equipment - building a simple flats panel for a tablet

 A Simple DIY Flats Panel Holder for Astrophotography (That Actually Works!)

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