ONIKKINEN

Something is a bit weird here, can you clarify a few things?

Did you use flats when stacking? If so, did you also take bias (or dark flat) and dark frames? Also, what camera, what scope etc?

Superstretched version for diagnostic purposes below:

Its difficult to tell for sure what is going on since there are so many different camera orientations going on at the same time, but to me it looks like you have quite severe overcorrection of flats going on (middle is darkest, opposite of what it should be). Could also be from dew/frost on a secondary mirror or maybe in the center of a refractor lens (that im not so sure about) if you did not take flats at all. There is also a weird looking diffraction spike on some stars that appears to not be a typical newtonian 4-prong one but just a 1 or 2 sided spike? Not sure what to make of it.

1 hour ago, herne said:

 

Different budget for different items.  A new mono camera + filters costs more than an HEQ5 Pro and a reflector such as a 130 or 150pds, but that (for me) doesn't mean the budget is transferrable.  So to my mind I'd say (ball park) up to £1000 for a mount, more (say £1500) for a mono camera and filters - or around £1000 for an OSC.  Telescope budget is as yet undecided but would be less for a 130/150pds than for a larger refractor.

And with regards the scope, I'm as yet undecided on going down the reflector or refractor route.  Neither would ever be really large and heavy so an HEQ5 Pro should be more than sufficient for future gear.  A 130/150 would be well within weight limits as would something like a StellaMira 90mm triplet or WO 91mm triplet for example.

 

What I was leaning towards but sometimes you just need to go through the logic 👍.

I would skip the 5 class mounts and go straight to an EQ6 class one if you are considering spending that much money in total. Youll thank yourself later and leave some breathing room for growing the setup.

I have an AZ-EQ6 with an 8" newtonian and the mount is not overkill at all even though im at less than half its rated capacity.

On 01/05/2022 at 22:14, Mr Spock said:

On the latest (insider program) update the systray is gone. You have to select individual items in taskbar setting for them to show on the taskbar.

Things like this are why i wont be upgrading until win10 support ends, and probably not soon after that either. I hate it when windows just decides to change a feature without asking!

Can you remove auto updates in win11? I have done so with registry edits in my win10.

28 minutes ago, herne said:

 Due to not having bottomless pockets, this needs to be done in stages so the question is what to buy first as I’d like to be able to use whatever is bought first in the mean time rather than have it sit in a corner gathering dust until the next purchase is made.

The mount it is then. No contest on this at all in my opinion.

You cant really overmount a scope so getting the best mount you can with your budget would be the best choice. You can keep using your current setup with the better mount and get somewhat sharper images due to much better guiding.

Does depend on your total budget a bit though, if you have enough to spare you could buy a mount + something else, but just guessing since you did not mention.

Periodic error is there regardless of payload weight, could it be that you are just now noticing it?

5 hours ago, Grant93 said:

 I'm interested to see what I'm missing . And anyone else reading this, please have a go .

result.fit 277.14 MB · 6 downloads

Did a quick process and got something that looks similar to yours so i dont think you missed anything:

I feel like i want to stretch it more, but things get noisy quite fast with more stretching so this one probably needs more time under the stars to show up more of the dark dust. Dark nebula processing is quite tricky so i could be missing something too of course 😃.

The focal point does not extend far enough outside the focuser to reach focus with a DSLR.

Youll need to either push the focal point outwards by moving the primary mirror up the tube, use a camera with a shallower flange distance like a mirrorless camera or a planetary camera, or use a barlow lens to push the focal point far enough.

With the barlow you will have some other issues but thats probably the easiest method.

Binoculars are hard to beat in terms of convenience, if that qualifies as a scope.

Lots of things to see with 7x50 binos if skies are dark enough!

For imaging purposes most mounts are almost self aligning, with only polar alignment requiring manual work (apart from the Avalon).

Polar alignment takes 2 minutes to get within an arcminute and the star alignment thing later on is not necessary at all. Both require there to be some kind of plate solver in play but for imaging purposes i think most people do have that capability and this way its mostly on autopilot.

Not seen this one before, very nice shot. Looks to me like its quite rich in Ha so am interested in seeing how adding that improves it more.

5 hours ago, vlaiv said:

Beautiful image!

Thank you Vlaiv, i have learned much from your expertise!

Actually not just much, perhaps most of what i know today 😅. I think i would still be drizzling DSLR images with 7'' FWHM stars if i had not found this place and the experts in it...

