Exploring a ToupTek Astro AE676M monochrome multi-purpose astronomy camera. Part 1.

The ToupTek Astro AE676M monochrome CMOS camera was attached to a Stella Mira 66mm ED APO  refractor which was fitted with a field flattener, an Altair V2 2" filter drawer, a camera rotator and a ZWO EAF focuser. A ToupTek GS-100, F=100mm, A=25mm quadruplet PAPO scope was mounted as a guide-scope with an Altair 462M2 monochrome CMOS camera as the guide camera as explained in the previous blog article . Autoguiding was done with PHD2 running on a Fedora mini computer via an INDI to control the Celesdtron AVX mount.

The equipment

The Altair 462M2 camera has an underpowered one stage TEK cooler with a detatchable fan unit that holds in place with strong magnets to enhance the weak cooling. The cooling is powered by the same USB cable that powers and streams data from the camera. Therefore we employed a 4 port SABRENT powered hub between the camera's USB-C to USB 3.0 cable and the USB 3 cable used to carry the signal indoors to the imaging computer. The cooling works but doesn't lower the temperature to those typically achieved by cooled astronomical cameras. Having said that, it did prove to be adequate for the job. It will clearly be better during the cold winter months. For solar imaging, the cooler helps prevent the camera from overheating.

The ToupTek Astro AE676M utilizes the Sony IMX676 sensor, which features a hardware architecture capable of a single-exposure dual-gain readout, often referred to in the industrial/surveillance sector as Clear HDR.

To understand how the HDR mode achieves a 16-bit output by combining HCG and LCG, it helps to break down the mechanics of the sensor's pixel design. 

Understanding LCG vs. HCG

In a typical CMOS sensor, every pixel acts as a tiny container storing light energy (photons) converted into electrical charges (electrons). The camera then converts these electrons into a digital number using an Analog-to-Digital Converter (ADC).

LCG (Low Conversion Gain): The sensor sets the pixel container to maximum capacity. This yields a high Full-Well Capacity (around 11,500 electrons for this sensor). It prevents bright targets like the core of a star, the moon, or the sun from instantly clipping into pure white. However, the trade-off is higher readout noise.

HCG (High Conversion Gain): The sensor electronically limits the container size but amplifies the signal intensely right at the pixel. This dramatically drops the Readout Noise (down to about 1.01 electrons), allowing you to see very faint signals buried in the dark background. The trade-off is that the pixel container overflows very quickly on bright details.

The HDR mode is intended for high-contrast targets: This mode  should be best for Solar, Lunar, and Planetary imaging, or highly uneven deep-sky objects like the Orion Nebula. In solar imaging, for example, it allows the capture of both the very bright solar surface and faint edge prominences simultaneously.

How HDR Mode Works (Single-Exposure Dual Gain)

The capture software must be set to capture 16 bit data for HDR mode to work properly.

Instead of forcing you to choose between the two, HDR Mode reads each pixel twice simultaneously from a single exposure using two independent readout paths on the sensor:

Simultaneous Capture: When the shutter closes, the camera reads the sensor through the HCG path (optimized for shadows) and the LCG path (optimized for highlights) at the exact same moment. Because this happens in a single exposure, it avoids the "ghosting" or motion blur artefacts caused by taking two separate exposures back-to-back.

On-Board Synthesis: The camera’s internal firmware compares the two readouts pixel by pixel:

• If a pixel is dark or faint, it extracts the data from the clean HCG readout.

• If a pixel is bright and saturating in HCG, it pulls the data from the high-capacity LCG readout.

16-bit Output Mapping: The native hardware ADC of the sensor is 12-bit. However, by stitching the shadow depth of HCG and the highlight headroom of LCG together, the total dynamic range spans past 12 bits. To accommodate this expanded range without truncating the data, the camera mathematically maps the blended information into a 16-bit container (storing values from 0 to 65,535). A number of camera manufacturers have this method available.

