sploo

14 hours ago, badgerchap said:

Yeah I think pre-cut disks are going to be essential. Cutting with a jigsaw would just be a mess!

There's always the right and wrong tool for a job. A jigsaw is always the wrong tool. Unless it's the only one available 😉

With care, discs can be cut using a router and a beam trammel. However, I do have a CNC machine, so if you just wanted a couple of 12" circles from MDF then give me a shout. I'm sure I'll have some offcuts I could chuck on the machine.

As a DSLR user, hopefully one day getting a "proper" astro camera, this thread is very useful.

For those with the mono cameras and filter wheels; do you tend to cycle the filter for each sub (to try to get a decent spread of each type of image across a single session), or do you tend to shoot with a single filter and just accept that it'll take several nights to get a complete image?

When I run a stack using DeepSkyStacker (with light, dark, bias and flat frames) it generates a "master" image for each of the dark, bias and flat groups. I understand you can then delete the original dark, bias and flat captures and use those master frames for further stacking operations.

Generally I will run a stacking operation on a night's shooting to take a look at the output from just that night; so I'll end up with 'O' (the output image), 'MD', 'MB' and 'MF' (the master dark, bias and flat frames), and of course my original light frames 'LLLLL'.

If I later combine multiple night's shoots of the same target (each with their own set of light, dark, bias and flat frames) I can set up each group in DSS with its light frames and just the three master dark, bias and flat images. I.e.:

Main group: 'LLLLLL', 'MD', 'MB' and 'MF' from shoot 1
Group 1: 'LLLLLL', 'MD', 'MB' and 'MF' from shoot 2
Group 2: 'LLLLLL', 'MD', 'MB' and 'MF' from shoot 3
...

Instead, is there a way to create "master light" frames; such that you use the output image 'O' from each individual shoot? I assume that as each output file has had the bias, dark, and flat data applied, you wouldn't need to add them again; thus you'd only be stacking a single file from each shoot. E.g.:

Main group: 'O' from shoot 1
Group 1: 'O' from shoot 2
Group 2: 'O' from shoot 3

The problem is that the output file from each shoot is usually a different resolution (due to the mosaic/intersection combination of light frames); so DSS refuses to stack them. Even if this worked, is there any point? Would this stacking method produce the same results as re-running all the light frames from each shoot in a single stacking operation?

2 hours ago, geoflewis said:

What did the images from this latest session look like?

About as mediocre as my usual images

It's about 44 minutes total data, on an old (unmodified) Canon 7D, though with a CLS filter. Pretty much everything else "wrong"; in that it's a very poor sensor (lots of read noise, combined with very short exposures [10s] as I was having some tracking issues). Seeing conditions were OK but not great (and obviously a full moon).

10 hours ago, Erling G-P said:

Good to hear that you're apparently zeroing in on the reason

You mention being able to spot the deteriorating quality through the viewfinder.  Does that mean you image with the viewfinder uncovered ?   It's generally considered a good idea to cover it up (most cameras comes with a small plastic cover to slide on), to prevent stray light entering through the finder and potentially mess up your image.  Can't say how much of an issue it is, but there must be a reason for those covers being supplied with cameras.

I paused the shooting a few times to check the view through the viewfinder and refocus (basically checking the last shot before I paused, refocused, and confirmed there was no difference - i.e. no drift in focus). That said, I do usually cover the viewfinder, but forgot on that shoot - and the full moon was pretty much behind the camera and shining into the viewfinder 

I do need to sort out some remote control/capture for the camera, as being able to remotely check images would be quite helpful.

Cross fingers I think the main issue did turn out to be temperature. I left the camera and lens outside last night for a good hour before I started imaging. A test of M42 did show a drop off in image quality over time, but much more gradual - and entirely expected as it moved closer to the horizon (I could see it getting worse even just looking through the viewfinder). While I deleted a number of images (approx IMG_6350 to IMG_6420) due to an obstruction (hence the gap in the graph below) you can see that the reported quality varied much more within a small time window, and only dropped off slowly. Each of those exposures were only 10s, so from IMG_6190 to IMG_6549 is almost exactly 1 hour):

After those image were taken, I pointed the camera due west, and probably about 45 degrees above the horizon. A run of 38 exposures (each 30s, so about 19 minutes) showed a pretty consistent quality level:

I think the widely varying quality of the M42 images over a short space of time is due to my Star Adventurer struggling with the load - a gripped DSLR with two batteries, a large ball head and a 100-400 lens comes in at around 4kg; so I'm probably pushing my luck with that little tracking mount.

