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Imaging session - Post Mortem feedback welcomed !

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#1 Diomedes

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Posted 18 October 2020 - 12:16 PM

Hey all, last night I travelled to my dark site, as in dark when compared to the city that is.  My chosen target was the Wizard Nebula. 

 

Equipment: 

 

- Celestron AVX 

- William Optics GT71

- Canon T6i 

- Hotech 2" SCA Self-Centering Field Flattener

 

The first mistake of the night was made during the day. My wife, and I visited the the super market before heading to the dark site. We ended up staying there longer than expected, and then hit traffic on our way back home. This all lead to us arriving late at the dark site, and having to set up in the dark. My apologies to any amateur astronomers who were there and we blinded with our car lights. 

 

 

Trouble focusing: 

 

Usually is easy for me to point the scope towards a bright star, and focus but tonight no matter where I pointed the scope I could not see the stars on the back of my DSLR's screen. As a result I spent 30-40 minutes just trying to get something on the screen. I made note using the markings on the focuser which was at perfect focus at 43mm out. So I'm hoping that won't be as big of an issue going forward. 

 

 

Polar Alignment 

This was my first time using Sharcap for polar alignment, and I was delighted and thrilled at how easy it was to polar align the scope.  I settled on 00°01'25" of alignment error which sharp cap considered good. 

 

 

AVX Issues(need feedback here)

 

Start Alignment 

 

I made sure the index for the mount were in the correct position. I entered date, time, and chose daylight savings.  The mount slewed to Vega but it was way off so I correct it. I forgot what the second star I chose. I then slew to Jupiter, and it was off so I corrected the alignment. I wen't back to Vega and the star  was on the center. So I was confident my star alignment was correct. 

 

This was one of the biggest errata of the night, and cost me the image all together.  The alignment was off, and I ended up pointing at NGC 7419 for the entire night.  Before tearing up for the night, I pointed the scope to M31 and noticed it was not on the frame, that's when I realized something was way off before I even saw the image when I got home. 

 

50501566568_d184e66cfa_z.jpg

 

 

any recommendations when doing star alignment with an AVX?  or should I use NINA ?  I'm thinking of getting an AISAIR so maybe this is a non issue. I haven't looked into it but I think the ASIAIR has a feature for star aligning the mount ? 

 

 

 

Power Cable 

 

I have a Celestron power tank that I use to power the AVX.  Where the cable meets the power input for the mount, seems a bit loose, and when I move the cable the mount turns off and on. I got the cable at the right angle so this does not happen but is really annoying and I alway risk the mount loosing power while tracking if the cable gets in a position it does not like. 

 

Is there a special cable I should use for the AVX as far as powering the mount?

 

 

Image 

 

My exposures were 1 minute and 33 seconds unguided. I have a guidecam on the way ! anyway I went with a minute thirty three because that's what got the histogram 1/3 of the way across.  I'm posting the image below in case your sharp eyes can see some issues I need to address. I noticed the stars on the corners are elongated despite having a field flattener. Not sure what's going there. 

 

 

Single Exposure

50501568738_0925de3bbc_b.jpg

 

Stacked  1 hr 17 mins 

 

 50501571493_11c168c5a7_b.jpg

 

 

When I got home and saw the random star field, I had no idea what I had shot. So I used https://nova.astrometry.net/ to plate solve the image. 

 

50502281376_abb6ee2bfa_z.jpg


Edited by Diomedes, 18 October 2020 - 12:24 PM.

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#2 bobzeq25

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Posted 18 October 2020 - 12:27 PM

The rice grained stars at the edges indicate the flattener needs to be more precisely spaced.  It can't properly correct field curvature unless it is.

 

There's a specification.  Some people find varying that 1-2mm works better.  There are thin washerlike shims.

 

Learning platesolving (not hard) means you can forget about star alignment.


Edited by bobzeq25, 18 October 2020 - 12:28 PM.

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#3 Diomedes

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Posted 18 October 2020 - 12:36 PM

The rice grained stars at the edges indicate the flattener needs to be more precisely spaced.  It can't properly correct field curvature unless it is.

 

There's a specification.  Some people find varying that 1-2mm works better.  There are thin washerlike shims.

 

Learning platesolving (not hard) means you can forget about star alignment.

How do I adjust the flatenner spacing ? 



#4 alphatripleplus

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Posted 18 October 2020 - 01:50 PM

 

Learning platesolving (not hard) means you can forget about star alignment.

+1 

 

Platesolving really does simplify things. There are several to choose from, and most are integrated with other imaging applications. My favourite platesolver, because of speed and reliability, is ASTAP, but there are other choices like AstoTortilla, ASPS etc.


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#5 bobzeq25

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Posted 18 October 2020 - 02:34 PM

How do I adjust the flatenner spacing ? 

With spacers between the flattener and the camera.  I have a drawer full of things like this:

 

https://www.amazon.c...g/dp/B0069VY7RG

 

and a package of these:

 

https://www.microglo...et-p-12759.html

 

Some people like adjustable spacers, which exist.

