M13 - Great Cluster in Hercules (16th night, first light for EL panel)

[MikeWilson]

Dear all,

After my last hopeful Ha imaging targets, and since I received a CLS filter, filter wheel and Gerd Neumann EL panel - I decided to try it all out together on a couple of targets.

I set the scope to M13 and captured an hour's worth of data split between 60 second and 180 second subs. 150P + QHY8L.

I also used the Gerd Nuemann EL panel which gave me the best flats I've had so far, but I suspect that I might still have a vignetting problem on longer subs. The jury is still out on this one and I'll feed back a review after I've used it for a couple more nights to rule out any possible operator error.

I also moved the dew heater from my ST80 guide scope to the filter wheel as there's quite a gap in it which would let moist air in.. I have had a dewing problem previously but I'm not sure where.

[MikeWilson]

The Gerd Neumann Aurora EL panel:

The Brightstar 4x2" filter wheel:

(note the air gap)

[MikeWilson]

I took these photos while imaging this object and thought you'd all like to see them:

[Deneb]

glad you got it sorted Mike, are you using a coma corrector with that setup ?

Nadeem.

[MikeWilson]

glad you got it sorted Mike, are you using a coma corrector with that setup ?

Nadeem.

Yup, and it was a pain to get spaced correctly; I think I've got it now.

[AndyUK]

Nice image Mike... and nice new kit! (I still don't know why I'm dithering on buying an EL panel - All I have to do is press CTRL-T, click on the FLO favourite and press buy...)

[MikeWilson]

Nice image Mike... and nice new kit! (I still don't know why I'm dithering on buying an EL panel - All I have to do is press CTRL-T, click on the FLO favourite and press buy...)

The EL panel makes a big difference, Andy. The price jump from 6" to 8" was a little bit of a sticker shock although I went for the 8" as it's more "future proof"

The instructions make you think that it's going to be insanely bright (it isn't) and the transformer with it's machined metal base makes you feel like you're going to be electrocuted (you're not). Other than that, it's a really robust feeling piece of equipment that does give off an even glow and I'm going to put some board on the back of it and mount the transformer and cables so that I can have an "all in one" light panel with a simple 12v plug on the end.

They are very useful, lights will be consistent and can be taken any time. I've already figured out the exposure times:

Offset: 120

Gain: 0

CLS filter = 300ms

Ha filter = 10s

OIII filter = 1s

So, point the telescope upwards, pop the EL panel on and switch it on and fire off a suitable set of frames. Perfect flats in under two minutes. It remains to be seen how reliable they are (my guess is very, but I don't know about the wiring in the transformer..). I've come a long way from having to use my boxer shorts over the end of the tube (note to any future second hand purchaser of my telescope: don't worry, they were brand new from a packet!).

:-)

All the best,

Mike

[ollypenrice]

Ditto Mike. Just do it, Andy. You have all this investment and bad flats screw it all up.

Olly

[AndyUK]

Cheers Mike / Olly... I AM definitely going to order one of these (thanks for the pictures Mike!) as it simply makes too much sense... Sadly though I do have to time it - I need to be the one who takes it off the postman (), and I'm on customer sites next Monday-Wednesday. If I order one Tuesday pm, hopefully it'll arrive Thursday or Friday (and then I'll have to hope it doesn't arrive when I'm taking the dog for a walk!). The idea of being able to set standard values / filter to get the required ADU will take all the guesswork out of taking flats (and the faffing about - The last (first) flats took me about 20 mins to take!

[roundycat]

one thing you might like to consider with your ELP is to take a range of exposures, one flat only will do - we are not looking for quality. Then see how well the different exposures flatten your lights. There is a distinct problem that over exposed flats (people are always banging on about 30,000ADU or more or 'put the histogram in the middle to upper third' and neither technique makes any allowance for non-linearity in the camera.

If your flat is over exposed it will not properly correct the light and you will have some vignetting left over. The dust and FPN may well disappear. Vignettes left behind due to poor flats should not be confused with a gradient.

Once you have established the correct exposure for flats with your camera/ELP then you can take ten or more and measure the noise contribution. If that is below the basic sky background noise in your light frame there is no need to shoot dozens of flats. With noise adding the way it does sufficient flats (5?, 8?, a dozen?) is all you need. Anything else is overkill and a waste of time.

Dennis

[MikeWilson]

Hi Dennis,

I haven't got much scope to take different exposures but I will try it.

I've posted a thread especially about my current flat taking/processing difficulties and the mysterious problem therein here:

http://stargazerslounge.com/imaging-image-processing-help-techniques/145126-extreeeeeeeme-stretching-ic-1396-nellys-nose-neb-2.html#post1844000

All the best,

Mike

[AndyUK]

Hi Mike - I'm obvously not familiar with the QHY8 or its capture software, but if reducing exposure is limited, maybe overlaying the EL panel with different layers of white cloth or something would do the trick? (I guess your old (well, not that old!) boxer shorts would do the trick ?)

Dennis - Your solution sounds very logical... I've been aiming for ADU between 22-24K (as that's what I'd read somewhere), but I guess the actual ADU doesn't REALLY matter as long as the flat works for each OTA/camera/filter combo...

[roundycat]

Andy, you are right about the exact value of ADU in the flat. A lot of people have a fixation about ADU levels and histograms but if the flat is non-linear the correction will also be non-linear. The major reason for having flats at a high level is to swamp the inherent noise. Figures of 500,000 ADU total are regarded as good but if your flats do not add too much noise (compare the flat noise with the sky background noise) then you should be good to go.

I notice people posting a typical flat and asking if it looks any good. The only way to tell is to use it and see, as you surmise.

Dennis