The lightbucket - Houghy's way for flats

[h0ughy]

Well I wasnt sure where to post this. But here goes!

During the week I was thinking if how will I be able to take a flat field shot when I am away in the field. Then it struck me - why not use a device to have a light on the inside to cover the front of the scope and take the flats that way. Well how do I do it?:shrug:

I started with a 99 cent bucket (red) and I bought some osram button lights (they have 3 bright leds powered by 3 AAA batteries and are held in place by 3M tape. (see photos. I havent actually taken a shot at the moment to prove the madness but all indications are that it will work. All I need to do is ally an opaque barrier in the optical train, but what to choose? any suggestions welcome!:thumbsup: . I also noted that on the ED80 the dust cover can be used for the same thing, the central cover is removes and with duck tape secure the light to the end.

good idea - dont know. I showed this idea to some esteemed and knowledgeable members of this site for their impressions. They suggested I wear it on my head whilest playing a theme from close encounters, to a quizzical what's it for! Personally I agree, but I think there is a practical use for this idea, for all those DSLR people out there in IIS land:) . i am open for input and bagging, but practical input is greatly cherished:P

[janoskiss]

Sorry, I don't understand what this thing is supposed to do. Lots of lights - looks like a bad thing for astronomy. Take away the "flats"? :shrug: Or is this a joke I don't get? :ashamed:

[acropolite]

Adds a new meaning to the term "light bucket":P
I'll be interested to know but I suspect that it's going to be difficult to get the light diffused enough from what are relatively point sources.

[h0ughy]

Steve,
to explain further - when processing images after you take the dark frames and bias frames, taking flat frames helps to highlight the camera's different marks and quirks and that can be subtracted from the images you have taken in the processing of the final image. So dust motes and hairs, fly poo can all magically disappear in the final image

[h0ughy]

given the fact that you do not touch thecamrea at all nor the focus these should be out of focus and not show up as point sources, I have yet to test this theory. but I am looking at usibng a diffuser of some description.

There is method in my madness:lol: just have to prove it thats all;)

[JohnG]

Hey david

Why don't you place a square of diffuse plastic or similar over the end as well, that will elliminate any concentrating of the individual light sources, even the light out better.

JohnG

[h0ughy]

Like of what John, plastic bag, opalescent?

Can you see this working? Do you know what I am trying to achieve?:D

[JohnG]

I know exactly what you are trying to achieve, I have seen similar setups. I was thinking of something like a thin translucent plastic or somtheing like that, you have to make sure the light sourse is big enough to encompass the complete field of view of the camera and is even over that area.

I just use the sky with a white T-Shirt over the end of the tube.

JohnG

[Striker]

Interesting Houghy...sounds way to technical for me...I do the same as John...simple white sheet over the scope and point it to the sky..preferably around 90 degrees away from the sun.

Looks like you had some fun...can't comment how it will work.

[JohnG]

David

Have a look on Eddie T's Astroshed site and you will see a version of a Lightbox, also, have alook here:

http://www.astrodon.com/oldsite/LearningCurve.html

There are others if you want to chase them up.

Good luck, I can't see why it won't work so long as the area that is lit is even and full frame.

JohnG :thumbsup:

[Astroman]

i am pretty sure the idea is to use this while taking the exposures, so no need to wait till daytime for it. I agree with john, use a white sheet houghy or pillow case or if you want to get teknickal try a piece of white acrylic, they use the white acrylic on still life photography and as a background light source for slides etc.... so why not flats.

[h0ughy]

well my point is that when you are going to be taking several shots of different targets the orientation is not going to be the same all of the time, and maybe is something blew onto the corrector or the front lens between targets you will need new darks and flats. Does that make sense or am I just confirming i am a raving looney:P :D so you cant do that during the day!:lol:

[h0ughy]

I have seen that a while ago, thanks, but as for it being portable for field conditions I couldnt see thatwould work for me. however this one fails I will go to that scenario and work out away to make it work.:help: :D

[h0ughy]

Thats a very sensible suggestion Andrew (very different to last night Eh;) :P ) the sheet sound easy and good. i will raid the linen press, failing that and the wifes wrath, maybe the plastic:D :thumbsup:

[JohnG]

Maybe I am missing something here, but I can see one small problem if you are out in the field, what are you going to shine it on to, to get your flats? or, do you intend putting it over the end of the scope?

