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Sun - 2025113

Published: 25 November 2025

At this time of year, I only have limited opportunities to observe the Sun in White Light. This is due to trees, houses etc and a low sun that seems to collect clouds.

However, on this occasion I wanted to try out the 'G' band filter. I also wanted a record of AR 4274, the large group that was responsible for a number of 'X' classification Solar Flares. 

This was my first image with the new filter and to say that I was astounded would be a huge understatement. I really couldn't believe the level of detail that I could record with an 80mm refractor.

Note the tilt of the Sun, North is to the top-left of the image.

Equipment used:

• SvBony 80mm (ED) F7 refractor
• EQ5 mount with driven RA
• ZWO ASI 138MM Mono Camera
• Altair G Band Solar filter
• Baader Solar Film for Energy Rejection.

Processing was straightforward:

• SharpCap4.1 (500 frames)
• AutoStakkert! 4
• Registax 6 for wavelets and curves

 

 

 

 

A brief comparison between a SCF filter and a G band filter for Solar WL photography

Published: 25 November 2025

Background

For many years, I have used a SCF (Solar Continuum Filter), produced by Baader for both visual and photographic observations of the sun. It has served me well, it is a green filter with a bandwidth of 7nm, centred on 540nm. It adds a nice level of concentration and adds clarity when seeing is not as good as I would wish for. 

Take One Step forward

On the BAA Solar Section WhatsApp group, I noticed that some images were a magnitude better than mine, both in clarity, sharpness and the level of detail that was visible. Further investigation revealed that an Altair 'G' band filter was being used. This has a bandwidth of approximately 2nm at 430.3nm. This is in the blue end of the visible spectrum.

It was duly ordered from FLO and it arrived in early November. I screwed it into the rear of my 8mm Baader Hyperion eyepiece, the eyepiece that I usually use for visual observations of the sun. Unfortunately, the image was too dim to be of any use for visual observations but after attaching it to my ZWO ASI178MM mono camera. I couldn't believe the difference in quality between the two filters.

Here are two images taken on 20251125, the first using the SCF for imaging:

This is not a bad image at all and normally, I would have been very happy with that. However, compare it with the following image, taken about 5 minutes earlier using the 'G' band filter:

Far more contrasty, plage and granulation convection cells are easily visible and the image appears to be much sharper.:

Both images were processed using:

• SharpCap 4.1 (Approximately 500 frames, best 50% stacked)
• AutoStakkert! 4 
• Registax for Wavelets and Curves

There is always a slight downside. The 'G' band filter needs an exposure about 10x longer than the SCF, about 100ms compared with 10ms. No digital gain was used.

Of course, the SCF will continue to be used for visual WL observations, but the G band filter looks like it will be a very useful addition to the armoury.

Deep Space imaging with a Small Telescope

Published: 20 November 2025

Background

Small in this context means a 80mm F7 refractor, focal length of 560mm. I appreciate that many 'smart' telescopes have much smaller objectives, but this is my experience of imaging with a fairly conventional astronomical set-up.

Most of my imaging with this telescope has been of the sun, either white light for observing and capturing sunspot detail or with my Spectroheliograph which I use for imaging the sun at very narrow spectral bandwidths.

Last night, 2025-11-19 was actually quite a decent night for observing, the moon was almost new, it had been clear and cold all day with quite a fresh wind although seeing was not perfect when I started setting up at 19:15, it improved as the evening progressed.

My original intention was to do some Spectroscopy but I decided that as I had my 80mm refractor setup and polar and 3 star aligned, I would tackle some of the larger Deep Space objects that would be too big to fit on the sensor of my old SXVR-H694 cooled mono camera if using a telescope with a longer focal length.

The selected targets were M31, the Andromeda Galaxy, M33, The Triangulum Galaxy and M45, Pleiades.

All 3 objects would have 100 exposures of 30 seconds each - about the limit for unguided exposures - with slight variations (between 5 and 15) in Digital Gain adjusted to suit the surface brightness. 

A bit of a false start as I managed (but was unaware) to knock the mount after alignment but before I started the first imaging pass on M31. I couldn't understand why the tracking was drifting slightly giving me elongated stars. A quick check on the polar alignment and I was about 1 degree out, so realigned and restarted.

My setup was as follows:

• SvBony 80mm F7 ED Refractor#
• Starlight Xpress SXVR-H694 Camera cooled to -20C
• Orion EQ-G mount (with GoTo) and tripod (rebadged EQ-6 mount).
• No guiding. I had forgotten that I had taken the guide telescope bevel mount off my refractor.
• Lots of warm clothing and hot tea, it was very cold.

The tracking was remarkably accurate, there was no obvious drift or elongation of star images. After almost an hour, the same peripheral stars in the capture area were all present. It really is worthwhile (essential!) setting up a good polar alignment if you are operating unguided.

Processing was very simple:

• SharpCap v4.1 (Binning 2x2)
• AutoStakert! v4 (Stacking 90% of the images)
• Registax v6 or GIMP

Note: this post is best viewed on a PC screen

M31, the Great Andromeda Galaxy

I have never successfully imaged this galaxy before. M31 is a huge object, several moon widths across the major axis and the only thing I can usually capture is an over exposed core with a hint of a dust lane somewhere.

With M31 centred in the eyepiece, I could see a fuzzy core but not much else. Connecting the camera and focussing and suddenly the dust lanes were just visible. Digital Gain was set to 10.

After realigning the mount, I started the long exposure sequence. 

After processing, I had this result.

I don't think that is too bad for a total 50 minute exposure time. The 2 dwarf galaxies, spiral M32 to the lower right and elliptical M101 to the left of centre. A few processing artifacts due to trying to get the detail in the dust lanes but I am quite pleased with that. It is certainly far better than I have achieved previously.

M33 - Triangulum Galaxy

This was not visible through the telescope eyepiece but was instantly visibly as a faint fuzzy when using the camera. I have noticed this before when imaging M51 and the Flame nebula. It makes a heck of a difference having a better eye attached to the telescope.

It is also an object that I have never managed to image in the past, I am not sure why, its a lovely face on spiral galaxy with lots happening.

As the surface brightness was lower with this object, the digital gain was increased to 15 (100 is max).

The ragged appearance of the galaxy is quite noticeable. However the amount of detail that I could capture is limited with only 100 exposures and an 80mm aperture. Very pleased with that and one to have another crack at with my 200mm F5 reflector.

M45 Pleiades

If you have read any of my earlier blogs you will know that all I wanted to achieve with this was to capture some of that wonderful reflection nebula wispiness that is the main characteristic of the Pleiades.

Digital Gain was reduced to 5 for this as it is obviously the brightest of the 3 targets for the evening.

My main criticism with this was that I didn't centre the object very well. It also very slightly out of focus which is rather irritating. I will have to go back and do it again! The nebula is visible, it is a shame it is not colour  as the nebula has a lovely blue tint.

 

So, all in all a good evening, from start to finishing pack-up it was almost exactly 5 hours. The temperature continued to fall with nearly everything covered in a fine layer of frost at the end of the evening. The dew shield on the telescope was very effective, no condensation at all, all evening.

Lessons learnt:

1. I need to improve my focussing technique. I'll try a Bhatinov mask next time.

2. The results were all better than expected. I am not a Deep Space imager but it is nice to have record of objects that you can't quite see.. I now have to decide what is the longest exposure sequence that I can live with.. Probably not much more than an hour at the moment.