SteveNickolls

Sorry to have taken so long to post these images. They are what I promised to do-restack the M31 and M33 images I posted before in DSS and reprocess using StarTools to see what visible differences might be seen when omitting dark frames but using kappa-sigma in DSS. I would class the M31 image as being easy to process in StarTools indicating the data quality was better (for a brighter object).

First M31 with darks and 'median' setting in DSS-

And now without dark frames but using sigma-kappa in DSS-

And now M33, first with dark frames and 'median' setting in DSS-

And next without dark frames and using kappa-sigma in DSS-

Changes in cropping were down to me.

Comments welcome.

Cheers,
Steve

2 hours ago, The Admiral said:

You are right Steve, so long as you are referring the the same star. But, a star on the edge of the frame will appear nearer the centre when used with a shorter focal length. Another star, again on the edge of the frame, will still move by the same amount as your original star with the longer focal length. Another way of thinking about it is imagine a line passing through the centre of the frame. If the camera, or image, rotates by, say, 1 degree, that line will appear to rotate by the same amount, irrespective of the fl of the lens attached.

Curry and a beer? The answer to most problems!

Ian

So if I crop out the star at the edge...I get to image for longer?

It's the beer talking.

Cheers,
Steve

13 hours ago, Herzy said:

Btw, Steve, those images of Andromeda are pretty awesome. I've heard it's bright, but is it an easy target? I've never imaged it before and I'm thinking of giving it a go.

Hi,

Thanks for the kind comments on M31. Yes it is an easily accessible target, it can be seen in the finder scope so composing your image is much easier than say with M33 which required taking snapshots to check its position in Live View. Right now if you are using an Alt-Az mount and have to consider the implications of field rotation M31 is well placed in the sky both in terms of azimuth and altitude. If you had an equitorial mount I guess you'd wait until it was at its highest position. With my SkyWatcher Synscan Alt-Az mount I have been able to take individual exposures of M31 lasting 60 seconds and the mount overall has produced a high percentage of frames acceptable to DSS (76%). Definitely go for it!

Cheers,
Steve

I can't articulate this very well but the idea I have is if the light from a small star in a set period of time could be detected on two adjacent pixels, that would be the start of a trail. However if the light in twice that period of time remained in the same pixel (because the field of view was so much wider) then you wouldn't see any apparent motion. It is possible then that longer periods of time (when using shorter focal lengths) could also show no apparent movement.

My head hurts. I'm off to have a curry and some beer.

Cheers,
Steve

4 hours ago, SilverAstro said:

Hi Steve very interesting very nice images, amazing in fact

The two of Andromeda - are they full frames or cropped ? Reason I ask is, are the scales of the images as presented comparable ?

Hi,

Thanks for your kind comments. They would both have been subject to some cropping, the one taken with the Canon piggybacked would only have been cropped slightly a few pixels around the edge. The piggybacked image was taken at 200mm FL (on a APS-C camera like the Canon 600D I think this works out at 320mm) while the other was through my refractor (500mm FL). The image through the telescope was cropped more vertically to remove a lot of poorer background. hope that helps.

Cheers,
Steve

Jimbo747,

A most interesting phenomenon you have imaged there for over an hour. Can I ask if you were imaging at 200mm with your DSLR? My thoughts would be that at that FL the percieved field rotation on the chip was insufficient to cause a streak to appear. When I process images in StarTools I often bin the original image by 50% or 65% as my 18M pixel camera image is mostly wasted (oversampled I think the term is). I know in his book, 'Using Short Exposures with Light Mounts..' Joe Ashley has a  technique for overcoming field rotation  based upon calculations involving 0.125 degree over 20 seconds which is close to Ian's value. You also need to remember that even if you can 'overcome' field rotation (using a tracked Alt-Az mount) by using a short FL lens your mount performance might limit your maximum duration of exposure from a mechanical viewpoint. Very interesting phenomenon though and well worth exploring more.

Cheers,
Steve

10 hours ago, Stub Mandrel said:

I did a comparison using kappa sigma and adaptive average and the kappa sigma appeared to have least noise.

I found leaving out darks made noise worse but 'your mileage may vary'.

Thanks for this, will see what happens! Fingers crossed.

Cheers,

Steve

8 hours ago, happy-kat said:

You should try swipe for typing on your hudl of you haven't yet

Ha, for that you need some typing skill, knowing where the keys are laid out. I often don't know where the hudl is ;-). I will put that down as an aspirational achievement, but thanks for the idea happy-kat.

Hi All,

Thanks for the comments Herzy, the colour issue is down I think to the data not being enough for StarTools to properly handle in its COLOR module, hence I skipped that out plus I tried just using the green channel hence the tint. I agree on more photons but as Ian makes the point 4-9 hours would require a number of imaging sessions, do-able at a pinch but we don't get lots of decent clear nights in the UK? Will see how it goes though-thanks.

Nige, good to hear you use kappa-sigma in DSS, I'll post my results as soon as I can. You have a nice collection on lenses and it will be great to see your images before too long.

