Delboy_Hog

Following this one with interest - I've encountered a similar thing in my last attempt at the Alnitak area, though my blueish blob appeared in a slightly different place.  5 min subs, ED80 and Canon 1100d.  I'd assumed it was a reflection, but wasn't sure what to do about it.  Is your image above cropped at all?  If not, both our bluish blobs appear to be roughly equally distant from the centre (or edges) of the frame from Alnitak, so I'm guessing that's the culprit, but which piece of glass is doing the bouncing was beyond me.  Given its location I'd struggle to process it out convincingly...

Like you MylesGibson, I was pushing the exposure length to give me a sporting chance of catching the nebulae...and similarly , ran short on total number of subs, and had no calibration files.  I guess a greater number of shorter exposures might help, and I gather that you can use star masks and the suchlike to 'contain' Alnitak, though those are processing skills well above my current skill level!

How long an exposure is too long, for a bright star like Alnitak?

Picture above wasn't hugely clear, so here's another - If there are any DSS experts out there, I'd be extremely grateful for any advice on what I might have done wrong here.  

Stacking FIT files - you can see the DSS output below (I've tinkered with the histogram so you can see the image properly - although I'm not sure what the X-shaped histogram is about??) - I've never seen this before.  It's always placed the data across the full screen, rather than cramming it all into just one quarter of it?  Any thoughts?

Hi all,

Attempting to stack and process a bunch of files in DSS, but the file that's churned out only seems to have data in the top left quarter......

Taken with a modified canon 600d with an Ha filter, but captured by an ASI-air as FIT files, rather than the usual RAW files I'm used to using straight from the DSLR (I haven't yet figured out how to save the images as RAW files to the DSLR at the same time as the ASI-air saves the files as FIT on its micro-SD card).  The tiny JPG file that the ASI-air produces of each photo suggests there's data registering across the sensor, so I'm hopeful I've just missed a step in the stacking process..............?

It's M33 in Ha, and on a slightly hazy night, so whatever's there is pretty faint!

Anyone seen this before, or know of a potential fix?  I'd be very grateful for any advice!

I didn't know if DSS had issues stacking FIT files so I even attempted to convert them to TIFF files first...still no luck...although I might have done it wrong!

Image below straight out of DSS....

Thanks everyone - I'll have a tinker with some alternative stacking softwares to see what I can do, and be sure to get my dither on (along with some proper calibration frames!) next time out!  Hopefully I'll be on here with a beautifully low-noise image in the not too-distant future..... (goes to check weather forecast)….

Thanks again 🙂

On 06/09/2020 at 22:27, ollypenrice said:

Hi Derek, I'd say that there was evidence, here, for the 'rain' effect to be a stacking artifact. Have you tried an alternative stacking software? AstroArt offer a free trial which won't save but would let you see if it did any better.

Olly

Thanks Olly, I'll take a peek at AstroArt over the weekend and see what I can do!  Thanks again!

Derek

18 hours ago, ollypenrice said:

Was it much warmer than on previous imaging nights?

The stacking has been done properly because the stars are aligned. Do you see the angled lines on individual subs?

Olly

Hi Olly, hope you're well?

It was a little warmer, I believe (I was trying to see if there was any data recorded on the individual files that would tell me the sensor temperature at the time it was taken - sure I've seen that before but can't find it now).  Maybe I need to do some testing to see how the 600d reacts to different temperatures when it comes to noise.  We've probably not got many warm nights left here this year now, but if it's going to get this ugly I might have to hibernate this camera next summer!

You can see a sample frame below, which is fairly representative of the others - looking at it now in more detail, it's not pretty!!  But I'm not sure I see the angled lines here?

For comparison, a sample frame of the Heart and Soul taken with an 85mm camera lens.  It's quite a striking difference in smoothness.  Taken with the same camera settings (5 mins, iso 1600), but as you say Olly, different nights, so potentially different conditions.  I'm wondering if there was some high level cloud that crept over while I was sneaking a hot chocolate inside?

23 hours ago, johneta said:

I haven't seen this type of streaking before without star trail.
Definitely give dithering a go if you are guiding with PHD etc.- pretty easy.

