QHY9 First light

[RobF (Rob)]

Over Christmas & New Year I thought I'd start a spreadsheet comparing various CCD specs, advantages/disadvantages, price, size, weight, pixel count, FOV, etc. Just in case I ever seriously considered going to the "dark side" from my trusty 450D.....

WARNING! - starting such a spreadsheet can be hazardous to your bank account!

It wasn't until I did the exercise that I realised how close the KAF8300 chips are to APS-C chips in pixel size and FOV, and why there is such interest in the newer SBIGS, QHYs, etc. After seeing some the very competitive prices on offer at the moment an idea started to form in my mind - just how much could I afford, and how important to me was my imaging?....

Anyway, the QHY9 + filterwheel and LRGB filters for $3000 before March 2010 was too nice to pass up. I was lucky enough to snare a camera in Theo's last delivery, so a week later I found myself the owner of a new QHY9 and trying to figure out what the heck "Gain and offset" are.

With help from Robin and Alex (and faultless and rapid support from Theo) I had learned enough to attempt my first shots on Saturday at Peter's (10 Chain Hill observatory outside Brisbane).

I'm still in the process of collecting suitable bias and dark frames, let alone figuring out what software to use for stacking etc, so I haven't processed much of the 4 or 5 objects I attempted. However, I did want to share my "first light" rite-of-passage on M42 and a more serious attempt on the Leo triplet, so here they are.

I'm looking forward to everything I'll need to figure out now to climb the LRGB mountain, but very happy with the initial sensitivity and resolution these pics offer.


1. M42/Running man (first pic taken) 1 x 30 secs, no cal, Gain 50, offset 100
2. Leo triplet, 3 x 5mins, no cal, Gain 40, offset 100

All pics mono (no filters), QHY9 + MPCC on 8 inch newt:

QHY9 pics


Also for comparison, a 30min stack of calibrated 3min images of the Leo triplet taken with 450D March last year - albeit with moderate noise reduction to help wash out light polution (no pollution filter used) and much less processing knowledge at the time:
http://picasaweb.google.com/UserRobF...41677845469922

[Hagar (Doug)]

Very nice start Rob. You should have a bit of fun with the camera. I do like the Leo triplet image, it has come up very nicely for such short exposures and only 3.

The only thing I would sugest is that you go to Craig Starks web site and read his directions on setting the gain and offset for any camera. After reading his explanation you may want to reduce the Gain figure a little bit.

Taken from the Nebulosity owners manual, but it is relevant for whichever software you use. Bare in mind the well depth of the QHY9 is 25.5Ke.

How to set Gain and Offset then forget it.
The best value for your camera may not be the best value for other cameras. In particular,
different makers set things up differently. For example, on a Meade DSI III that I recently tested,
running the gain full-out at 100% let it just hit full well at 65,535 ADU. Running below 100%
and it hit full-well at 40,000 or 30,000, or 10,000 ADU. There's no point in running this camera
at anything less than 100% gain. On a CCD Labs Q8-HR I have, even at gains of 0 and 1 (on its
0-63 scale), the camera would hit 65535 on bright objects (like the ceiling above my desk).
There's no point in running this camera at gains higher than 0 or 1.
Why is there no point? The camera only holds 25k e-. If a gain of 0 or 1 gets me to 0.38 e-/ADU
(so that those 25k e- become 65535), running at 0.1 e-/ADU will only serve to limit my dynamic
range. Each single electron already comes out to more than 2 ADU.
So, to determine the gain and offset to use:
1) Take a bias frame and look for the minimum value in it. Is it at least, say 100 and less than a
thousand or a few thousand? If so, your offset is fine. If it's too low, boost the offset. If it's high,
drop it. Repeat until you have a bias frame with an offset in, roughly 100 - 1000. Don't worry
about precision here as it won't matter at all in the end. You now know your offset. Set it and
forget it. Never change it.
2) Aim the camera at something bright or just put it on your desk with no lens or lenscap on and
take a picture. Look at the max value in the image. Is it well below 65k? If so, boost the gain. Is
it at 65k? If so drop the gain. Now, if you're on a real target (daylight ones are great for this) you
can look at the histogram and see the bunching up at the top end as the camera is hitting fullwell.
Having that bunch-up roughly at 65,535 plus or minus a bit is where you want to be. If you
pull up just shy, you'll get the "most out of your chip" but you'll also have non-linearity up there.
You've got more of a chance of having odd color casts on saturated areas, for example, as a
result. If you let that just clip off, you've lost a touch but what you've lost is very non-linear data
anyway (all this assumes, BTW, an ABG chip which all of these cams in question are). Record
that gain and set it and forget it. Never change it.
By doing this simple, daytime, two-step process you've set things up perfectly. You'll be sure to
never hit the evil of zero and you'll be making your chip's dynamic range fit best into the 16-bits
of your ADC. Again, all the cameras in question have full-well capacities below 65,535 so you