Yikes. That's a car wreck.

Still might be possible to move them back carefully though, then very gently insert a card to line them back up.

Are any of the CF pins inside the camera shorting to one another? It's feasible that might prevent the camera starting (either electrically, or because the firmware believes there's a card and is then locking up trying to read from it).

Have you tried leaving the camera for a while with no batteries (including removing the CR2016 coin cell) and then reinserting the batteries? E.g. follow the steps at https://martybugs.net/blog/blog.cgi/gear/bodies/Canon-350D-Lockup.html

It is possible to fix bent CF pins with tweezers or a fine screwdriver, but you have to be really careful not to snap them.

A dodgy connection to the lens can cause issues, but it looks as though you don't have one connected at the moment.

43 minutes ago, vlaiv said:

+1 temperature shift.

Let the gear cool to ambient before you start and then refocus roughly at every 1C of ambient change (if you have slow scope - you can go for 2C, but anything F/5 or faster - odds are you'll need to refocus on ~1C).

If you have motor focuser - make your sequence check for focus every hour and on filter change of course (even if you have par focal filters).

A motor focuser is one of the things on the cards. I've just started putting together a prototype for a tracking mount for the 300P scope (stepper motor driven - from your advice on a post of mine some weeks back).

It did occur to me that it should be possible to control focus with another stepper; certainly at high magnifications it's so easy to lose a target simply by bumping the focuser (and very hard to focus when the target is moving around).

37 minutes ago, Notty said:

Was there much of a temp drop between start and end of imaging? I’d always understood correct focus does change with temperature so as it drops you’d need to refocus

Good question. It's not something I recorded (or was aware of) so couldn't say for sure.

It's interesting that on both of the quality graphs I posted earlier there's a strong fall off in the image score over the first ~50 frames (25 minutes) and then it tends to flatten out. I assume that a camera brought outside from a warm room will experience a higher rate of temperature shift initially, then settle down. I think the important test next time the skies are good here will be to get the camera outside for a good 30 minutes before I start to shoot.

6 hours ago, jimjam11 said:

So:

1. This happened every/most nights you attempted to image?

2. It happens in all parts of the sky?

3. You are confident you are accurately focussed? If so, how are you judging this?

4. Presumably you are guiding? If it was high clouds the guide star mass would vary like this:

 

1. Yes, but that's only a handful of times, and at one location - so perhaps not that significant (in the sense of being able to say it always happens with that equipment)

2. Maybe not. I'm pretty certain there have been a couple of times where I've moved the camera to point at a different area of sky and got a better result

3. Generally I'm using the liveview autofocus on a bright star (though the 5D4 is much more reliable than the 7D), switching the lens to manual, then swinging to the target

4. As in - a separate autoguiding camera? No - just using the Skywatcher Star Adventurer for the moment

I think a comment made earlier in this thread (about acclimatising the camera before shooting) is pertinent. It makes sense that focus might change as the lens and camera cools (assuming I've set up focus when the camera had just come outside from a warm room).

However, when I've experienced the problem of the soft images - and been present to check the camera - I'm pretty certain I've never got the image sharp again by attempting to refocus. The front element of the lens has never shown any fogging in those scenarios, so unless there is something fogged up inside the camera then maybe it is just atmospheric issues. I.e. I've just been unlucky in that every time I have gone out to image I've had some cloud roll over a few tens of minutes after starting.

1 hour ago, jimjam11 said:

Could you have tilt in the imaging train?

Not sure what that is: unless you mean the lens not being parallel to the sensor?

1 hour ago, jimjam11 said:

Which lens are you using? Some of them can be very difficult to focus accurately, although it is strange you get this pattern every night?

For these, it's all been a Canon 100-400II, sometimes with a Canon 1.4x or 2x extender.

"Every night" probably covers only a handful of occasions to be fair (I'm a noob), so probably statistically dodgy!

1 hour ago, jimjam11 said:

Have you looked at some good and bad frames to visually compare? Is the only difference focus? 

