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EAA with a manual Dobson... it´s working!

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#101 SonDob

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Posted 01 March 2019 - 02:47 PM

Ok Ill read into the differences and try out. Thank you

#102 descott12

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Posted 01 March 2019 - 03:55 PM

Here is an example M42/NGC1977 with and without flats. I posted these in another thread but couldn't quite remember where...

Anyway the "without flat" image looks alot like yours with a bright circle in the center.

 

It did occur to me that you might have a bit of trouble getting this to work without automatic tracking but it would be an interesting experiment.

 

Note: I had to shrink and resize these image to upload. The vignette effect was actually quite a bit more noticeable on screen.

 

EDIT: I forgot to include the exposure settings. Both shots were 1 minute stacks with a 5 second exposure using my Evo 8 + Hyperstar + ASI 294 MC

Attached Thumbnails

  • M42-withflat.png
  • M42-withoutflat.png

Edited by descott12, 01 March 2019 - 06:14 PM.


#103 SonDob

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Posted 01 March 2019 - 04:54 PM

Thank you for the example. I agree it looks very similar. Ill try it out. Also the camera can compensate vignetting but i never enabled that function before. Ill try both out

#104 Ubuntu

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Posted 07 March 2019 - 02:13 PM

NGC2207, 2 galaxies in interaction: 173 frames, total 87s

Stack_173frames_87s_WithDisplayStretch V2.jpg

 

NGC4762, paper-kite galaxy: 183 frames, total 92s

Stack_183frames_92s_WithDisplayStretch V2.jpg

 

NGC4535, The lost galaxy of Copeland: 304 frames, total 152s

Stack_304frames_152s_WithDisplayStretch V2.jpg

 

M49: 105 frames, total 53s

Stack_105frames_53s_WithDisplayStretch V2.jpg

 

M86, M84, NGC4402: 172 frames, total 86s

Stack_172frames_86s_WithDisplayStretch V2.jpg

 

M99: 184 frames, total 92s

Stack_184frames_92s_WithDisplayStretch V2.jpg

 

M91: 225 frames, total 113s

Stack_225frames_113s_WithDisplayStretch V2.jpg

 

 


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#105 Ubuntu

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Posted 11 March 2019 - 01:58 PM

ARP 321: 94 frames, total 47s  Sharpcap pro 3.2

Stack_94frames_47s_WithDisplayStretch V2.jpg

 

M13: 23 frames, total 6s

Stack_23frames_6s_WithDisplayStretch V2.jpg

 

Centaurus A, hamburger galaxy: 70 frames, total 70s

Stack_70frames_70s_WithDisplayStretch V2.jpg


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#106 SonDob

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Posted 08 April 2019 - 06:20 AM

some new pictures. Again with the 8"/1200mm manual Dobson. This time I played around with more magnification at slow native ~f/6. Of course I need longer integration times. So all pictures are were covered with a lot of drifts. All single frames are captured with 0.64sec. All captured with sharpcap using histogram stretch, only. Did not use dark frames, yet.

 

Eskimo Nebula in b/w 35sec

 

Stack_718frames_35s_WithDisplayStretch.png

 

and in color 9s

Stack_192frames_9s_WithDisplayStretch.jpg

 

 

NGC3628 in Leo 143sec

Stack_876frames_143s_WithDisplayStretch.png


Edited by SonDob, 08 April 2019 - 06:29 AM.


#107 SonDob

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Posted 08 April 2019 - 06:27 AM

M66 in Leo 159sec

Stack_2396frames_159s_WithDisplayStretch.jpg

 

M65 in Leo 152sec

Stack_932frames_152s_WithDisplayStretch.png

 

NGC4567 and NGC4568, b/w 165s

Stack_973frames_165s_WithDisplayStretch.png

 

 

 

and the highlight of the night:

 

Jet in M87, b/w 100sec

Stack_32bits_622frames_100s.jpg

 

 

 

 

 


Edited by SonDob, 08 April 2019 - 06:32 AM.

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#108 Ubuntu

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Posted 02 May 2019 - 05:43 AM

Little session yesterday with the Dobson XT10 and the Risingtech IMX385.