In this first part of exploring the Astro AE676M we only used the LCG and HCG modes and will reserve the HDR mode for future testing. The camera was fitted with a Baader UV/IR cut filter otherwise the image would be swamped by IR light to which the camera is very sensitive.

We used AstroDMx Capture to image the Aun in H-alpha light through a Coronado Solarmax II 60, BF 15 H-alpha scope mounted on a Skywatcher Solar Quest solar finding and tracking mount.

A 1000-frame SER file was captured in LCG mode in 8 bits. The best 80% of frames in the SER file were stacked in Autostakkert!4, wavelet processed in waveSharp3 and further processed in PixInsight and GIMP3.

Click on an image to get a closer view.

The Sun in H-alpha light

Even in 8 bits, the prominences could still be seen and captured.

Similarly we used AstroDMx Capture to capture a 1000-frame 8 bit SER file of the Moon through the Stella Mira 66mm ED APO  refractor fitted with a Pegasus L-UV/IR cut filter. The best 80% of frames in the SER file were stacked in Autostakkert!4, wavelet processed in waveSharp3 and further processed in GIMP3.

The 93% Moon

Deep Sky imaging in HCG mode

One and a half hours of total exposure were captured by AstroDMx Capture; half an hour's worth of 1 minute exposures through each of H-alpha, O3 and S2 Altair 2" 7nm narrowband filters, plus calibration frames using an Aurora electroluminescent flat panel for the flats.

Electroluminescent flat panel

The camera focused on a bright star using a Bahtinov mask

Screenshot of AstroDMx Capture capturing 60s exposures of M17 in H-alpha

The data were stacked in PixInsight and further processed in PixInsight, GraXpert, SetiAstroSuitePro and GIMP3.

M17 Hubble Palette

(H+S)OO L palette

Hubble - (H+S)OO L palette blend

HOS Canada, France, Hawaii Telescope palette

HSO palette

OHS palette

OSH palette

SOH palette

Pixelmath images were constructed using Siril

ForaaX palette

Gendler palette

Natural palette

In Part1 we have established that the Touptek Astro AE676M monochrome multi-purpose astronomy camera delivered good results using standard LCG and HCG modes. The results on a quite bright nebula, M17 with 60s exposures in HCG mode was good. Similarly in LCG mode on the Moon and on the Sun in H-alpha were good.

We look forward to Part 2 in which we shall explore fainter nebulae with longer exposures in HGC mode and also HDR 16 bit  mode with solar and lunar imaging and also, when it becomes available, the Orion nebula.

Using the GS-100 as a guide-scope and fixing PHD2 for Linux's lack of Altair camera Support.

Following our tests of the Touptek GS-100 PAPO, A=25mm, F=100 mini quadruplet as an imaging scope, we set it up as a guide-scope in conjunction with an Altair 462M2 monochrome guide camera fitted with an IR/UV cut filter.

The guide-scope/camera setup

The guided rig in action

The scope was brought to focus on a bright star using a Bahtinov mask and then both the camera and the focuser were glued with a small amount of epoxy resin glue to prevent any movement of the camera or focuser during use. It should be noted that the epoxy resin can, with care, be removed should that become necessary.

This guider setup was mounted on a Stella Mira 66mm APO refractor with a field-flattener and a ZWO EAF focuser. The scope was also fitted with an Altair V2, 2" magnetic filter drawer and a ZWO ASI585MC uncooled OSC camera.

AstroDMx Capture for Linux pre-release version 3 was running on an Ubuntu Linux computer and PHD2 for Linux was running on a separate Fedora Linux computer. The mount and focuser were controlled via an INDI server running on a Fedora mini computer.

We discovering that PHD2 for Linux surprisingly didn’t have Altair camera support. Nicola checked out the latest source code from github (https://github.com/OpenPHDGuiding/phd2) and built again but, this failed to add Altair camera support.

At this point, She looked through the source code and found cam_altair.cpp. On inspection of this source file she found that all the SDK calls were in place and essentially cross-platform but there was no implementation for POSIX dynamic library loading for Linux. 

