As 2025 draws to a close

 Here are some of the images I've taken this year. 

This will be my last post of 2025.  If you have been following the blog I hope you have found it useful and inspiring; that it has helped you in a small way on your astronomy/astrophotography journey

I wish you and your family a happy Festivity, holiday and New Year. 

Clear skies, stay safe and have fun out under the night sky

Steve 

NGC 1499 The California Nebula

Comet Lemmon

NGC 869

IC 63 The Ghost of Cassiopeia

IC 1318 Sadr region 

IC 1396 and The Elephant Trunk Nebula 

IC 1805 Heart nebula 

M13 globular Cluster

M 92 Globular Cluster 

NGC 7000 The North America Nebula

NGC 6888 The Crescent nebula

M42 and The Flame and Horsehead Nebulae

The \Milky Way above the National Trust Mill cafe 

The Milky Way above Wembury Church 

equipment tutorial - building a simple flats panel for a tablet

 A Simple DIY Flats Panel Holder for Astrophotography 

Taking flat calibration frames can be one of the more frustrating parts of astrophotography - especially for beginners. Ask ten astrophotographers how they shoot flats and you’ll probably get ten different answers.

Like many newcomers, I started with, and continue to use, the classic stretched white T-shirt method. And while it works… in theory… the reality is often less elegant.

If you’ve ever tried to balance a glowing tablet against a stretched T-shirt while simultaneously firing a remote shutter - all with frozen fingers at the end of a long winter night imaging session - you’ll know exactly what I mean.

I can never keep my flats tablet still after a long night of imaging - especially on cold winter nights! 

So, in today’s post, I’m sharing a cheap, lightweight, homemade flats panel holder that solves those problems and makes capturing flat frames far less painful.

 

Why I Needed a Better Flats Panel Solution:

Until now, my process looked something like this:

• A white T-shirt stretched over an embroidery hoop
• The hoop balanced on the front of my refractor dew shield
• One hand holding a tablet with a white screen
• The other hand operating a remote shutter

It worked… most of the time. But it was fiddly, unstable, and downright annoying after a long imaging session – especially when my cold hands were shaking.

I wanted something secure, repeatable, and easy to use - without spending a fortune.

 

I want a flats tablet that won't need me holding it in place with one hand! 

Something that will fit onto the dew shield and stay snuggly in place!

What I Set Out to Build:

The goal was simple:
A DIY flats panel holder that would securely hold both:

• a diffusion panel (embroidery hoop or white paper)
• a tablet displaying a white screen

…on the dew shield of my Samyang 135mm lens and William Optics Zenithstar 61 II  - which, by happy coincidence, have almost identical dew shield diameters.

Key Design Requirements:

• Lightweight
• Snug fit for tablet and diffusion panel
• Stable on the dew shield
• Easy tablet insertion and removal
• Cheap and quick to build

 

Materials You’ll Need:

Build Materials

• One sheet of A2 foam card (5mm thick – model-making grade)
• Parcel tape
• Double-sided sticky tape
• Suitable strong glue

Tools:

• Sharp craft knife
• Cutting mat or board
• Pencil
• Ruler
• Right-angled set square

 

My Flats Panel & Tablet Dimensions:

• Tablet size: 210mm × 125mm × 8mm
• Finished holder size: 270mm × 155mm × 30mm

This thickness gives the panel enough rigidity while keeping the weight down.

 

The base panel which formed the template for others. The next panel up was identical to this one. 

Step-by-Step Construction:

1. I already had an embroidery hoop slightly larger than the outer diameter of my lens and telescope dew shields. This was fitted with white T-shirt material, which I ironed flat before mounting.
2. I measured and marked out the bottom panel on the foam card.
• There would be six stacked panels in total
• The first panel acted as the template for the others
3. After tracing the outline of the tablet and embroidery hoop, I carefully cut out the hoop opening in the first panel.
4. I repeated this process for the second panel, adding a small finger notch to both panels to make tablet removal easier.
5. Panels three, four, and five were identical - cut to the tablet outline only, with no hoop opening.
6. Panel six had no cut-outs at all, apart from the finger notch.
7. Once all panels were cut, I stacked them and bonded everything together using a combination of glue and double-sided tape.
8. Finally, I wrapped parcel tape around all exposed edges, adding durability and protecting the foam card.

