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Heads up.....very cost effective LED dimmable flat screen panel.


RobH

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I'm heartily sick of Gerd Neumann's Aurora panels on which the cables fail without fail. I've had four failures on three cables (quite an acheivement but one failed at both ends!) so a good alternative would be great to know about. The big question will, I think, concern the spectrum. I've encountered one sort of bulb which couldn't generate an Ha flat and another which couldn't generate a blue. I don't know anything about the LED spectrum, though. I hope it works. Thanks for the tip off.

Olly

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Thanks for the heads up Rob I've been looking for one to use at the dark site & this looks like it may fit the bill, plus it has the added bonus of running on 12v. I did a bit of snooping around on Amazon & found a cheaper one with a pink surround but I don't think it has the adjustable lighting so not sure if it would be suitable to use as a light panel.

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Olly....just looking at it, the light is pretty well pure white, so there's no reason why it shouldny work with Ha.

Tich....the ability to dim it is a big plus. With my Earlsmann panel, I had to put sheets of paper4 in the way to dim it enough for shooting luminance flats.

I might just take it down to the obs and do a few experiments later.

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Fantastic find Rob. Im just looking as to whether the A4 version will fit the 130pds. Or I could go for the larger version, dim it with some A2, then back the telescope off a bit to reduce unwanted light from bypassing the primary/secondary and making its way up the drawtube (so its a bit more like a sky flat).

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Roger, dimming is really handy if you have a camera with a mechanical shutter, where you can't use below a certain exposure without the shutter being picked up in the flat.....I had this with my H18, and other cameras are the same, the Atik 383 for example. I found that I could just about get away with it by using lots of paper in front of the screen, but dimming is much easier.

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Thanks Rob - I had this problem recently when I made a new LED light box (which I've yet to use in anger!!).  I ended up with several layers of opal acrylic in order to stop the "dark edge" due to the DSLR shutter.

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Let us know how this works out, Rob. A possible difficulty with 'white' LED lights is that their spectrum will probably not be continuous, but rather a mix of two or three discrete colours with gaps between that gives an overall subjectively white appearance - not the same as an E-L panel spectrum. I'm interested to know if this actually makes a difference in practice.

Adrian

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Let us know how this works out, Rob. A possible difficulty with 'white' LED lights is that their spectrum will probably not be continuous, but rather a mix of two or three discrete colours with gaps between that gives an overall subjectively white appearance - not the same as an E-L panel spectrum. I'm interested to know if this actually makes a difference in practice.

Adrian

Yup, this is the thing. However, on more or less parfocal filters I no longer bother with individual flats since a lum flat seems to fit all quite happily.

Olly

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I see no reason at all why it would make any difference, if light can make it through the filter, it doesn't matter at all what colour it is, as long as there's enough illumination to shoot the flat. Flats are monochrome anyway.

I'm going to pop down the obsy now and shoot a few.

Back later with some proper results :-)

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Well, I went to try some flats and my filter wheel appears to have lost it's mind! The initialisation is taking ages, then it just keeps going round the filters continuously.

I did shoot a couple though, as I disconnected the wheel and pushed the filters into place manually, although I've no idea what filters although one of them was a narrowband one from the difference in light levels.

Very even illumination, and good flats.

The A2 is only just big enough for my 12 inch RC though.

The surface is very reflective being glass, so you either need to shoot your flats with no extraneous light around, or put some opaque film over the panel, which is what I'll probably do anyway.

Back to SX for the filter wheel !!

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I bought an A2 sized LED light panel- you need A2 for a 12"  scope.

It was similar to this one but second hand so a bit cheaper. The eveness of illumination seems good even with the larger apertures.

A trick you can use while taking flats with these is to move the panel around during exposures to even out field still further.

Here's a stretched range flat (12" F2.9 Newtonian) with said LED panel

Dsir8785_12inchf28_zpse5088224.jpg

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I see no reason at all why it would make any difference, if light can make it through the filter, it doesn't matter at all what colour it is, as long as there's enough illumination to shoot the flat. Flats are monochrome anyway.

If you're shooting mono through broadband filters it might be OK, since you can vary the exposure length between filters to ensure you get the same amount of signal in each.  As Olly said above, you could still have problems if you are shooting through narrowband filters; LEDs do not give out a continuous spectrum, rather they emit in one or two (or maybe three) very narrow bands.

This is due to the quantum nature of the beast (the electrons can only jump specific band gaps in the semiconductor in the diode, so they only give off photons of very specific wavelengths).  'White' LEDs are usually UV emitting LEDs treated with a phosphor that converts the UV to a visible wavelength, similar to old-style fluorescent tubes and modern CFLs.  They appear white to the human eye, but again you'll find they only emit a limited set of wavelengths which may not cover some of the narrowband filter bandwidths.

If you're shooting OSC (e.g. DSLR or CCD with bayer filter), then you're almost certainly going to have problems.  You can only use one exposure length for all three channels, and you'll usually find that at least one (if not two) channels will be much noisier than the others since there is virtually no light coming through at that wavelength.  Which channel depends on the LEDs in question.

I've had several attempts at building LED powered lightboxes for OSC cameras, and all have been failures.  I tried two different types of 'white' LED, both of which were very dim in the red channel leading to massive additive noise in that channel post-flattening.  I also tried some tri-colour LEDs (R,G and B LEDs packaged in to a single housing), same problem with much weaker red.

Finally I tried (very, very hard) to get separate R, G and B LEDs with similar output ratings, and added mini-potentiometers to the set-up to adjust the output of each within the available specification. Even this was a complete bust - I just cannot get decent output in red, or dim the green/blue LEDs enough (beyond a certain cut-off point they just stop emitting altogether).  So I'd be surprised if a non-designed panel just happened to have a well matched RGB output suitable for OSC cameras.

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The fact is, if you can see the light through the filter, then it's fine for doing flats. The NB filter I tried yesterday had no problem allowing enough light through. I'll take practical experimental evidence over theory any day. I tried it, and it works. I can see how there might be a problem with some very narrow bandwidth filters, such as 3nm, but my Baader 8 nm filters don't seem to be affected.

I must say, that of all the methods of flat framing I've tried, I find that sky flats work the best, but that's often not practical. Where my obsy is, there's a busy public trail into town, and opening the obs in anything but the dark isn't something I like to do, for reasons of security.

Also, you may need to remove your camera etc mid session, so being able to shoot flats at night is really handy too.

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Okay....filter wheel is fixed (the backplate had come slightly loose, so the filter carousel had dropped slightly and wasnt sending the correct position info) and flats taken.

both sets are a stack of 20 subs. Ha and Luminance.....they look the same as my skyflats.

post-1757-0-56422000-1402325118_thumb.jp

post-1757-0-62865200-1402325136_thumb.jp

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Is that dark bottom edge credible, Rob? I guess it will be or you'd have mentioned it. I sometimes get the opposite, a light edge, and I know this isn't right. It seems to arise when I shoot panel flats in light conditions, though I have never found out why. I always do panel flats in the dark for this reason. They can be a business, flats!!

Olly

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I always get the dark edge with the 460, SX wheel, OAG and RC Olly....no idea why but it doesn't have any negative effects so I'm not bothered by it :-)

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