38 replies to this topic

[SuperSirLink]

First experience with guiding last night.  Got my PA to 14", but noticed the guiding was jumping around a lot so disabled dithering to rule it out.  But even so, I found some of my exposures were trailing a bit.  Admittedly I went straight to the extreme and was shooting 5 min exposures.  But seeing a few that were pin point, I was optimistic.

 

Wasn't sure about the focus of the guide cam, if this was good enough, or should be better?

 

Would love any and all input and suggestions.

 

Edited by SuperSirLink, 22 May 2023 - 07:29 AM.

[matt_astro_tx]

Looks like you selected a single star to guide on.  Don't do that.  Let the ASIAir select multiple stars on its own, that's much more accurate.

 

Focus could be sharper.  Once you get it dialed in you won't have to refocus again.

[SuperSirLink]

Ohh, wasn’t aware that was an option. Will have to do more research. I didn’t choose the star, but maybe I skipped a step.

[vidrazor]

Focus could be sharper.  Once you get it dialed in you won't have to refocus again.

I don't know what he's using for a guide scope, but the ZWO Mini Guide Scope that I use never looks more focused than that.
 

[matt_astro_tx]

Ohh, wasn’t aware that was an option. Will have to do more research. I didn’t choose the star, but maybe I skipped a step.

So after you've done your calibration, you click the button to start guiding and the ASIAir will auto-select a number of stars in the field of view to guide on.  There isn't any extra steps.  It is possible it didn't find more than one suitable guide star, but the screen shot you posted looks like there are at least a half dozen it could've used.

[SuperSirLink]

I don't know what he's using for a guide scope, but the ZWO Mini Guide Scope that I use never looks more focused than that.
 

Using the SV165 with the 120mm mini

[SuperSirLink]

So after you've done your calibration, you click the button to start guiding and the ASIAir will auto-select a number of stars in the field of view to guide on.  There isn't any extra steps.  It is possible it didn't find more than one suitable guide star, but the screen shot you posted looks like there are at least a half dozen it could've used.

gotcha, unfortunately looks like clear skies is predicting clouds for the next several nights, so will have to wait to try again.

[matt_astro_tx]

Using the SV165 with the 120mm mini

I use that same pair and I can get a sharp focus on mine.  However it's been about a year since I last messed with it.

[unimatrix0]

Increase the pulse aggression for the DEC.  20% is not cutting it, it's unable to pull the mount back, that's why the red line is floating above. Try 30% or 40% and keep going up until it gets it down to the zero line. If it starts too much zig-zagging up and down with large numbers, then relax it down to smaller. Small zig-zag is ok, if it's stays below 1". Yours is floating at 4".    You want the average error down to minimum. It can take a few minutes and some experimentation to find what is good. 

 

Here is mine  last night, just saying honestly it's not always this good, but usually around an 0.60-0.70, I get large swings in the RA, if I'm imaging towards the South. 

 

 

Edited by unimatrix0, 22 May 2023 - 12:02 PM.

[SuperSirLink]

Increase the pulse aggression for the DEC.  20% is not cutting it, it's unable to pull the mount back, that's why the red line is floating above. Try 30% or 40% and keep going up until it gets it down to the zero line. If it starts too much zig-zagging up and down with large numbers, then relax it down to smaller. Small zig-zag is ok, if it's stays below 1". Yours is floating at 4".    You want the average error down to minimum. It can take a few minutes and some experimentation to find what is good. 

 

Here is mine  last night, just saying honestly it's not always this good, but usually around an 0.60-0.70, I get large swings in the RA, if I'm imaging towards the South. 

Got it, will give that a try next outing...  It was higher and I tried backing it down slowly to try and stabilize the graph... But I may not have waited long enough between changes.  Never did see it either axis stay under 1" for any length of time. But also didn't know what I was supposed to be seeing.

[SuperSirLink]

I use that same pair and I can get a sharp focus on mine.  However it's been about a year since I last messed with it.

Will try getting better focus.  Did you just go based on visual or am I trying to get that star size number down lower?

[vidrazor]

Will try getting better focus.  Did you just go based on visual or am I trying to get that star size number down lower?

Focus from the camera itself, and keep the the fronts focus ring extended almost to coming off, then lock it down tight. Using the front focus ring can cause significant focus shift when trying to lock it down. Partially tighten the camera's compression ring so it's taught, but you can still carefully move the camera in and out. When you're focused, carefully tighten the compression ring, and keep and eye on the visual, as focus can still shift a bit.

 

That said, it's probably not going to look much better than what you have now. It's just simple optics. It's not a big deal however, it's been reported that having the optics slightly out of focus aids in averaging out seeing conditions, and actually helps to track better. Also, what exposure time are you using? You should be between 2-3 seconds on your exposure time to additionally average out seeing conditions.

Edited by vidrazor, 23 May 2023 - 12:28 PM.