It appears to be. I've just picked three frames from an attempt to capture M81 and M82 and cropped a small section from each:

The top image is one of the first captures, the middle is about 47 minutes later, the bottom is 114 minutes into the session.

I've increased the brightness slightly for web viewing. I notice that the bottom image has a much more obvious red hue in the background, and obviously the stars have become blurred "blobs". Maybe it is just atmospheric issues?

1 hour ago, Adreneline said:

This may be irrelevant but when I use my 70D - controlled by EoSBackYard - for long exposures I notice that as the imaging session goes on the sensor temperature creeps up - not by very much but nevertheless it gradually increases as the evening goes on. Increasing temperature means increasing noise.

Just a thought.

 

I should definitely look into some software for controlling the camera remotely (rather than walking back and forth between the house and garden). Certainly the non-cooled cameras may well suffer, but the issue I'm seeing is almost as if the image is defocussing (stars become larger and dimmer "pools" of light), so I'd assume that isn't a heat/noise issue.

14 minutes ago, geoflewis said:

M42 is currently transiting around 6pm BST, so assuming that you didn't start imaging until after dark at say 9pm (astro twilight is actually not ending until nearer 9:30pm BST) then it's going to down below 20 deg altitude heading close to 10 deg altitude an hour later, which is going to be a significant contributor to your deteriorating images in that part of the sky. You will also be experiencing atmospheric dispersion with a DSLR (colour) camera at those low altitudes, so there's a lot going against you.

That makes, thanks. There's a house "in the way" from my line of sight and it's been interesting noticing how the position of M42 changes over the months. Not something you pay attention to until you actually start "looking".

14 minutes ago, geoflewis said:

Hmm, so that's intriguing, I agree it's not poor seeing at the horizon for that target. Do you acclimatise your camera before imaging or just take it outside and get going? I'm wondering whether you are seeing some focus shift, or if not that, then whether the glass in front of the sensor or the sensor itself is misting over a bit as the evening progresses.

Good point. I don't have the camera + lens outside for very long beforehand. I'd always assumed it was misting (so I need to get a dew heater) but every time I've checked the front element of the lens it looks perfectly clear. Perhaps some fogging is happening internally.

I've just checked the data from another session - this time of M81 and M82; so pointing broadly east, and high in the sky (well away from the horizon).

A similar pattern through the ~350x 30s frames (about 3 hours). Unfortunately DSS rejected all but 64 frames (~32 minutes), so it was a lot of wasted data.

40 minutes ago, Adreneline said:

Can you tell us a bit more about the equipment you are using, e.g. is the camera a dslr/cmos cooled/ccd cooled? Are you using a telescope or a camera lens.

 

Sure. I've seen this pattern with a Canon 7D and a Canon 5D4; both unmodified (though using a CLS filter), and using camera lenses.

37 minutes ago, geoflewis said:

Where were you imaging and what duration does the graph cover? If you start imaging close to or after the meridian it could be that the diminishing results are due to the scope steadily pointing lower and lower into the murk as it gets closer to the horizon.

On the example above, each sub was 30s; so just over an hour. DSS rejected over half the frames; such that only about 58 (~29 minutes) were usable.

This was M42, which means I'm pointing south towards a major city and I do indeed end up moving towards the horizon over a session.

I've noticed a fairly consistent pattern on the (admittedly relatively few) attempts I've made to capture a number of light frames of a DSO; namely that the first few shots are usually pretty sharp, then over time it looks as though the image has become defocused.

Running the light frames through DeepSkyStacker and looking at the quality scores, I usually get a pattern similar to that shown below. The Y axis is the frame score, and the X axis is the capture number:

Broadly, the earlier captures are better, and later are worse - though that's not 100% true.

Checking the camera lens I see no fogging or condensation on the front element. If I (later in a shooting session) attempt to refocus on my current target, the image is still soft (so I assume the lens losing focus isn't the problem). Occasionally I can swing to another area of the sky and that might be be sharp (or not).

So - my assumption is that it's as simple as clouds/moisture in the atmosphere rolling in; which just happens to coincide some tens of minutes after each of the (few) shooting sessions I've attempted - and therefore there's nothing practical I can do to combat this?