 

Sharpcap 3.2, gain: 5000, save as seen, no darks, no flats

 

M100: 104 frames, total 52s in B&W for more details... in color I could not bet the supernova clearly:

Stack_104frames_52s_M100.jpg

 

And here is the SN:

Stack_104frames_52s_M100 CropSN.jpg

 

NGC 4302 : 88 frames, total 44s

Stack_88frames_44s_NGC4302.jpg

 

M57: 55 frames, total 7s, I worked with 125ms exposures

Stack_55frames_7s_M57.jpg


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#109 Ubuntu

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Posted 04 May 2019 - 02:53 PM

Little session yesterday night dedicated to the south at the beginning of the night... with the Dobson in horizontal position for Omega Centauri... :D

 

M83, Southern Pinwheel galaxy: 62 frames, total 31s
Stack_62frames_31s_M83.jpg

 

Centaurus A: 74 frames, total 74s
Stack_74frames_74s_Centaurus A.jpg

 

Omega Centauri: 8 frames, total 4s
Stack_8frames_4s_Omega Centauri.jpg

 

NGC 4038, Antennae: 172 frames, total 86s, difficult to get the antennas...
Stack_172frames_86s_NGC4038 Antennae.jpg

 

 

NGC 4027 - ARP 22: 59 frames, total 30s
Stack_59frames_30s_NGC4027 - ARP22.jpg

 

 

NGC 4449 - C21: 106 frames, total 53s

Stack_106frames_53s_NGC4449 - C21.jpg


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#110 OliverToth

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Posted 22 July 2019 - 03:26 PM

Awesome pictures, how do you confirm you have your object in the field of view, short exposure tests or do you switch from camera to eyepiece, because simple intuitive star hopping with a fully push-to telescope sounds complicated (high chances of the object being just outside the fov or not centered). Is a reverse adapter 100% needed because i have no idea how to find one... 

I will be getting an orion XX16g next spring but for now I would love to try some untracked EAA with my XT10i it would also be a great way to learn about using sharpcap


Edited by OliverToth, 22 July 2019 - 03:28 PM.


#111 mikenoname

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Posted 22 July 2019 - 05:50 PM

SharpCap give a live image of what it is seeing so you know what the scope is pointed at at all times. It's like having a ~6mm eyepiece in the focuser.



#112 Ubuntu

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Posted 26 July 2019 - 10:01 AM

Awesome pictures, how do you confirm you have your object in the field of view, short exposure tests or do you switch from camera to eyepiece, because simple intuitive star hopping with a fully push-to telescope sounds complicated (high chances of the object being just outside the fov or not centered). Is a reverse adapter 100% needed because i have no idea how to find one... 

I will be getting an orion XX16g next spring but for now I would love to try some untracked EAA with my XT10i it would also be a great way to learn about using sharpcap

Hi Oliver... for me if the target is difficult to find I search with an eyepiece... but most of the time I go from star to star with the help of stellarium. The problem with the change from eyepiece to cam is that you have to refocus...

As for the negative adapter, it was home made with a adapter 1.25" to 2" that I grinded... some are also printing 3D

 

Hope it helped :D


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#113 JonNPR

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Posted 11 August 2019 - 01:42 PM

Ubuntu I have been amazed at your results WITHOUT tracking! Coincidently, an ATM friend of mine in Toronto wants to try EAA with an extremely fast 14” alt az non tracking scope he just finished building. Specs are native f/2.6 and 925mm fl. His budget for a camera is about $500 or less. Can you offer advice on a camera and anything else besides Robin’s SharpCap to help him out? 

 

Thanks!

 

Jon



#114 Ubuntu

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Posted 12 August 2019 - 08:59 AM

Ubuntu I have been amazed at your results WITHOUT tracking! Coincidently, an ATM friend of mine in Toronto wants to try EAA with an extremely fast 14” alt az non tracking scope he just finished building. Specs are native f/2.6 and 925mm fl. His budget for a camera is about $500 or less. Can you offer advice on a camera and anything else besides Robin’s SharpCap to help him out? 

 

Thanks!

 

Jon

Hi Jon!! good to hear some people want to try this technique smile.gif

F/D 2.6 native... that's a very nice scope he built laugh.gif

 

Ok... let me resume a little bit what are the constraints of this technique:

- You need a scope as fast as possible

- The exposure time is very short (less than 1s or even 500ms - or even less if the fl is over 500mm)

- The cam should NOT have too many pixels (to be able to live stack at 500ms or shorter)... typically 2M pixel max

- The field should be wide enough to get enough stars to stack

- The cam needs to be very sensitive with very low noise at high gain

 

You can see that there are a lot of constraints and he has to find a fine balance between them.

 

With around 500mm of fl, i'm stacking around 500ms almost all the time (1s is an exception) with F/D at 1.88: Therefore your friend will have to stack at 250ms because of his higher fl.