Excuse any spelling mistooks as I'm on the hudl with it's tiny keys and random spelling :-)

Cheers,

Steve

Hi Ian,

Thanks for your advice here, sadly I'm only repeating what I have read elsewhere regarding kappa-sigma as a means of removing pixels that are out of line with adjoining ons so I have no personal evidence either way. If I get chance I'll reprocess recent images in DSS using 'Kappa-sigma' in place of 'median' and leave out the dark frames as an experiment. The thought that the tracking limitations of our Alt-Az mounts can be used to advantage to 'dither' is intriguing. Will post what I find to help us all.

Best Regards,
Steve

The recent clear dark night skies have allowed me to image M31 and M33 using the combination of Synscan SkyWatcher Alt-Az mount, 102mm Startravel refractor and Canon 600D DSLR. This season I have been trying out ISO 800 after finding ISO 1600 was producing images which on the camera histogram were well to the right hand side. I've also been using stock dark and bias frames. I realise I can't control the temperature of the camera chip but the dark frames do help with bad pixels. I am going to try using the kappa-sigma clipping in DSS as it's meant to be an alternative to using dark frames for removing rogue pixels.

The following two images were both taken using 60 second exposures since both objects were well placed in the East for field rotation mitigation purposes.

M31

x50 light frames, x50 dark frames, x60 flat frames and x50 bias frames. Stacked in DSS and subsequently processed using StarTools. Taken 29th August 2016.

M33

Again x50 light frames, x50 dark frames, x60 flat frames and x50 bias frames. Stacked in DSS and subsequently processed using StarTools. Taken 30.8.2016.

DSS was happy to accept 72% of the M31 exposures and 75% of the M33 ones. At sixty seconds I'm averaging 76% acceptable frames from all my exposures up until now.

This season I've obtained a Canon 75-300mm USM III lens to have some fun taking wide-ish piggyback shots using the Synscan Alt-Az mount and below is my first attempt at M31 in wide view taken on the 26th August this year. Taken with a camera lens setting of 200mm f/5.6.

The image is made from x50 sixty second light frames at ISO 800, x50 dark frames, x60 flat frames and x50 bias frames. Stacked in DSS and subsequently processed using StarTools. DSS was happy with all the light frames taken.

Cheers,
Steve

2 hours ago, Nigel G said:

Hey guys.

Sorry for not contributing,  my mother has been taken into hospital,  I will catch up on posts later on. But for now I have a mother who needs her son.

Nige.

Hi Nige,

Sorry to hear about your Mum. Hope she is discharged soon.

Best regards,

Steve

I do like your latest image very much Nige, lots of detail and good colours. You should be very pleased  how it has come out :-)

Cheers,

Steve.

That's come out very nicely indeed Nige the Bubble Nebula is shown very well. Dark background too. Look forward to NGC 7000. I also admire your fortitude imaging so late, 'erm I mean so early :-) The large size of your objective certainly pulls in the photons.

Cheers,

Steve

22 minutes ago, Nigel G said:

Steve

If I can line up the same then I will add to the collection and experiment with different stacks for sure  When the mount is on form I can get 90 second exp on this dso with about 75% keep rate, hopefully a good clear Friday or Saturday night will come soon.

Hi Nige,

I've found DSS isn't too worried about having objects perfectly lined up over sessions. Good luck for the weekend. Your mount is really performing well 90 seconds is great.

Cheers,
Steve

I really thought the seasons imaging had ended but last Sunday evening (5th June) I stopped up and managed to image M27 despite a lot of moisture in the air. I attempted 70 second exposures for the first time but the results over the evening were mixed, my primary target M71 was so poor I dare not post on here and only 3/20 (15%) of the exposures we usable in DSS. M27 fared somewhat better and 13/30 frames were usable (43%). I might have found the tracking limits of the Synscan Alt-Az mount. The duff frames all showed star trailing indicating the mount was struggling. Both target objects were ideally placed in the East for mitigation of field rotation issues. I still think the Synscan mount is great allowing 60 second imaging for such a modest price.

The image of M27 below was taken using my SkyWatcher Startravel 102mm f/4.9 refractor , Synscan Alt-Az mount and Canon 600D DSLR. The image was stacked using DSS and processed in StarTools. x13 ISO 800 light frames, x50 dark frames, x30 bias and x50 flat frames were used. Hope you like it.

Cheers,
Steve

Hi Nige,

Good going with NGC 7000, will you add the additional images to what you already have? I'm intrigued how much exposures this object will soak up :-) From what I've experienced with StarTools it likes lots of exposure time, it makes all the subsequent processing steps easier and you find you can actually use some modules to produce nice images. You can find odd colours here and there in an image with little data and in the WIPE module selecting Vignetting can help remove odd colours and gradients. Good luck taking more images.

Cheers,
Steve

4 hours ago, Stub Mandrel said:

It amazes me how some parts of the sky are overflowing with stars like that shot, and others are almost empty - at least until you use a Hubble to spot the zillions of galaxies hidden in the background.

Yes, your eye sees nothing in the light pollution then the camera opens up a vista of stars across unimaginable stretches of space, quite breathtaking.

