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Flats, Brightness & EL Panel

Mav359

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Mav359

Mav359

Posted
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Hi guys

getting ready to build a light box and was searching the forum for ideas when i came across a link for EL Panels.

1) Anyone use them? Any good? Did you Mod them in anyway or just lay them over the top of the Dew Shield?

2) Does the brightness of the light source matter as long as its uniform?

3) Laying them on top of the Dew shield means turning the scope vertical, i thought flats were suppossed to be taken at the same time and orientaion as the lights?

:)

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ollypenrice

ollypenrice

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After my no name French electronics outlet panel croaked at an early age I went for a Neumann panel with known spectrum. Gerd Neumann jr.-Aurora Flatfield Panels-

It gives perfect flats, narrowband included. Herr Neumann warns that not all panels will do likewise.

Where your telescope is pointing matters not a jot. You are photographing your telescope's own light path, nothing else. It can't see past the glowing panel sitting on top of its dewsheild so it doesn't care about what it might otherwise be looking at!

You can adjust exposure times to get about half way up the well depth of your camera. I would leave bitter wrangling about whether it should be one third, one half or two thirds to more abusive forums. I find it makes no difference that I can see.

Given the cost of one's kit and the importance of good flats I would say put your hand in your pocket...

Olly

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MartinB

MartinB

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I have an Earlsmann panel EL Panels which covers my 10" SCT. The panel itself is very flexible so I sandwiched it in polar white perspex.

The Earlsman has a slight pink colouration but isn't a problem.

I also have one of Gerd Neuman's panels for smaller scopes. This is a fully made up product but a lot more expensive. Gerd makes big claims for the spectrum of his panels but I can't see that this is anything but hype. This panel is brighter than the Earlsman and the light has a blue tinge.

I have found my panels to be a fantastic way to get good reliable flats, far easier than other methods I have used in the past

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todd8137

todd8137

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to be fair all i do is put a whit tshirt over the end of the scope and point the scope at the daytime sky works welland has never given me any problems yet,my dad suggested to get some strips of led lights to make a light box he tried it and it works for him but still a t-shirt and the morning skies work for me

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obscura

obscura

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Hang on. How do you judge 33%, 50% well depth?

I looked at these and for the EL panel I did get concerned at some reports of shocks from them and flimsy connectors. For a 3" frac, I thought at the end of the day the price differential between the Gerd and the EL was minimal.

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ollypenrice

ollypenrice

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I just use a laptop screen with notepad open, I would rather spend the cash on something else and besides this works very well for me :)

Mine wouldn't give me an Ha signal. Does yours?

I can't get T shirt flats to work at all, either. I get gradients and light leaks, maybe because the sunlight is so strong here, I don't know.

You can look at the histogram to see where the peak comes.

Olly

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MartinB

MartinB

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For the Earlsmann panels you do need to reinforce the lead into the panel with duct tape. The big price differences come when you want to use with larger scopes.

It is important that flats are taken with the chips linear response range. For most chips the response to light stops being linear at brighter levels. If you want to be really **** about things you should be familiar with the well depth and the gain and this will enable you to work out a safe max level for flats. In reality this data isn't always readily available for DSLRs and you should just make sure the histogram isn't creeping too far over to the right.

Dimmer flats work very well, you just need more off them. As a rough guide, for 16 bit CCDs, aim for 1 million ADUs. May be better to go for more dimmer flats than fewer bright ones.

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MikeWilson

MikeWilson

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post-18683-133877630455_thumb.jpg

I use a Gerd Neumann EL Panel. It's excellent, very bright indeed.

With a QHY8L OSC CCD and a 6" f/5 Newt, I need 15ms (0.015s) exposures to get an ADU value around 20k. You can check this by taking a sub and then inspecting the summary values in FITS liberator.

Narrowband takes much longer, but I get more or less perfect flats now.

Best,

Mike

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daz

daz

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Hi guys

getting ready to build a light box and was searching the forum for ideas when i came across a link for EL Panels.

1) Anyone use them? Any good? Did you Mod them in anyway or just lay them over the top of the Dew Shield?

2) Does the brightness of the light source matter as long as its uniform?

3) Laying them on top of the Dew shield means turning the scope vertical, i thought flats were suppossed to be taken at the same time and orientaion as the lights?

:)

I use an DEarlsmann EL panel sandwiched between two semi-opaque sheets for my ED80. I found the panel on its own was actually too bright for the clear/r/g/b filters and the semi-opaqueness gives a nice difusion. I am building one for my 12" as the price for the panel to fit that is quite prohibitive!

WRT orientation, etc, it is important that nothing changes in the light path between lights and flats, not (as Olly says) where the scope points.

So, if you were to change the orientation of the camera you would need a set of flats for before you moved it and for after you moved it.

What most people tend to do is to take all the lights, and then do flats/bias/darks during the packing up phase, or in the observatory with the roof shut (as I do). There is an argument that you should take the flats when you change filter but this would of course eat into time available for the lights!

Calibration frames will make a huge difference to your images, so its worth a bit of effort/cost to get them right.

;)

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MikeWilson

MikeWilson

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Cheers for all the advice guys, the light panel deffo sounds the best option i reckon

It is!

If you can get a nice wide uniform light source it works great. I was using my iPad for a while before I got the EL panel - it did a perfect job. After moving to the Aurora EL panel I had problems. Those problems were caused by light ingress into the filter wheel (that didn't happen to a noticable degree with the iPad display).

I couldn't get consistent lights using a laptop TFT.

Anyhow, using an artificial light source for flats has to be the way to do it if you're using a CCD and have to specify the exposure parameters. If you're using a DSLR, the t-shirt and sky method work fine.

Best,

Mike

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  • 2 months later...
MikeWilson

MikeWilson

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Anybody else's Neumann panel look stripey? I noticed mine doesn't appear entirely flat last time I switched it on. Do they need to warm up, or is it normal, or have I just got a duffer?

Stripy? Can you take a picture of it?

Mine is flat and very, very bright.

All the best,

Mike

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