Thanks. Definitely too few (good) light frames, plus some mistakes with the darks, so the noise could certainly be reduced. Each frame could have been better too with a longer exposure time, but I'd done a lazy job of polar alignment. Ironically I got that nailed OK last night to shoot M81... and failed to even find it in the sky 

My first proper stab at a DSO - obviously M42.

So many things wrong with this - I was using the Star Adventurer mount with my old 7D DSLR with a CLS filter (not a great sensor at high ISO settings), my polar alignment wasn't great (15s lights max), plenty of the frames were soft due to some atmospheric issues, I made a mistake with the settings for the darks, there are no flats, and in total there's only about 25 minutes' worth of light frames. But... I'm pretty happy with it as a first go.

If and when I ever get round to making a tracking mount for the Skywatcher 300P (and get the 2" CLS filter I ordered) I'll be able to use the 5D4 (much better sensor), and the 300P will suck in light at about 16x the rate of the lens I used on the 7D; which is a positive thing to look forward to.

I'm feeling very jealous, as I spent two hours last night failing to even find M81 in the sky 

1 hour ago, Louis D said:

True, you could use an equatorial platform instead to move that 13.1 inch Coulter he used to take DSO astrophotos.

Ah. Yes, the http://www.equatorialplatforms.com/ products. Certainly an option with a Dob.

14 minutes ago, Louis D said:

DSO imaging can be done with a driven Dob with enough patience and experience.

Yea, but why use two stepper motors when you can just tip the Dob a bit and only use one 😉

On 11/03/2020 at 15:50, Stephanos said:

Hello everyone!

I am new here and about to buy my first telescope and wondering if you could help me make up my mind!

I have been looking at the skywatcher explorer 130P on an eq2 mount and the skyliner 200P Dobsonian. There is obviously a price difference, as well as the diameters and mounts are of course different.

The skyliner supposedly has 'direct slr connection' which is a big plus, as I would like to connect my ancient Canon 1000D to the telescope I buy. Would it be that hard to connect the camera to the explorer (i.e. would it be more than a t-adapter?)

Also anyone had experience with the EQ-2 mount? Not worried about the alignment etc as I am confident I can do it with a bit of practice, it're more if it's stable enough and offers a good experience? Also does the optional motor help with taking long exposures or is it not that precise? 

I like the simplicity of the Dobsonian but as far as I know there is no option to 'motorise' it (so I'm wondering whether I will need a completely separate rig in the future if I want to take long exposures etc?)

Thank you so much, apologies if any of the questions are a bit obvious to the experienced. Any other advise (or alternatives) are most welcome

All the best,

Stephanos

 

Speaking as a new scope owner (with a fair bit of photography experience, but basically none with telescopes); a Dobsonian (Alt Azimuth) mount is great for observing - intuitive to point and "bump" to follow objects in the sky. You can also get yourself a much larger scope for the money, as the Dobsionian mount is obviously cheap to construct.

An equatorial mount will allow tracking of objects in the sky, but for astrophotography exposures of any real length the mount needs to be quite substantial. I'm told that many of the cheaper Skywatcher EQ mount + scope combinations are not really suitable for cameras, as the mount isn't up to the task.

The direct SLR connector is (on my 300P at least) just a 2" adaptor that fits into the telescope's focuser, with an M2x0.75 "T" thread. A "T" to EOS EF adaptor is cheap, and will work fine.

With a Dobsonian mount you will be able to get images of the moon, and whilst I haven't had chance yet, possibly the planets (because you take many short exposure frames, so blurring isn't a problem). Any DSO imaging will need an EQ mount.

My advice then would be to get a smaller scope and get input on suitable astrophotography mounts from more experienced users here, or get the 200P Dobsonian, and later get a (probably quite substantial) EQ mount to use it for photography work.

11 hours ago, laser_jock99 said:

I only use DSLR's at the moment. With a DSLR you have a rectangular imaging area superimposed over an imaging circle. The trick is to get the pick off prism in the area of the long side of the DSL image rectangle so it doesn't intrude into the imaging area.

That makes sense, thanks. I'm using a DSLR too.

I'm starting to build up some of the parts for the DIY racking rig so with luck I'll be able to start putting together some designs in the next few weeks. If I can get that to track for some tens of seconds then guiding will be the next step.