Abell 1656 is a rich cluster of galaxies with a mean distance of 336 million light years from us here on Earth and contains as many as a thousand galaxies. In this image i can confidently say that at least a few hundred individual galaxies can be seen, some better than other of course. The cluster contains mostly photographically uninteresting elliptical galaxies which lack star formation and so have a uniform warm white colour to them due to the lack of young hot blue stars. There are some spiral galaxies and irregular galaxies too of course, but none have cleared the noise level yet to be well resolved with their features (perhaps with the exception of NGC4921). Everywhere i look in the image i see a faint background galaxy, its really mind boggling to be honest at just how many stars could be in this image and how many of those could have rocky planets and how many of those have someone pointing their version of a newtonian reflector towards us at this moment? I dont think its unreasonable to say that the number is not 0. I could daydream about stuff like this forever, which is why i wanted to shoot this target that, lets be honest, is not the most photographically interesting one.

And the (silly) annotated version:

Shot with my stuff which is the VX8, RisingCam IMX571 OSC camera and the AZ-EQ6.

Shot over 4 nights in total, of which the last one i unfortunately scrapped completely due to seeing, so 3 nights and 9h stacked for this shot. Was aiming for a much longer integration and i dont think its quite "there" yet but the season has ended, so this will have to do for now. I shot from a bortle 4 zone using only 60s exposures, just to prove to myself that the process of taking short subs and getting faint stuff out of them works, and i can say that it does since the subs themselves only had as few as 30 electrons of median background signal! Also, it was windy as hell so not much sense taking longer subs from that sense too.

Processing tools used: SiriL, GraXpert and photoshop.

After calibration i split the subs to their individual colour filter channels without debayering and vetted those with the plot drawing function in siril. I used simple measurements to make the calls, like: FWHM, roundness, background level etc to remove outliers. In the end i stacked somewhere around 500 red and 550 blue subs and more than 1000 green subs to recomposite back into a colour image, but now with improved SNR and a more reasonable sampling rate of 1.84'' per pixel compared to not bothering with splitting. The red channel ended up lacking since i had a bit of an oopsie with an uncovered rear of my scope and a red LED on the mount blasting light directly inside the tube for a while on my first night, but since i split the data i was left with working blue and green channels for that, so not a huge loss.

Comments and feedback welcome!

4 hours ago, ollypenrice said:

If you want to chase the faint stuff you will need to do so, I think. The Hamburger Galaxy in the Triplet, for instance, has a long but very faint tidal tail. https://www.astrobin.com/335042/

The tidal tail was starting to form in an image i took a while back with just 2h of 60s OSC subs containing only 40 electrons of median signal in the green channel:

Not anywhere close to being drawn out to a presentable image of course but i did notice it was there so i think you could get away with short subs as well as long ones. Just takes a long integration to draw it out from the sea of noise i think. Not sure how to estimate how long but judging from my image around 10-20h would probably form the tidal tail nicely with similar quality short subs.

21 hours ago, tomato said:

I'm sure this will be on the list at some point but do a JWST 'Deep Field' just like  the HST.

This would be on the top of my wish list as well. Would be interesting to shoot the same patch of the sky as hubble did to do a direct comparison. Some of the hubble deep field objects are redshifted to outside what hubble was meant to image and i think JWST would be right at home for those faint fuzzies.

I have mixed 30s and 60s subs and also 2 different gains in a stack and i dont think there were any issues.

Normalization did its thing and less than 1% was clipped in the end with sigma clipping, so i dont think in that case there were any issues.

16 minutes ago, Stuart1971 said:

It’s only in the top right and left corners though, surely it would show all over if a collimation issue….🤔

Actually i think thats common, at least when my scope was out of collimation (still is sometimes 😅). One side of the image was always better or less apparently bad than the other. If all of the field of view is bad then the scope would be nowhere near collimation, like my first scope, an Astromaster 130 was.

If you didn't mention that it was a refractor i would have assumed the picture is from an out of collimation newtonian. Looks very similar to that.

Could the scope be out of collimation? Dont know how common that is with good scopes like a takahashi though.

3 hours ago, Bibabutzemann said:

Thank you @Stefan73 and @alacant !

 i compared all our flats. I did a background extraction of 2nd order in Siril, to see if any complex gradients are left. 

First is Stefans, 2nd is mine and last is alacants.

On all three i could make out that "hook" like structure in the middle of the flat, but it was less pronounced on alacants. 

I tried with flocking and and a baffle ring, but still didnt get rid of those gradients. Maybe im overthinking and i should just focus on doing better flat frames.

 

This blotchy look is because of running the tool, not somethig that exists in the flats themselves.

Your flats are fine, they just dont match your lights because of mechanical problems, and using someome elses flats is guaranteed to be worse. 

I dont recommend the smaller Celestron power pack (the 7.2 amp one).

It can only supply power via 12v DC or the USB port, so no accessories like dew heaters off USB power at the same time. It also has some "smart" features like shutting off power if power consumption is too low, or too high. I found that it was not in fact enough to run an equatorial mount and during go-to it shut off instantly so its not really useful for much. The 12v output is also not regulated, or at least not that well, and will drop below 12v before power runs out. Build quality is also poor with the plastic covers just breaking off after one use. Terrible product and hilariously expensive!

