Using an Altair Quadband OSC narrowband filter or an IR/UV cut filter with an SV605CC OSC camera, a William Optics Zenithstar 81 ED APO doublet refractor with an 0.8 reducer-flattener and AstroDMx Capture.

The Altair Quadband OSC narrowband filter transmits two spectral bands: 

FWHM spans 477.5nm - 512.5nm at the blue-green end of the visible spectrum and FWHM spans 642.5nm - 677.5nm at the red end of the spectrum.

The first band contains the emission lines of H-beta at 486.1nm and OIII at 495.9nm and 500.7nm and is centred on 495nm.

The second band contains the emission lines of H-alpha at 656.3nm and SII at 672.4nm and is centred on 660nm.

The Filter is called ‘quadband’ because it contains the emission lines of these four elements.

Each of the two transmission bands has a FWHM of 35nm and the rest of the visible spectrum is essentially blocked.

FWHM (Full Width Half Maximum) diagram 

The four wavelengths of the four elements’ emission lines will pass through the filters of the Bayer matrix of the OSC camera sensor and produce an RGB image. This image can then be processed to produce a colour image akin to but not the same as those produced by monochrome cameras and three narrowband filters. 

For example, with the quadband OSC filter, H-alpha and SII will both contribute to the red whereas H-beta and OIII will contribute to the blue and green components of the image. 

It could be argued that whilst there is no doubt that the various palettes produced by monochrome cameras and separate SII, H-alpha and OIII filters are false colour images, the colour images produced from an OSC camera and a quadband filter more closely represent the RGB nature of the colour images produced.

The Equipment used

A William Optics Super Zenithstar 81 ED APO doublet fitted with a 0.8 flattener/reducer at f/5.5 was mounted on an AVX GOTO mount.

The mount was placed on permanent marks on the concrete base.

Dew-prevention heater strips were placed around the objectives of the imaging and guide scopes.

An Altair Quadband filter was placed in the optical train via an Altair magnetic filter holder. Between imaging sessions, by means of the adjustable flattener/reducer the spacing between the flattener/reducer and the camera sensor was gradually increased until the flatness of the field was deemed satisfactory.

The hand controller was connected to the Raspberry Pi running an INDI server and communicated with the indoor computer running AstroDMx Capture via WiFi. An anti-dew heater strip was placed around the objective cell of the scope. An SVBONY SV165 guide-scope fitted with a QHY-5II-M guide camera was mounted on the handle dovetail of the imaging scope.

AstroDMx Capture passed the time, altitude and location coordinates to the hand controller via the INDI server. The hand controller which now contained all of the correct information was set to its previous alignment and was unparked by AstroDMx Capture.

AstroDMx Capture connected the SV605CC OSC camera natively by USB, and sent the scope/mount to Vega.

The William Optics patented Bahtinov mask was used to bring Vega to focus.

AstroDMx Capture was used to send the scope/mount to  ɣ Cygni Nebula a HII region in Cygnus, plate solve and centre the object.

AstroDMX Capture recorded 55 minutes of 2.5 min Fits exposures of the Gamma Cygni Nebula

The images were stacked and partly processed in Siril and post processed in the Gimp 2.10 and Neat Image

The Gamma Cygni Nebula

The quadband filter performed well on this HII region

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The quadband filter was then replaced by an IR/UV cut filter. AstroDMx Capture then sent the scope/mount to M45. The scope was refocused with the Bahtinov mask, plate solved and the object centred.

AstroDMx Capture was used to record 20 x 3 min FITS exposures of the Pleiades.

The images were stacked and part processed in Deep Sky Stacker and post processed in the Gimp 2.10 and Neat Image

M45 the Pleiades

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The Altair quadband filter was replaced and the next night, AstroDMx Capture was used to send the scope/mount to the Pelican nebula, Plate solve and centre the object.