JohnG

[janoskiss]

Thanks for the explanation Houghy. When I first read the thread title I figured you came up with a telescope for high-rise apartment dwellers. :lol:

[h0ughy]

the 5th image shows it over the scope John

[JohnG]

Gee, glad you told me that, would not have know otherwise. The impression I got was that you were going to shine it on the ceiling or some other flat, even surface. Would like to see a flat, looks way to bright to me if you intend using it over the tube..

Too complicated, I will stick with the white T-shirt over the tube, I know my flats are even then.

FWIW my opinion only.

JohnG

[matt]

Anyone???? Anyone feel like going anywhere near that one????:lol:

[[1ponders]]

h0ughy, how about using a white shopping bag? Put that over the end of the scope first and then your bucket?

[Astroman]

If its too bright wire all the LEDs together and run off a variable power supply or controller to dim the lights to the correct intensity needed.



Amazing what a little sleep does to a person... Must have come to me lastnight in a dream, my wife said I was mumbling in my sleep so I guess I was working it out :D

[asimov]

Sand blasted glass Houghy.

[h0ughy]

sounds a good idea too paul, will try that one too
:thumbsup:

[Dennis]

Hi Dave

10 out of 10 for effort mate – well done! You may find you have too much power in your set up? I have built a flat field box, but used a shallow washing up bowl. I have 6 flashlight bulbs around the circumference of the rim, pointing inside the bowl so their light bounces off the bottom of the bowl and then onto the back side of a sheet of milky white Perspex. The front side of this Perspex is what my C9.25 then sees.

I made a plastic ring/shield that sits inside the bowl to prevent any light from the flashlight bulbs shining directly onto the back of the opaque Perspex. I also sanded the bottom of the washing up bowl as I read somewhere that this produces an effect called "Lambertian reflection". Apparently the light reflected from a roughened surface is more even than from a shiny surface.

With my ST7, my flat fields are ½ sec using the above apparatus. The flashlight bulbs are wired in parallel and I use a 1.5A power pack that is adjustable from 3V to 12V dc. I usually have it set to 3V dc and that provides sufficient illumination to half fill the charge wells (pixels) on my ST7.

I took a series of flat fields and then rotated the apparatus 90 degrees on the end of the OTA, and then took another series. I then subtracted them and got null, implying I had a true flat field, evenly illuminated.

Gee, this is difficult to describe in words. I'm off to get the flat field box and take some pictures so I can post them later.

Cheers

Dennis

[h0ughy]

that would be great to see Dennis, please post them up

[ballaratdragons]

It's a very nice looking Flying Saucer Houghy! But even with the best of effort, I don't think anyone will believe that they are genuine UFO pics.

[Dennis]

Hi Dave

Here are the pictures. Whilst taking the apparatus apart, my memory was jogged as follows:

I only use 4 flashlight bulbs, even though I wired it for 8.
I sandwiched one layer of x2 Neutral Density (ND) film with the opaque Perspex to reduce the overall illumination.
The black, circular ring is made from computer binder plastic covers and prevents the bulbs from directly illuminating the Perspex/ND filter sandwich.
I use the power pack at 4.5V dc to provide adequate flat field illumination.
The inside walls and bottom of the bowl have been sanded, to roughen the surface, a la Lambertian Reflectance (the surface luminance is the same regardless of angle of view) which I am hoping will produce a more even illumination.

As stated previously, the illumination is sufficient to half saturate my ccd so I'm thinking yours may be too bright?

Cheers

Dennis

[h0ughy]

:rofl:

[h0ughy]

Mmmm thats way better that what i concocted, might have to rethink and regig afew things, thought the dslr is not as sensitive as the ccd in that respect

[Dennis]

Hi Dave

Yawn – just woke up for the England/Ecuador soccer match, so I thought I’d post a flat field taken with the above flat field apparatus. This one had the Celestron F6.3 Corrector/Flattener in the optical train on the C9.25.

Good luck with your mod’s.

Cheers

Dennis

[Roger Davis]

Whatcha need is something like the material used on the old light tables.
Needs to be somewhat thick (2-3 mm) so that it can be epoxied into the bucket. If you go to Bunnings they sell storage bins for between $5 - $30 which are made of similar material. You could buy a square one and chop the side out? Maybe?

[ving]

crikey! my brain hurts!

[The Unbeliever]

:screwy:
Well well well, this has to be a trick question. Without breaking the laws of physics wouldn't it be easier to empty the contents of the bucket to make it a truly light bucket.

PS even take the handle off!!

[The Unbeliever]

Hi Dave,

All jokes aside check out this link.

http://www.ghg.net/cshaw/flat.htm


:thumbsup: