Date   

Re: Back Focus Troubles #Absolute_Encoders

Seb@stro
 

I always wondered what the impact would be on these systems when a Crayford focuser is used and the primary mirror is locked at a specific focus position, effectively swapping the variable and fixed portions of the optical chain. 

I too had that question on my mind for quite some time for the EdgeHDs (I own the C8). 

From my readings, my understanding at this point is that with a crayford-type focuser in the optical chain, the backfocus spacing from the last optical element still needs to be pretty accurate (to < 1 mm) to optimize the field flatness over the entire sensor area / illumination circle. 

Hence, with a crayford on these scopes, the focus point needs to be pre-set with the primary mirror focuser prior to locking the clutches and should then only be fine-tuned by the crayford (auto)focuser to microns precision. The backfocus spacing tolerance for field flatness being an order of magnitude or so greater than that of focus point, field flatness should not, in theory, be impacted (much) by the change in backfocus spacing from the crayford reaching the focus point.

But as I said, this is my understanding only. If someone has a better explanation, I'm very interested in hearing it too.

Sébastien


Re: counter weight shaft

dvjbaja
 

Great idea!  



Sent via the Samsung Galaxy Note9, an AT&T 5G Evolution capable smartphone


-------- Original message --------
From: Konstantin von Poschinger <KPoschinger@...>
Date: 6/2/21 1:05 PM (GMT-08:00)
To: main@ap-gto.groups.io
Subject: [ap-gto] counter weight shaft

Hello,
I told a while back, that I will post a image of the counter weight adapter, that I have made. With this part I have no more trouble to mount the shaft. The diameter is 25.54mm. On my AP1600 I had a lo0t o trouble with the assembling. The gears were „zergniddelt“ as we say here in Germany. ;-))
It took me sometiome minutes to assemble.

Greetings

Konstantin



Konstantin v. Poschinger

Hammerichstr. 5
22605 Hamburg
040/8805747
0171 1983476


counter weight shaft

Konstantin von Poschinger
 

Hello,
I told a while back, that I will post a image of the counter weight adapter, that I have made. With this part I have no more trouble to mount the shaft. The diameter is 25.54mm. On my AP1600 I had a lo0t o trouble with the assembling. The gears were „zergniddelt“ as we say here in Germany. ;-))
It took me sometiome minutes to assemble.

Greetings

Konstantin



Konstantin v. Poschinger

Hammerichstr. 5
22605 Hamburg
040/8805747
0171 1983476


Re: Planetarium software

Andrea Lucchetti
 

Shailesh,
That’s quite interesting.
With the PMX you can use direct guide in skyx.
As you probably know the setting are very different from normal guiding but when done usually works very well. I used to ha e a Tec 140 with FF @1016mm, and in 10 years I’ve never had a guiding issue. But I am happy you found an alternative that works for you. Andrea 


Re: Planetarium software

Shailesh Trivedi
 

Hi Andrea,

My experience is positive for camera addon and Tpoint addon, but autoguiding is a bit hit or miss at higher focal lengths; for example when I use it with Astrodon MMOAG on my TEC 180FL at 1134mm focal length, even if I find several stars and with perfect polar alignment of my PMX on a permanent pier, the autoguiding performance was suboptimal and the star would be lost often. When I switched to PHD2, I got consistently better star shapes, with no star lost issue, and hence better overall images.

Shailesh


Re: Back Focus Troubles #Absolute_Encoders

Andrew J
 

On Wed, Jun 2, 2021 at 08:11 AM, ap@... wrote:
the majority of what the external focuser on the SCT is doing is restoring the same focus length (and so same back focus length), not so much changing it.
ap,

Thank you for that explanation. Using a focuser to correct or compensate for these changes makes sense in a standard SCT without any correcting elements in the light path. Moving the Primary Mirror or moving camera sensor should have the same net result.

I think this becomes more complicated when using an Edge HD system due to the glass correcting element in the baffle or adding the .07x focal reducer. 146.05mm is a very specific number. I always wondered what the impact would be on these systems when a Crayford focuser is used and the primary mirror is locked at a specific focus position, effectively swapping the variable and fixed portions of the optical chain. It is not something i necessarily need an answer to as I no longer own and Edge HD, but just curious. 