She defined struct SDKLib using <dlfcn.h> so that libaltaircam.so would be dynamically loaded and then rebuilt the source code. After building the source, we were able to connect PHD2 to the Altair camera in Linux and could calibrate the guider in the usual way. Guiding performed perfectly during the imaging session.

AstroDMx Capture for Linux running on an Ubuntu mini computer was used to capture an hour's worth of 2 minute exposures through each of a Askar Colour Magic HaO3 and S2O3 dualband C filters, along with calibration frames.

Screenshot of PHD2 auto-guiding on a Fedora Linux computer

Screenshot of AstroDMx Capture for Linux capturing HaO3 data

Screenshot of AstroDMx Capture for Linux capturing S2O3 data

The data were stacked and part processed in PixInsight and further processed in GraXpert, SetiAstroSuitePro and GIMP 3.

(Ha+S2)OO rendering

Hubble Palette

(Ha+S2)OO - Hubble palette blend

HOS (Canada, France Hawaii Telescope palette)

OHS palette

The ZWO ASI585MC uncooled OSC camera performed well as a deep sky imaging device. The GS-100 mini scope proved its versatility as a guide scope (as well as previously, an imaging scope) and paired with the Altair 462M2 monochrome camera provided a wide field of sharply focused stars for PHD2 for Linux to guide with once the lack of Altair camera support had been resolved.

Nicola will submit her solution to PHD2 via the appropriate channels when she has written it up.

Again, these tests allowed us to uncover issues in the pre-release version 3 of AstroDMx Capture which will help the final release to be stable and feature rich.

A very small, wide-field, guided imaging rig Part 3. Second tests

The equipment in operation

This time a Mars-C II camera was used which has an optical window with very good, multi-layer anti-reflection coatings.

There was no moonlight during this session but there is a streetlight close to the imaging spot that has to be shielded by the occultation board visible on the right.

B142-43 dark nebulae centred on the star HD185898, captured by AstroDMx Capture (pre-release-version3) through a GS-100 PAPO quadruplet ED f/4 (F=100mm, A=25mm) mini scope with a Player One Mars-C II camera (with a SONY IMX662 1/2.8" CMOS colour sensor). 60 minutes of 60s exposures with a Pegasus Astro L-UV-IR cut filter. Captured by AstroDMx Capture pre-release version 3. Processed in PixInsight, GraXpert, SASPro and Gimp3.

B142-43 dark nebulae

Also the North America and Pelican nebulae centred on the star HD199479, captured through the same scope and camera. 60 minutes with L-UV-IR cut, 30 minutes with quadband, 30 minutes with HaO3 and 15 minutes with S2O3 filters. Captured by AstroDMx Capture pre-release version 3. Processed in PixInsight, GraXpert, SASPro, Gimp3 and CS2, blending the various filter results.

North America and Pelican nebula

The stars are from the Pegasus Astro L-UV-IR cut filter because they are true RGB stars and did not produce halos.

During this session we were able to observe that different filters introduce various gradients across an astronomical image? some produce large gradients that have to be removed whilst others produce no gradient on the same object at essentially the same time.

Screenshot of AstroDMx Capture saving 5 minute exposures of the North America and Pelican nebulae through the Pegasus Astro L-UV-IR cut filter,

 

It can be seen that there is a huge gradient across the image.

Screenshot of AstroDMx Capture saving 5 minute exposures of the North America and Pelican nebulae through the Altair quadband filter

It can be seen that the gradient has gone but some of the brighter stars now have halos. A similar result was obtained when using an Askar  HaO3 filter, and also with an Askar S2O3 filter.

Screenshot of AstroDMx Capture saving 5 minute exposures of the North America and Pelican nebulae through an Asker S2O3 filter

Animation showing the gradient produced by the Pegasus Astro L-UV-IR cut filter vs the absence of the gradient produced by the Altair quadband filter but the presence of star halos

Different astronomical filters introduce vastly different gradients because of the type of light they let pass and how they interact with wide angles of incoming light. When shooting the exact same target at the exact same time, a broadband filter like the Pegasus L-UV-IR cut filter can show a massive sky gradient, while a narrowband filter like the Altairquadband filter can appear completely gradient-free. This is driven by two main factors: the nature of environmental sky glow and the physics of interference filters. 