When I started dithering and stopped using darks on my images (DSLR), everything got a lot easier.
(except for Dec Backlash, but that's another story)

Thanks for this Johneta, yes dithering sounds like the best way forwards on this one to clean up future images significantly!  I've seen a bit of debate on the dithering vs darks topic on here - you've found that you don't need darks if you've dithered?

10 hours ago, gilesco said:

About power, not that I profess to know about electricity, but in my opinion I try to power from an AC / DC regulated power supply. Drawing power from batteries seems to raise issues for me, although I'm planning on getting the larger Skywatcher / Celestron power bank for dark sky site stuff... i would not power stuff from regular AA batteries, as I'm not sure whether the intermittent draw is provided quickly enough, and it is something that might change over a long session.

Hmmm, yes I did wonder, as you say, especially with a long (and last night was cold too!) session.  It's clear-ish here tonight so I'll have another tinker with the kit and see if I can resolve this!

The desire to have a nice, portable, plug-and-play setup for taking to dark sky sites was one of the big motivations for me trying to get the SA up and running effectively, and going down the ASI-air / 120mm mini-guider route.  I have an old Celestron 7ah power tank which has served me very well over the years, and if I can figure out the right adaptor / regulator, may yet be the solution here!

Thanks again for your input on this.

Some other possibilities I've been pondering...

Mechanical: I've seen a couple of cases of this error message being (potentially) linked to 'backlash'.  I don't really understand this too well, though there are some references to some SAs being too "tight" and apparently there's a screw (or something) that can be loosened off to reduce this.  Does anyone know if the issue I described sounds like something that could be caused by strong backlash?  The distance the mount travels each step of calibration is small, and does seem to go back on itself occasionally, rather than smoothly and continuously moving away from the guide star....

Power to the mount: I'm currently using the 4 AA batteries rather than the DC 5v / USB approach.  The AAs are all a quarter to a half 'full' - I wonder if it's safe to assume that if the batteries can drive the mount when pushing the slew buttons, they have enough power to drive the mount via the guiding?  O should I be trying again with batteries at 100%....but then I would think that standard batteries maintain their function reasonable well through the second half of their lives?

Power to the ASI-air: I'm using a 5v 3.4a USB power bank - that should be more than enough to power the ASI-air (to avoid confusion, this is the old version, I gather the 'pro' has different power requirements) to do it's thing and to send pulses to the mount......right?!  I do have a 4a+ power bank somewhere that I could try, I guess, but can't imagine the Air pulling that much, especially as the power requirement to move the mount comes from the mount batteries, not the Air, on this version. 

Settings: I appear to be doing things differently from the various youtube tutorials I've found, in that I don't have the ASI-air connected to the DSLR, and just have the main camera set as 'none' and the telescope set as 'on-camera ST4'.  I can't imagine that not connecting to a main camera would impact on the guide camera's ability to calibrate though?  Unless as Gilesco mentioned, the settings might have to be a certain way...

Any and all thoughts / suggestions would be much appreciated!

10 hours ago, newbie alert said:

I've just thought of someone that guides with a SA, I ask the question for you

Many thanks, that's very kind of you!

9 hours ago, gilesco said:

Well when using Ekos for guiding, you can either guide via the Guide Cam (i.e. via the ST4 cable that connects from the Guide camera to the Autoguider port on your mount), or you can get Ekos to directly talk to the mount via the Handset connection (I have a CGX). I don't bother connecting the ST4 cable and usually set Ekos to guide via the Telescope Mount. Of course sometimes I forget to set that up, and as the ST4 cable is not connected (in my case), then the pulse commands don't move the mount.

If you're using an SA then I think your only option is to guide via the ST4 cable.

Did I hear with PHD that there were multiple places to disable the Dec guiding??, perhaps have a look around the extra settings.

Ah okay, that makes sense, and thank you for describing - yes I think the ST4 cable is the only option with the SA.

Hmmm, your point on the need to have multiple options set a particular way could well be the issue, and the ASI-air interface is (I'm told) very similar to PHD.  I'll have another scroll through the menus and see what I can find.

