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

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#1 Ubuntu

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Posted 09 December 2018 - 05:07 AM

Good morning, everyone,

 

After acquiring an Orion XT10 😍 and returning to astronomy after 30 years of abstinence... I tried to take some pictures with my smartphone but I quickly saw the limits of the 🤔 camera. I saw in the forums that today there are cams that are not too expensive and sensitive and when I read the topics about VA I thought that this is exactly what I was looking for: to see live what my eye could not see....

 

I also saw that all those who were doing VA were using a motorized mount... but I already have my manual Dob so I can't buy an EQ6 or a 130/650 style goto setup with an alt/az.

 

So I thought I'd try to do some live stacking with my Dobson and see what it could do... 😎 so I knew I would work in an ultra short pose....

 

My constraints for the cam were therefore:

- The price: less than 300€

- As little noise as possible with as much sensitivity as possible due to ultra-short exposures

- A cam with USB3 because of the number of frames per second that must be transmitted to the computer

- A cam with a long sensor to put the object on one side of the sensor and stack it as it passes over to the other side

- A cam stick because with a focal reducer I didn't know if I would have enough backfocus (and indeed it didn't miss... I had to tinker with something to get the cam into the PO 2")

 

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

 

When I compared without reducer and with.... well there is no comparison possible... with the reducer at the end of the cam (which is provided with an extension) I get to X0.4 so that my Dobson goes down to F/D 2 and therefore 500mm focal length for 254mm diameter 😋

 

I use Sharpcap pro 3.2.

The poses of 1s without any follow-up are too long and we see the trail of stars so I worked between 125ms and 500ms with the gain at 5000.

I put the camera in the direction where the stars go to have more time to stack.

 

In general I start stacking with 500ms which gives a little noise and after a few seconds I go down to 250ms or 125ms which removes the noise from the images (I guess it amounts to stacking darks) and so for the moment I don't do darks.

 

I am waiting for your advice to improve myself wink.gif  but I am already very happy with what I can see... EAA is really greatttttt grin.gif

 

M42: 131 frames, total 33s

Stack_131frames_33s_WithDisplayStretch.jpg

 

M42 again: 72 frames, total 18s. I varied the poses starting from 500ms and finishing with 125ms

Stack_72frames_18s_WithDisplayStretch.jpg

 

M31: 101 frames, total 51s

Stack_101frames_51s_WithDisplayStretch.jpg


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#2 Ubuntu

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Posted 09 December 2018 - 05:10 AM

the flame: 67 frames, total 34s

Stack_67frames_34s_WithDisplayStretch.jpg

 

M27: 59 frames, total 25s

Stack_59frames_25s_WithDisplayStretch.jpg

 


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#3 Ubuntu

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Posted 09 December 2018 - 05:12 AM

Helix: 56 frames, total 28s

Stack_56frames_28s_WithDisplayStretch.jpg

 

NGC 253: 102 frames, total 39s

Stack_102frames_39s_WithDisplayStretch.jpg

 

Pleiades: 36 frames, total 18

Stack_36frames_18s_WithDisplayStretch.jpg


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#4 Ubuntu

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Posted 09 December 2018 - 05:14 AM

M81: 127 frames, total 27s

Stack_127frames_57s_WithDisplayStretch.jpg

 

M82: 156 frames, total 60s

Stack_111frames_35s_WithDisplayStretch.jpg


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#5 Asbytec

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Posted 09 December 2018 - 05:31 AM

:gotpopcorn:



#6 TOMDEY

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Posted 09 December 2018 - 08:18 AM

That's VERY interesting! I want to take some "casual" pictures with my Dob... maybe this would be a good approach!  Tom



#7 alphatripleplus

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Posted 09 December 2018 - 08:19 AM

Very interesting. Back in 2015, (deceased) member nytecam had a similarly interesting thread , which also illustrated that you could stack and capture DSOs with a non-tracking telescope and a small 1/2inch sensor (SX Lodestar). His sub-exposures were around 100ms to 400ms with a 12inch SCT operating at f/4.


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#8 nic35

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Posted 09 December 2018 - 09:29 AM

U:

 

I think you are there !  just keep playing with Sharpcap and your camera and your skills will improve bit by bit. No pun intended.

 

Let me make a forecast:  An equatorial platform is in your future !

 

Welcome to the money pit.

 

john


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#9 Asbytec

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Posted 09 December 2018 - 07:25 PM

Back in 2015, (deceased) member nytecam had a similarly interesting thread...

