dph1nm

On 08/04/2019 at 15:54, Evaldas_Saulys said:

So that means I need to mark every star? (sorry for silly question, I'm new with DSS).

No - when you hover over the image with your mouse it pops up something which says "add this star?" or "remove this star?" (or words like that).  It does therefore  have to have detected something in the first place (and for whatever reason decided it is not a star) for this to work, so it isn't as simple as you manually selecting the positions of the stars you can see, and if it really hasn't detected anything then it will not work.

On 08/04/2019 at 15:43, Evaldas_Saulys said:

It detects from 5 to 15 stars from each light, but when I try to stack it, it still says that only 1 frame will be stacked.

My suspicion is that most of these are noise/hot pixels and not real stars. These can, and should, be removed with the star editor again. The other, less likely, possibility is that that it has found different stars in each image - you do have to have 8 stars in common between the subs.

NigelM

You could try superpixel mode - that halves the resolution but seems better at detecting blurred stars, or try the manual star editor (the red  star on the right hand panel above the comet) and see if you can pick any up with that,

NigelM

30 minutes ago, happy-kat said:

You stars are nicely controlled, there's no CA evident. 

It is not a bad scope in that respect (given it is at the cheap and cheerful end of refractors), but if you get the focus just a little out then colour horrors can happen (as they did in the subsequent image of NGC5866 which I am not going to show!).

NIgelM

Rolled out the Nexstar 102 SLT for the first time in a couple of years. This is from a reasonably dark site in South Wales. 30 sec subs, total of 1620 sec exposure with a Canon 1000D at ISO1600. Image binned 4x4 (8" per pixel) for web display. M52 and NGC7635 (Bubble nebula):

NigelM

The 12S Quattro comes with a Losmandy dovetail - so it is obviously possible for Skywatcher to produce suitable rings.

NIgelM

It claims to be an alt-az mount with built-in field rotator and autoguider. It will be interesting to see how well it works. Maybe this is the future of amateur astronomy ...

NigelM

I still have my 8.5 inch f6 Newtonian with plastic tube (which was bought as a bunch of components rather than the finished article - cheaper that way I think), although as of last September it has been swapped out for a Skywatcher 12", so not strictly still in use. It now sits forlornly in the corner of the obs under a white sheet. Somewhere in the garden shed I still have the MkII mount it used to sit on, but I don't think this has been used in earnest for 40 years or more!

NigelM

sync is different from alignment - whenever you redo an alignment the old alignment data is always cleared (and I suspect the sync data - it wouldn't make sense not to). Personally even after starting the EQ8 from park I find it worthwhile to redo a 2-star alignment, although in theory (if you get the time exactly right) you should not need to. If you have good polar alignment and are fixed in an observatory I don't really see why you would need sync at all.

NigelM

On 22/09/2017 at 13:51, certx said:

Go to menu Utility Function -> Show Position, DEC changes on the display by 1 arc second every 20 to 30 seconds. After several minutes, it's several arc seconds off the coordinates I specified, and after a couple hours, it is several arc minutes off of the coordinates I specified in the slew.

What happens if you then tell the mount to go back to that object/position? Does is slew several arcminutes in dec and hence no longer align on the object, or does it stay where it is? i.e. is the problem with the displayed coordinates or does the telescope really think it has moved that far.

NigelM

Decided to take the plunge and replace my (very) old Fullerscopes 8.5" f6 Newtonian by a 12" Quattro (which at f4 has much the same focal length as the Fullerscopes). Turns out that I can't get anything much bigger in the observatory, so although an f5 12" would have been easier on coma etc, it would probably have hit the walls!

It arrived in two parts - one box for the OTA (large enough to hide a person in) with secondary attached and one smaller one for the primary mirror (in its cell) and a pack of springs and screws. Seems I got the last one in OVL's warehouse, and it went 'missing' for a few days, so for a while it wasn't clear if there were any at all in the warehouse! Turned out someone had 'put it aside' then promptly forgotten about it. Anyway it turned up only a few days late in the end. Strangely there were no instructions in either box, so attaching the mirror to the OTA required a bit of guesswork - turns out you need to unscrew the white 'collar' at the end of the OTA and attach this to the back of the mirror support, then man-handle the whole lot back into the OTA.

The assembled beast is not exactly light, but it can be carried by one person, although attaching to my EQ8 was a bit of a struggle. Did a quick collimation with a laser, which showed the secondary was surprising well-aligned to the centre spot on the primary, which is just as well so far I have not been able to loosen either the centre screw on the secondary, or any of the three adjusting hex screws! No idea how Skywatcher have managed to get these so tight.

Another slight issue is that I was planning to buy a Skywatcher Aplanatic coma corrector, but due to production difficulties none are expected in the country until the end of October. Anyway, in the meantime, here is the first light image of Albireo (28secs, ISO1600, Canon 1000D), cropped to hide the coma!

