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static telescope "drift-scan" imaging works!

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#1 nytecam

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Posted 24 June 2015 - 04:03 AM

Rather than add to the predominently negative opinions of JKoelman's thread
http://www.cloudynig...k/#entry6643034
I thought I'd start a new thread of my positive results from last night shown below - drift scan, with a static telescope, works!

The diurnal motion of stars is fully understood and predictable [unlike supersonic misiles quoted elsewhere!] and the stellar 'motion' is maximum at the celestial equator and minimum at the celestial pole. This technique is not something I need with my equat mounted goto scope but has the potential to bring EAA to the vast majority of amateur scopes on simple undriven mounts including Dobsonians. The fun would be in finding and centering the DSO targets prior to viewing and recording them!

Used my Meade 12" [30cm] f/4 LX200 SCT+SX Lodestar-Cx2 [Sony ICX829 sensor] colour camera in very brief sub-exposures from 0.1s - to 0.4s [to counter trailed stars] in multiple stacks up to 50 or 60 images per object under SX s/w autostack mode. Exposure details in image headers. Although a colour camera was used colour can't be extracted in SX s/w easily as the colour data is scrambled via the trailed image!

They confined here to objects of high declination in M57, starting in late twilight, then M51 and M82 near the zenith. No flats or darks used and these artefacts evident in the images - the undriven examples with the static scope, show as horizontal bands or hot pixel trails and are generally noisy as one would expect. Nevertheless drift-scan works!

Hope my tests are of interest and that others can repeat them with their gear.

Nytecam

Attached Thumbnails

  • m57dc150623x6strail.jpg
  • m51dc150623x20strail3.jpg
  • m51dc150623x20sdriven.jpg
  • m82dc150623x16strailx.jpg
  • m82g150623x16smgx.jpg

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#2 GlennLeDrew

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Posted 24 June 2015 - 04:10 AM

Very nice work! This has application for mounts which track poorly, or if one is working under conditions of wind gusts which would ruin too many longer exposures.

#3 Mittag56

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Posted 24 June 2015 - 08:08 AM

Never being that good at polar alignment and keeping my gear tracking good i have been doing this on occasion for a couple years...point the scope in rough area and lock it down and just watch what drifts through the eyepiece......now it looks like i'll have to put my camera on and give live view a try....Thanks for the knowledge share 



#4 Dom543

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Posted 24 June 2015 - 11:20 AM

Very nice convincing factual evidence Nytecam!

 

Your images also clearly demonstrate that registered stacking, that is an essential part of any stat-of-the-art capture support software, has key significance and usefulness way beyond its traditional role to improve S/N ratio. It extends the potential for EAA to mounts and cameras, as well as impatient observers, that would otherwise not be ready to handle long enough exposures.

 

Your post also nicely dovetails with Martin's earlier study, where he demonstrated the, to me surprising, apparent equivalence of stacking very short exposures. http://stargazerslou...0-x-1s-1-x-30s/.

 

Clear Skies!

--Dom


Edited by Dom543, 24 June 2015 - 04:18 PM.


#5 JKoelman

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Posted 24 June 2015 - 12:06 PM

I thought I'd start a new thread of my positive results from last night shown below - drift scan, with a static telescope, works!

This technique [..] has the potential to bring EAA to the vast majority of amateur scopes on simple undriven mounts including Dobsonians. The fun would be in finding and centering the DSO targets prior to viewing and recording them!


Thanks! I was hoping someone would actually do this. As always, the proof of the pudding is in the eating.

#6 nytecam

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Posted 25 June 2015 - 02:36 AM

Thanks everyone for your interest ;-)

Another brief session in late twilight 'till midnight last night on some globulars. Here's M13 in 12sec exposure with static scope + Lodestar in 40 x 0.3s autostack. No processing. Again no flats/darks but hot pixel trail to left matches the slow drift of M13 across the frame viewed in realtime - notes in progressively unexposed right margin as M13 drifted [via static scope] to the left.

This is fun ..and for good luck another 'static' Ring Neb;-)
Nytecam

Attached Thumbnails

  • m13gc150624x12strailx.jpg
  • m57dc150624x12strail.jpg

Edited by nytecam, 25 June 2015 - 02:45 AM.