 

Panels 3, 4 and 5 were shaped like this - a big cut-out for the tablet. 

Build Time & First Impressions:

• Build time: ~2 hours
• Weight: Very light
• Fit: Snug and stable

Unfortunately, the weather hasn’t yet allowed me to test it under the stars - but once I do, I’ll add a PS update at the bottom of this post with real-world results.

 

Panels 3 and 4 stuck in place

What Do Flat Calibration Frames Do?

If you’re new to astrophotography and want a deeper understanding of flat frames, what they correct, and why they matter, I’ve covered that in detail in a separate post here:

 

Trial fitting of the tablet 

Total Cost of the Project

• Foam card: £4.00
• Double-sided tape: £2.00
• Embroidery hoop & fabric: donated by my wife (she’s into dressmaking and quilting - very handy!)
• Glue & parcel tape: already in the garage

Grand total: £6.00

Not bad for a custom astrophotography accessory!

 

All the panels securely in place - image shows the slot for the tablet. 

The embroidery hoop is in place in the bottom two panels 

Final Thoughts:

If you decide to give this DIY flats panel holder a try, I’d love to hear how you get on. Drop a comment below with:

• your method
• any improvements
• how well it worked with your setup

As always - clear skies, stay safe out there, and keep enjoying the journey under the stars.

Steve

Vecro straps slide out of the way to allow the tablet to be inserted and then slide back into place to hold it securely

Should we be using a white T shirt method for taking our flat calibratiuon frames? 

Advantages and Disadvantages Explained

The white T-shirt method is one of the most common ways beginners take flat calibration frames in astrophotography. It’s simple, cheap, and widely recommended - but it isn’t without its limitations.

Advantages of the White T-Shirt Method

1. Extremely Low Cost

The biggest advantage is obvious:

• You probably already own a white cotton T-shirt
• No specialist equipment is required

For beginners just getting started with calibration frames, it’s hard to beat the price.

2. Easy Entry Point for Beginners

The method is conceptually simple:

• Stretch a white T-shirt over the telescope aperture
• Point the scope at a bright, evenly lit surface (sky, tablet, laptop, or light panel)
• Take exposures that place the histogram around the middle

This makes it an excellent learning tool for understanding how flat frames work.

3. Good Light Diffusion

Cotton fabric acts as a natural diffuser, helping to:

• Smooth out uneven light sources
• Reduce hotspots from tablets or LED panels

When done well, it can produce surprisingly usable flats.

4. Flexible and Adaptable

The same T-shirt can be used with:

• Refractors
• Camera lenses
• Newtonians (with some creativity)

It’s also easy to add or remove layers to adjust brightness.

5. Portable and Lightweight

Perfect for:

• Field imaging
• Travel setups
• Quick sessions where minimal gear is desirable

Disadvantages of the White T-Shirt Method

1. Inconsistent Tension = Inconsistent Flats

This is the biggest drawback.

If the fabric isn’t stretched evenly:

• You can introduce gradients
• You may create subtle brightness variations
• Dust motes can be blurred inconsistently

Each setup can produce slightly different results — which reduces repeatability.

2. Fabric Texture Can Be a Problem

Not all T-shirts are created equal.

Potential issues include:

• Visible weave patterns
• Uneven thread density
• Logos, seams, or worn areas

These can imprint subtle artefacts onto your flat frames, especially with high-resolution sensors.

3. Susceptible to Wind and Movement

Outdoor astrophotography often means:

• Cold temperatures
• Wind
• Fatigue at the end of the night

A shifting T-shirt can:

• Move during exposure
• Change diffusion characteristics mid-sequence

This is particularly problematic when taking longer flat exposures.

4. Awkward to Use in the Cold

Anyone who images in winter will recognise this problem:

• Cold hands
• Shaking arms
• Balancing a tablet or light source
• Trying not to disturb the imaging train

It works - but it’s rarely comfortable or elegant.