The jackery sounds reasonable and future proof however. I have a similar product from another brand (ecoflow river 300) and its been flawless.

I liked the second one best, the one with the lifted background. I think in your third pic the contrast inside the galaxy went a bit too far and it looks a bit out of place compared to the rest of the image.

M51 looks maybe a bit too high in magenta, almost like you imaged without an IR cut window/filter or H-alpha blending went wrong or something. Minor gripe though since the picture looks great anyway.

2 hours ago, Captain Scarlet said:

Haha that was the other thing I thought I'd wait until someone else noticed before talking about it! You suggest it might be "ventilation hole for the fan on the cell to pull air from in front of the mirror". Well, yes it is, er, sort of, by default though.

There are two explanations:

1. I'd designed the whole thing to the nth degree, worked out where I needed all the holes etc etc. I measured and measured and checked and checked before drilling all the small holes: spider-holder holes, mirror-cell attachment holes, finder-bracket holes, and the single pilot hole to act as a guide for my 80mm hole-cutter for the big focus-tube hole. I have to say, I drill very nice holes with great accuracy, working up from 1mm hand-held spotting-indentation, drilling then all the way up to the required size. Very careful. Finally I got my 80mm hole-cutter, run backwards of course for easier cutting without catching, lovely smooth and also a good job. Lovely lovely. 10 seconds later I realized that I'd used one of the spider-holes as my pilot hole, not the focus-hole pilot hole.  ........................................... Oh God. Oh my God. You can imagine the stream and volume of swear-words as I strode around the house holding my head in my hands. How could I be so BLOODY STUPID!

2. In the design phase, I had given a lot of thought to the thermal management of closed Newtonian tubes, especially extremely well-insulated ones like this with its epoxy-carbonfibre skin and 5mm hardfoam inner liner. I had genuinely been mulling about creating a focsuer-sized ventilation hole near the primary mirror. But in the end I decided to "go conventional" to begin with , and decide later.

This stupid mistake made my decision for me. Once I'd calmed down, I realized I could simply turn the tube back to front and start again. Which I did, being very careful second time to use the correct pilot hole! Hence the makeshift "hatch-cover". If you look carefully at the images, you'll see various random "unused" holes and bits of tape covering holes, the collateral damage of my idiocy.

 

You also say "nice shiny tube". It is, of course, it's beautiful, but more to the point it's extremely stiff, more so than I was expecting. Exerting some serious force to the laser when in the focus tube, I could not get the spot to move. Very pleased and well worth the wait for Klaus Helmerich.

Oh my, i can imagine my heart skipping a few beats after a fumble like that, especially since these tubes are not easily replaceable. I think it shows the tube is plenty strong enough if it handles an extra hole like that and still shows no flexure, so you could call it an improvised stability test. 😉

Looks like a useful hole for ventilation and maybe some light mirror dusting though, so not a disaster i hope!

I notice a few things with the images and it does seem that flats dont work quite as they should here, but the blotchy result from siril background extraction always looks like that when my flats have not worked perfectly so that is more of a symptom that only is visible after running the tool rather than the actual issue. The tool really doesn't like mechanically failed flats and so the background remains flawed. I noticed that you have rotation between the single sub and the stacked image. Was this taken on 2 different nights so with different camera orientations? Or did you remove the camera during shooting? In any case, each time you remove the camera you need separate flats for that specific rotation and the previous ones will not work if you remove the camera and put it back.

First issue with the flats is that they are rather dark at 3115 ADU out of 16384 (14 bit camera). Would probably be better to either expose a bit longer or use a brighter light source for the flats. Not sure how much this effects all the other things here but i would look at bringing the flats exposure to around 50% of the histogram first.

To my eye it looks like you may have some kind of small motion in your optics between the flats and the lights, which is not a shocking surprise given you are imaging with a newtonian where many parts can move and so ruin flats. Its most apparent in the worm looking shadow on the top of your flats:

The same spot in your calibrated sub clearly shows that the shadow is still there and has not been removed by the flats:

It could be some hair or fiber that has moved on its own during imaging, but if not it tells of more issues.

To me it tells that there must have been movement somewhere in your imaging train between taking the lights and the flats. That could be the primary mirror moving in its cell, the cell itself being weak, the tube itself bending, the focuser drooping (quite likely will, if stock focuser), or the camera being rotated in the focuser. Dont know how that last thing could happen by accident, other than if you removed the camera between shooting the lights and flats but in that case not really by accident.