 

The length of my stacks are generally max 1min (the time that the object goes out of the FOV) but if needed I can stop and resume the stack after repositionning the scope. He can do the same and stack 30s... reposition the scope and resume the stack.

 

At 250ms he might likely get one out of 2 images rejected but if his laptop is good who knows maybe the stack can be done in less than 250ms (this is for 2M pixels). If he wants to go for 1M pixel, the FOV will be very small and the stack might not happen (he needs minimum 10 stars), the length of the stack will be very short and the positionning of the scope a real challenge.

 

I decided to take the IMX385 for the FOV bigger than the 224 and the 2M pixels as well as low noise and high sensitivity.

 

In conclusion: I am using a IMX385 with F/D1.88 and a fl of 470mm...I have never seen this technique used with a so big fl although I have been able to stack M57 without focal reducer, therefore with a fl of 1200mm. But as you know M57 has a quite high light density. So if your friend is not afraid to be disappointed he can try by himself... I'd be very curious to see his results laugh.gif


Edited by Ubuntu, 12 August 2019 - 09:07 AM.


#115 Adun

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Posted 12 August 2019 - 05:40 PM

Ubuntu I have been amazed at your results WITHOUT tracking! Coincidently, an ATM friend of mine in Toronto wants to try EAA with an extremely fast 14” alt az non tracking scope he just finished building. Specs are native f/2.6 and 925mm fl. His budget for a camera is about $500 or less. Can you offer advice on a camera and anything else besides Robin’s SharpCap to help him out? 

 

Thanks!

 

Jon

 

Hi Jon.

 

The problem is that 925mm FL is a lot. As it is, your friend would get star trails sooner than Ubuntu, meaning he'd be forced to use shorter exposures, which would mean poorer results. Your friend would really need to either get that focal length down using focal reducers, or use a much larger sensor with much larger pixels.

 

I'm not an expert, but please allow me to explain my perspective:

 

As I understand, in photographic terms, the difference between your friend's 14" F2.6 reflector and a small F2.6 photo lens  will be the focal length, and the size of the image circle.

The larger image circle of the 14" telescope will mean he can use a larger sensor. 

 

The longer focal length of the 14" telescope will produce a more magnified image (for any given pixel size) than the photo lens... The need to get enough stars for stacking, and the need to be able to fit non-tiny objects (not just tiny planetaries) means that the longer the FL, the more you want larger sensors.

 

And for manual non-tracking EAA it's even more paramount to have shorter focal lengths (using focal reducers), or failing that, to use much larger pixels (spending money on big sensors, and/or through binning)

 

I'd say Ubuntu's success owes a lot to his ability to get his dobsonian down to F1.88 and under 500m FL. It's not just about which camera to get, but also about which focal reducer to get, and how to put it in the light path while avoiding problems such as lack of focus travel, misaligned problems, or edge aberrations creeping in.

 

I think your Toronto Friend would be better off with a ($630) ASI294MC, mostly to get the larger sensor (8 times larger area than IMX385), plus the larger pixels (4.6um vs 3.5um, or 70% larger by area than IMX385). Although the read noise of the ASI294 won't be as superb and on Ubuntu's IMX385, which would indeed hurt for stacking the super short exposures, I think the larger sensor would have a better chance of actually allowing 250ms~500ms exposures (perhaps through binning) without star trails, at such focal lengths on a manual dob.

 

Binning would also address Ubuntu's advise about "2 Mega Pixels max" to avoid huge images slogging down the computer.

 

Ideally he'd do it all: use focal reducers (even "just" 0.8x would help), a large sensor - large pixel, low noise camera (ASI294) and use binning. The only problem is, that won't fit in $500, and it's large body might not fit in the focuser (although for a DIY dob that could be solved)


Edited by Adun, 12 August 2019 - 05:57 PM.


#116 Adun

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Posted 12 August 2019 - 06:01 PM

So my choice was the Rising Tech IMX385, I got it at 285€ on offer and I took an X0.5 reducer from SVbony... I know the reducer is not of good quality (besides it was mounted upside down) but good as I didn't know where I was going and I preferred to ensure at the budget level smile.gif

 

Hi Ubuntu. I have a question:

 

Which of the two 0.5x SVBony reducers are you using? I have both, a thick one and a thin one. 

 

Maybe it's about time I try this with my dob and my RT290 camera, to see what can they do together.