5. Not Ideal for Automation

The white T-shirt method is fundamentally manual:

• Requires hands-on setup
• Difficult to repeat precisely night after night
• Unsuitable for remote or automated observatories

More advanced workflows benefit from flat panels or sky flats taken automatically.

6. Colour Balance Can Vary

Depending on:

• Fabric thickness
• Material type
• Light source used

The spectral transmission may not be perfectly neutral, which can affect colour calibration - particularly with mono cameras and filters.

When Is the White T-Shirt Method a Good Choice?

The white T-shirt method is best suited for:

• Beginners learning astrophotography
• Casual imagers on a tight budget
• Portable or travel rigs
• DSLR and widefield setups
• Occasional imaging sessions

It’s a perfectly valid method - just not the most consistent or convenient one.

When Should You Consider an Alternative?

You may want to move on from the T-shirt method if you:

• Want repeatable, high-quality calibration frames
• Image frequently or remotely
• Use narrowband filters or mono cameras
• Value speed and ease after long sessions
• Are building a more permanent setup

DIY or commercial flat panel solutions offer better consistency and long-term convenience.

Final Thoughts

The white T-shirt method has earned its popularity - it’s accessible, effective, and forgiving. An excellent starting point for taking calibration frames. But as your astrophotography skills grow, its limitations become more apparent.

Many astrophotographers start with a T-shirt… and eventually build or buy something better.

Clear skies, and happy calibrating

Workflow tutorial: using SIRIL 1.4 including GraXpert and Cosmic Clarity Suite Pro python scripts

 Optimal workflow using SIRIL with COSMIC CLARITY SUITE PRO, GRAXPERT and AFFINITY PHOTO

I have written a previous post about my SIRIL workflow which you can find here  https://undersouthwestskies.blogspot.com/2025/01/a-beginners-guide-to-using-siril-some.html

This post was updated early December 2025, late December 2025. 

In this post I 

·       share my more simplified, reorganised workflow - which is based on SIRIL vs 1.4, and the python scripts for Cosmic Clarity Suite (by Seti Astro), Veralux and GraXpert. 

·       Try to give notes and tips which will help beginners

·       Share some useful, helpful YouTube tutorials

So, let’s get stuck straight in to my latest workflow: PLEASE NOTE - screenshots will be added when I process my next image - so please bear with me until then 

NOTE: I am assuming you have a little knowledge of how to organise your images – if you are going to be using SIRIL – if you are new to SIRIL the jump down to the bottom to watch one or two of the videos first.

Below is a simple graphic image which simplifies my workflow approach: 

and here is a simple infographic I tried to design based on SIRIL and not using the latest cosmic clarity and veralux python scripts 

A.      Organisation:

1.      Organise your folders into one folder called SIRIL and then sub folders for – lights, biases, darks and flats

2.      Set your home directory top menu bar left hand side

3.      Choose scripts – siril script files  - OSC pre-processing.ssf  to start the stacking process

 

B.      Crop and gradient removal:

1.      Be in autostretch mode on bottom task bar

2.      Load results.fits file produced from your stacking script – find in your home directory

3.      Crop edges to remove stacking artefacts

4.      Tools – astrometry  - image plate solver  on the pop up window:

a.      In pop up window - search catalogue number; (S box = if southern hemisphere image); click metadata from image; check – siril solver, solution order – cubic, flip image, auto-crop for wide field, star catalogue auto, catalogue limit – auto.