Not to derail the thread, only to express my condolences. I didn't know. Saddened. 


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#10 Alien Observatory

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Posted 09 December 2018 - 09:08 PM

U:

 

I think you are there !  just keep playing with Sharpcap and your camera and your skills will improve bit by bit. No pun intended.

 

Let me make a forecast:  An equatorial platform is in your future !

 

Welcome to the money pit.

 

john

Nice Job, I can not see how you could do better with your non tracking set up...Very Nice...Pat Utah :)



#11 Adun

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Posted 09 December 2018 - 09:50 PM

Very interesting. The image scale you're able to get without aberrations is very nice, that reducer is doing a lot of magic!

 

I did some experiments with my RT224 (same pixel size / image scale) a year ago on my 10" dob, but never got around to try adding the reducer. Maybe I should try, your images look better than what I get with my 114mm EAA scope


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#12 Ubuntu

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Posted 10 December 2018 - 03:49 AM

Very interesting. The image scale you're able to get without aberrations is very nice, that reducer is doing a lot of magic!

 

I did some experiments with my RT224 (same pixel size / image scale) a year ago on my 10" dob, but never got around to try adding the reducer. Maybe I should try, your images look better than what I get with my 114mm EAA scope

Hi Adun,

 

For the photography the F/D is the most important... if you divide by 2, you shorten your exposition by 4.

Therefore the reducer is of utmost importance, not only because it gives a wider view but also because of this factor.

 

I tried my camera without and it was very difficult to stack.

Good luck and post your results smile.gif


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#13 Adun

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Posted 10 December 2018 - 10:26 AM

Hi Adun,

 

For the photography the F/D is the most important... if you divide by 2, you shorten your exposition by 4.

Therefore the reducer is of utmost importance, not only because it gives a wider view but also because of this factor.

 

I tried my camera without and it was very difficult to stack.

Good luck and post your results smile.gif

 

Back then I even got a 2" antares reducer, but when I tried to add it to the light path, I couldn't reach focus (couldn't get the camera close enough to it). I was about to collapse the trusses of my dob (Skywatcher collapsible) but then it got cloudy and I called it a day. I later got a lowish profile 1.25" adapter to replace the one that came with my dob (withmore in-focus), but when it arrived it turned out to have no threads, so I couldn't attach it to the reducer. Over time I just kept using my 80mm F4.3 refractor for EAA, until I recently managed to mount my 114 F4 reflector on an EQ mount. 

 

Maybe I should try again, perhaps combining the antares reducer with my GSO coma corrector (the corrector pushes the focal plane out). It did work with my 20mm UWA eyepiece on the 10" dob, it might just work

 

I think short exposures will limit this "no tracking" approach to the brightest DSO, I believe your image of the helix is already showing this, but still, it's worth it, although like John said, this might lead down the math towards a costly EQ platform.

 

After 2 years of EAA, my battleplan to go deeper/fainter was to go mono: I recently got an RT290 camera and I'm waiting for a clear night (it's been cloudy since october) to see what I can get from it on my EQ 114 F4, but if I can get my dob to join the EAA team that'd be great.


Edited by Adun, 10 December 2018 - 11:25 AM.


#14 star drop

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Posted 10 December 2018 - 12:06 PM

Very nice. Your Helix looks quite similar to what I see in a 25 " at 88x magnification, color included.



#15 Oukifrench

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Posted 10 December 2018 - 03:43 PM

Heyyy Ubuntu i am happy to see you here.
Congratulations for this challenge.
Very good job my french friend.

Ouki
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#16 Ubuntu

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Posted 11 December 2018 - 05:49 AM

Heyyy Ubuntu i am happy to see you here. Congratulations for this challenge. Very good job my french friend. Ouki

Merci ouki :)



#17 SonDob

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Posted 11 December 2018 - 08:30 AM

Hi Ubuntu,

 

very interesting stuff. Can you please describe how you actually push it. Is it 'blind' pushing. My understanding is that Sharpcap can display the live stack or the live camera feed but not both at the same time. So i wonder how you make sure that you are still in the area you want to capture. I thought about doing similar things with my RI2 but i did not solder a video split cable yet to feed my capture dongle for the stacking and at the same time my little monitor for the live feed needed for pushing the dob.