are sure to have enough ADUs to fit every electron you record into its own intensity value.

Good luck with it all and have fun. Very nice start.

[Tandum (Robin)]

I like the triplets and only 3 shots ... not bad is it. Bugger about the wheel.

Can you run zero gain? As I said in pm, you will lose star colour if you bump it up.

[marki]

Rob, your gain setting seems very high. I used the method Doug posted here to set offset and gain on my QHY 9 and came up with gain = 15%, offset = 102. It seems to work for my camera without clipping the data so it might be worth giving it a try. My bias frame has min of 120 ADU and a max of 435 ADU. With the camera pointed straight into a light the max is 65 530 ADU.

Mark

[richardo (Rich)]

Well done Rob on your first light with your new investment!
Looks as though you'll get things nailed pretty quickly I'd say

Yeah, I've had a setback money wise with any new ccd purchase, but I keep looking around anyway!
Although the ST8300 looks to me like a great choice, however the value for money that you have with your purchase even beats this.

I'll be looking for more images from you in the future.
Have lots of fun!

Rich

[AlexN]

Good stuff Rob.. That Leo trio was hard to frame right, but it's come out nicely mate! Well done indeed...

[RobF (Rob)]

Originally Posted by Hagar

Very nice start Rob. You should have a bit of fun with the camera. I do like the Leo triplet image, it has come up very nicely for such short exposures and only 3.

The only thing I would sugest is that you go to Craig Starks web site and read his directions on setting the gain and offset for any camera. After reading his explanation you may want to reduce the Gain figure a little bit.

Good luck with it all and have fun. Very nice start.

Thanks Doug - very handy reference. I had struggled to figure out how bright the surface should be for determining max gain. I'm sure to give it another go. Theo has already recommended I rein in my Gain too.

Originally Posted by Tandum

I like the triplets and only 3 shots ... not bad is it. Bugger about the wheel.

Can you run zero gain? As I said in pm, you will lose star colour if you bump it up.

Yeah - I think I'm going to have to come back a long way Robin - you were right. I spent some time on the phone with Theo Sun night troubleshooting my sticking filterwheel, and here it is Tue and I have a brand new one sitting here on my desk.

Good support feedback I've heard here was definitely a big reason I was happy to go QHY.

Originally Posted by marki

Rob, your gain setting seems very high. I used the method Doug posted here to set offset and gain on my QHY 9 and came up with gain = 15%, offset = 102. It seems to work for my camera without clipping the data so it might be worth giving it a try. My bias frame has min of 120 ADU and a max of 435 ADU. With the camera pointed straight into a light the max is 65 530 ADU.

Mark

Thanks Mark - I was a little surprised how difficult it was to find recommended starting values via Google. Should have just posted here of course..!

