How to make your own cheap and simple, but effective, Flats Panel.
Update, Jan 2023
After I bought my new Askar 130PHQ telescope, I needed a bigger Flats panel. I took the advice of Kurt, who left a comment on this article recommending tracing lights widely available on Amazon (click here for an example) as an effective but cheap Flats panels. It works well! I’ll leave the instructions for a DIY Flats panel here though, in case anyone does want to make one for themselves.
DIY Flats Panel instructions
Flats are a type of calibration frame that help to correct for any dust on your camera sensor, as well as vignetting around a photo’s corners. They improve the quality of your final image, but there’s no denying that they’re a hassle to take.
Beginner astroimagers often use a technique called “t-shirt flats”, where you attach a white t-shirt, pulled tight, over the front of your telescope. During twilight you point your telescope at the sky and capture your Flat frames. It does work, but needs to be done when the sky’s brightness is at just the right level. You’ll also get very strange looks from the neighbours.
A modified version involves using a laptop or tablet screen as a light source, or perhaps an artists’ light box — all valid options. Astroimagers with plenty of cash to splash may buy a proper Flat Field Generator, but these tend to be quite expensive for what I’d always thought should be a fairly simple piece of kit. Surely it’s possible to build your own Flats Panel for about 30 quid? Spoiler alert: yes it is.
I’m certainly not the first person to make a DIY Flats Panel. There are a few designs out there, and I’m not saying that mine is the best; just that I found it easy to make and effective in use. My DIY skills are more at the duct tape than soldering iron side of the spectrum, so if I can make this, you can too.
You will need
* Electroluminescent (EL) panel, with power source
* MDF for the back
* Double-sided tape
* Duct tape
* Velcro or glue
* Elastic bands
* White paper
The EL panel is something you’ll need to source, but it shouldn’t be too difficult to find a supplier local to you. I’m in the UK, and used EL Wire Craft. You’ll want a panel that can display white light, and is comfortably larger that your telescope aperture. I.e. it can completely cover the front of your telescope, with some room spare. I went for this 13cm x 13cm panel.
You’ll have the option to choose a power source (called “driver type”). I chose “car lighter attachment” meaning it can be powered via a Lynx Astro cable for consistency with my other astro kit. With hindsight, I think I’d recommend AA batteries as they’re a bit more convenient. It’s down to how you run your set-up.
Next, you’ll want something hard for the backing. I bought a square of MDF from eBay. You could do the same, or you might have something lying around already. It should be at least as big as your EL panel, and a bit bigger is a-ok.
When you’ve got these ingredients, use double-sided tape to attach the EL panel to your MDF board.
Then you can use duct tape to cover any loose electronics on the back. To attach the power unit, I used some Velcro strips. Glue would also be fine if you’re confident you’ll never want to remove it!
Then you’ll want to cut some sheets of A4 paper to be just little bigger than the EL panel. These will be useful for the next step, which is…
…testing your new DIY Flats Panel! Hold it in front of your telescope, pushing it flat and tight to ensure a good seal, and take some test shots. Adjust your camera’s exposure length as necessary; you’re aiming for your image’s histogram to be peaking around the middle, or slightly to the right. Place the sheets of A4 paper in front of the EL panel, held in place by elastic bands, to dim it down if necessary. I use five sheets of paper. If you’re using an ASIAIR Pro / Plus, it has an Auto Flats function that takes the guesswork out of getting the right exposure.
Tip: you don’t want your Flats Panel to be too bright, otherwise you might get some internal reflections off your dewshield or inside the telescope itself. These will cause brighter patches in your Flats. Use enough sheets of paper so your exposures are at least a few seconds long.
Hey presto
You’ve now got a DIY Flats Panel! Enjoy (tolerate) taking Flats and get consistent results at any time that’s convenient for you. (You’ll still get odd looks from the neighbours, though).
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I just fold a sheet of A4 into an L, hang it over the objective, point the lens or scope at an illuimated wall, and shoot away. I drop gain down to make eposures longer to avoid strobe effects.
Thanks, I hadn’t heard of that technique before. I suppose you need to ensure that the part of wall you’re imaging is evenly illuminated? No more of an issue than taking t-shirt flats of the sky though I guess!
While looking for EL panels like those you used, I stumbled across ‘Tracing Lights’ on amazon that are effectively the same as your finished product… USB powered, dimmable A4 sized panels. $20 to $30USD.. Far cry cheaper than the ones the astro websites are pushing for sure.
Anyhow your build idea looks great, but it seems like I’ve found a finished product that allows me to be lazy instead. Thanks for the inspiration to look.
That sounds great if they work as we need them to — I’d be interested to know how you get on with them, if you do go ahead and make the purchase.
Brilliant – thanks for this. My EL panel just arrived today!
Great, good luck with making your Flats Panel!
Hi Lee, love you website and the info! I’m shooting from a heavily light polluted city with an OSC as well. Recently I got myself an LED panel as well, could you outline how you’re taking your flats with it as I had some troubles with the AAP and the way the flats turn out. For example, auto exposure typically gives me very short exposure times even on the dimmest level of the LED panel. So I started using a white T in between the panel and the telescope.
Thanks!
Hi Logan, thanks for your message. Have you actually tried calibrating your data with these troublesome Flat files? I’ve heard people say things like “Flats should be at least xx seconds long”, but I’ve never paid much attention to that. I just checked the Flats I took for my Pinwheel Galaxy photo (no filter used) and the Flats are 320ms each. They work just fine. So I guess what I’m saying is, don’t assume your Flats are no good based on what people say they should be like; give them a go and see if they actually work.
Thanks for the comment, Lee! I actually did try them (75 ms flats) and they seemed to work fine; I have limited experience and still try to figure out how to get a good set of flats for calibration. Do you adjust the brightness to the lowest setting on the LED panel? Do you still recommend a white T-shirt or A4 paper sheets in between?
I set my panel to its lowest brightness. I don’t use A4 paper or a t-shirt. You can see a photo of this in action here. If your 75ms flats work fine then my advice is to not look for problems where none exist!