Light box for SW 200P

[Bizibilder]

I've just started to make a light box for taking flats for my Skywatcher 200P. The construction is conventional, using foam board and an opal perspex diffuser. The light source will be four bright white LED's and it will have a brightness control. I've included a few pics of progress so far: Most work is simple pencil/ruler/scalpel cutting of the foam. I used a couple of jewellers piercing saws to cut the perspex - though you could use a hacksaw and lots of abrasive paper instead! The final pic is of all the basic parts of the box which will be 28 x 28 x 42cm the whole thing being cut from four sheets of A2 foamboard.

[Beyond_Vision]

It will be interesting to see if you can get an even illumination. Have you considered an EL panel?

[Bizibilder]

I have considered an EL but the cost of an A3 panel is prohibitive at the moment!!

[Bizibilder]

I've added a few more pics of progress.....

Note that one of them shows that a "rogue" resistor got into the strip that I bought!! It was only when I cropped the picture that I noticed! Corrected in the lower picture.

[Bizibilder]

Lots of spaghetti!! One LED on test - variable from blindingly bright to almost "out".

[Bizibilder]

A bit more progress today - I've assembled the box of electrics and attached it to the outside of the box. Just got to wire up the LED's and finish the assembly now.......

[Bizibilder]

Further progress and first "light"!! It seems to work, which has surprised me as I'm no electrician, even if the box has only three sides at the moment.

I've had a thought though...... HOW do you calibrate the box to see if the illumination is even??

Ive had a "looksee" in PS and wherever I click with the "sample" dropper tool I get the same RGB values (within +/- 1 across the "disc")

It looks OK with the naked eye but that is far from a good method!! The pics show a "close up" and a general view of the box so far (sorry about the bits of wire!!)

[Sparrow]

Hi Bizibilder - nice project there - could you post the wiring diagram for it please - I know I could probably find one online but yours looks nice and simple and you've obviously got it working.

Thanks in anticipation

John

If you could pm me that would be great

[Bizibilder]

I will post it for you John but you will need to wait a while!

Currently there is a 100K pot to operate the "dimmer" which actually acts more or less as an on/off" switch!!!! (ie its too big - a fraction of a turn and the lights go out ).

I will be replacing it with 10K and testing it out. If that works I will post the circuit.

[Bizibilder]

Here is the circuit "picture" (I don't do diagrams with all the correct symbols etc!!). i've tried to show how I put the components on the strip board.

The resistors (R1-R4) are 330ohm. The variable resistor is 10K linear. The switch is a simple "on/off" SPST. The battery is a 9v "square" battery (PP3?). The LED's are "White LED 8000mcd 5mm" (N50GK Maplins code). The circuit is an off-cut from a "strip board". The box is 85x54x30 ABS box. These were bought from Maplins and Bitsbox.

I hope you can understand the diagram!!

PS I bought a "resistor pack" from Maplins and played around with them and the LED's until I got the "light" I wanted - all very scientific!!

PPS The variable resistor has three "tags" - I used the end one and the centre - I used a multimeter to get things the right way round but you could use trial and error.

Hope this helps

Oops I forgot - I changed the 100K pot for 10K and now I have full control of the light level over the whole range from "bright" to "only just visible in a darkened room". I must admit that I have no idea as to why I needed a variable light source - it just seemed fun to do

[Bizibilder]

A couple more pictures before I seal the box for good by adding the fourth side. The first shows the wiring between the two sheets that will go over the end of the 200P (the scope will enter via the top of this picture).

The second is a view showing the LED's alight and the baffles that prevent the light from going directly to the perspex diffuser screen. The light has to travel "towards you" to the end of the box, hit the "near" end (including the four triangular reflectors that are glued into the four corners at that end - this end is out of shot) and reflect back "away from you" down the box to pass through the opal perspex diffuser and into the telescope.

Hope that makes sense!

[Bizibilder]

A picture of the "reflecting" end of the box - illuminated by the four LED's. You can make out the "beam" from each hitting at the junction of the box top and the triangular corner piece.

[Sparrow]

Thanks for the wiring diagram Bizibilder - it's absolutely fine and just what I need. Makes perfect sense to me.

Regards

John

[Bizibilder]

No problem!