The primary driver of gradients is sky glow, which includes artificial light pollution, moonlight, and natural atmospheric airglow. During these tests there was no moonlight.

Broadband filters pass wide windows of light (often 100nm or more). Because light pollution (especially from LEDs) and moonlight scatter across the entire visible spectrum, they create a thick background glow. Because the telescope points at an angle through the atmosphere, one side of the image frame is always closer to the horizon or a light source than the other. This creates a steep, highly noticeable brightness gradient across the sensor. 

Narrowband filters isolate an incredibly tiny sliver of light (usually between 3nm and 7nm) centred precisely on the emission lines of nebulae. They block up to 99% of all scattered sky glow.

H (656nm) and SII (672nm): Moonlight and urban light pollution contain very little energy at these deep-red wavelengths. Thus, the background stays completely dark and gradient-free across the whole sensor.

OIII (501nm): Unlike H, Oxygen-III sits in the blue-green spectrum where moonlight and LED scattering are very strong. Even with a narrow 3nm filter, if the Moon is out, OIII will often suffer from severe gradients while an H-alpha frame taken at the exact same moment remains completely clean. As we had no moonlight and the fluorescent streetlight nearby, the S2O3 filter didn't produce a gradient.

Some gradients are not in the sky at all; they are generated inside the imaging equipment itself. Modern astrophotography filters are interference filters, meaning they use microscopic chemical layers to reflect unwanted light and pass specific wavelengths.

When light rays hit an interference filter at an angle (which happens frequently at the edges of a wide-field telescope or fast f-number optics), the physical distance the light travels through the filter layers increases. This shifts the filter's passband toward shorter wavelengths. With broadband filters, this shift doesn't matter because the window is wide enough. But with ultra-narrowband or complex multi-band filters, a bandpass shift means the edges of the sensor stops capturing the target's light and starts capturing background light noise, creating colour gradients.

Some filters have poor off-band blocking performance. When a filter fails to block out-of-band light completely, that light enters the filter glass and creates intra-filter reflections. The light bounces back and forth between the front and back surfaces of the filter glass before finally escaping toward the camera sensor. This reflected, slightly offset pool of light is what produces a halo around bright stars. The halos we observed are most likely due to this cause.

In conclusion the GS-100 mini scope can be used successfully as a wide-field imaging scope in conjunction with the appropriate camera and filters.

We have used these tests to simultaneously test pre-release version 3 of AstroDMx Capture.

A very small, wide-field, guided imaging rig Part 2. First tests

 

The equipment

The scope and guide-scope mounted on the AVX mount

Although a number of components can be added to the rig, such as a filter drawer or filter wheel there are very limited degrees of freedom to develop a setup that is truly flexible. For example, there is such limited back-focus with probably any camera, that it is impossible to fit even a very thin camera rotator to facilitate the framing of astronomical targets. There is room to fit a very small number of spacer shims so by varying the number and thickness of these and tightening up the camera, it may be possible to approximate the desired framing, or not!

It should be possible to build in a camera rotation system into the scope’s design without reducing the back focus. This is of no consequence if the scope is used as a guide scope, but is of huge importance for an imaging device for which it is heavily marketed and hopefully Touptek will consider this.

Considering the components that we used for the first test, a number of important lessons can be learned.

The GS-100 is a fast scope that may cause problems with larger sensors due to the angle of incidence of some of the rays hitting the sensor. The faster the scope, the steeper these can be. This can increase crosstalk between pixels resulting in poorer colour fidelity and contrast.