#117 Ubuntu

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Posted 13 August 2019 - 03:18 AM

Hi Ubuntu. I have a question:

 

Which of the two 0.5x SVBony reducers are you using? I have both, a thick one and a thin one. 

 

Maybe it's about time I try this with my dob and my RT290 camera, to see what can they do together.

Hi Adun... I got this FR:

https://fr.aliexpres....27426c37Ys1O1V



#118 Ubuntu

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Posted 13 August 2019 - 05:39 AM

 

 

I think your Toronto Friend would be better off with a ($630) ASI294MC, mostly to get the larger sensor (8 times larger area than IMX385), plus the larger pixels (4.6um vs 3.5um, or 70% larger by area than IMX385). Although the read noise of the ASI294 won't be as superb and on Ubuntu's IMX385, which would indeed hurt for stacking the super short exposures, I think the larger sensor would have a better chance of actually allowing 250ms~500ms exposures (perhaps through binning) without star trails, at such focal lengths on a manual dob.

 

Binning would also address Ubuntu's advise about "2 Mega Pixels max" to avoid huge images slogging down the computer.

Indeed, binning could be a solution if the number of pixel is too high laugh.gif


Edited by Ubuntu, 13 August 2019 - 05:39 AM.


#119 Rickster

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Posted 13 August 2019 - 09:50 PM

Wow.  This thread is up to 5700 views.  Good job!!!



#120 JonNPR

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Posted 15 August 2019 - 03:34 AM

Ubuntu, Adun thank you so much for your detailed replies, explanations and advice. I will forward them to Tom for his consideration. I remain amazed and awed by the images Ubuntu has posted here - unguided. Yes, it takes some careful effort. But holymoly, unguided Dob EAA!!

 

Thanks again,

Jon


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#121 totvos

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Posted 15 August 2019 - 08:01 AM

Ubuntu, Adun thank you so much for your detailed replies, explanations and advice. I will forward them to Tom for his consideration. I remain amazed and awed by the images Ubuntu has posted here - unguided. Yes, it takes some careful effort. But holymoly, unguided Dob EAA!!

 

Thanks again,

Jon

Thanks Jon, Ubuntu, and Adun for the advice. Parallel to this, I have been exploring augmenting my setup with an EQ platform that would allow tracking for roughly an hour at a time. From the sounds of it, that would offset my issues greatly, but then doesn't fit this particular topic of unguided. I'll be sure to try unguided too and report back. But I still want to find something sub-$500 before going all in with a major expenditure.

 

But back on the OT, the key for untracked success is FL, not F/D. The F/D will dictate your FOV and light gathering, but FL defines whether you can avoid tracking. And the sweet spot is 500mm or less.



#122 Ubuntu

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Posted 16 August 2019 - 03:49 AM

Thanks Jon, Ubuntu, and Adun for the advice. Parallel to this, I have been exploring augmenting my setup with an EQ platform that would allow tracking for roughly an hour at a time. From the sounds of it, that would offset my issues greatly, but then doesn't fit this particular topic of unguided. I'll be sure to try unguided too and report back. But I still want to find something sub-$500 before going all in with a major expenditure.

 

But back on the OT, the key for untracked success is FL, not F/D. The F/D will dictate your FOV and light gathering, but FL defines whether you can avoid tracking. And the sweet spot is 500mm or less.

Hi Tom, F/D is also very important because it can allow you to stack (or not) thanks to the number of stars that will appear on your screen. Like I also said... I stacked M57 at 1200mm of focal length... so yes it is possible.

Maybe with your configuration you might not be able to stack really faint objects but I'm sure you can stack quite a lot with your scope.

 

If you don't want to invest a lot, for a start I recommend you to buy the IMX385... I bought the Risingtech one, it's 300USD so the investment is still reasonnable :)



#123 pedoc

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Posted 23 August 2019 - 05:23 AM

Do you use focal reducer 1,25'' or 2''?
How much more inward travel is required with the FR and without FR?

#124 Ubuntu

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Posted 23 August 2019 - 05:27 AM

Do you use focal reducer 1,25'' or 2''?
How much more inward travel is required with the FR and without FR?

I use a FR of 1,25":

https://fr.aliexpres....27426c37cD4mYo

 

The travel inward is 66mm, that's why I made a special adaptor to be able to put the cam inside the focuser :D



#125 pedoc

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Posted 23 August 2019 - 12:15 PM

66 mm more inward than without FR??

I tried webcam, I can reach focus and still have about15mm more space to travel.
Would that be enough?
I think astro camera will have more or less same focal distance aswebcam. Is that true?


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