[Bizibilder]

Finally finished the box today. I have tried it out once and it seems to work very well (although it is not, so far, "calibrated"). The only mods have been to cut out a space to fit around my new dual speed focuser and to cover all the edges with duct tape. The foamboard is very easily damaged so I reckon that the tape is necessary. I used what was left of the foamboard to make a dust cap - one of the circular offcuts was trimmed slightly to be a loose fit in the "hole" and a flat top makes the whole thing reasonably dust proof. There are four pieces of blue foam (you can see two of them) around the "entrance" - these are to guide the scope into position when mounting the box into "working position" and to provide a gentle "grip" to the top of the scope tube.

[yesyes]

Looking great. Would you be able to check how much it weighs, please? I'd like to compare it to my acrylic version... ;-)

[Bizibilder]

800g precisely (including lid!)! The battery box/controller is glued to it so the "box" alone would be lighter, however a trailing lead set-up would be a real pain! - especially in the dark.

[yesyes]

ah, great, thanks. So it's about half the weight of my acrylic version. I thought there would be more of a difference...

[Catanonia]

mmm, very nice and simple. Loving it and saved this thread for when I need one.

Thanks

[Nick]

I have just build a similar box out of expanded polystyrene, I got an LED torch from a cheap shop (£1.50), it had 24 LEDs, current limit resistor, switch etc. I took all the LEDs off the circuit board and re-wired them into the light box. To calbrate the easiest way I know is to photograph the illuminated circle and load the frame into photoshop or GIMP then adjust the levels so that the contrast of the circle is almost maximum, say 5 to 10 levels wide. This will show any brighter or darker spots, I found it took quite a while to "tune" the box in this way, by moving baffles etc. However I managed to get a big improvement (on what already looked fine to the eye).

[Gina]

This is the thread I was looking for - thank you Roger

[Gina]

Is foamboard actually strong enough? I don't have any experience of it myself. Looks easy to work.

[Bizibilder]

Foamboard is quite strong enough but its main advantage is that is is very lightweight.

You do have to be careful not to bash it about as it will dent easily - I usually only take my lightbox out to the scope at the end of a session when I'm ready to take my flats - you may have room to store yours in the warm room.

With mine I taped all the edges and corners as these are the most vulnerable parts. The basic box is hot glued (why I havn't been using that stuff foe the last 30 years i shall never know!! It's brilliant!).

To cut foamboard, first mark it out with a sharp pencil - but don't damage it! Then cut with a new scalpel blade held against a good straight edge. For circles buy youself a circle cutter from any good stationers - it will make a far better job than you ever will freehand - even with a template!!

I made all my boxes to "fit" the foamboard sheets - for the 200P the box is A3 sheet "longways" and for the ED80 the box is A3 "acrossways" for the longest dimension. Saves cutting as the boards come with perfect 90° corners and dead straight edges.

[Gina]

Foamboard is quite strong enough but its main advantage is that is is very lightweight.

You do have to be careful not to bash it about as it will dent easily - I usually only take my lightbox out to the scope at the end of a session when I'm ready to take my flats - you may have room to store yours in the warm room.

Yes, if I clear the tools out of my warm room there is plenty of space

With mine I taped all the edges and corners as these are the most vulnerable parts. The basic box is hot glued (why I havn't been using that stuff foe the last 30 years i shall never know!! It's brilliant!).

I find hot glue very useful too - use it for all sorts of things - great for fixing wires and cables to keep them tidy. My home made weather station is held together with hot glue Two small problems - it tends to form thin whiskers of glue that seem to get everywhere and it has a very strong attraction to your fingers

To cut foamboard, first mark it out with a sharp pencil - but don't damage it! Then cut with a new scalpel blade held against a good straight edge. For circles buy youself a circle cutter from any good stationers - it will make a far better job than you ever will freehand - even with a template!!

That's a good idea, I'm always cutting circles it seems and they never come out very round!

I made all my boxes to "fit" the foamboard sheets - for the 200P the box is A3 sheet "longways" and for the ED80 the box is A3 "acrossways" for the longest dimension. Saves cutting as the boards come with perfect 90° corners and dead straight edges.

Good thinking

[RAC]

I think i know what my next project is going to be now. Thanks.

I do have a spare dead 23in monitor here and with the lcd off it looks to light up real nice but it needs a video input from a pc to turn the back light on.