 

https://www.cloudyni...e-spacer-05326/

 

Note that spacing is measured from a certain point on the flattener to the camera sensor, not the camera itself.

 

Figuring all this out is a basic skill to be acquired.  <smile>


Edited by bobzeq25, 18 October 2020 - 02:36 PM.

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#6 TelescopeGreg

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Posted 18 October 2020 - 06:15 PM

The AVX (mine, at least) takes 2 "alignment" stars PLUS at least 2 "Calibration" stars to get a good overall alignment.  The calibration stars are added by you manually aiming at some other targets in the sky (something other than the two it chose), and hitting the Align button, then the Scroll up/down keys to bring up "Calibration" on the screen where Align was.  Follow the on-screen instructions to add them in.  For me, 2+2 was enough to get pretty close to being on-target, adding another one or two as I played with the scope during the night.  It seemed you could never have enough.

 

But another recommendation for using Plate Solving instead.  I no longer bother to do any alignment (other than the mechanical Polar alignment of the mount itself).  Just power it up, choose "Quick Align" to get past the built-in alignment stuff, and then tell the software (I'm using CCDciel + ASTAP) where I want to go.  It then takes me there.  Done.

 

If your DSLR isn't supported by whatever software you're using, when that Guide scope arrives, take some care in getting it aligned to where your imaging scope is pointed, and try using that instead.  That co-alignment is best done during the day with some distant object.


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#7 Diomedes

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Posted 18 October 2020 - 09:50 PM

With spacers between the flattener and the camera.  I have a drawer full of things like this:

 

https://www.amazon.c...g/dp/B0069VY7RG

 

and a package of these:

 

https://www.microglo...et-p-12759.html

 

Some people like adjustable spacers, which exist.

 

https://www.cloudyni...e-spacer-05326/

 

Note that spacing is measured from a certain point on the flattener to the camera sensor, not the camera itself.

 

Figuring all this out is a basic skill to be acquired.  <smile>

thanks for sharing, I just ordered a caliper to measure. Do I need 55mm  from the lens of the flattener to the sensor ? 

 

The AVX (mine, at least) takes 2 "alignment" stars PLUS at least 2 "Calibration" stars to get a good overall alignment.  The calibration stars are added by you manually aiming at some other targets in the sky (something other than the two it chose), and hitting the Align button, then the Scroll up/down keys to bring up "Calibration" on the screen where Align was.  Follow the on-screen instructions to add them in.  For me, 2+2 was enough to get pretty close to being on-target, adding another one or two as I played with the scope during the night.  It seemed you could never have enough.

 

But another recommendation for using Plate Solving instead.  I no longer bother to do any alignment (other than the mechanical Polar alignment of the mount itself).  Just power it up, choose "Quick Align" to get past the built-in alignment stuff, and then tell the software (I'm using CCDciel + ASTAP) where I want to go.  It then takes me there.  Done.

 

If your DSLR isn't supported by whatever software you're using, when that Guide scope arrives, take some care in getting it aligned to where your imaging scope is pointed, and try using that instead.  That co-alignment is best done during the day with some distant object.

Thanks Greg ! I think I will go the plate solving route and avoid the possibility for human error. Finding out that I did all that work just to end up with a random star field was painful enough for me to get interested in plate solving. I think the ASIAIR does this by default so I might go with the ASIAIR pro.  



#8 imtl

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Posted 18 October 2020 - 09:56 PM

Your spacing between flattener and camera needs a bit more. Add 1-2mm spacing and take an image and see what you get. You're not that far off


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#9 Diomedes

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Posted 18 October 2020 - 10:14 PM



Your spacing between flattener and camera needs a bit more. Add 1-2mm spacing and take an image and see what you get. You're not that far off

so just 1-2mm ?

 

I was reading the description on HP(https://www.highpoin...tener-sca-fft58) and it says 

 

"A short profile design maintains the stability of the installed camera under windy conditions from low frequency oscillation transferred from the telescope. The necessary back focus distance for this non-reducer flattener, from T-thread shoulder to the CCD chip, is 55 mm."

 

Right now I have the flattener is directly connected to the thread on the T6i. I noticed the flattener has the lens on the back  of it near the camera's sensor.  Here is a picture of my setup in case is helpful. 

 

50504389047_31651bf694_z.jpg

 

50504389037_fdf306c111_z.jpg

 

 

 

base on the description above, does this mean 55mm between the T-Ring and the sensor. I highlighted it yellow, the space I understand to need 55mm. 

50504407637_a0dbfdaa04_z.jpg

Thanks for the help, I'm a bit confused about this part confused1.gif


Edited by Diomedes, 18 October 2020 - 10:17 PM.


#10 imtl

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Posted 18 October 2020 - 10:39 PM

so just 1-2mm ?

 

I was reading the description on HP(https://www.highpoin...tener-sca-fft58) and it says 

 

"A short profile design maintains the stability of the installed camera under windy conditions from low frequency oscillation transferred from the telescope. The necessary back focus distance for this non-reducer flattener, from T-thread shoulder to the CCD chip, is 55 mm."