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#7 nytecam

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Posted 04 July 2015 - 06:34 PM

I've prepared a short YT vid @ https://www.youtube....h?v=Un8sGf-Pwoo
showing some summer DSO via a static [eg fixed] telescope in sub-exposures of typically 0.3s auto-stacked under Lodestar s/w to a max of 60 subs eg 60x0.3s = 18s total exposure etc. Min gross exposure = 8s [Ring Neb]

Exposures, before star images trail, can increase away from the celestial equator towards the celestial pole and relates to the scope focal length and image scale.

I'm using a 'long' 1250mm fl on my 12" SCT so with shorter fl like 600mm the sub duration can be doubled at least before trailed star images occur. Such a technique may also help those with scopes with a poor tracking performance.

Hope it's of interest ;-)
Nytecam
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#8 netwolf

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Posted 09 July 2015 - 07:18 AM

would Astrovideo software from COAA work with the loadstar as i think it has a drift integration routine. it also has a off camera integration

 

http://www.qcuiag.or...iftIntegration/

 

but it only works with certain cameras or cameras with a wdm or vfw driver


Edited by netwolf, 09 July 2015 - 07:19 AM.


#9 Dom543

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Posted 09 July 2015 - 12:29 PM

would Astrovideo software from COAA work with the loadstar as i think it has a drift integration routine. it also has a off camera integration

 

http://www.qcuiag.or...iftIntegration/

 

but it only works with certain cameras or cameras with a wdm or vfw driver

 

Interesting! Do you have a link to the COAA page? I can see the examples but the link on them to the COAA site doesn't work.

Thanks,

--Dom



#10 photo444

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Posted 09 July 2015 - 07:03 PM

Dom,

 

Here is the site.

 

https://www.coaa.co.uk/astrovideo.htm

 

Paul


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#11 Adun

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Posted 22 January 2018 - 09:16 PM

I'm sorry for resurrecting this, but I did a little experiment tonight, and I ended up with questions.
 
Seeing conditions were terrible, but I just wanted to see what would happen, how fast things would drift, how much would be observable, so I did a little experiment:
 
Telescope: Skywatcher Dobsonian 10" (collapsible but using full length)
FL: 1200mm
Camera: RisingTech IMX224
Camera settings: see here, 64 total, short 250ms exposures, for a total stack of 16s exposure
Target: the Trapezium.
 
Notice I'm running at the native huge focal length of the dob, 1200mmFL, which with the tiny 6mm sensor makes for a whooping 200x. I didn't spend much time focusing, I wasn't looking for quality image, just curious about seeing what the live view would be like.
 
The dob is manual, there is no goto, no auto-tracking, I just let the object drift, and I paused sharpcap's stacking, to move the dobsonian up, reposition the trapezium, and let it drift again. I may have moved it a little during the whole process, but not much.
 
Anyway, here's what I got:
 
Drift scanning: Trapezium  (dobsonian experiment)

 
Pretty zoomed in, out of focus, yeah, but I learned a few things:
 
During the live view, longer exposures (1s) showed a lot more, but left trails. By shortening exposure to 250ms I got rounder stars, but a lot less was seen. Still, there's something there. There's potential. With a focal reducer, this could be useful enough to see some tough objects that are too small for my regular EAA gear.
 
Obviously the huge problem here is the enormous focal length.
 
My experiment was intended to be first at the native 1200mm, and then using a cheap 0.5x focal reducer. Since the dob is a "collapsible" skywatcher, I figured I could get all the in-focus I needed.
 
I don't think the problem is the scope, but the "C" adapter that comes with the camera, which must be used in order to thread a 1.25" filter (or focal reducer). That adapter is long, and using it I've measured the distance from the sensor to the reducer's lens to be 43mm. I don't know what the proper spacing would be. Just when I was tinkering with the collapsed position of the trusses, clouds covered everything (they had been coming, seeing was terrible).
 
So I want to do another experiment, but I need to get this focal reducer to work (never been able to, in any of my scopes).
 
¿Do you guys know to get the proper spacing for a cheap 0.5x focal reducer with the touptek cameras? Is there an alternative to that long C adapter, or something else one might try? I've seen the Revolution Imager RI224 comes with a reducer, ¿how is it attached?

Edit: nevermind, I finally got the reducer to work, focusing on the moon. With the IMX224 I got a TFOV in which the moon fits, with some extra space on the sides, somewhere between 0.6° to 0.7° wide, and 0.4° to 0.5° tall. I guess there's room to play some more with drift scanning.