[SuperSirLink]

Focus from the camera itself, and keep the the fronts focus ring extended almost to coming off, then lock it down tight. Using the front focus ring can cause significant focus shift when trying to lock it down. Partially tighten the camera's compression ring so it's taught, but you can still carefully move the camera in and out. When you're focused, carefully tighten the compression ring, and keep and eye on the visual, as focus can still shift a bit.

 

That said, it's probably not going to look much better than you got it now. It's just simple optics. It's not a big deal however, it's been reported that having the optics slightly out of focus aids in averaging out seeing conditions, and actually helps to track better. Also, what exposure time are you using? You should be between 2-3 seconds on your exposure time to additionally average out seeing conditions.

I was using 2 second exposures.

[vidrazor]

I was using 2 second exposures.

That should be decent. You can always try 3 seconds as well. Also, did you make a dark library for the camera?

[SuperSirLink]

yeah, I did that when I took my main darks...

 

The stacked result doesn't look to bad considering some of the subs had some elongated stars...  They are definitely not round though...  Clearly I have to work on my flats too...

 

 

Edited by SuperSirLink, 22 May 2023 - 08:15 PM.

[matt_astro_tx]

Will try getting better focus.  Did you just go based on visual or am I trying to get that star size number down lower?

I just do it visually by making adjustments until the stars are as small as possible.  Unlike vidrazor I focused using the main objective/compression ring.  I guess I lucked out.  You can try their method as well.

 

+1 on a slightly out of focus guide scope.  Like I said I haven't focused mine in like a year now.  Works great.  If you like to nit pick then by all means focus every session, but its not necessary.

[SuperSirLink]

yeah, it was my hope to set it and forget it... 

[SuperSirLink]

I wonder if my guide performance can be dependent on which mount option I choose for the ASIAir to control the mount?  I have seen some use EQMod, but I have been using one of the Skywatcher specific settings.

[SuperSirLink]

Have not had a chance to make another attempt, hoping the weather cooperates this weekend.  But did double check the focus of the guide scope against a terrestrial target.  This was the best I was able to achieve.

 

[RedLionNJ]

Checking the focus against a terrestrial target isn't the best thing - definitely better off in a starfield.

 

Since your guidecam is a mono, it won't have any filtering on it by default. You might want to consider adding an IR-cut filter to it in order to get slightly sharper stars from the guidescope. You'll lose a little light, but what you do get will result in tighter stars. Bloated stars are simply the result of inexpensive refractor optics in the guidescope - not all wavelengths come to exactly the same focus.  By eliminating the longer wavelengths with the IR-cut filter, you should see a difference.  I had to do this with my 290mm guidecam.

[fmendes]

Will try getting better focus.  Did you just go based on visual or am I trying to get that star size number down lower?

I usually make the star size lower. You just need to be patient as for every time you adust the focus, you need to select stars again.

[Etoimos]

Checking the focus against a terrestrial target isn't the best thing - definitely better off in a starfield.

 

Since your guidecam is a mono, it won't have any filtering on it by default. You might want to consider adding an IR-cut filter to it in order to get slightly sharper stars from the guidescope. You'll lose a little light, but what you do get will result in tighter stars. Bloated stars are simply the result of inexpensive refractor optics in the guidescope - not all wavelengths come to exactly the same focus.  By eliminating the longer wavelengths with the IR-cut filter, you should see a difference.  I had to do this with my 290mm guidecam.

How did you add an IR filter to it and what filter did you use?

[jaydeepappas]

yeah, I did that when I took my main darks...

 

The stacked result doesn't look to bad considering some of the subs had some elongated stars...  They are definitely not round though...  Clearly I have to work on my flats too...

 

 

Screenshot 2023-05-22 at 8.58.15 PM.jpg

Your main scope is out of focus as well as your guide scope. How are you focusing?

 

Edit: I didn't even see the post above of you focusing on a terrestrial object. You should definitely get a bahtinov mask if you don't have one. You can get them for pretty cheap on amazon, or even 3D print one yourself.

Edited by jaydeepappas, 26 May 2023 - 09:41 AM.

[SuperSirLink]

Your main scope is out of focus as well as your guide scope. How are you focusing?

 

Edit: I didn't even see the post above of you focusing on a terrestrial object. You should definitely get a bahtinov mask if you don't have one. You can get them for pretty cheap on amazon, or even 3D print one yourself.

That terrestrial image is not my main scope... I do use a bahtinov mask for that and it was dead on.

Edited by SuperSirLink, 26 May 2023 - 11:50 AM.

[SuperSirLink]

I managed to get a chance to image again last night, weather surprised me...  Think this is better, grabbed some subs of M101, stuck to 180 seconds and didn't have any that showed any star elongation till the meridian flip.  First time I have done that with this setup and didn't realize the ASIair defaulted to stopped guiding 5 min ahead of the flip.  Through me for a loop and wonder what the heck was going on... So a few subs lost on each side of the flip, but now I know how that works and so much easier than doing it manually!

 

I am guessing these numbers are probably the best I am going to expect from the GTI.  If I can get consistent 3 min subs, that should be really more than enough for a while.

 

Edited by SuperSirLink, 26 May 2023 - 11:56 AM.