NigelM

Just to note that 8 years on from my original post in this thread my Nexstar 102 SLT is still working, albeit with some rather random speeds when you try to move it quickly!

NigelM

18 hours ago, Uranium235 said:

Its about finding what point your camera becomes "ISOless", which turned out to be ISO200 for my Canon 1000d...

I don't think the 1000D ever becomes "ISOless". The read noise at ISO1600 is half that at ISO200

NigelM

Holiday outing in South Wales at the end of March with a south facing site. Venerable Nexstar 102SLT + Canon 1000D + Skywatcher LP filter.  Subs are all 30secs - total exposures between 10-30 minutes. ISO1600, processed with DSS and Gimp; flats and bias used. Have to throw away the 25-30% of the subs with very bad tracking, but the rest I keep and stack, and the result is round (if rather fuzzy) stars.

NigelM

I frequently have this problem with the skytracker! For some reason, it is very easy to point the polar scope at the wrong star, especially if you are in a hurry, usually one on at a similar altitude. My only advice is to double check. There is a hole near the top of the body (for lining up if you don't have a polar scope) but I find this very difficult to use.

NigelM

On 2/24/2016 at 19:50, ollypenrice said:

Can you tell us something about autoguiding in de-rotated alt-az mode? The only professional scope I know from experience is direct drive and so 'encoder guided.' This is hardly the thrust of the thread but I'm interested. I know that there are still plenty of professional EQs but are many being built these days? I thought alt az and de-rotator had become the norm.

Yes, mostly alt-az + derotator these days, but they are still autoguided. Usually picked up with either a separate ccd built-in to the camera or a moveable pick-up mirror. Of course, anything with adaptive/active optics is also guiding, almost as a side effect! There is some mention of the WHT guider here http://www.vikdhillon.staff.shef.ac.uk/teaching/phy217/telescopes/phy217_tel_ag.html

On most 2m class or above scopes I would think you would be pushing your luck to do more than a couple of minutes unguided (remember most of them have pretty small, i.e. sub arcsec, pixel sizes).

NigelM

10 hours ago, ollypenrice said:

The prfessionals don't autoguide, though.

Ohh, we do you know! Except perhaps for sub-1min exposures, as the overheads in finding guide stars becomes too high.

NigelM

I should also say that I use the kit 55-250 zoom (when tracking). I am quite happy with it, but it isn't perfect by a long way.

I have some pictures with the 18-55 here

and some with the 55-250 here

NIgelM

The standard Canon plastic 18-55 f3.5 kit lens is actually quite good at the wider end! If your aren't tracking then your really need something wider than 50mm in my opinion.

NigelM

23 hours ago, The Admiral said:

Forgive me asking a stupid question, but how is binning done on 4-pixel arrays?

You simply treat the red green and blue pixels as separate images and bin up adjacent pixels of the same colour. You can then reform this back into a bayer array (if you want). Unfortunately I don't know whether any readily available software does this!

I think there were some Kodak CCDs which genuinely did hardware colour binning, by some fancy clocking of the readout so that the different coloured pixels ended up in different registers, but you don't hear of these much nowadays.

NigelM

The advantage of hardware binning is that you only get one dose of read noise per binned pixel, whereas e.g. with 2x2 binning you would have four doses of read noise in the unbinned image covering the same area of sky. So the read noise contribution per square arcsec goes down. With software binning you always have the four doses of read noise whatever you do. This is the only real reason professional observatories hardware bin their cameras - mostly for spectroscopy I think, although it is sometimes possible to do it for imaging.

NigelM

21 hours ago, Uranium235 said:

Thats a question I've been asking myself for quite some time! And it confirms my hunch (ie: in relation to Maxim 2x2 software binning) - no, its not as good as hardware binning.

If your pixels are sky noise limited then software or hardware binning should give the same effect. If you have a significant read noise contribution then hardware binning is best.

NigelM

p.s. if you are going to software bin a DSLR it needs to be done before debayering the data.

Yes, if you are truly sky noise limited then you won't get any benefit.  Whether you are depends on may things - your telescope aperture, pixel size, sky brightness, camera efficiency & read noise etc, so it is really something you have to determine for your particular situation.

NigelM

Hmm - with only 40s exposures I suspect a typical DSLR shot might be read-noise limited. In which case a focal reducer might improve the overall S/N per object (less read noise per square arcsec on the sky), whereas software binning will not.

NigelM

M22 and NGC6642, 15x30secs, Canon 1000D, Celestron Nexstar SLT 102mm Alt-Az - taken from Lincolnshire last month - rather low in the sky at the time!

NigelM

lovely pics, what AZ mount did you use for these?

All done with one of these

Celestron Nexstar 102SLT

I put tube rings on the OTA to help get the balance point with the camera attached, but the mount is straight out of the box.  Yes, you have to throw some subs away, and binning up the final image is usually a good idea, but it still gives a half decent picture if you get enough total exposure time.

NigelM