Thanks again!

15 hours ago, gilesco said:

Sometimes I get this if I have set guiding via the ST4 cable, which is not connected, rather than directly to the mount.

Hi Gilesco,

Could I check what you mean when you say 'directly to the mount'?  I've been relying on the ST4 cable from ASI-air to the mount (and did check it was plugged in!), but haven't clocked a setting I could change to suggest a different way - have I made a ridiculously rookie error and there's something else I should be doing?!

Thanks for your thoughts!

15 hours ago, MarkAR said:

Usually I get the same message when using Ekos, it's picked a hot pixel as a guide star. Try to pick another manually.

Thanks MarkAR, definitely checked that one - picking stars manually that blur etc with guide-cam focus change and that blur and move when I nudge the mount!

15 hours ago, newbie alert said:

Assuming the mount can take guide pulses? I know people do guide with the SA but I'm not sure on how it works.. you need to turn DEC guiding off as it hasn't got that axis,so maybe it's trying to send pulses in Dec and it's not moving 

Thanks for your thoughts, Newbie!  I think it can?  It does move slightly when the calibration starts, but they just don't seem very strong or consistent, so it'll move to 0.3 at the first step, 0.5 at the second, then go back to 0.2, then go up to 0.7, then back to 0.5 and so on, so it gradually creeps up, just not enough to reach a point that satisfies the software.  I've tested the buttons that drive the mount (on the side of the SA) and they seem to work okay (and if you press them while it's doing the calibration, it registers as a many-pixel movement, as you'd expect).

And yes, I have the DEC guiding switched to off, though I really appreciate the sense-check - I'm sure there'll be a setting like this that I've missed somewhere!

This one is really puzzling me!

Hi folks,

How do I get the star to move enough?! And how much is enough?

This is the message I'm getting using an ASIair (the older version, but fully updated software I think) on the Star Adventurer, with an ASI 120mini finder-guider. The star is moving a little bit, but never more than dist = 5 or thereabouts, and after 60ish steps it stops trying.

I've tried bumping up the calibration step amount from 500 in various intervals up to 10,000, no luck.

Any ideas? I'm at a total loss. Have tried numerous different stars, balanced the mount perfectly and tried unbalancing it a little just in case, locking the mount down more and less in case I had it too tight / loose...

The mount appears to be working fine on normal tracking mode, but hoping to get the guiding working to get those longer subs....

Any ideas would be hugely appreciated!

Derek

On 30/08/2020 at 20:57, almcl said:

It does have the appearance of walking noise and your comment about the gradual object shift tends to support that.

Are you able to dither between frames?  If so, you may find that helps particularly if you then stack with sigma clip in DSS (needs at least 20 subs and more is better).  There are software solutions as well but it would be better to eliminate at capture time, if possible.

Another question to ask is how tightly bolted down is your guide scope/imaging scope combination?  I found the rather floppy focuser on my ST80 was very good at generating this sort of gradual drift.

Thanks Almcl, that's really helpful.  I've dabbled with dithering before, as an alternative to doing dark frames, so will try it again.  I hadn't noticed this kind of effect before when I didn't dither though, so I'm scratching my head as to why it's so apparent this time around.  I'm guessing that's because of the gentle creep across the frame - as you say, I'll check everything is bolted down properly, as something must either have been slowly slipping or possibly an unbalanced mount pulling gradually in one direction...

I really need to get a better understanding of the possibilities in DSS too, as the sigma clipping sounds very handy!

Thanks again, very helpful and thought-provoking information!

Derek

On 16/07/2020 at 04:47, Ken Mitchell said:

After reading nothing but positive comments on the optics I was thrilled to give it a go myself. My goal was to do a mosaic of the Moon. The first opportunity I got, which was 8 am during sunrise, I got out and started imaging. 

What a great feeling seeing the Moon so close! It felt like 30 years ago, a 10 year old kid looking for the first time through a telescope at the Moon. 

It's an absolutely stunning image, Ken - I agree with Danny, it's one of the most striking images I've seen!