Andrew


Re: Will the Mach 2 support .....

Luca Marinelli
 

Roland,

I don’t know if you can charge gain in Maxim DL but you can certainly change the gain of the ASI6200MC in the ASCOM driver. Modern image acquisition software (NINA, Voyager, SGP) will also allow you to change the gain dynamically (per filter, per target, or whatever you want). 

If Maxim DL is a 32bit application, it will likely suffer greatly from the large files produced by these small pixel, full-frame cameras. That was the case with Sequence Generator Pro before they released a 64 bit version and now there are no data issues.

Luca

On Jun 2, 2021, at 12:59 PM, Roland Christen via groups.io <chris1011@...> wrote:


No model in APCC.

Roland



-----Original Message-----
From: Khushrow Machhi via groups.io <kmachhi@...>
To: main@ap-gto.groups.io
Sent: Wed, Jun 2, 2021 11:46 am
Subject: Re: [ap-gto] Will the Mach 2 support .....

Hi Roland,

Prior to this guiding run do you have a model built in APCC?  

Khushrow

--
Roland Christen
Astro-Physics


Re: Planetarium software

Andrea Lucchetti
 

My experience with skyx and camera addon it is very positive. I use it with ccdautopilot for automation. It worked well with the paramount and it works perfectly with the mach2.  Skyx has also one of the best solver in my opinion. Andrea


Re: Planetarium software

Shailesh Trivedi
 

Thanks Linwood, good thoughts. I currently have TSX with camera add on and Tpoint add on, and I agree with your thought that PHD2 is a better autoguider.


Re: Planetarium software

ap@CaptivePhotons.com
 

>Hi Dale,

>Thanks for reading my post. My goal is to use a planetarium app primarily for astrophotography with a path to automation and occasional light viewing. 

I’m not Dale, but will offer 2 cents as a TSX user.  TSX is an unusual package, in some ways, in that it is Planetarium, camera control, guider, and session manager wrapped up in one.  There are some others of these, mostly older software.

 

Perhaps because it is a bit of everything, it is not the best at any one.  In my mind, PHD2 for example is a better guiding program, with a lot more flexibility.

 

I find it better to build up a collection of best-of-breed tools and use them for what they do.  For me a planetarium software is mostly to identify targets I may want to image, find rise/transit/set time, altitude, etc. I then use a session manager (NINA) to actually execute what I plan, as it handles meridian flip (something TSX doesn’t do at all), coordinates flips and dithering with exposure, can do multiple targets in sequence based on time or altitude or exposure counts, etc.  So my planetary software at most feeds a coordinate set to NINA, then it is done.  (NINA has a limited set of planetarium features to help with framing/rotation as well as rise/set/transit times).

 

I’m not pushing NINA (though I like it), there are others like that – Voyager for example, or the venerable APT.

 

Personally I like Stellarium as a planetarium software but to me that’s mostly a function of screen appearance and one’s subjective taste – once you decided it is just a planning tool, it is easier to pick Planetarium based on UI and appearances more so than mount integration.  In fact, I do not even tie Stellarium to my mount (though it can).

 

The ability to plug and play different tools for different purposes is one success story in the otherwise pretty fractured astrophotography ecosystem, which can’t agree on much of anything else, from thread size to terminology to how to measure backfocus.  Pick the best of each, rather than a compromise that does it all.

 

Linwood

 


Re: Back Focus Troubles #Absolute_Encoders

Andrew J
 

Update: I mentioned in my original post that I hand contacted a Telescope and Eyepiece manufacture and got two different answers to the following scenario.

 

Assume there was correcting element that moves with the focuser that requires 50mm of fixed back focus and the imaging chain had a camera and filter wheel (with no filters) with a physical length of 25mm. In this configuration a 25mm spacer would be required to achieve back focus. If a 3m thick filter that adds 1mm of back focus is installed in the filter wheel, what would be the length of the spacer needed to achieve the correct back focus?

 

One person told me 24mm, another said 26mm.