5.      Background extraction – image processing – python scripts - AutoBGe seti

a.      use default settings in the pop up window initially i.e. sample points 100, polynominal 2 RBF smoothness – 0.1.  (L-Enhance note - Use degree 2 to avoid flattening extended Ha regions).

b.      On the pop up window – can opt to click add exclusion area – (this is what you don’t want extracted) – free hand draw in around nebula area to be excluded – if make a mistake – click clear selection and start again – then when ready click process

c.      Use undo/redo arrows to compare before and after to see the changes

NOTES: background extraction

1.      Can use GraXpert for BGE  – GraXpert uses AI model - don’t do denoise now just BGE – severe gradients <0.5; mild gradients >0.5

6.      If using SIRIL BGE – grid tolerance 3, squares off nebula and bright stars; click dither to on; subtraction on; polynominal – increase for very bad gradients – RBF tab – smoothing default 0.5

 

C.     Colour calibration:

1.      NOTE – must have done image plate solver before doing colour calibration

2.      Autostretch mode on lower menu bar

3.      Remove chromatic aberration – python script - aberration remover – can do now or after colour calibration – either

4.      Plate solve image – if not already done above MUST DO BEFORE COLOUR CALLIBRATION WORK  - needs internet connection - astrometry - image plate solve

5.      Colour calibration – image processing tab – colour calibration - Spectrophotometric colour calibration

a.      SPCC – needs internet – tick the following: average spiral galaxy, one shot colour, osc sensor – closest, osc filter – optolong L pro OR if narrow band – check narrow band box and enter your filter details ( L enhance details for table – see below; tick background reference to auto detection.

b.      Settings if using L-enHance filter - – wavelength : blue OIII – 500; Green HB – 486; red H-alpha 656.3 and BW – OIII green 24; red 10; Blue 24

 

D.     Cosmic clarity sharpening  before denoise

a.       DO BEFORE STRETCHING I.E. LINEAR DATA

                                                  i.      stellar = stars only; non stellar = background and other objects - do both stellar and non stellar on pop up window OR experiment using undo/redo arrows – use GPU, clear input directory, (stellar sharpening  - 0.5 default and play with slider; or move first slider to 0.20 to 0.25; non stellar slider to 0.80; non stellar strength to 3. Zoom in a check – use undo and redo buttons to see differences made

b.      OPTIONAL – could do DENOISE now – scripts – python scripts - CC denoise – use RGB channel; check GPU and Clear input directory.     ** New veralux silentium python script is also a denoise option - must be done on linear images i.e. before image is stretched. To get this new script - go to scripts tab and get scripts and then go down the list - select the veralux script bar and check the box at the end. NOTE: as of late december 2025 - note that under scriupts tab - veralux now has its onw heading

c.      Now find output folder in Cosmic Clarity home folder on C drive and delete files as you go.

** If you use the new veralux silentium denoise script - I tend to use the default settings. when the preview box appears - it shows the settings in effect. To see the original image just press and hold down the space bar. the red box on the preview screen can also be moved about and acts as a zoom in function - so drag and drop it to the area you want to focus on. 

E   OPTIONAL stretching now – using Veralux hypermetric Stretching  NOTE – SEE F BELOW BEFORE DECIDING

a.      MUST DO PLATE SOLVING AND SPCC COLOUR BEFORE HAND

b.      Linear view – then Scripts – python scripts – processing – Veralux hypermetric stretching

c.      Settings for pop-up window:

a.      Processing – ready to use

b.      Sensor calibration – top one or canon 600d or 709re recommended.

c.      Click live view – use mouse scroll wheel to zoom in and out

d.      Target background – start 0.10 (0.2 is default) (lower the number the more contrast and darker the image – higher the number the less contrast and brighter the image)

e.      Log D – strength of stretch – leave at default 2.00

f.        Click auto calculate

g.       Protect B – how protected stars are during stretch – leave on default

h.      Star core recovery – leave default 3.5

i.        Process

j.        Make adjustments and experiment with setting inputs until happy

k.       If over saturated use the slider – but RECOMMENDATION IS DON’T TOUCH THE SLIDER – chromatic preservation colour one  - after alteration click auto calculate again

l.        Can also now apply curves transformation if image looking too washed out etc – or wait until starnet

d.      If choose scientific – then after do series of transform curve stretches in siril to bring up contrast and colour – s curves to raise darks, MT and HL’s

F. Star removal: I always DO BEFORE STRETCHING so I'd do section E above AFTER doing the starnet separation

1.      Optional first step: Image processing – star  processing desaturate stars

2.      Image processing – star processing - Starnet – tick prestretch in pop up window

3.      Stretching starless nebula – keep linear below in bottom menu

a.      OPTIONS: either Veralux hypermetric stretch as above OR Cosmic Clarity statistical stretch – see below

                                                  i.      Statistical stretch – in linear mode - target median 0.11 for anything not filling entire frame; normalise- no curves adjustment; if fully fills frame target median at 0.25 starter.