The imaging computer indoors

AstroDMx Capture recording 23 x 2.5 min FITS images of the Pelican nebula

The images were stacked and partly processed in Deep Sky Stacker and post processed in the Gimp 2.10 and Neat Image

The Pelican nebula

To date, the Altair quadband filter has compared well with the Optalong LeNhance triband filter. In future tests other objects will be covered, particularly those with a strong SII signal such as the Horsehead region and the Jellyfish nebula. These experiments will be reported here in a future article.

Meanwhile the refining and testing of the advanced features of AstroDMx Capture has continued. Nicola has made changes to the UI for efficiency and clarity as well as making substantial advances with the object database. The software is now in feature freeze, and when it is ready, Nicola will make a release. That release will be announced on this blog and Nicola will make a guest contribution to the writing of the blog to explain the modus operandi of the new AstroDMx Capture.

First light for a William Optics f/6.9 Zenithstar 81 ED APO doublet refractor with AstroDMx Capture

A William Optics f/6.9 Zenithstar 81 ED APO doublet refractor, f/5.5 with 0.88 APO flattener-reducer, AstroDMx Capture and an SV605CC OSC camera; first light. The APO telescope has a Synthetic flourite ED doublet element.

This scope has a unique front dust cap

Unscrewing the end of the dust cap reveals the patented built-in Bahtinov mask

A handle attached to the scope rings has a standard dovetail to which a guidescope can be mounted in a fairly well balanced position.

The equipment used

The scope was placed on permanent marks on the concrete base.

A UV/IR cut filter was placed in the optical train via an Altair magnetic filter holder.

The hand controller was connected to the Raspberry Pi running an INDI server and communicated with the indoor computer running AstroDMx Capture via WiFi. An anti-dew heater strip was placed around the objective cell of the scope. An SVBONY SV165 guide-scope fitted with a QHY-5II-M guide camera was mounted on the handle dovetail of the imaging scope.

AstroDMx Capture passed the time, altitude and location coordinates to the hand controller via the INDI server. The hand controller which now contained all of the correct information was set to its previous alignment and was unparked by AstroDMx Capture.

AstroDMx Capture connected the SV605CC OSC camera natively by USB, and sent the scope/mount to Vega.

The patented William Optics Bahtinov mask was used to bring Vega to focus.

A guide computer running an INDI server was used for multi-star PHD2 pulse auto-guiding and the guide camera was connected by USB.

AstroDMx Capture was then used to send the mount/scope to M31, plate solve the field of view, and centre the object.

AstroDMx Capture was used to capture 70 x 1 min FITS exposures of the Andromeda galaxy

The 70 images were stacked and partly processed in Deep Sky Stacker and post processed in The Gimp 2.10 and Neat Image.

The Andromeda galaxies, M31, M31 and M110

The William Optics f/6.9 Zenithstar 81 ED APO doublet refractor, f/5.5 with 0.88 APO flattener-reducer performed very well showing extremely good colour correction and good stars.

I had been struggling for several months with a Skywatcher Esprit 80 ED Triplet APO refractor in which the stars flared badly, ruining the results. Rother Valley Optics were very helpful and organised a return of the scope and the issuing of a new Zygo tested William Optics Zenithstar 81 ED APO doublet at my request plus a 0.88 William Optics APO flattener-reducer. I was very happy with their cooperation and felt that it should be mentioned here with the first light results of the new scope.

I shall be able to tweak the spacing with the adjustable 0.88 flattener-reducer until I have the field as flat as it can be.

Workflow paradigm shift with AstroDMx Capture.

Nebula imaging while testing advanced functionality in AstroDMx Capture.

Although it is, of course, possible to use a finder scope and an illuminated reticle eyepiece to do a scope/mount alignment, it is not required if the mount can be placed in the same position each time so that the previous alignment can be used. In our case, marks on the concrete slab on which the mount is placed are sufficient for us to be able to place the mount in essentially the same position for each imaging session.

The imaging scope, an Altair Starwave ASCENT 60ED doublet refractor with flattener, was mounted on a Celestron AVX GOTO mount. An SVBONY SV165 guide-scope fitted with a QHY-5II-M guide camera was mounted on the imaging scope. A Raspberry Pi computer running an INDI server was connected to the hand controller and communicated with the indoor computer running AstroDMx Capture via WiFi. The guide camera was connected by USB to the indoors computer running PHD2 auto-guiding software. An Altair 2” magnetic filter holder version 2 containing an LeNhance narrowband filter was placed in the optical train.