Probably the biggest problem with using the ZWO ASI585MC camera concerns reflections back and forth between the sensor and the filter. The camera used does not have anti-reflection coatings on the sensor window glass which means that the reflected light is not inhibited and passes back and forth between the sensor and the filter wheel, passing through the quadruplet lenses on its journey. The shifting of the originally parallel light rays leads to the development of Newton’s rings interference patterns which are particularly noticeable towards the ends of the long axis of a rectangular sensor. There are limited options for changing the distance between the filter and the sensor, which would probably have little effect anyway. There is no tilt plate built into this camera so no way of using tilt to mitigate the problem. The filter itself has inadequate anti-reflection coatings which could have reduced the impact of the interference patterns. After consideration, the quadband filter may not have been a good choice. I am not sure whether ours is V1 or V2. If it is V1 then this filter was renouned for poor anti reflection coatings and producing bad halos around stars. We clearly had reflection problems and some stars did have bad halos which were unsatisfactorily cosmetically treated during processing. A high quality UV/IR filter may have been a better choice.

Unlinked channels stretched image showing the concentric interference bands

The interference bands are more evident at the left hand side of the image where the star density and nebulosity are lower.

Careful post processing can reduce these artefacts but not completely eliminate them

North America and Pelican nebulae test

Sadr region test

The images were improved by cropping out the central area where the interference was less evident. However, this partly defeats the object of using the ZWO ASI585MC camera.

Cropped and reoriented images

North America and Pelican nebulae

Sadr region

For a future test our Player One Mars-C II IMX662 Colour Astronomy Camera will be used. Learning from our previous experience, this camera seems to have a number of advantages over the ZWO ASI585MC. It has Diameter 21 * 1.1 mm High Quality AR Plus (Anti Reflection) Multi-Layer Coating. Instead of a single layer of anti-reflective material, this optical element has multiple microscopic layers cooked onto the surface. Multi-layer coatings are superior because they cancel out reflections across a much wider spectrum of light wavelengths (colours), rather than just one. It also has a built in front tilting plate that allows for adjustments to avoid interference patterns if required.

Further camera details:

SONY IMX662 1/2.8" CMOS sensor (color). 2.1 Mega Pixels.   Maximum Resolution  1936×1100

2.9μm square pixels.   Sensor Size  5.6mm×3.2mm

If we centre on the star HD198597 the field of view is such that much of the Cygnus Loop can be framed.

Stellarium simulation of the field of view framed by the GS-100 with the Player One Mars-C II camera. The framed area is within the red frame lines.

The Player One Mars-C II camera will be used in conjunction with a Pegasus Astro L/UV-IR cut filter which offers a transmission range of >95% between 410–680nm. This blocks the ultraviolet and infrared bloat while letting the crucial visible spectrum (including Hydrogen-Alpha at 656nm) pass cleanly through to the sensor. It intentionally leaves a gap between the green and red bands. This blocks the primary Sodium light pollution line at 589nm, resulting in cleaner colour separation. 

The glass  features anti-reflection and anti-halo coatings which is crucial for UV/IR filters. It has a 1/4 wavefront polish.

The Player One Mars-C II camera on the test rig

It is hoped that this setup will allow capture without interference banding and star halos.

Again, the testing will be done with a pre-release version 3 of AstroDMX Capture, so we will be testing not only the hardware but also the software.

The Soap Bubble nebula (PN G75.5+1.7)

The Soap Bubble nebula (PN G75.5+1.7) from 1 hour of narrowband data (Ha and O3). 5 minute exposures (30 minutes through each filter) captured by AstroDMx Capture through a William Optics 81mm APO refractor with a QHY Minicam 8 camera/filter wheel. Processed in PI, SASPro and GIMP3. Rendered as HOO. 'RGB' stars were constructed in Siril from narrowband data using the Standard Continuum Mapping pixelmath procedure. 

If we include the 30 minute worth S2 data in a SHO/NBN palette (giving 1.5 hours total exposure), the Soap Bubble is much less pronounced. This is because most of the information on the Soap Bubble is in the Ha and O3 channels. A blend of HOO and SHO gives a reasonable compromise, with the Soap Bubble being visible along with some of the hues associated with the SHO.