 

This discrepancy is what led me to post the question here. I am happy to report that the person who told me 24mm tracked me down today and changed their answer to 26mm. They explained that adding the filter to the optical path increased the total back focus of the system. Introducing the filter increases the total back focus of the correcting element from 50mm to 51mm. Therefore the length of the spacer required to achieve the correct back focus for this scenario would be 26mm (50mm native BF + 1mm BF from filter – 25mm physical length of other components = 26mm spacer). I have to say, I was really impressed that the company would take the effort to contact me to correct their mistake. This is a rare thing.

 

This correction helped validate my initial thinking that adding a filter that adds 1mm of back focus changes the total back focus of the system as the starting point for the spacer calculation, before subtracting the physical distance of other components in the imaging chain. It is easy to get this backwards and add the 1mm to the components that are subtracted from the native back focus of the correcting element. This is the mistake the person made who said I would need a 24mm spacer.

 

I found this explanation helpful so thought I would pass it along. It also demonstrates how easy it is to make a mistake that would lead to a 2mm error in the calculation.

 

If adapters are ordered 1 – 2mm shorter than required and shims are used to achieve the correct back focus as described in Dale’s post then this mistake is easy to correct. If adaptors are ordered to the exact calculated length as I use to do, this can be a cost mistake to correct. After talking to the person yesterday who told me 24mm, I thought I was going to have to order a bunch of new adapters because I had ordered them to exact length and if what he told me was correct, it meant that all my adapters were 2mm to long. Thankfully, it appears I might be OK if I ignore the tolerances. Ordering them shorter than needed is definitely the way I plan to go in the future.

 

I hope this was useful.

 

Andrew


Re: Planetarium software

Shailesh Trivedi
 

Hi Dale,

Thanks for reading my post. My goal is to use a planetarium app primarily for astrophotography with a path to automation and occasional light viewing. 

Shailesh


RA stuck at a certain point on AP 1600

Kenneth Tan
 

I am using the mount controlled by the ASI air pro. On the left side the RA goes all the way on the right R A goes to a point and then reverses. Any idea why? I do not use the hand controller sp completely controlled by the ASI pro


RA stuck at a certain point on AP 1600

Kenneth Tan
 

I am using the mount controlled by the ASI air pro. On the left side the RA goes all the way on the right R A goes to a point and then reverses. Any idea why? I do not use the hand controller sp completely controlled by the ASI pro


Re: Will the Mach 2 support .....

Roland Christen
 

No model in APCC.

Roland



-----Original Message-----
From: Khushrow Machhi via groups.io <kmachhi@...>
To: main@ap-gto.groups.io
Sent: Wed, Jun 2, 2021 11:46 am
Subject: Re: [ap-gto] Will the Mach 2 support .....

Hi Roland,

Prior to this guiding run do you have a model built in APCC?  

Khushrow

--
Roland Christen
Astro-Physics


Re: Will the Mach 2 support .....

Khushrow Machhi
 

Hi Roland,

Prior to this guiding run do you have a model built in APCC?  

Khushrow


Re: Planetarium software

Dale Ghent
 

Hi Shailesh,

It's note really clear as to what your goals are. Is it to use a planetarium app to drive the mount around the sky for visual and occasional light astrophotography use, or are you looking for something that's primarily for automated astrophotography that can also lean on a planetarium app for target coordinates and such?

On May 27, 2021, at 19:07, Shailesh Trivedi <strivedi@brightfeathers.com> wrote:

[Edited Message Follows]

Does anyone have a recommendation? The Sky X vs Maxim DL?

I used to have a Paramount MX (PMX) which I have sold in lieu of AP1100 with AE and a soon expected Mach2.

I used The Sky X with camera addon and Tpoint on my PMX, but now that I do not have this mount, I am inclined to help the PMX buyer transfer the TSX license. I would like to know what the good folks here use on AP mounts with or without APCC.

Options I am considering

1. Continue TSX with Tpoint + camera add on or use the imaging edition from Bisque
2. Use MaximDL, but not sure if it is as good as TSX. I especially liked the "closed-loop slew" in TSX; I don't know if Maxim DL has the equivalent of closed-loop slew, and if the planetarium sw of Maxim DL as good. I have heard of auto meridian flips of MDL and multi-star auto-guiding, plus integration with ACP.