Hello folks,

I wonder if anyone's seen anything like this before?  Focus not perfect though stars seem reasonably well aligned, but background looks like I clean my equipment with a brillo pad (I promise I haven't!).  This is only my second attempt at stacking Ha data in DSS, so I'm sure it's user error - though the other image (which was taken later) didn't show any sign of this, which confuses me, but reassures me it's not the kit.

About 2 hours of 5 minute subs, , ED80, modified Canon 600d and Astronomik 12nm Ha filter, no calibration frames.  Straight out of DSS - didn't seem to be much point trying to process it!

Looking back over the frames, there appears to have been a gradual shift of the object across the frame over the two hours, but nothing that caused any star-trailing in the individual subs, which makes me wonder if I've just got a stacking or alignment setting wrong in DSS?  Or is the lack of calibration frames the issue here - is this the dreaded "walking noise" that I've heard of?  Though I don't appear to see anything like this when just stacking light frames of other objects?

I'd be super-grateful for any thoughts / help with diagnosis!

Derek

2 hours ago, jiberjaber said:

You could probably do all that with a Raspberry PI and Ekos/Indi (which is almost what the ASIAir is anyway!).  If you've got a Raspberry PI kicking around it's quite easy to try it out.

Take a look at Astroberry as a starter.  https://www.astroberry.io/

I used to run my mount, guide cam and DSLR (Nikon) on mine and now its running most of the same but the DSLR is replaced with a focuser, filter wheel and ASI1600 

 

Thanks Jason!  I don't have a PI, unfortunately, and I'm not terribly tech-savvy, though I'm quite intrigued.  I think it'd take me so long to figure out what I was doing I'd be better off just paying for the version that someone else has already done! 🙂

2 hours ago, Adreneline said:

I use one and I am very pleased with it.

I don't use a dslr but that said there are no power out sockets on the ASIair other than via the usb sockets. My dslr requires 7.2 volts - not what you'd normally expect in the 12V/5V astro world.

It does and as far as I can tell on the occasions I have used it, it works pretty well. Having said that I use a PoleMaster and that definitely works well.

There is an auto stretch and I can't see why it wouldn't work with a dslr.

The ASIair has transformed my imaging experience when used with a ZWO ASI1600, EAF and EAW on an iOptron mount all controlled from an iPad running SkySafari and the ASIair app. I love it!

 

 

Thanks Adreneline, that's really helpful.

Hi folks,

Yes, I'm behind the times - I gather the new (pro) version is out now, and people may have switched out the old ASIair for the new, but was wondering if anyone had experience with the older model?

I have the opportunity to pick one up second hand to help with guiding (with an ASI120mm mini) of either a Star Adventurer or the HEQ5.  I’ve had a look around online, but can't find the answer to a couple of questions…

1)      Does the old version of the ASIair power your DSLR?  I’m assuming the DSLR still needs a battery as usual, but it would be a bonus if the ‘air’ powered it!

2)      I gather there were updates to the ‘air’ since it came out, so that you can now polar align with it too.  Have people found this feature to be reliable?

3)      Finally, I gather there’s an auto-stretch feature.  Does that work with DSLRs (if attached by the appropriate cable, presumably) or just ZWO ASI cameras?

 Many thanks for any information you can offer!

Derek

On ‎23‎/‎08‎/‎2019 at 09:13, vlaiv said:

There are couple of things going on here and all are quite "normal".

First, you are using full frame sensor with a scope that does not have such a larger corrected field - hence distortions in the corners. It's the limitation of the gear used and you can't do much about it except crop.

Star trailing in your stack in the corners is another consequence of gear used and imaging method - as noted, you did quite a large dithers between subs. You have fairly large field covered with this setup, and when trying to map a "round" thing onto a "flat" thing there will be distortion - sky is a sphere and imaging surface - sensor, is flat. This leads to slight distortion in star positions over the surface of the sensor. It is very similar to barrel / pincushion distortion that you get from wide lens in regular photography (or some eyepieces in visual).