Nicola has implemented an INDI Configurator in AstroDMx Capture which is capable of configuring up an INDI server on another computer running the Linux operating system, in this case, a Raspberry Pi running Raspberry Pi OS. It can configure the INDI server for whatever tasks it is to perform. This can be done even if AstroDMx Capture is running on a Windows computer or a macOS computer.

The AVX mount was placed on the alignment marks on the concrete base. The mount was powered on and AstroDMx Capture passed the time, altitude and location coordinates to the hand controller via the INDI server. The hand controller which now contained all of the correct information was set to its previous alignment and was unparked by AstroDMx Capture.

AstroDMx Capture connected the SV605CC OSC camera natively by USB, set the camera temperature to -10 degrees C and sent the scope/mount to Aldebaran. AstroDMX Capture plate solved the field and centred Aldebaran in the field of view. A Bahtinov mask was placed on the imaging scope and Aldebaran was brought to sharp focus.

AstroDMx Capture was then used to send the scope/mount by means of the INDI server to the California nebula, plate solve and centre the nebula in the field of view. The mount nudge function was then used to compose the image as required.

AstroDMx Capture captured 20 x 3 min FITS exposures of the California nebula

The images were stacked and partly processed in Deep Sky Stacker and post processed in The Gimp 2.10 and Neat Image

The California nebula

AstroDMx Capture was then used to send the scope/mount to the star Alnitak in Orion’s belt, plate solve and centre in the field of view. Then AstroDMx Capture’s mount nudge function was used to compose the image so that the Horsehead nebula and the Flame nebula were optimally positioned in the field of view.

Twelve 5 min FITS exposures were captured of the Horsehead and Flame nebulae region.

The imaging computer indoors

Screenshot of AstroDMx Capture saving 5 min FITS exposures of the Horsehead/Flame nebula region

The hour’s worth of data were stacked and partly processed in Deep Sky Stacker and post-processed in the Gimp 2.10 and Neat Image.

The Horsehead and Flame Nebulae

The scope/mount was then sent by AstroDMx Capture to the Monkeyhead nebula, plate solve and centre the nebula in the field of view.

AstroDMx Capture was used to capture 12 x 5 min FITS exposures of the nebula

The data were stacked and partly processed in Deep Sky Stacker and post processed in the Gimp 2.10 and Neat Image.

The Monkeyhead nebula

Finally, AstroDMx Capture was used to send the scope/mount to the Jellyfish nebula, plate solve and centre the nebula in the field of view.

Only 5 x 5 min FITS exposures were captured before clouds moved in and stopped imaging. In fact the last two images were captured through very thin clouds.

All five images were stacked, partly processed in Deep Sky Stacker and post processed in the Gimp 2.10 and Neat Image.

The Jellyfish nebula

No dark frames were captured for any of these images. The SV605CC OSC camera produces no significant amp glow and the images produced were satisfactory. In a poor and changeable weather system such as we frequently have in the UK, such an amp-glow free camera allows for more time to be spent on image capture. Of course, dark frame calibration is desirable, but with this camera it is not essential.

The paradigm shift mentioned here is that with a mount that is not permanently installed and which requires placing on the ground for each separate imaging session, it is possible to acquire the desired objects and to image them without first having to align the mount. In fact, the mount only needs to be aligned once and at least for several sessions can be set to previous alignment before proceeding, as long as it is placed carefully on marks on the concrete upon which the tripod rests.

Nicola’s newly implemented INDI Configurator in AstroDMx Capture allows the configuring of an INDI server on any Linux computer, such as the Raspberry Pi that we use. It allows for the INDI server to be configured for any of the tasks for which it may be required without having to manually login to the remote computer via SSH (Secure Shell).

Again, these features bring AstroDMx Capture that much closer to a major incremental release. We shall report here when that happens.