Light Box

[Fay]

I am going out tomorrow, to Maplins & Homebase to get bits for a light box. I realised that it will be a palaver to do flat fields the next day or done before imaging, too much of a chance that I will be out of focus. 

Must wire it up correct! 

[mickw]

Don't forget you can use a "white screen" on your laptop as a light box - Nothing to buy, nothing to make or wire up - Speak to Mark

[Daniel]

Hi Fay, would be great to hear how you get on with this project, since i was thinking of doing the same after I've made my hartman mask, would be especially interested to hear how you diffuse the light over a short distance, i was worried I'd get a hotspot if the light was too close.

Daniel
:O)

[Fay]

Mick, I did have a go at that, but found it was difficult holding the scope flat up against the screen, also it could damage the screen.

Mark, if you are there can you tell me more about this method?

Daniel, I will let you know how I get on. There are various websites on how to make one, all on a similar theme.

[Fay]

Also Mick, I found the scope + camera + filter wheel very heavy to try & hold up to the screen. Then you have to do darks, which means putting it all down & putting the cap on the end, without disturbing the camera position, and work the computer as well. 

[mickw]

I thought the idea was to do the darks first, then lift the laptop in front of the scope without touching it.
I could be totally wrong though

[Fay]

I have just read on UKAI, that this chap does his flats that way, but holds his scope about a foot away. That would be easier than trying to hold it flat against the screen, as I did.

Doing the darks first, I am thinking you still have to put the equipment down, to take the lid off, & risk moving the camera for the lights.

[MarkS]

There's no "official" way of doing it - I invented the method for myself but I'm sure it's not an original idea.

After an evening's imaging I just took the scope and camera into my study and placed it on the desk pointing at my LCD screen to take some flats - with the room lights switched off to avoid stray light.  The same thing can be done in the garden by holding your laptop screen near to the scope but my scope is too big for my laptop screen.  The screen should be displaying a uniform white image. 

But I've just realised that could be a problem if you need your laptop simultaneously to control your camera!

In principle there's nothing to stop you using the TV in your living room (again with the room lights switched off) if it is flatscreen and you can persuade it to display a uniform white image.

[JohnP]

Mark - that was going to be my question - I tried to take flats using laptop screen in field & big problems are:

- You have to move scope to position in front of screen - ideally it's best to leave scope in same position as you took lights (just to make sure no flexure/ movement of dust etc)

- You can't control camera & have laptop screen white at the same time.... Big Problem!!!!

- Ideally you should take flats for all the filters you use which means moving between exposures which will make realignment difficult etc...

All in all I think portable light box setup is best....

John

[Mike]

Here is my Lightbox...



It is made out of white foam-board. At the top you can see there are two layers of foam-board with a hole the size of the ED80. This holds it in place. Below that is a further layer with another larger hole in with a sheet of opaque material (like a waxy tracing paper I found in Hobbycraft) around this are lights that shine down into the box (you can just see the wiring in the photo). This means the light bounces off the bottom of the box before being reflected off the white surface back into the tracing paper which makes it diffuse. That way there is an even illumination without any hotspots. it is important to only have a few lights and keep them dim as not much illumination is needed. The whole thing is hot glued together and on one side I fitted a 12v jack socket and a switch, you could easily fit it up with batteries instead.

[mickw]

Just to confuse things even more........
Does colour temperature have any relevance ?
White is not always "white".

[Fay]

Mike, how many lights did you put in? What sort of lights? Did you get foam board from Homebase or similar?

[JohnP]

Just to confuse things even more........
Does colour temperature have any relevance ?
White is not always "white".

Mick - yep - good question & I believe it does - CCD's respond differently at different wavelengths- also you need to ideally take flats through the RGB filters as well so if you find your light source doesn't emit enough in RGB wavelengths you might have to find you need long exposures to get reasonably exposed flats...? I think white LEDS are best - don't use regular tungsten type filament lamps - torch bulbs etc.

John

[mickw]

Thanks for that John, I'm actually starting to understand this stuff 

So the purer the white the more balanced RGB should be and less messing around with exposures for the flats ?

[Fay]

Also, I am going to use an old wine box or something, as long as it's white inside.