Date   

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.


Re: Back Focus Troubles #Absolute_Encoders

Andrew J
 

Hi Mike.

This is really good example of the two "types" of back focus, fixed vs. variable. The X back focus distance is fixed will not change when the focuser is repositioned. In this case I could understand the argument for getting the back focus distance as close as possible per the specs of the Field Flattener. However, the Y back focus is variable and will change when the focuser is repositioned. When the back focus is variable, I believe the documented back focus is a "recommended" value to help ensure focus can be achieved within the travel limits of the focuser. In the case where the back focus distance is variable it probably is not worth stressing over every mm of back focus. As long as it is close and still within the travel distance of the focuser then that should be good enough. 

I think you nailed the explanation of the two different types. This has helped me get my head around back focus and understanding the difference between fixed vs. variable back focus. Thank you for your detailed post. 

Andrew


Re: Back Focus Troubles #Absolute_Encoders

Andrew J
 

On Tue, Jun 1, 2021 at 02:01 PM, Dale Ghent wrote:
at it's a good idea to not fixate on a single exact number when it comes to back focus dista
Hi Dale.

I think this is really good advice. In the past I always ordered my Precise Parts adaptors to be exactly the calculated length based on the scope/correcting element's published specs minus the other elements in the optical path. Probably not a good practice as even PP states their parts have +/- 1mm tolerance. Combined with the +/- tolerances of the other components in the optical path you mentioned and it is probably never going to be the calculated distance. I actually sent a note to Precise Parts last night on how to create shims using their configurator for non-standard thread sizes. Agena Astro Products sells Fine Adjustment Spacer Rings for standard thread sizes. Going forward, I will follow your advice and always order my Precise Parts 1mm short and use shims to get to the correct length. 

Andrew


Re: Back Focus Troubles #Absolute_Encoders

Andrew J
 

Hi Jeff.

You are right, I picked a bad example. I remembered after my initial post that the FF on the TEC140ED moves with the focuser and because it is the last correcting element before the sensor means that the distance between this element and the sensor will not change when the focuser is repositioned. So, again bad example.  My understanding is that the back focus is determined by the LAST correcting element in the light path before the camera sensor. Therefore, I should have used the example of the TEC140ED without the FF which I think has a recommended BF of 170mm.

Another example I am familiar with is the Celestron EDGE HD scopes that have a correcting element in the baffle tube of the scope. Celestron states in their Edge HD White Paper that back focus for the EDGE HD 925, 1100, 1400 is 146.05mm. However, it is fairly common for people to add Crayford focusers to the back of the EDGE HD scopes and lock the primary mirrors. 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?

Andrew


Re: Back Focus Troubles #Absolute_Encoders

Andrew J
 

Hi Linwood.

Thanks for the OPT link. I hadn't seen that before and is quite helpful. I have book marked it for future reference. 

Andrew


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

Luca Marinelli
 

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


Re: Will the Mach 2 support

Harley Davidson
 

Thanks for the information and photo Roland!

tony

On 6/1/2021 8:06 PM, Roland Christen via groups.io wrote:
Hello AstroNuts,

We get this question many times, "will the Mach2 support my scope, camera etc." I can't really answer specific setups since I don't have infinite variety of scopes at my disposal. However, to give you some idea I am presently testing two scopes piggybacked on the Mach2.

Here is my present setup. I am using it to test various optics, cameras and field flatteners. It consists of a 160EDF refractor with QTCC and a full frame ZWO 6200 color camera, which provides a very wide field. On top rides an oldie but excellent 130 EDF refractor with 2.7" focuser, 67PF562 Flattener and my QSI 683WSG camera, Lodestar off-axis guider and an 8x50 Baader finder for good measure. Both scopes sit in rings that are attached to dovetail plates. When you add up all the parts, the whole shebang weighs close to 70 lb with the weight centered about 9 inches from the top of the Dec axis. I have approximately 75lb worth of counterweight which includes the weight of the standard Mach2 cwt bar and the shorter extension.

Is it stable and does it slew, track and guide effortlessly? Yes on all counts. It does need to be closely balanced, but not ridiculously so. Using MaximDL6, in poor seeing i get on the order of 0.4 arc sec rms guiding. In good to excellent seeing I get 0.1 to 0.15 arc sec rms guiding. My guide exposure is between 2 and 5 seconds with 1.5 seconds between exposures. Best guiding seems to be when the exposures are 4 to 5 seconds, and I get very few excursions that are larger than 0.5 arc sec pk.