3 hours ago, The Admiral said:

Good capture Steve, and well done for having the fortitude for imaging at this time of year!

Ian

Hi Ian,

Thanks for the endorsement, I had thought we had seen the last of the clear skies in May but the past few days have made it a bumper month.

Cheers,
Steve

Hi,

The month of May has certainly provided a greater than usual number of imaging nights this year and on the 28th I was able to image the Cocoon Nebula IC 5146 (C 19). The image used x75 one minute exposures at ISO 800 plus x60 darks, x50 flat frames and x50 bias frames. The frames were stacked in DSS and the master image processed using StarTools. The equipment used was my SkyWatcher Startravel 102mm f/4.9 refractor, Synscan Alt-Az mount and Canon 600D DSLR. x91 light frames were taken and DSS accepted 75 for stacking (82%). The dark nebulosity around IC 5146 and extending above it and apparently trailing to the right is Barnard 168. While the Cocoon nebula is around 12' in angular measurement its true size is around 15 light years, amazing. I hope you like the image.

Cheers,
Steve

57 minutes ago, Filroden said:

Beautiful image. Do you think the stock darks and bias had any effect?

I've been quiet for a few days. Although it's been clear here, the moon is getting too bright in the evenings and I've not had the stamina to wait until 2am for it to darken. Also, even though it's often looked clear, there has been a high haze that has reflected more light than usual.

I did take some subs but they were so bright from the moon plus normal background lights that I've not been able to integrate them with earlier subs. However, I did drag myself outside last night at about 2:30 and what a sight! I could almost make out the Milky Way (may have been imagining it but I thought it was there, overhead) and I could definitely make out mag 4.3 stars with direct vision. I was so tempted to set up and take some subs as the North America Nebula was at about 60deg altitude. Antares was quite high and another tempting target, though by 2:30 it was already behind the houses near me. I'm now wondering whether I need to set up and start imaging around 1:30. Though I suspect that now the moon will destroy any attempt other than globulars.

Hi Ken,

Thanks for your kind comment. It might be my last effort for this season as the nights are taking longer to darken and I need my sleep unfortunately. Good luck imaging from 1.30 AM it's really what's needed at this time. Yes, the Moon seems to have an agreement with the weather about coinciding with clear skies!

I don't believe using stock frames has done any detriment Ken (but no way to objectively tell really) and I'm getting more confident in StarTools with the mask tool and FILTER module. Still a long way to go but getting there. I'm sure using 60 seconds exposures and doing a fair number of them helped this time though. 

Seeing the Milky Way would have been a great sight, the light pollution affecting your sky sounds similar to that here as I can make out the Mag 4.3 stars in Ursa Minor but seldom the fainter ones. I've only glimpsed the MW once from here and that was about 4 years ago in August if i recollect correctly. I'm waiting until the county council swaps all the remaining sodium street lights for leds and we might get to see the MW again. Fingers crossed anyway.

I would love to be able to view the Southern sky low down, I've only observed Sagittarius and Scorpio when on holiday at a dark site and there's a lot of Messiers I would like to see. There is a newly opened public park nearby with views to the horizon over the Trent Valley so if I can rope in some heavies to come along for security I might get to see Sagittarius and Scorpio later in the year.

Cheers,
Steve

Hi folks, here is my latest offering taken on the evening of the 14th May 2016 of the Crescent Nebula NGC 6888 in Cygnus. The image was taken using a SkyWatcher Startravel 102mm f/4.9 refractor, Synscan Alt-Az mount and Canon 600D DSLR. Due to the position of the target I was able to employ 60 second exposures. I took 91 sixty second light frames at ISO 1600 and for the first time used stock dark frames (x50) and bias frames (x50). x50 flat frames were taken the following morning. The frames were stacked in DSS and further processed in StarTools. Of the 91 light frames taken DSS was happy to use x67 (just under 74%).

Hope you like the image.

NGC 6888 Crescent Nebula-

Cheers,
Steve

2 hours ago, Filroden said:

Here's a 90 second exposure at ISO 1600. It's at 80% but it does develop and I have star colours so it hasn't been over exposed. I guess some trial and error is needed to know what your conditions allow. 

Thanks for this comparison, I might see what effect using ISO 800 has on the histogram and on images taken.

Best Regards,
Steve

Hi Mike, Thanks for these posts. I can understand some of the article but floundering elsewhere. I took a look on my camera at the RAW exposures I took a few nights ago with the histogram also showing. I found that the histogram, whether for brightness or RGB channels was showing well off from the LH side about 60-70% along not the 10% in the article. Now this was for 50 seconds exposures at ISO 1600. I presume it means the image is being swamped by light pollution (it's bad here) so I should reduce the exposure time or drop the ISO value? Or does it matter? Unfortunately I have no background in photography to draw upon, just learning from mistakes and successes.

Cheers,
Steve

This is all getting very interesting!

Cheers,
Steve

I use the "Linear, was Bayered, is not white balanced" (the second) option for my Canon camera Nige. You might want to experiment. 

Cheers,
Steve