 

Right now I have the flattener is directly connected to the thread on the T6i. I noticed the flattener has the lens on the back  of it near the camera's sensor.  Here is a picture of my setup in case is helpful. 

 

base on the description above, does this mean 55mm between the T-Ring and the sensor. I highlighted it yellow, the space I understand to need 55mm. 

 

Thanks for the help, I'm a bit confused about this part confused1.gif

Well, few comments about your questions.

 

Your FF is not specific for your scope which means that the 55mm is in "theory". But it will be relatively close to that.

 

This FF is designed for F/5 to F/8. That is quite a broad range of telescope speeds in my opinion and add to that that it is not specifically designed for your scope, gives you quite a bit of play with spacing. Since you have 55mm already and it is clearly back space too short (see how the elongation is going radially out from the center?). The way to go about with these things is not with huge steps, hence the suggestion to add 1-2mm and see what your image looks like. Don't forget that what you need is for the flat field to cover the size of your camera chip. That is an APS-C size in your case. Not the easiest of things but doable.


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#11 Diomedes

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Posted 18 October 2020 - 11:07 PM

Well, few comments about your questions.

 

Your FF is not specific for your scope which means that the 55mm is in "theory". But it will be relatively close to that.

 

This FF is designed for F/5 to F/8. That is quite a broad range of telescope speeds in my opinion and add to that that it is not specifically designed for your scope, gives you quite a bit of play with spacing. Since you have 55mm already and it is clearly back space too short (see how the elongation is going radially out from the center?). The way to go about with these things is not with huge steps, hence the suggestion to add 1-2mm and see what your image looks like. Don't forget that what you need is for the flat field to cover the size of your camera chip. That is an APS-C size in your case. Not the easiest of things but doable.

makes sense, will these work for adding the the 2mm ?

 

these are out of stock

https://www.highpoin...ing-set-t2ring 

 

would these work as well

https://www.cloudyni...ics-custom-etc/

 

also if I grab this one 

https://www.amazon.c...g/dp/B0069VY7RG

 

and use the 5mm, is there a pattern to tell if I have too much spacing ? 



#12 Diomedes

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Posted 25 October 2020 - 10:41 PM

I learned that the distance from sensor to the flange on my Canon t6i should be around 44mm, for my Flattener to work I need 55mm. The T-ring adds 10mm so that leaves me with 54mm, I added two spacers adding up to 1.23mm which theory should bring it to 55.3mm and the flattener should work properly. Lest see if that works out.



#13 DRK73

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Posted 25 October 2020 - 11:01 PM

Agenastro has been my goto for spacers for years. I like Highpoint, but they always seem out of stock on everything. I seriously doubt that spacing needs to be precise to the submillimeter level and until you rule out everything else with your imaging train I wouldn't go tearing your hair out over that spacing. I would recommend prioritizing your issues before trying to sweat the sub-millimeter stuff. 

 

I use an AVX. It's not perfect and neither are my images, but at the moment the mount is not the greatest of my problems. I'm not familiar with NINA or programs other than MaximDL, but Celestron's alignment routine is poo. What's worked for me with this Celestron mount is just to do the "Quick Align" *after* polar aligning with Sharpcap. Then I hook up the mount to my laptop and run it with Maxim where I slew to an obvious star, platesolve, sync to the platesolve solution, then slew again to my chosen star and BOOM it's bang on dead center. Alignment done. 

 

I'm not saying to go out and buy Maxim, but I'm sure there are other programs out there that can run your mount and incorporate platesolving. It makes thing stupidly easy. 


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#14 Diomedes

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Posted 25 October 2020 - 11:04 PM

Agenastro has been my goto for spacers for years. I like Highpoint, but they always seem out of stock on everything. I seriously doubt that spacing needs to be precise to the submillimeter level and until you rule out everything else with your imaging train I wouldn't go tearing your hair out over that spacing. I would recommend prioritizing your issues before trying to sweat the sub-millimeter stuff. 

 

I use an AVX. It's not perfect and neither are my images, but at the moment the mount is not the greatest of my problems. I'm not familiar with NINA or programs other than MaximDL, but Celestron's alignment routine is poo. What's worked for me with this Celestron mount is just to do the "Quick Align" *after* polar aligning with Sharpcap. Then I hook up the mount to my laptop and run it with Maxim where I slew to an obvious star, platesolve, sync to the platesolve solution, then slew again to my chosen star and BOOM it's bang on dead center. Alignment done. 

 

I'm not saying to go out and buy Maxim, but I'm sure there are other programs out there that can run your mount and incorporate platesolving. It makes thing stupidly easy. 

agreed, I just ordered a ASIAIR pro  which includes plate solving as part of the alignment process so hopefully I'm covered on that side of things. Fingers crossed grin.gif


Edited by Diomedes, 25 October 2020 - 11:05 PM.

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