By the way, I don't usually guide with one scope and image with another. In this case I am guiding with the lighter weight 130EDF and I am getting perfect round stars with the 160 below. The 160 is shooting at 960mm focal length with a 3.75 micron/pixel camera, 0.8 arc sec per pixel. ZWO 6200 camera. resolution with this camera in medium seeing has yielded 1.4 arc sec FWHM stars in a 5 minute exposure.

I will be shooting tonight if the weather holds, and I can record some guide graphs for anyone interested. Seeing is supposed to be good (4 out of 5) but transparency will be poor. I'm doing a shootout between the CMOS camera with 3.75 micron pixels and my older QSI683 CCD camera with 5.4 micron pixels. Which camera records images faster? Which has better contrast? Any bets on the winner?

Rolando


--
Roland Christen
Astro-Physics


Re: VIDEO - Mach2 Right Ascension Belt Adjustment

Harley Davidson
 

Thank you Mike!

tony

On 6/1/2021 7:34 PM, M Hambrick wrote:
Another great video Tony.

Like you, I have always been impressed to see how A-P machines so many of their parts from solid aluminum bar stock. 

That cogged belt is also impressive. The part number indicates that it is a 3 mm pitch belt. What is the width ? I am guessing that it is at least 3/8" wide. That seems to be more than strong enough for the application.

Mike


Re: Question: How do I safety replace the CW shaft adapter (got it off, grease?)

Konstantin von Poschinger
 

Hi,

if you have trouble loosing the counter weight shaft, use a mounted counter weight and turn that till the shaft get loosened!

Grüsse

Konstantin


Konstantin v. Poschinger


Hammerichstr. 5
22605 Hamburg
040/8805747
0171/1983476

Am 02.06.2021 um 03:39 schrieb Roger Howard <cargostick@...>:

1100GTO.  I got it free with the help of my neighbor, but just wanted to post that I used some lube on the insert to hopefully keep it from happening again.  Yes, I do have the insert.


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

Roland Christen
 

Result #2: Tracking with 2 refractors piggyback

The sky unfortunately was not pristine during my imaging session. High level clouds continued to drift thru the image, so the tracking was at times a bit unsteady, but overall not too bad. Here is one tracking graph that was typical of the evening. 1 pixel = 1.45 arc sec in this graph. In this 15 minute period the tracking was less than 0.5 arc sec pk, and approx 0.14 arc sec rms.

Rolando





-----Original Message-----
From: Roland Christen via groups.io <chris1011@...>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Sent: Tue, Jun 1, 2021 11:47 pm
Subject: Re: [ap-gto] Will the Mach 2 support .....

Result #1: CMOS vs CCD

The 683 has an 8300 chip that's not very efficient but it's monochrome. There are better CCD chips with much higher quantum efficiency such as the Starlight Xpress Pro36, which is a full frame camera with exceptional low noise. It has a 7.4 micron pixel size.

The ZWO 6200C is a color CMOS camera with very low noise, but is it as sensitive as a monochrome CCD? It turns out that it isn't as sensitive as the 8300 monochrome chip. In a side by side test of these two cameras, the ZWO produced a peak intensity of the core of M106 that was only 75% as high as the QSI camera. And that's with a 50% greater light grasp of the 160 EDF vs the 130 EDF that the QSI was attached to. The CMOS did have a signal/noise advantage because of the low noise chip, but part of that was due to the higher light grasp of the 160 mm aperture.

See image below:
Rolando


--
Roland Christen
Astro-Physics


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

Roland Christen
 

Result #1: CMOS vs CCD

The 683 has an 8300 chip that's not very efficient but it's monochrome. There are better CCD chips with much higher quantum efficiency such as the Starlight Xpress Pro36, which is a full frame camera with exceptional low noise. It has a 7.4 micron pixel size.

The ZWO 6200C is a color CMOS camera with very low noise, but is it as sensitive as a monochrome CCD? It turns out that it isn't as sensitive as the 8300 monochrome chip. In a side by side test of these two cameras, the ZWO produced a peak intensity of the core of M106 that was only 75% as high as the QSI camera. And that's with a 50% greater light grasp of the 160 EDF vs the 130 EDF that the QSI was attached to. The CMOS did have a signal/noise advantage because of the low noise chip, but part of that was due to the higher light grasp of the 160 mm aperture.

See image below:
Rolando





-----Original Message-----
From: M Hambrick <mhambrick563@...>
To: main@ap-gto.groups.io
Sent: Tue, Jun 1, 2021 7:51 pm
Subject: Re: [ap-gto] Will the Mach 2 support .....

Thanks for showing us this imaging setup Roland, and yes, please share your results including your guiding graphs.

Mike

--
Roland Christen
Astro-Physics

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