Thoughts?

Shailesh


Re: Will the Mach 2 support .....

George
 

The ASI 6200 camera is also looking through colored filters.

 

Regards,

 

George

 

George Whitney

Astro-Physics, Inc.

Phone:  815-222-6538 (direct line)

Phone:  815-282-1513 (office)

Email:  george@...

 

From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of Roland Christen via groups.io
Sent: Wednesday, June 2, 2021 11:03 AM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Will the Mach 2 support .....

 

Thanks for your reply,

 

I did not adjust the gain in the 6200M. I could not find any way to do that in MaximDL. Perhaps I need to read the manual more closely.

 

The 160 EDF has 51% more light grasp, so the signal/noise is considerably higher. A real test of course would be to run each camera on the same scope with similar pixel size. I will do that when I test the Starlight X-Press Pro 36 on the 160 refractor. That camera has much higher efficiency than the QSI, and the 7.4 micron pixel size will be a good match for the 6200C binned 2x2 at 7.5 microns. That said, i suspect that the 6200M would be the clear winner, not only because of the lower noise and somewhat higher efficiency, but also because you can run it binned at 1x1 on those very steady nights to get the highest resolution.

 

Running this 6200C on my laptop presented some interesting challenges. I could not do an automated run of consecutive images because the laptop ran out of memory after the first image was downloaded. I don't know why that is, the laptop has lots of memory but for some reason had trouble with the 359 megabyte images and would crash each time. I also could not calibrate dark frame and flat frame in one step without MaximDL crashing. Even though I was very careful to get good flat frames, the results were really strange, especially when more than 2 calibrated images were combined. All of these problems went away when I used only 80% of the chip area for each image.

 

Rolando

 

-----Original Message-----
From: Luca Marinelli <photo@...>
To: main@ap-gto.groups.io
Sent: Wed, Jun 2, 2021 5:09 am
Subject: Re: [ap-gto] Will the Mach 2 support .....

Thank you for sharing your results, Roland. I was imaging with the Mach2 and my solid tube 10in f4 reflector last night (40lbs fully loaded but with a fairly significant moment arm) and the absolute encoders on the mount make it track smoother and easier than when I use the same scope on my AP1100 without encoders. The difference encoders make in ease of use of a mount is truly remarkable. Obviously imaging results are the same, provided one guides the non-encoder mount appropriately, but it certainly takes a bit more finesse and knowledge with the non-encoder mount.

With regards to the comparison between the QSI683 and the ZWO 6200MC, I wanted to offer some considerations to keep in mind:

1) In spite of the larger diameter of the 160mm optics, the etendue per pixel is 1.76x larger for the 130mm scope given the bigger effective pixel size of the binned KAF8300 sensor. This means that the solid angle of sky seen by each pixel of the KAF8300 sensor  is almost twice as big as the ZWO 6200MC system and signal will accumulate accordingly, even before taking into account quantum efficiency.
2) The ZWO 6200MC has a Bayer matrix in front of the signal. You did not mention what filter you were using with the QSI683 camera but if it was a luminance filter, you are allowing up to about 4x more wavelength bandpass than any of the R, G, or B filters in front of each of the pixels of the ZWO ASI6200MC.
3) The ZWO 6200MC is a variable gain camera. You did not mention what gain setting you were using. If you were using the camera with default gain in the ASCOM driver, it is probably gain 0 (CMOS gain 0.8 e/ADU), which corresponds to the highest full well capacity and dynamic range, but the lowest sensitivity of the camera (signal accumulation measured in ADU per unit time). It should be noted that the camera circuitry changes acquisition mode at gain 100 (CMOS gain 0.28 e/ADU) with a step change in read noise from 3.5e to 1.5e per read. This is a particularly useful gain setting when large full well capacity is not the paramount concern.

Best,

Luca


--
Roland Christen
Astro-Physics


Re: Will the Mach 2 support .....

Roland Christen
 

Thanks for your reply,

I did not adjust the gain in the 6200M. I could not find any way to do that in MaximDL. Perhaps I need to read the manual more closely.

