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!
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
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)
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.
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.
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 :-?
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.
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.
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
Here is my Lightbox...
(http://www.amateur-astronomy.org/Images/LightBox.JPG)
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.
Just to confuse things even more........
Does colour temperature have any relevance ?
White is not always "white".
Mike, how many lights did you put in? What sort of lights? Did you get foam board from Homebase or similar?
QuoteJust 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
Thanks for that John, I'm actually starting to understand this stuff :oops:
So the purer the white the more balanced RGB should be and less messing around with exposures for the flats ?
Also, I am going to use an old wine box or something, as long as it's white inside.
I don't think it would matter, even for OSC's as the important thing is to get flat field frames with all the optical defects (dust bunnies/field illumination etc). The situation is more complex for mono chipped cameras as you will have to take one set for each filter position - that's 4 positions for LRGB + another for Ha. OSC's and Digital SLR's just need the one set with the LP filter in place. As long as your optical train does not move they should be valid for a number of months.
Don't forget that flat field images are scaled by your imaging software and that would be valid for DSLR's to.
Flat field frames should be as evenly lit as possible, Mikes design looks good to me. Some people have more than two screens but that's probably over the top for us. I've heard of the rounded lens end of LED's being filed off and can imagine that would help a lot.
Hope that helps
Robert
QuoteI am going to use an old wine box or something
Fay - make sure you drink the wine first or you could end up damaging your optics.... :lol: Probably also best to make sure that the white surface is not too shiny as you may end up with strange reflections etc.
John
John,
I have got a bag of tricks from Maplins, it will be like that cookery programme where they throw a few items on the table & the chef has to make of it what he can!!!!!!!!
I will probably blow something up anyway. Does the mount cable, when clipped onto the 12v battery, need a 3 or 5 amp fuse? I got both in case.
Fay
I think you should be OK with 3A - I think spec is something like 2A max - give it a go... If the mount is cold (depths of winter) & is fully loaded then I guess it may get close to 3....????
John
you might find the fuse blows if the mount gets jammed against something. Probably not a problem for you Fay, but with my newt, the mount was always trying to put the mirror where one of the tripod legs was :evil:
Note, this is not necessarily a bad thing, but just make sure you've got several spares in your box of bits. That'll make your box a little less light. That bit was a joke... :oops:
Ok, thanks for that.
I have got these LEDS which have their own cables coming out of each one. Do these go into the cigarette connector or is there something in between?
I'm on a mission now.
If all else fails, like a free box in Tesco's, I saw sheets of white sided hardboard in B & Q. Do you think this is too heavy? I have also bought a sheet of white sturdy card, but may not be man enough.
Fay - what is the PN of the LEDS you got from Maplin's. LED's have a MAX current you can supply to them (something like 20mAmps) if you just connect them to 12V without a current limiting resistor you can watch them smoke...!!!! Also LEDS have polarity - you need to make sure they are connected the right way around...
John
Whoops, stumbling block No.1
I was going to say, do you want a photo before it blows up & after!!!!!!!
All I can see is 12volt. the ref is:A27FJ.
According to Maplin FAQs for these LEDs, they can be connected directly to the battery so should have internal resistor - Can't find their spec. though.
Presumably they have red and black wires ?
If so, red to positive (+ve) and black to negative (-ve)
QuoteI have got these LEDS which have their own cables coming out of each one. Do these go into the cigarette connector or is there something in between?
If they're long enough yes, but don't forget a fuse ;)
It has 4 lights inside, one on each corner.
Thanks for that Mick. Do you think I should put a switch on or just let them either come on, or blow, up when I connect to battery?
Mike where did you get the foam board?
Don't bother with a switch, you'll only be connecting it when you want to use it anyway.
Besides, you'll be a little further away when it goes BANG
Quote from: Fay on Apr 22, 2008, 08:17:27Mike where did you get the foam board?/quote]
Hobbycraft at Crayford.
I rang them & they only do one that is plastic both sides. They don't seem to do the boarded sides now then. Thanks for that Mike
The one I used IS the one with plastic both sides. I never mentioned them having cardboard sides :-?
Great Mike, because you described it as foam board, I assumed it would be like cardboard or something.
Being that I have developed a fetish for looking at any box anyone is carrying & weighing it up, & only looking at box's when in M & S, I will go to Hobbycraft tomorrow.
Thanks a lot.
Weighing it up? I thought "light box" meant it wasn't dark!
:o
Quote from: Fay on Apr 22, 2008, 12:27:46Being that I have developed a fetish for looking at any box...
You'll spend ages in Hobbycraft then ! :o
Don't know whether it helps but I found this artical on buiding a light box today...
http://www.asignobservatory.com/LightBox.aspx (http://www.asignobservatory.com/LightBox.aspx)
I was looking for that site Robert, good.
My lightbox has been started now. I noticed in 2005 Mike had put details of how he made his box on UKAI.
Blimey if Mike had to put instructions on UKAI about how to make a box it reinforces my opinion of most people on that site....
The light box bulb wires are now going to be connected to the cigarette connector that goes into the battery.
Can anyone tell me which position in the connector the red goes please?
Should be the one going to the centre pin of the plug.
Bonus Info:
This months Practical Astronomer has articles on Flats and Light Boxes ;)
Thanks Mick, for wire information. Yes I saw the articles, would you believe they are in there this month!
Put the scope thru the hole in the light box & it seems like a snug fit, but it does not stay in that position, it settles at an angle, with the box weight. Does the scope glass have to be level with the bit of plastic with the lights behind?
Also, when you take a light frame & hold the mouse on the image, I will aim for around 28,000 ADU, should the mouse show this level over the whole frame or will it vary?
Thanks
Does it have TWO layers of foambaord so that it holds it in place?
NO, I think that is the problem. Will have to be sorted! Thanks Mike
Should have followed my design ;)
I know
Box has had a modification, now there are two lids each with a hole to hold the ED80 a bit better. The lid has not been glued but is fixed with low tack sticky tape in case access is needed. Hope the light is ok. Until it's tried, I don't know if another mod will be made.
Have put another picture on the next post as could not do two on this page, probably doing it wrong.
(http://farm4.static.flickr.com/3253/2456170079_e17120fb51.jpg)
(http://farm3.static.flickr.com/2018/2456167253_7a0b4c5784.jpg)
Looks like a very complicated design, but I see no reason why it should work well. If teh lights are too bright you can always install a pot, or even better some sort of permanent resistance once you know how many ohms are necessary to allow you to dim them. Are they LED's or filament bulbs?
LEDS, the light is quite calm, not too bright. Mike should the whole image be the same ADU measurement or should it just be an average of just below the well depth?
I believe an average ADU across the image of half the well depth will suffice.
Fay - Like I said before the whole image will not be the same ADU e.g where there is dust & vignetting (if you have any) the readings will be less (darker). It's only approx - you don't need to be too exact.....!
John
Thank God for that! I did a quickie, indoors & the ADU was fluctuating,& I thought, good grief!
I did not realise you had already told me that.