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Guiding through main camera

astrophotography beginner refractor
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#1 Astro Babak

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Posted 07 April 2020 - 11:59 AM

Hello all,

I'm new to AP world and I'm setting up my rig with HEQ5 mount, SW 72ED refractor telescope and Canon 70D unmodified DSLR camera. I'm getting started with APT and it seems to be very feature-heavy. I can see everyone doing guiding with an extra guide camera and scope, so I was wondering why not use the main camera?! To be clear, I'm not talking about off-axis-guiding where I can use an extra camera + main scope to do guiding.


On another note, how long of an exposure can I go without guiding? I heard that HEQ5 should do a fine job of tracking without guiding. 


Thanks all

#2 Jim Davis

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Posted 07 April 2020 - 12:13 PM

Your guide camera needs to take lots and lots of short pictures, and make corrections based on each one. The main camera is busy taking long exposures.

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#3 D_talley



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Posted 07 April 2020 - 12:14 PM

Guiding with main camera has been asked many times before. Here is a link to one of them.



https://www.cloudyni...ing main camera

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#4 Madratter


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Posted 07 April 2020 - 12:16 PM

With your 72ED and the EQ5 you can probably go at least 30s. You might need to reject some subs, but a fair percentage will be at least usable on some level. I recommend doing some imaging without guiding first before jumping into the world of guiding.


Guiding is usually done with a camera other than the main, because the main camera usually is using exposures too long to use for guiding.


It is possible to guide with the main camera with mounts that have negligible Periodic Error. There you are essentially just correcting for small changes over time like the refraction index changing as the object changes altitude, any residual drift do to polar alignment errors, flexure in the system as the attitude of the equipment changes, etc. I know software has been written to do that, but I don't recall what it is. Most mounts that are capable of using such a system, are already capable of doing unguided imaging for at least significant periods of time (minutes, not seconds).

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#5 klaussius



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Posted 07 April 2020 - 12:18 PM

Most guiding software doesn't have that function.


If I understand your question correctly, you'd like to capture with the DSLR and also use those same captured frames to guide, avoiding the second camera.


Problem is, the whole point of guiding is to be able to make corrections while the DSLR is shooting a long exposure. You can't read the sensor off the DSLR until that exposure is done, so that's not possible.


All a "self-guiding" solution can do (as I call it) is correct drift, and try to build predictive models to correct periodic error.


Many go-to mounts have the ability to build those models, so you could try, they're called PEC or PPEC. See if yours has it.


But that's not nearly as effective as guiding with a secondary guide camera. The reason for it is that with a second camera you can have that camera take 1-second exposures and have it make corrections every second while you're shooting 10-minute exposures with your main camera. You can't do that with a single camera, so you can't correct unpredictable random errors, only predictable (periodic or constant) errors.

Edited by klaussius, 07 April 2020 - 12:33 PM.

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#6 drd715



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Posted 07 April 2020 - 02:25 PM

The length of time you can get a good image without auto guiding (tracking) is dependent upon your subject framing size. Short focal lengths (wider angle) images can be untracked with a supior polar alignment for a couple of minutes. Long focal length (narrower angle) imaging might be limited to 30 seconds or so untracked. Errors in perfect tracking are much more noticeable at long focal lengths, smaller sensors and or smaller pixels .

Short = 200mm fl
Long = 1000mm fl
As examples; it is relative.

Much depends upon the ability of your mount and how well you have polar aligned the mount before imaging.

Sent from my SM-N950U using Tapatalk
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#7 kathyastro


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Posted 07 April 2020 - 02:44 PM

Basically because the main camera is busy taking your images.  If you are taking two-minute subs, the camera is busy for those two minutes.  You could only guide in between those two-minute exposures, because that's the only time the camera is not working.  But the whole point of guiding is to guide during the exposure.  If you could get away with guiding between exposures, there would be no point in guiding at all.

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#8 Birddogoby


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Posted 07 April 2020 - 03:47 PM

My two cents based on my own experience.  I'm new at AP beginning in late February and started off  unguiding for a month with a EQ6-R Pro mount.   You can see the details of my AP rig in my signature. 


The EQ6-R has a heavier payload capacity and upgraded belt drive system compared to the HEQ5.  Keeping that in mind, I was consistently able to get good unguided subs up to 180 seconds, which frankly surprised me.  My targets were exclusively galaxies.  The sweet spot seemed to be up 120 seconds.  That was shooting my Nikon DSLR on the Tak 120 at prime focus ( f/7.5 - 900 mm) since I didn't have the reducer at that time.  I got the Lacerta MGEN-3 auto guider and reducer later.  Hope that helps.


Of course, as the ad says, "your results may vary...."



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#9 Astro Babak

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Posted 08 April 2020 - 03:42 PM

Great replies everyone, thank you very much. I never connected the dots that the guiding is happening while the main camera is having the shutter open and gathering data. So that clears that one up. 

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