Edited by Adun, 23 January 2018 - 08:12 PM.

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#12 mclewis1

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Posted 24 January 2018 - 10:32 AM

The other benefit of the focal reducer (aside from the shorter focal length producing less "trailing" and making it easier to frame objects) is the resulting faster f ratio which will show you more color and fainter details with the same exposures ... or allow you to use even shorter exposures.

 

So doing everything you can to reduce the f ratio will deliver benefits for "drift imaging".



#13 Adun

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Posted 24 January 2018 - 01:32 PM

The other benefit of the focal reducer (aside from the shorter focal length producing less "trailing" and making it easier to frame objects) is the resulting faster f ratio which will show you more color and fainter details with the same exposures ... or allow you to use even shorter exposures.

 

So doing everything you can to reduce the f ratio will deliver benefits for "drift imaging".

 

This could be a rabbit hole / Pandora box. 

 

I could use some yellow filter I no longer use, to remove the glass and add it as a spacer to get a more aggressive reduction. I don't think the shorter FL would affort longer exposures than 250ms, but it might increase the amount of features revealed at that exposure.  Than wouldn't  come for free, though. I didn't readily see coma with the reducer on the moon but with starfields it might be different. So close to F2 something's gotta give, right?

 

Going beyond that, I recently read how this guy matched a GSO coma corrector with a 0.5x focal reducer, for night vision on a 6" F4 reflector. He seemed satisfied and didn't even notice at first the triangle-flared stars in the outer part of the field of his PVS7 device, which from pictures I assume is a "wide sensor" (at least wider than 6mm). Now that's gotten my curiosity piked.

 

I understand the GSO coma corrector pushes the focal plane "out" 35mm. There might be a way to set up the GSO CC, a focal reducer (2" or 1.25") some spacers, and prayers to get an ultrafast but decent view on the 6mm sensor. Perhaps some binning might help.

 

Once I get a coma corrector I'm gonna try that.


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#14 Rickster

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Posted 25 January 2018 - 03:53 PM

I ("this guy" smile.gif ) have been continuing to make slow progress with FRs and my DSLR.  For clarification, the NV sensor is 18mm dia.  I am getting close to updating the other thread.  In the meantime, here are some previews.

 

First, this image is with the GSO coma corrector and no focal reduction in a 6in f4 newt (AT6IN):  01/04/18, effective f4.4, 660mmfl, single 30 sec exp, iso 3200, straight out of the camera, resized for the forum.  I usually see aberrations in the corners of the field with this scope, but now with the CC, operating at the mfr recommended spacing, the aberrations are essentially gone.

 

Second, this image is with the Antares 0.5x 2 element FR screwed onto the end of the CC and sensor to CC spacing of 52mm  (minimum I could achieve) yielding .55x, in a 16" f4.4 1800mm SW collapsible Newt ("collapsed" 4.5in), 1/20/18, effective f2.5, 1000mmfl, single 15sec exp, iso 3200, straight out of the camera and resized for the forum.

Attached Thumbnails

  • m42_0113 (Large).JPG
  • m42_0291 (Large).JPG

Edited by Rickster, 25 January 2018 - 06:12 PM.

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#15 Rickster

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Posted 25 January 2018 - 04:02 PM

Some notes on the above.

 

Effective focal lengths determined using All Sky Plate Solver.

 

Collimation becomes more and more critical as focal ratio is decreased.

 

I think the 52mmish spacing is probably optimum for this combo.

 

Images taken with a Canon t4I, sensor size 22mm X 15mm

 


Edited by Rickster, 25 January 2018 - 09:25 PM.

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#16 Adun

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Posted 25 January 2018 - 11:16 PM

Hello Rick!

 

That's a really good view for a full frame DSLR on an F2.5 dob! 

 

So the way you are stacking them is  FR - CC - 52mm spacers - sensor?

 

I already have the GSO CC and spacers in my shopping cart, I guess it won't hurt to add a 2" Antares FR to see what happens... fingerscrossed.gif


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#17 Rickster

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Posted 26 January 2018 - 12:21 AM

Hi Adun,

Yes, you are correct, FR - CC - 52mm spacers - sensor.  Here are a couple of pictures to save 2000 words. 

