Astronomer’s Sketch pad

[markse68]

I only started sketching recently and have been really enjoying it but I’ve been looking for a better way to transport and protect my sketch pad- till now it’s been in a bubble wrap bag but that’s not really ideal. I’ve been using a book light held to the back of the pad with left hand while sketching with the right. A bit awkward and the book light is a bit bright- ok for Mars but would be a night-vision nightmare for other targets.

So I came up with this- an astronomer’s sketch pad that protects the pad and has built in red light illumination. I just finished putting it together

I bought a bicycle rear light on ebay for the illumination and 3D printed a new housing for it- i removed all the LEDs and re-attached one of them with thin wires. The light has a built in LiPo cell and is USB rechargeable which is nice. Should last a while with only one LED to drive too.

I used an acrylic rod as a light pipe and there’s this neat trick where if you paint a white line down the length of it, the light bounces around inside the pipe till it hits white pigment, diffuses and bounces straight out the opposite side. This creates a curtain of fairly even illumination and quite a narrow beam dependent on width of the line that can be directed by turning the acrylic rod. I polished the ends of the rod and glued a piece of silver foil onto the end opposite the LED with uv cure glue- very handy stuff.

Ideally it would have been mounted higher to better illuminate the paper but I think it should be good enough and I didn’t want to make it all too bulky.

The 3D printed housing has little nubbins sticking out that clip into the outer binding spring coils and hold the pad quite firmly whilst allowing simple removal for turning the pages.

I bought a scrap of leather on eBay to make the cover and a few nice brass leathercraft fittings- modifying them to fit. I cut the leather with a laser- it cut really nicely but pongs a bit- that should dissipate with time though i hope.

An aluminium plate stiffens and supports the pad and a thin plastic sheet levels the brass fittings.

I used one of those nice brass ball pin closures- would have liked the closing flap to be a bit longer but the scrap of leather wasn’t big enough. I designed it so the front flap folds behind the pad and can be gripped with left hand while sketching- seems quite comfortable.

I might try it out tonight but it looks a bit windy.

Mark

Edited November 16, 2020 by markse68
editing, spelling

[globular]

Very impressive.

It’s hard to tell from your picture but you might find it too bright when trying to stay dark adapted - even quite a dim red light can spoil things.
Maybe a baffle of some sort over the top of the rod will keep down stray light? 
Or possibly add some sort of dimmer control? It’s surprising how dim a light can be while still being sufficient to sketch by once you’re fully dark adapted.
I’m sure you’ll tweak things if necessary. And I could easily be wrong about the apparent brightness of your excellent gadget.

Let us know how your first trial goes.

 

[markse68]

Thanks Glob

the camera seems to increase the contrast and make it look brighter than it really is I think but yes it could be baffled so you can’t see the light pipe at all-  it was a struggle to get the light high enough without making it all too bulky and resulted in compromises but I guess i’ll see how it goes in use and modify as necessary 😊

Mark

[markse68]

You were dead right in your observation Glob- it is too bright. Tried it last night and could really feel my eyes adjusting from looking at it to looking at the sky- not good! I’m going to look into ways of dimming it- maybe there’s a way to change the pwm duty cycle, maybe just adding a resistor or maybe changing the LED to a deeper red less bright alternative. I think a baffle is essential too- I kinda wanted to be able to see the acrylic rod as i thought it was quite cool looking but that’s completely counter to its usefulness lol! 

Mark

[globular]

The rod is very cool. I agree it's a shame to cover it up, but needs must.
Can't wait to see mark 2.

[markse68]

As an interim attempt to fix I ordered some deeper red LEDs- in fact they’re almost in the IR 100nm redder than the red ones!  Not sure if that was such a good move... They’re definitely a lot dimmer and deeper red! A baffle of aluminium sticky tape helps too. Maybe too dim now 🤦‍♂️ We shall see

Mark

[DaveL59]

perhaps an LED at each end would even up the illumination across the page a bit?

I wonder too if roughing the surface of the tube would help diffusion?

The 850nm IR LED's emit a red glow that doesn't light too much so may do what you need, tho taking a pic they'll still look very bright simply because the camera will react to the IR glow but our eyes won't of course. Downside could be that you'll also attract insects because of the IR so beware of a sneak bat attack if they start swarming around you 😉 

[markse68]

1 minute ago, DaveL59 said:

perhaps an LED at each end would even up the illumination across the page a bit?

I wonder too if roughing the surface of the tube would help diffusion?

The 850nm IR LED's emit a red glow that doesn't light too much so may do what you need, tho taking a pic they'll still look very bright simply because the camera will react to the IR glow but our eyes won't of course. Downside could be that you'll also attract insects because of the IR so beware of a sneak bat attack if they start swarming around you 😉 

Yes Dave it does look like an LED at each end would help even it up-  might try that too. I’m thinking now that a better idea might be a diffusion panel from the back of an lcd screen placed underneath the top paper for ultimate even illumination but that might get a bit fiddly. Anyway it’s really hard to judge if it’s too bright or too dim without actually going out in the dark and letting your eyes adapt- I thought the original was pretty dim till i tried it for real!