The 160 EDF has 51% more light grasp, so the signal/noise is considerably higher. A real test of course would be to run each camera on the same scope with similar pixel size. I will do that when I test the Starlight X-Press Pro 36 on the 160 refractor. That camera has much higher efficiency than the QSI, and the 7.4 micron pixel size will be a good match for the 6200C binned 2x2 at 7.5 microns. That said, i suspect that the 6200M would be the clear winner, not only because of the lower noise and somewhat higher efficiency, but also because you can run it binned at 1x1 on those very steady nights to get the highest resolution.

Running this 6200C on my laptop presented some interesting challenges. I could not do an automated run of consecutive images because the laptop ran out of memory after the first image was downloaded. I don't know why that is, the laptop has lots of memory but for some reason had trouble with the 359 megabyte images and would crash each time. I also could not calibrate dark frame and flat frame in one step without MaximDL crashing. Even though I was very careful to get good flat frames, the results were really strange, especially when more than 2 calibrated images were combined. All of these problems went away when I used only 80% of the chip area for each image.

Rolando

-----Original Message-----
From: Luca Marinelli <photo@...>
To: main@ap-gto.groups.io
Sent: Wed, Jun 2, 2021 5:09 am
Subject: Re: [ap-gto] Will the Mach 2 support .....

Thank you for sharing your results, Roland. I was imaging with the Mach2 and my solid tube 10in f4 reflector last night (40lbs fully loaded but with a fairly significant moment arm) and the absolute encoders on the mount make it track smoother and easier than when I use the same scope on my AP1100 without encoders. The difference encoders make in ease of use of a mount is truly remarkable. Obviously imaging results are the same, provided one guides the non-encoder mount appropriately, but it certainly takes a bit more finesse and knowledge with the non-encoder mount.

With regards to the comparison between the QSI683 and the ZWO 6200MC, I wanted to offer some considerations to keep in mind:

1) In spite of the larger diameter of the 160mm optics, the etendue per pixel is 1.76x larger for the 130mm scope given the bigger effective pixel size of the binned KAF8300 sensor. This means that the solid angle of sky seen by each pixel of the KAF8300 sensor  is almost twice as big as the ZWO 6200MC system and signal will accumulate accordingly, even before taking into account quantum efficiency.
2) The ZWO 6200MC has a Bayer matrix in front of the signal. You did not mention what filter you were using with the QSI683 camera but if it was a luminance filter, you are allowing up to about 4x more wavelength bandpass than any of the R, G, or B filters in front of each of the pixels of the ZWO ASI6200MC.
3) The ZWO 6200MC is a variable gain camera. You did not mention what gain setting you were using. If you were using the camera with default gain in the ASCOM driver, it is probably gain 0 (CMOS gain 0.8 e/ADU), which corresponds to the highest full well capacity and dynamic range, but the lowest sensitivity of the camera (signal accumulation measured in ADU per unit time). It should be noted that the camera circuitry changes acquisition mode at gain 100 (CMOS gain 0.28 e/ADU) with a step change in read noise from 3.5e to 1.5e per read. This is a particularly useful gain setting when large full well capacity is not the paramount concern.

Best,

Luca

--
Roland Christen
Astro-Physics


Re: Back Focus Troubles #Absolute_Encoders

ap@CaptivePhotons.com
 

Andrew:


> In this case the last correcting element does not move with the focuser and distance between the last correcting element and the sensor will change as the focuser is repositioned. In examples where the last correcting element does not move, why is dialing in a specific back focus distance using spacers so critical if the distance is going to change depending on the position of the focuser?

In a terrestrial lens focus distance (indeed even focal length) changes with distance to the subject, due to angles of the corresponding light rays changing with distance.  In Astro work, everything is effectively at the same distance from us (parallel rays, effectively infinity) and the primary reason we actually need a focuser (beyond initial setup) is to correct for temperature change, which is primarily a dimensional changes in the focal path.  While more complex optics make it more complicated (and in theory temperature could affect the glass not just dimensions of the OTA and train), the majority of what the external focuser on the SCT is doing is restoring the same focus length (and so same back focus length), not so much changing it.

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