 

Note that the sensor in a DSLR is recessed at the back of the camera to allow room for the viewfinder mirror to flip up and down.  The center line mark on the top of the camera designates the sensor plane.  So, to get my spacing down to 52mm I had to get a short Canon to 2" adapter (actually, it is two adapters, a 2" to tmount adapter threaded into a tmount to Canon adapter). 

 

Oh, and my t4i Canon DSLR has an APS-C sensor which is 22mm x 15mm whereas a full frame camera, such as a Canon 6D, has a 36mm x 24mm sensor.  http://photoseek.com...ds-1-inch-type/

Attached Thumbnails

  • 52mm (Medium).jpg
  • short canon adapter (Medium).jpg

Edited by Rickster, 26 January 2018 - 02:37 AM.

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#18 Stephen Kennedy

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Posted 11 August 2018 - 01:18 PM

Adun, on 22 Jan 2018 - 7:16 PM, said:

I'm sorry for resurrecting this, but I did a little experiment tonight, and I ended up with questions.
 
Seeing conditions were terrible, but I just wanted to see what would happen, how fast things would drift, how much would be observable, so I did a little experiment:
 
Telescope: Skywatcher Dobsonian 10" (collapsible but using full length)
FL: 1200mm
Camera: RisingTech IMX224
Camera settings: see here, 64 total, short 250ms exposures, for a total stack of 16s exposure
Target: the Trapezium.
 
Notice I'm running at the native huge focal length of the dob, 1200mmFL, which with the tiny 6mm sensor makes for a whooping 200x. I didn't spend much time focusing, I wasn't looking for quality image, just curious about seeing what the live view would be like.
 
The dob is manual, there is no goto, no auto-tracking, I just let the object drift, and I paused sharpcap's stacking, to move the dobsonian up, reposition the trapezium, and let it drift again. I may have moved it a little during the whole process, but not much.
 
Anyway, here's what I got:
 

 
Pretty zoomed in, out of focus, yeah, but I learned a few things:
 
During the live view, longer exposures (1s) showed a lot more, but left trails. By shortening exposure to 250ms I got rounder stars, but a lot less was seen. Still, there's something there. There's potential. With a focal reducer, this could be useful enough to see some tough objects that are too small for my regular EAA gear.
 
Obviously the huge problem here is the enormous focal length.
 
My experiment was intended to be first at the native 1200mm, and then using a cheap 0.5x focal reducer. Since the dob is a "collapsible" skywatcher, I figured I could get all the in-focus I needed.
 
I don't think the problem is the scope, but the "C" adapter that comes with the camera, which must be used in order to thread a 1.25" filter (or focal reducer). That adapter is long, and using it I've measured the distance from the sensor to the reducer's lens to be 43mm. I don't know what the proper spacing would be. Just when I was tinkering with the collapsed position of the trusses, clouds covered everything (they had been coming, seeing was terrible).
 
So I want to do another experiment, but I need to get this focal reducer to work (never been able to, in any of my scopes).
 
¿Do you guys know to get the proper spacing for a cheap 0.5x focal reducer with the touptek cameras? Is there an alternative to that long C adapter, or something else one might try? I've seen the Revolution Imager RI224 comes with a reducer, ¿how is it attached?

Edit: nevermind, I finally got the reducer to work, focusing on the moon. With the IMX224 I got a TFOV in which the moon fits, with some extra space on the sides, somewhere between 0.6° to 0.7° wide, and 0.4° to 0.5° tall. I guess there's room to play some more with drift scanning.

Actually you need more focal length to cleanly split the A and E stars.

 

IMG_2665 (5).JPG

 

This is a single unguided 30" image taken with my 210 mm aperture, 1,623 mm focal length Mikage Newtonian reflector on a Pentax MS-5 GEM.  The camera was a Canon T3 DSLR.


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#19 Adun

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Posted 11 August 2018 - 04:31 PM

Actually you need more focal length to cleanly split the A and E stars.

 

attachicon.gif IMG_2665 (5).JPG

 

This is a single unguided 30" image taken with my 210 mm aperture, 1,623 mm focal length Mikage Newtonian reflector on a Pentax MS-5 GEM.  The camera was a Canon T3 DSLR.

 

Actually very nice split, but the thread (and my question) is about drift scanning, which means no tracking, manual (as in: dobsonian). Your newtonian on a GEM can afford the long FL and still expose for 30", I wanted the reducer to afford a few more milliseconds of exposure without getting star trails.




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