More test images with QSI 683wsg

[SkyViking]

Hi everybody,

Last week we had a sting of lovely clear nights here, so I managed to get some more testing and tuning done with my new camera.

First up is a deep imaging test of the Antennae colliding galaxies (NGC 4038/4039) taken with the QSI 683wsg-8.
Image is here: http://www.pbase.com/rolfolsen/image/142471748/original

This was the first attempt at some deep imaging to see what the camera could pick up under suburban Auckland skies. Total imaging time was L:350 R:50 G:50 B:60
The image is a 100% crop of the central area of the frame because the coma was still not fully corrected. This was because I calculated that I needed a 6mm T spacer in order to bring the Baader MPCC to 55mm from the CCD chip. The spacer arrived but it turned out I still needed about 0.5mm more which I later added temporarily by cutting a thin plastic wafer and fitting it on the thread of the 6mm spacer.
There seems to be some vertical banding in this image, I'm not sure where it came from. I haven't seen it in any of my other test images.:shrug:

The second image is taken after I added the 0.5mm temporary spacer. This time of Centaurus A but only a stack of 4x10min luminance frames and one each of 200s in RGB (Clouds interruped this session early unfortunately).
Image is here: http://www.pbase.com/rolfolsen/image/142471747/original

As the image shows, compared with the first tests stars are now very close to being evenly focused from edge to edge, I think it's good enough for now. However there is still evidently some guiding inaccuracy to deal with. I suspect upgrading my old standard Losmandy RA/DEC worms on the G11 will help with this.

Overall I'm very pleased with the results, and there is some good detail visible in the core of the Antennae so there is definitely a lot of potential with this camera. I also ran the cooling entirely at -30C without problems. Based on this I expect to be able to do -35C or even -40C in winter here but I don't know if that will be necessary.

Regards,
Rolf

[cventer]

That shows a lot of promise. Once you get guiding nailed those images will be spectacular.

Love the colliding Antennae galaxies. Your color processing is great. What LRGB filters are you using ?

[alpal]

Good start.
Are you using an OAG?

[bmitchell82]

Ide say your not using the OAG yet because those issues do not come into play unless you have some really shocking wind or your setup is that far out of whack.

That also looks like flexure why? because i have seen it before with the same smearing of the image. Rolf if you are using a guide scope ditch it unless your 10" is impartial to flexure which generally they are not in one form or another be it tube/mounting/accesories. Thats why when ever i see people with 8"+ newts, unless they are high end construction, then its OAG all the way!

As for the images they are looking nice, the Antenna have been my bane so far every time i have looked at them i have been thwated one way or another!

Brendan

[SkyViking]

Thank you, I'm using the Astrodon Tru-Balance Generation 2 E-Series. I'm very impressed with them, seems like excellent quality and very easy to work with.


Thanks, yes I'm using the in-built OAG.


Thank you Brendan, I am using the QAG but I have since made some adjustments to my setup. I knew my polar alignment needed a bit of an update, after all the work I did when I built the new truss tube OTA it must have come slightly out of alignment. After polar aligning again the guiding now seems much tighter. I also switched to using the guiding in Maxim rather than PHD, and what a difference that made! Some more work on collimation also paid off, so I'll post an update with some new images soon.

Thanks all for your comments so far.

[bmitchell82]

Ahhh :) then it was that far out of whack.

Tip:

Maximdl guiding.

If you do not have a perfect L shape.... start again. the star should land within a pixel of its original starting spot apon the conclusion of the calibration. Polar alignment is the key to this point + lack of wind...

Get your calibration somewhere in the east/west and try to do it within 10-15 ticks the quicker the better!

Guide with 2x2 binning. don't ask me why it just works better!

Maxim will use the same calibration anywhere in the sky without issue one calibration to rule them all!

I know you know a fair bit about it all but this is my little blog about guiding and some of the errors that cause grief!

http://brendanmitchell.net/?p=386:thumbsup:

[Peter Ward]

There looks to be some (subtle) vertical banding in the the Antennae colliding galaxies image....which would concern me... hence you might want to investigate the cause a little further while the camera is still under warranty.