                                                 ii.      Stretch until: - Nebula structure is visible      Background is not clipped   Stars not blown out – NB if done colour correction already must check linked stretch box.
Now the image is nonlinear and ready for detail work.

b.      NOTE – CAN STILL DO OLD WAY IF DESIRE – SEE BELOW:

                                                  i.      OR – asinh stretch first followed by HTF stretch –  (HTF stretch using lhs and middle triangles or placing points on curve line to get shallow s curve  - watch clipping % - ensure no clipping of data –  ( can use ROI – draw box on part of nebula – right click select |ROI – select ‘set to selection’ and do adjustments; to remove – go back to menu and click ‘clear ROI’

                                                 ii.      OR Can also retry with curves adjustment ticked – try boost slider at 0.5 – the greater the boost the more contrast and fainter detail at expense of more noise and artefacts - 

                                               iii.      OR can do curves transformation – tiny iterative changes and repeat image processing – stretches – curves transformation – click on line and drag up or down – aim shallow s curve – don’t clip data – make very small adjustments – repeat gently LESS is MORE 

EXPERIMENT WITH EACH UNTIL HAPPY – use undo/redo arrows

4.      Complete denoise now – scripts – python scripts – processing – cosmic clarity denoise Denoise

a.      In pop up windopw - full strength – do zoom in and undo/redo to check difference

b.      alternative is denoise in siril  - if using GRaXpert – default stretch 0.5 so try 0.8

 

(NOTE – could try  SETI ENHANCER if you have it downloaded — Star Control, Detail Boost, Color Punch at this stage -
Load the denoised stretched image into SETI Enhancer.

·        Star Reduction - Use after stretch, not before.   Strength: 10–30%    Helps separate the nebula from crowded star fields      Avoid “donut-shaped” stars—dial back if seen

·        Nebula Detail Enhancement   Use:   Local contrast      Midtone sharpening    Texture boost
Moderate levels keep it natural.

·        Color Enhancement
Increase nebula saturation       Adjust hue sliders for Ha/OIII separation      Use vibrance before saturation
Avoid boosting star colours too strongly

·        Background Balancing
Use background equalizer if available     Ensure background is smooth and neutral
Remove remaining gradients)

G. Process starmask:

1.      Could Desaturate stars now – see above where outlined previously

2.      Can do Asinh stretch or  htf stretch – keep mild – use square and eyedropper Asinh Stretch:  Broadband: 5–15 L-Enhance: 3–8    Black point: 0.001–0.003   

3.      If doing GHS: Stretch: 0.8–1.2     Midtones:  Broadband: 0.3–0.5  L-Enhance: 0.2–0.35

Stop here.  Do not adjust saturation, HDR, clarity, sharpening. OR

4.      Could Reduce star size now – image processing - morphological transformation – selection – strength 5 – 20%

5.      Optional Slight saturation boost  - image processing – colour saturation: do globally

H. Star re-composition:

1.      Image processing – star processing – star re-composition

2.      On pop up histograms - RHS is starmask; LHS is starless

3.      Do black point adjustment to starmask to reduce number of stars

4.      Adjust blend to avoid halos and bright stars – inspect fine details – zoom to check edges

5.      Final noise reduction – optional light GraXpert or cc denoise – avoid over-smoothing background or killing faint dust

Final tweaks:

1.      Vibrance, colour balance

2.      Final cropping/rotation  to choice

3.      Green noise check – SCNR (Green Noise Removal) – BEST = SIRIL   Broadband: Strength: 0.60–0.75  L-Enhance:  Use none or mild (0.20–0.35)      OIII contains green, so don't destroy it.

4.      Export 16 bit TIFF

PS Videos that I found useful: 

Look for AstroIslander's part 2 and 3 as well