There would be no problem if you had your frames pointed to same place every time (small dither), but large dither means that different parts of image are stretched / distorted, so DSS is having trouble aligning them as it can't handle image distortion of this sorts. It expects "flat" images - meaning geometrically flat, or each frame having stars the same distance from each other, which is not the case here.

Using different software that is capable of correcting for distortions of this kind will help get better stack. I think that APP can do it as it says among its features: " advanced image registration using true optical distortion correction ".

Thank you Vlaiv, that's a helpful explanation of what's going on here.

I'm currently looking into the various bits of software that I use as compared to some others, so I'll take a look at APP - it would be helpful if there was something out there that could help with this, though I'll certainly be looking to significantly reduce the size of the dither on my next session, so hopefully that'll give DSS a helping hand in the meantime!

Thanks again,

Derek

On ‎11‎/‎08‎/‎2019 at 17:34, david_taurus83 said:

I think you've got some really nice data there considering its just over an hours worth. You are probably pushing the limits of the flattener with your 6D but apart from the corners and edges the stars look nice and round. I stacked in DSS with the standard settings and I got something similar to your stack with just the light frames. I set the star detection slider to 89% and ticked the box to reduce noise. This gave me a figure of around 250 stars. It might sound silly but you didn't accidentally mix your flat frames into the light frames tab? I don't know whats happened your stack above with calibration frames!

 

I done a quick process in Pixinsight. The difficulty with this object is its within a dense starfield so it kind of washes out the nebulosity.  We are used to seeing beautiful narrowband images of this but Ha and OIII filters really make the supernova material stand out. I've never been good at processing OSC images but I've managed to reduce the stars a bit. I reckon if you were to add another 3 or 4 hours worth you'd have a brilliant image with a bit of careful processing!

 

Autosave.tif 171.59 MB · 3 downloads

Hi David,

So sorry for the slow reply, especially after the efforts you went to with the data - I've had to be away with work and it's given me no spare time at all. 

Many thanks for taking the time to run through with the data and seeing what you could get out of it...HOLY MOLY!  That's looking nice!  Especially with limited data, as you say.  You seem to have managed to minimise the tragic corners better than I did, and it has a really nice balance to it, to my eye.  My processing always seems to come out a bit stark and...obvious, if that makes any sense?  I've still not had time to run this through in Photoshop, so I must try it.  Hoping for some clear nights to get some more data in the stack too.

As for whether I included flats in the light frame stack...ha ha, possibly!  I've made more stupid mistakes than that in the past!!

Thanks again for your help with this, and for walking me through what you did in the stacking phase, that's very much appreciated.  I really like seeing the starless version too, really interesting to see - I'm assuming that's a Pixinsight feature - lovely!  Hopefully I'll be back on here before too much longer with a bit more data and having had slightly more success through the stacking!

Thanks again 

Derek

15 hours ago, david_taurus83 said:

That single sub looks really good. Is it unstretched? Your data looks good so something is going wrong with your DSS settings. I use the standard settings in DSS but I do adjust the slider to detect just over 100 stars. You could post a link to your data on here and see if anyone else gets the same result in DSS.

Thanks David, much appreciated.  Yes, straight off the camera - I was really pleased with the individual subs, so was a bit bewildered with what came out of DSS!

Oh I'd be intrigued to see what anyone else could get from the data - I've uploaded the light frames to Dropbox here (hope this link works?):

 https://www.dropbox.com/l/scl/AACWyRfxTlCwi4kLul4poTuMl6zmhaN8Vew

It took an age so I haven't uploaded the flats and bias frames as well, but if anyone is particularly keen to play with the data, I'd be happy to!

Many thanks,

Derek

14 hours ago, michael8554 said:

The corners look fine to me in all but the last one, given the combination of gear you used. 

What star threshold did you use ( how many stars used?) 

Dither should be 12 or so pixels for a DSLR.

Michael 

Hi Michael, 

Many thanks for coming back on this.  The Star Threshold is an interesting question actually - I think I went with the standard DSS setting, and remember it found several thousand stars, which seemed a bit many - I've read somewhere since that about 100 stars is optimal, does that sound about right?  Do you have a particular threshold that works for you, or would it vary depending on your target?

Thanks again!

Derek