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Old 04-08-2016, 08:05 AM
garymck (Gary)
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Cheap Flat Field Led Panel

Hi

just bought a light panel from ebay for art/photo purposes and realised it would be a great cheap flat field illuminated panel. A3 size, couple of steps illumination which looks very even. Powered by 12v adapter. Pic below.

got it here for $49.95:

http://www.ebay.com.au/itm/291817626...%3AMEBIDX%3AIT

delivered quickly (3 days). No connection to vendor other than as a customer.

cheers
Gary
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Old 04-08-2016, 08:10 AM
spiezzy
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Hi there Gary just bought this at the beginning of the week for just that purpose
cheers Pete
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Old 04-08-2016, 08:57 AM
glend (Glen)
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Bought one, thanks for the link.
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Old 04-08-2016, 09:03 AM
Dennis
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Hi Gary

Thanks for the information, it looks like a nice, portable unit.

I would be interested in any results you obtain in terms of how even the illumination is in the field of view of your set up. In particular, will it produce an acceptable edge to edge flat?

My home made LED illuminated Bunnings plastic bucket flat box is quite bulky in comparison!

Cheers

Dennis
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Old 04-08-2016, 10:55 AM
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OICURMT
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In particular, will it produce an acceptable edge to edge flat?
+1
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Old 04-08-2016, 04:18 PM
julianh72 (Julian)
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One thing that concerns me a bit about using "white" LEDs - particularly if you are using a one-shot colour (RGB) digital sensor:

"White" LED displays do not actually produce "white" light. Depending on the LED technology, they either have 3 fairly narrow-band spectral peaks, corresponding to the RGB LED elements, or the newer "bright white" LEDs use a strong narrow-band blue LED as the main driver, and yellow phosphor which produces a broad-band yellowish light which combines with the blue to simulate white light.

In addition, the peak wavelength and "width" of the Red, Green and / or Blue LEDs can vary depending upon the technology used - I'm sure we've all seen how some "white" LEDs seem to be "bluer" than others.

Either type of "white" LED can work well for human perception, which is remarkably adaptable in "filling in the blanks" when the source "white" light is actually missing some wavelengths - but I wonder what happens when you are using a digital sensor?

Your digital RGB sensor has three rather narrow (but overlapping) spectral sensitivities (for the RGB filters of the Bayer matrix respectively). These will typically be calibrated to simulate human perception of a wide range of colours, but what if the peaks of the emission spectra of your "white" source happen to not correspond with the peaks of sensitivity of the sensor? E.g. if you are using a "Bright White" (yellow phosphor + blue LED) source, the "white" light might actually be quite low in true "red" light. Will the process of capturing and processing the "white" flats introduce imaging errors by thinking your Red sub-pixels have a lower sensitivity than the Green and Blue sub-pixels (because there is less red light actually being emitted from your light source), and therefore give an inaccurate flat calibration?

Just a thought - I've captured plenty of spectra from various LED and fluorescent sources, and I know they can have very variable spectral signatures across Red, Green and Blue, but I've never tried to use a "white" LED source to produce a "white" flat calibration.
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Old 04-08-2016, 04:21 PM
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codemonkey (Lee)
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Looks interesting. How bright is it? I see that the brightness is adjustable, but is it dim enough to get multi-second exposures without sticking something else over the panel?
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Old 05-08-2016, 08:00 AM
garymck (Gary)
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I haven't had a chance to try it yet - perhaps over the weekend. I bought it for other purposes, but when I saw it I thought it looked ideal for flat fielding. I've never had an issue using different light sources shining on white cardboard in my obs to create flat field images, so not sure about effects of spectra etc. Shouldn't be to much of an issue with filtered imaging I would have thought? I guess I'll just suck it and see!! For $50 worth a punt....

cheers
Gary
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Old 09-08-2016, 10:37 AM
glend (Glen)
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Mine arrived this morning and i have powered it up to check it out. Just the right size for up to a 10" scope. There is a little brighter gradient near the edges, but if positioned correctly (ie in the middle) it is not an issue up to 10". Of the three power settings( selected by pushing the power button sequentially) i think the high power gives the best flat even illumination, low is just too low imho. I need to do some testing through the scope and camera, but first will have to find a way to hang it up on the wall of the observatory in a spot where i can easily aim the scope at it. The paper work that came with it describe it as a green led source, but certainly seems white to me. I can detect no green light emitted from the edges.
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Old 09-08-2016, 11:09 AM
Dennis
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Originally Posted by glend View Post
Mine arrived this morning and i have powered it up to check it out. Just the right size for up to a 10" scope. There is a little brighter gradient near the edges, but if positioned correctly (ie in the middle) it is not an issue up to 10". Of the three power settings( selected by pushing the power button sequentially) i think the high power gives the best flat even illumination, low is just too low imho. I need to do some testing through the scope and camera, but first will have to find a way to hang it up on the wall of the observatory in a spot where i can easily aim the scope at it. The paper work that came with it describe it as a green led source, but certainly seems white to me. I can detect no green light emitted from the edges.
Thanks Glen, I appreciate the feedback. I have a small LED panel sitting somewhere which I once purchased to view 35mm colour negatives must dig it up and see if I can use that.

Cheers

Dennis
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Old 12-08-2016, 06:16 AM
garymck (Gary)
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Hi Glen,

I haven't had a chance to try mine out yet - the one clear night I have had was screwed up by Windows 10 doing multiple uncontrollable updates (can't turn them off in Windows 10) due to not being fired up for weeks due to clouds. The bright setting looks pretty good on mine. The VERY slight edge gradient could be flattened I think by putting anothe rlayer of white perspex over the top with a slight spacing... I will experiment with this when the weather is better.

Can you let us know how it goes if you manage to try some flats?

cheers
Gary
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Old 15-08-2016, 05:29 AM
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Originally Posted by garymck View Post
...Windows 10 doing multiple uncontrollable updates (can't turn them off in Windows 10)...
Yes you can. You have to tell windows it is using a metered wifi network and it will then not download updates until you tell it to...assuming you use wifi of course...
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Old 15-08-2016, 06:57 AM
garymck (Gary)
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Yes you can. You have to tell windows it is using a metered wifi network and it will then not download updates until you tell it to...assuming you use wifi of course...
I'm hard wired so this doesn't work.......tried all sorts of registry hacks etc...

Going back to W7 when I can get the time to reinstall everything.

Gary
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Old 15-08-2016, 10:13 AM
Sato (Dom)
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You can make win 10 see your ethernet connection as metered...

http://www.windowscentral.com/how-se...red-windows-10

You will likely need to check it after any allowed major updates & redo it.
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Old 18-08-2016, 01:45 PM
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sungrazer (Karen)
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thanks for the link

Hi

thanks for that link

I also spotted:

http://www.ebay.com.au/itm/160861478695

for a smaller panel - for the price i am going to try it with my ED 80

cheers
Karen
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