I little more attention to focus, guiding and RGB registration and you'll be producing top shelf results :thumbsup:

[SkyViking]

Thanks for the link Brendan, that's an excellent summary there - it pretty much sums up what I have learned over the last couple of clear nights.
I think the 2x2 binning allows for a more accurate stellar profile, if the guide star is relatively faint, and hence as a result more accurate guiding probably? I've noticed too that it seems to work a lot better this way. Also, in PHD I can't bin the guide cam, but in Maxim I can, which means I can now comfortably use 0.5s guide exposures and guide with a higher frequency, just another benefit.

[SkyViking]

Thanks for your comment Peter. Yes there is some banding evident. I think it might be due to calibration issues - so far I have let Maxim take care of it and automatically handle the set of calibration darks, bias etc. But I probably need to check that it's doing it correctly. Just as a test I'll try stacking again without calibrating and see if there is a difference, to pinpoint the issue.

[strongmanmike]

Nice steady improvement there Rolf :thumbsup:

It's great following your new journey.

Brendan is well versed in all the trials abnd tribulations of ATM newt imaging and he is the man to look to for advice..not that you aren't capable of course ;)

Mike

[gregbradley]

I agree with Peter that banding may be a defect. I doubt it is related to callibration and more to do with the adjustment of the timing in the chip electronics. Does it only show up when the image is stretched heavily?

Perhaps it is always there but fades into the background unless heavily stretched.

Greg.

[leinad]

Check your 2x2 bias frames and master bias , and calibration routines.

Join QSI Yahoo group; get Kevin's input.
QSI have pretty solid QA testing, and always helpful to assist.

[alpal]

It's strange that the guiding was that far out.
You must have something loose in your system - maybe tube rings,
counter weights or mirror?

When I finally used an OAG with my 8" Newt with proper saddle plates,
tube rings & a proper counter weight holder & bar I got excellent guiding
except when wind hit the OTA.
I'm using PHD guiding.

[marc4darkskies]

Fix your guiding problems and you'll be smokin' Rolf! :thumbsup:

Cheers, Marcus

[SkyViking]

Thanks all for your comments again.
A quick update: Banding issue doesn't seem to be related to calibration, but I now suspect me not having taken any flat fields yet may be the cause?
Unfortunately I haven't been able to sneak out to the obs and take flats during twilight but I have ordered one of the Aurora panels for this purpose so I'll know soon enough.
It's only very subtle variations across the chip but it does show when the image is stretched. Attached is a screen shot of how it looks in Maxim with a stack of 10 frames. There is both vertical and horizontal banding. The pattern seems to be identical in every frame so should be possible to get rid of with proper flats I suppose. On this occasion the full Moon had just begun to cast a nasty gradient over the field but at least that made the banding easier to spot.
Fortunately the stars are much tighter now thanks to Maxim's guiding abilities. :D

Also attached is a quick shot of open cluster NGC6231. This is from before I improved the guiding, but I still thought it turned out reasonably well for a test image. It's clear though how the colour is not flat fielded properly, I just used the DBE feature in PixInsight on each channel but it was obviously a little off.

[leinad]

Sent you a PM Rolf.

[SkyViking]

I spent this evening taking 'pseudo' flats with the camera just pointing into an evenly lit wall. I tried a couple of different things to pinpoint the cause of the banding:
*Using a brand new 1m USB cable instead of my old 4m cable that runs under the obs floor.
*Running it through a USB hub or not.
*Connecting the QSI power adapter to another power point.
*Connecting the QSI power adapter to a 110v adapter

I created a stack of 20 flats for each configuration. Result: All have exactly the same banding pattern... so it must be a property of the chip I guess. Maybe that's just how ccd chips behave?

The good news is that when I then divided one of my stacked light images with the stacked pseudo flat the banding disappeared completely. :D
See attached screenshots: First image is a corner of the psudo flat showing the banding pattern, second is light image before flat fielding and finally after applying the flat (Ignore the gradients, that was still because of the full moon...)
So the problem seems to be solved, I just need to take proper flats now and add them to the calibration routine.

Though I'm still curious to know if this banding is something others have seen too? I can't find any mention of it on the web.

[Paul Haese]

Hi Rolf, looks like you are making good progress.

Your dark frame looks pretty similar to mine. Mine has bands but I don't get banding showin up in my images. Not sure what is going on there. Might well be a calibration issue.

Guiding looks like it has improved out of sight. Looking forward to that first cracking image.