 

Cheers

SonDob



#18 Ubuntu

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Posted 11 December 2018 - 12:38 PM

Hi Ubuntu,

 

very interesting stuff. Can you please describe how you actually push it. Is it 'blind' pushing. My understanding is that Sharpcap can display the live stack or the live camera feed but not both at the same time. So i wonder how you make sure that you are still in the area you want to capture. I thought about doing similar things with my RI2 but i did not solder a video split cable yet to feed my capture dongle for the stacking and at the same time my little monitor for the live feed needed for pushing the dob.

 

Cheers

SonDob

Hi Sondob,

When I put my camera 16/9 in the direction of where the stars are going and I place the object a bit on one side, I know I have around 1min before the stacking ends. Anyway I stop the stacking when sharpcap tells me that he cannot stack anymore. The object might still be on the captor of the cam, but the referent stars might have gone. But you're right i´ts blind pushing as I only see the resulting stack...

Hope it helps smile.gif


Edited by Ubuntu, 11 December 2018 - 12:40 PM.

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#19 SonDob

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Posted 14 December 2018 - 05:31 PM

Hi Ubuntu,

 

yes that helps. Thank you very much for explaining your workflow. I did some tests with my 8" f/6 Dobson. I adapted the camera to 2" to reach focus with the svbony reducer. Star drift timing showed 1:30 min in 4:3. That looks really promising. Unfortunately the sky is overcasted since my first experiments without a notebook nearby. I will report as soon as the clouds pass.

Thank you for the hint with reversing the reducer. That made all the difference.

 

Cheers

SonDob


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#20 Rickster  Happy Birthday!

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Posted 14 December 2018 - 10:41 PM

Nice work Ubuntu! This should open the door to yet another technique in EAA.
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#21 Ubuntu

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Posted 15 December 2018 - 02:56 AM

Hi Ubuntu,

 

yes that helps. Thank you very much for explaining your workflow. I did some tests with my 8" f/6 Dobson. I adapted the camera to 2" to reach focus with the svbony reducer. Star drift timing showed 1:30 min in 4:3. That looks really promising. Unfortunately the sky is overcasted since my first experiments without a notebook nearby. I will report as soon as the clouds pass.

Thank you for the hint with reversing the reducer. That made all the difference.

 

Cheers

SonDob

Hi Sondob... can't wait to see your results :)

 

What is you resultant F/D... the SVbony reducer focal is f=70mm.

If d is the distance between the camera chip and the middle of the reducer, then K=1-d/f.

On my IMX385, d=42mm which gives me a K=0.4X reduction and therefore my F/D=1.88

Reduction is key... if you don't reduce enough you can still put some spacers to have a bigger reduction.

 

Hope you can get clear skies soon :)



#22 Ubuntu

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Posted 15 December 2018 - 02:59 AM

Nice work Ubuntu! This should open the door to yet another technique in EAA.

Thanks a lot Rickster! 

I hope the manual dobson owners can realize that there are new possibilities without tracking... because at the end the dobson is cheap, the cam are much cheaper than before but the mounts are still very expensive...


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#23 SonDob

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Posted 16 December 2018 - 10:07 AM

Hi Ubuntu,

 

still clouds :-(. I measured 27mm for d. So it brings me to F/D of 3.6. Am I right that the reduction value is independent of the scope I use? If so I may try my ST80 looking at a measure stick with and withoud reducer to get a more precise number.  If i add additonal spacers then I run out of focus.I might try to sand one spacer down....


Edited by SonDob, 16 December 2018 - 10:10 AM.


#24 Adun

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Posted 16 December 2018 - 09:20 PM

Am I right that the reduction value is independent of the scope I use? If so I may try my ST80 looking at a measure stick with and withoud reducer to get a more precise number.  If i add additonal spacers then I run out of focus.I might try to sand one spacer down....

 

Yes, reduction should be a function of distance between camera sensor and the reducer lens (the center of the lenses I believe), so you can try spacers with -say- a guidescope and the reduction will be the same on another scope (although your ability to reach focus probably won't)



#25 SonDob

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Posted 17 December 2018 - 06:19 AM

Thank you Adun! I measured now with the measure stick and got down to a reduction of 0,58x which leads to F/D of 3.4. So a little bit better. On the ST80 i can reduce further with some spacers if I do not use the diagonal. However that is not an option on the dob. I'll try how it goes with 3.4. Doesn't sound too bad actually. There is always the option to stack multiple drifts.I assume Ubuntus stacked single drifts.


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