The resulting stacked image shows a dark center half-circle (purple:darkest, red:brightest) and a nonlinear gradient. I made the fine artwork below with paint and a screenshot in the rainbow false colour rendering mode and histogram stretch mode in siril:

This kind of error could be from light leaks, mechanically failed flats or both. Or inner reflections. Anything goes really. You do mention that things are flocked and light leaks proofed but i cant help but think that it still looks like light leaks are getting in somehow. Have you blocked the DSLR viewfinder? That would be light leak source number 1, leading stray light directly to the sensor.

If flats had worked there would not be this kind of nonlinear circle-y look to the center and it would be edge to edge linear (like the line i drew diagonally). Could be some overcorrection at play as well since the center is slightly darker than maybe it should, but not sure how to go about fixing that.

On 23/04/2022 at 20:03, Bibabutzemann said:

There is only one way i could cange the form of the gradient: When i change the focus. But i dont know what to make out of it.

Your focuser probably has some side to side travel in it when you rack the focuser in and out, which is why you should collimate in the focus position. Racking the focuser in and out will change the collimation in the case if this happens and that is why you see the effect change in different positions. Try putting a laser into your focuser and rack it in and out, i wouldn't be surprised if you see the dot move a bit on the primary mirror.

So my thoughts: Mechanical issues somewhere preventing accurate flats from being taken, if they were taken for each session and before touching the camera. I would look at the focuser first. I have mostly removed issues like this with my newtonian with an upgraded focuser and looking at reinforcing my tube so that there is less flexure.

To try and band-aid fix this since you cant really retake flats now, you can try to run background exctraction per sub in siril. It might leave a cleaner background than running the tool in the stacked image. You can also then see which subs had functioning flats and which did not, and could remove the ones where the background is messy after the extraction. If you are unsure how to do this, calibrate your images like you normally would and open the sequence of the calibrated subs. Then open the background extraction tool and set it to 1st degree order, 20 samples per line and 1.0 tolerance and generate the samplers. Then just click the Apply to sequence and siril will remove the background from all of your subs this way. Then you can browse the file list and see if you spot some of them being out of line (probably wise to look at first and last sub and compare) and remove those if you want a cleaner background. I think the image you have here is workable though and it wouldn't be that difficult to clean up later in Photoshop or gimp or whatever you use.

I wrote quite a ramble above, i hope there is at least half a sentence that makes sense somewhere in there 😃.

Nice and shiny tube, looks very nice!

Curious as to what this bit is though, ventilation hole for the fan on the cell to pull air from in front of the mirror or just some placeholder thing?

Looks like the trailing is mostly in declination.

Could mean polar alignment issues resulting in DEC drift or differential flexure of the guidescope and the imaging scope. I would guess a bit of both. Your tripod could sink or something other in the mount could "settle" after polar alignment, taking you out of what you thought was good polar alignment. If you have guide logs you can look through, you can see what the actual accuracy of your polar alignment was. Dont know if that's something you can do with your guiding (stellarmate internal?) but i would hope there is a log of some sort written by the software. The differential flexure thing is also quite likely since you are imaging with an SCT where the primary mirror can move or "flop" around in the scope without you being aware of it. Guiding through a separate guidescope means the guidestar stays in the right position on the guidescope, but the imaging scope drifts away. The fix for that would be an OAG. The total amount of drift is not an issue, as long as you have the sensor area to spare for it and the drift is not apparent in a single sub.

The soft stars thing is probably what leads to the failed alignment. If no stars are detected, or worse: hot pixels are detected as stars then the alignment will fail like it did with your shot. How many stars does PI report from the subs?

Are you talking about one of these kinds of filters?

For emission nebulae you will still have the 2 most important wavelengths captured, OIII at 500-ish and Ha at 656nm. This means you cut light pollution quite a lot depending on what kind of lighting you have around you (with LED lighting, not as much, since they are broader spectrum white instead of the old orange-yellow lights CLS filters are meant to block).

For stellar objects, like galaxies, some reflection nebulae, dust clouds etc you will lose up to half of the incoming signal and almost all of the orange-red components in them. The resulting image tends to be very green and difficult (impossible really) to present as a real colour image. Up to you to decide whether a real colour result is what you want in the end, but if it is then i wouldn't use a filter like this. For galaxy imaging there really is no filter that cuts just light pollution and preserves the starlight signal, since they share the same spectrum. In my opinion light pollution filters have no place in galaxy imaging as i think there are more negatives than positives with the missing colours and the arguably not helpful at all LP reduction.

In both of these cases you will need to expose longer to reach the same amount of signal as an unfiltered shot since you have less signal coming in to swamp your read noise. But if you are considering a light pollution filter im going to assume you have a lot of it and in that case you probably dont have to worry about the exposure length thing too much. The more you have light pollution the shorter your subs can be. No harm in longer subs of course, but also no need to.

Here is a recent thread discussing the exposure length thing in detail (gets technical and math-y, not sure i understand half of it):

In short: Yes, you might need to expose longer.