Mark

[globular]

Looks a lot dimmer overall and without too much glare from the rod. 
I'm not sure the unevenness of the illumination over the page will be too big a problem; it's amazing how your eyes even things out. I think the key is not to have any really bright spots.
Give it a test drive before you try a whole new concept.

[globular]

Can I ask your advice?

I don't have the skills to make things from scratch and was wondering if I started with something like this....

https://www.amazon.co.uk/dp/B07WMQQZ6M

.... could I disconnect all but one of the LEDs?  And paint the clear plastic cover over the LEDs with some red paint of some kind? And then use it on the 20% dimmed setting?

[markse68]

Hi Glob, that looks neat- I should have used something like that with dimming 🤦‍♂️

Not sure if it’ll be easy to get inside to remove LEDs unless it’s screwed together but worth a try as it’s not a huge outlay if it goes wrong?  The LEDs will likely be surface mount so you’d need to desolder them, or you may just opt to destroy them in situ or physically remove them with pliers? 

Worth a go I’d say 👍

Mark

[globular]

Thanks Mark.  I'll give it a go.  

Have you tested yours since the mods?

[markse68]

8 minutes ago, globular said:

Thanks Mark.  I'll give it a go.  

Have you tested yours since the mods?

Not at the scope yet Glob- only sitting in a darkened room and it does seem very dim- am contemplating fitting second LED later on today. Interestingly the deep red light seems to pass through the black died 3d printed housing a lot more than the shorter wavelength did 🤷‍♂️ The whole housing glows dimly from it!

Mark

Edited November 21, 2020 by markse68

[globular]

One each end of the rod will probably do the trick... bit brighter and more uniform.
Good luck 👍

[DaveL59]

hi Glob

as Mark says, likely in that lamp the LED's will be SMD, easy enough to desolder with a regular 25W iron if you don't care if they survive. Painting over the ones left with red nail varnish may do what you need and then a red film inside the lens, perhaps 2 layers of. Dismantling could be fun, hopefully it's clipped and not sonically welded.

@Mark - when I needed to cull the IR for the cameras mounted behind glass what I found worked best was a layer of tin foil under a black felt pad, no stray IR bouncing off the glass. Perhaps similar on the casing would help with your build to eliminate the stray light, tho you'll need to be sure not to short the connections of course.

[markse68]

11 minutes ago, DaveL59 said:

 

@Mark - when I needed to cull the IR for the cameras mounted behind glass what I found worked best was a layer of tin foil under a black felt pad, no stray IR bouncing off the glass. Perhaps similar on the casing would help with your build to eliminate the stray light, tho you'll need to be sure not to short the connections of course.

You’re reading my mind Dave 😉 Part of the reason is these LEDs are actually designed for quite high power and are built with the die directly onto a ceramic back plate and no reflector- the ceramic is translucent and passes light out the back. I think some double sided tape to cover the backs and solder pads then some tin foil over that should cut most of the leakage 👍

Mark

[DaveL59]

I have an IR illuminator ring off a camera that wasn't working, not tested it but they are regular old-style LED's rather than SMD type. If useful I could always remove a few if you want to try a few of those along the top edge. Will see if I can fire them up and check that they are the type that glow red as some don't.

[globular]

10 minutes ago, DaveL59 said:

Dismantling could be fun

Thanks @DaveL59.  Nail varnish tip duly noted! Dismantling I think will likely be tricky.  Breaking it off and taping/gluing it back on would be next option, albeit a poor second best.  Failing that I'll just add thick black tape to mask off the unwanted LEDs and apply layer(s) of red to the outside over the remaining ones.

[markse68]

9 minutes ago, DaveL59 said:

I have an IR illuminator ring off a camera that wasn't working, not tested it but they are regular old-style LED's rather than SMD type. If useful I could always remove a few if you want to try a few of those along the top edge. Will see if I can fire them up and check that they are the type that glow red as some don't.

Thanks Dave but they wouldn’t fit in the housing - they need to fit into a 2mm slot. or did you mean for Glob’s lamp?

Mark

[DaveL59]

ahh true, I thought you were considering the alternative of a few LEDs along the edge instead of the clear rod but if not then these wouldn't help. For sure not enough glow to light up the rod even halfway and give much light spread.

[markse68]

Yep, 2 LEDs is much better than 1-  I think this might just work

 

[globular]

My book light arrived a few days ago and without major (and probably fatal) surgery I couldn't see an easy way to get at the LEDs.
Instead I've been applying coats of red acrylic paint to the outside of the frosted plastic housing. 
I was a bit worried that in cold and dewy conditions it might rub or flake off - but I tried it last night in very severe conditions and it all survived very well.
I think I need another coat or two of red to darken it further (and I might add some black paint along the edges to narrow the beam of light) but it looks promising.