Click on any image to get a closer view

HOO NBN

HOO NBN SHO blend

SHO NBN

This session was revisiting an object that we imaged in September 6, 2023 in narrowband with the same scope but using a 14 bit SVBONY SV605MC using a total of 5 hours of accumulated exposure.

The QHY Minicam 8 camera/filter wheel camera used here is a 12 bit camera and a considerably shorter total exposure time was used. Nevertheless, we were able to make a good capture. The best image was the HOO image with just 1 hour of total exposure time.

Steve Wainwright and Nicola Mackin

A very small, wide-field, guided imaging rig Part 1. The equipment

The imaging scope is the latest edition to the Touptek family of guide scopes; the Touptek GS PAPO Guide scope. It is a 4 element self-flattening Planar Apochromatic ED refractor. It is truly tiny: F = 100mm, D = 25mm, f/4. it has a 1“ imaging circle and gives good stars to the corners of a sensor such as the Sony IMX 533.

There is very little back focus so it is not possible to use a camera rotator to facilitate the framing of subjects. One slight concession to this is that I have fitted two 1mm spacer shims, as each one is added the camera can be rotated to a different position to tighten it up. It remains to see if they will have to be discarded when we attempt to focus on a star using a Bahtinov mask.

We have mounted a 2“ Altair filter drawer on the front of the scope and have added a 30mm M48 extension tube after that to act as a dew/ light shield.

This is an unconventional setup and it will be interesting to see how it performs.

View of the equipment

A view from the front

The guide-scope to be used is the  SVBONY SV165 Guide-scope with F = 120mm paired with a QHY-5II-M guide camera. This harks back to the days when manual guiding used a guide-scope with a longer focal length than the imaging scope, creating forgiving guiding for the image being captured with the imaging scope. A small movement in the guide-scope is an even smaller movement in the imaging scope.

The camera we are using initially is the uncooled ZWO ASI585MC. The ZWO ASI585MC uses an IMX585 sensor which is BSI, and built on Sony's STARVIS 2 technology. It has a full well depth of 40k to 47k electrons and a Read noise of 0.7 to 5.5 electrons depending on gain. It has a high QE of 91% at 500nm and 80.9% at 656nm.

Simulating the field of view of the GS-100 and the IMX585 in Stellarium, if one centres the image on the star HD198626, the whole of the Cygnus Loop can be framed:

Framing of the Cygnus Loop

Even though it is called the GS-100 Guide scope, it is heavily marketed by Touptk as a mini, very wide field imaging scope because of its high quality optics. They show that is is a good match for the new innovative cooled/uncooled camera the Touptek Astro AE676C as well as other cooled or uncooled cameras. They also show that filter drawers, electronic filter wheels and filters can be attached to the front of the scope and that it is directly compatible with the ToupTek Astro AAF electronic focuser.

Whilst as I said earlier, we are using an unconventional configuration, we will be, by no means using the scope out of spec.

Cable clips placed at strategic positions to facilitate cable management

A Bahtinov mask was contructed by using epoxy resin to attach a 3D printed Bahtinov mask intended for a Seestar S50 onto a 10mm M48 extension tube so that is can be screwed onto the 30mm M48 extension tube dewshield.

The attached Bahtinov mask

This will be needed to get the stars well focused.

It can be stored conveniently in a small plastic box of the type we use to store 2“ filters.

An opportunity arose to test the focus of the rig with a Pegasus Astro UV/IR cut filter in the filter drawer. A pre-release version 3 of AstroDMx Capture was used. The field of view of the GS-100 was plate-solved and the scope was sent to the star Vega. The Bahtinov mask was then used to bring the star to focus.

Screenshot of the focused star on the preview screen of AstroDMx Capture

Clouds prevented further testing but this test was a success!

In Part 2 this wide-field imaging rig will be tested with the latest pre-release of AstroDMx Capture version 3