Originally Posted by richardo

Well done Rob on your first light with your new investment!
Looks as though you'll get things nailed pretty quickly I'd say

Yeah, I've had a setback money wise with any new ccd purchase, but I keep looking around anyway!
Although the ST8300 looks to me like a great choice, however the value for money that you have with your purchase even beats this.

I'll be looking for more images from you in the future.
Have lots of fun!

Rich

Thanks Rich. I've certainly got plenty to learn, but that's half the fun. Wow - impressive website you have there! Weight was another major issue for me. I really couldn't afford another 3-400 grams for the heavy duty quality SBIG is renowned for with my mount and focuser even if I did have the dollars. I'm hoping the QHY9+FW behaves on my setup.

Originally Posted by AlexN

Good stuff Rob.. That Leo trio was hard to frame right, but it's come out nicely mate! Well done indeed...

Thanks for your help Alex. I was surprised how much detail I could see in the end. A thoroughly enjoyable first light!

[AlexN]

Seems we both thoroughly enjoyed our first lights on Saturday mate.. I really wanted to attack some galaxies but once I got enough Lum data on Eta I figured I may as well finish it off with a little colour... Next time hey...

[RobF (Rob)]

I ran off a decent set of bias and darks for the 40% and 50% gain settings I tried that night, so I'll have to get stuck into the horsehead and crab too now, as well as calibrating the Leo T effort.

All fingers and toes crossed for this Sat
Even though I don't have MPCC to Filterwheel adaptors, may not be necessary for the colour R,G,B exposures, as long as the L is shot manually attached to MPCC?

[AlexN]

shouldnt matter much Rob... The only thing you will want to make sure of is that your camera angle is as close as possible to the same.. coma will warp the look of the stars and make it hard to align the colour to the Lum..

Have you looked into the adapter required any further? Have any thoughts on how you are going to do it?

[RobF (Rob)]

Turns out MyAstro Shop sells male M54 to female M42 - I just didn't look hard enough. I'm not sure how soon I can get one yet - expecting the worst....

[AlexN]

I sent Steve Massey an e-mail a few days ago asking about a few things, he's not replied yet so I'm assuming he's on holidays still..

[marki]

Originally Posted by RobF

Turns out MyAstro Shop sells male M54 to female M42 - I just didn't look hard enough. I'm not sure how soon I can get one yet - expecting the worst....

I got the last one from Steve about a week ago and although they fit into the filter wheel nicely it causes a lot of vignetting. May just be my combo though.

Mark

[mill (Martin)]

Very nice first light

Still waiting for my QHY9, Maybe in 2 weeks

[RobF (Rob)]

Originally Posted by marki

I got the last one from Steve about a week ago and although they fit into the filter wheel nicely it causes a lot of vignetting. May just be my combo though.

Mark

Hmm - that's what Steve just said too Mark!
Looks like I'll be waiting a while to see if I get any vignetting....

Originally Posted by mill

Very nice first light

Still waiting for my QHY9, Maybe in 2 weeks

Thanks Martin - will look forward to hearing your experiences too.

[pmrid (Peter)]

Originally Posted by RobF

Hmm - that's what Steve just said too Mark!
Looks like I'll be waiting a while to see if I get any vignetting....



Thanks Martin - will look forward to hearing your experiences too.

That's pretty impressive Rob. I'm envious. I'm going to have a run at the Leo Triplet tonight - after a couple of hours on the Cone - the QHY8 on the back of the ED127 - should be a good combo. I have just installed a new 100mm Orion F6 guider as well so all being well, I ought to get some competitive results.

Peter

[RobF (Rob)]

Originally Posted by pmrid

That's pretty impressive Rob. I'm envious. I'm going to have a run at the Leo Triplet tonight - after a couple of hours on the Cone - the QHY8 on the back of the ED127 - should be a good combo. I have just installed a new 100mm Orion F6 guider as well so all being well, I ought to get some competitive results.

Peter

Thanks Peter. You're certainly assembling some formidable gear at 10 Chain. With your skies there's nothing holding you back now!