G2V filter calibration with a Gerd Neumann EL Panel?

[MikeWilson]

What an interesting thread.

I'm not sure about the spectrum of the GN EL panels either, having had mine out of action for a while (the damn wire broke, but I've fixed it now). Wouldn't the whole concept of imaging GV stars add more time and complexity to your nightly imaging that could be better spent getting more time on the target?

Is there much of a benefit to this type of calibration given that you're almost certainly going to want to adjust levels and colour saturation in PS anyway?

Just a thought

Good luck with the project, Andy!

Mike

[AndyUK]

Cheers Mike - I don't "think" this needs to be done that frequently... but as it happens last night's test (using the supposed values above) didn't come out quite as I'd anticipated! I'll certainly give Rob's "white card" a go (as that seems pretty simple too!), but I have a feeling there's no substitute for doing it the hard (proper?) way...

You're obviously right that you can tweak the colours almost any which way you like in PS... I was just hoping to see if by performing a G2V calibration it would reduce the amount of colour tweaking in post-processing and give me better star colour straight out of the blocks.

(PS Glad you got your panel fixed!)

[swag72]

How did it go then last night Andy?

I have recently done a G2V calibration and my thinking behind it is that I will probably still need to tweak things, but the more I can get right out of the camera, the less fiddling I have to do in post processing.

[AndyUK]

How did it go then last night Andy?

In short, I managed to avoid magenta... but ended up with yellow! I managed to mostly salvage it, but I had a few other issues / tests to perform last night as well... not all of which had a positive outcome, but I know what needs doing (and I think I might even be able to do it myself!)

[MikeWilson]

In short, I managed to avoid magenta... but ended up with yellow! I managed to mostly salvage it, but I had a few other issues / tests to perform last night as well... not all of which had a positive outcome, but I know what needs doing (and I think I might even be able to do it myself!)

Sorry to hear about that, Andy. Sounds like the calibration is adding unwanted colour cast rather than correcting.

[AndyUK]

Cheers Mike - I'm not going to proeed with this EL panel experiment further as it certainly did induce a colour cast. Basically not enough blue at all (despite the ADU output recorded with the panel) - The way I salvaged it was by tweaking the blue back in via curves. I don't think I can call it a failure though, simply an experiment with a -ve outcome!

[MikeWilson]

Cheers Mike - I'm not going to proeed with this EL panel experiment further as it certainly did induce a colour cast. Basically not enough blue at all (despite the ADU output recorded with the panel) - The way I salvaged it was by tweaking the blue back in via curves. I don't think I can call it a failure though, simply an experiment with a -ve outcome!

"If I find 10,000 ways something won't work, I haven't failed. I am not discouraged, because every wrong attempt discarded is another step forward." - Paraphrasing Thomas Edison.

And.. you've saved me some time by putting me off trying this one

All the best,

Mike

[AndyUK]

Thanks Mike! If it had worked, it would have been oh so easy (and also for anyone with an EL panel). I do still have one last thing to explore with the panel as I've also been advised that the effect may not necessarily be linear across the ADU values... However, as they look pretty similar at both c. 22k and c. 60k, I'm predicting a similar ratio result at 40k.

(I'm still very intrigued to try out Rob's solution with the white card at midday though! )

[RikM]

Does Baader solar film mess with the spectrum or just cut it all at the same rate? I would find it easier taking a shot through a WL filter rather than pointing at a piece of white card ? Do you need to hold the card (accurately) perpendicular to the OTA?

[RobH]

Sounds like you're making the easy look impossible

Just point your OTA roughly perpendicular to the card and do a couple of exposures (you'll have to stop down the aperture probably...I use aluminium foil with a hole in the centre).

White is white....if it looks white then it is white....just balance to that.

It's a repeatable, reliable method.

Rob

[AndyUK]

Cheers Rob - I hadn't considered the aluminium foil bit - Good idea!

Although I know you said you took yours in the summer, would I be right in saying that midday(ish) any day about now would probably be sufficient, and does it actually need to be sunny? I recall from my photography days that a flat light was sometimes best... but I forget what it was best for!

[RobH]

No, it doesn't need to be summer, and it doesn't need to be sunny either.

Just make sure that the card isn't getting any secondary reflection from a brightly coloured wall or suchlike.

Rob

[AndyUK]

Fantastic... Thanks!

[andrew s]

I see the thread has moved on but I have a Gerd Neumann EL Panel and a spectroscope! It has a smooth continuous spectrum but it is double humped and nowhere near approximates a G2V star.

I hope that helps.

Andrew

[RobH]

Thanks Andrew....very useful info

[AndyUK]

Thanks Andrew - That's very useful to me too... I now know that it wasn't me making an error (other than making the assumption that a G2V star and the GN EL Panel might have the same output )

[Sp@ce_d]

No, it doesn't need to be summer, and it doesn't need to be sunny either.

Just make sure that the card isn't getting any secondary reflection from a brightly coloured wall or suchlike.

Rob

This sounds much the same as setting white balance on a dslr for instance?

[RikM]

This sounds much the same as setting white balance on a dslr for instance?

That's exactly what I am going to try. Setting a custom white balance for a G2V star with my LP filter in place

[swag72]

Andy, just get out there and find a G2V star!!!!!!

[AndyUK]

Andy, just get out there and find a G2V star!!!!!!

... But it's raining... ... (and I'm lazy !). To be honest, I'm going to try and do both (just to be ever so sure), as at the very least it might help wean me off the handset - I reckon tracking one of those little fella's down will be much easier with EQMOD

However the "white card" will be my first port of call - I'll be intrigued to see how different the ratio comes out from the EL panel and I can test that out in daylight (if the rain lets up!)

[Uranium235]

Not sure if youve already seen this, but there is an Astrodon tutorial on how to do it:

Astrodon Astronomy Filters - G2V Tutorial

Basically, the higher up the star, the better. A complete list of G2V stars is available here:

G2V Star Catalog

[Uranium235]

I'm not sure about the spectrum of the GN EL panels either, having had mine out of action for a while (the damn wire broke, but I've fixed it now).

Exactly the same thing has happened to mine, the power cable is really quite flimsy and breaks quite easily - maybe GN should re-design this part of the panel as its quite poor.

Havent been brave enough to take it all apart yet because the wire has broken just where it enters the panel

[AndyUK]

Cheers Rob...

[MikeWilson]

...at the very least it might help wean me off the handset - I reckon tracking one of those little fella's down will be much easier with EQMOD ...

I'm pretty sure we had a deal on, didn't we Andy?

Mike

[AndyUK]

I'm pretty sure we had a deal on, didn't we Andy?

Mike

hmmm... yes.... . No excuse other than weak will power (and a little impatience). I'll have to use if to this G2V stuff, and with shorter nights now coming, I'm sure a night of visual hopping will help convert me fully... (I've just see the weather forecast - Rain until at least the end of the month )