes.html

Regarding the need to collimate, the Quattro is a fast newtonian where the secondary mirror is offset. This may mean that the secondary mirror holder is offset. If so, the out of focus doughnut will not be symmetrical. Another Quattro owner should be able to clarify this. (The alternative is that the holder is mounted symmetrically, but the mirror is offset on its holder.)

A small section of the Coma Cluster of galaxies.

This is 5 hours of RGB data on this galaxy-rich part of the night sky, captured with my MN190 and ASI294MM camera, and processed in Pixinsight. Captured during two clear nights April 11 and April 12.

For the annotated version I used the ngc/ic (pink), LEDA (blue), and GMP (yellow) catalogues. GMP is a compilation of 6724 galaxies in the Coma cluster, published by Godwin, Metcalfe and Peach in 1983. Apparently, this catalogue only goes up to DEC 29^o 16'

Some of the most distant galaxies in this image are more than 2 billion light years away from us. I targeted this area because of the interacting galaxies ngc 4922 in the upper part of the image. The tidal stream was just about visible in the captured data.

2 hours ago, StevieDvd said:

You are likely to say:

"Alexa, polar align and focus my scope on M42 and image for 4 hours. And don't forget to use the cloud removal filter"

And of course add "Please"  as bio AI appreciates good manners.

You forgot one thing. The future 'Alexa' will be customisable. Mine will say, with that typical Dirty Harry voice (yes, I'm old enough to remember that): "D'you feel lucky, punk? It sure looks mighty cloudy from where I stand."

On 11/04/2024 at 21:56, tomato said:

That's a very nice image. The only problem I see with it, and that touches on the problem with bought data, is that it lacks Ha. I haven't seen any other image of this target, but the blue arms with all their knots just scream H-alpha. And since this is from a bought set, where others have decided what to capture, you'll probably never get it. When we capture our own data, we get to decide the what and how. 

21 hours ago, M40 said:

how do you all get over this problem?

Live fast, die young, that's my motto.