First light with QHY8L

[scagman]

Well after get my new qhy8l back in feb. I finally got out to try it out.

After wasting the whole night triing to get a good polar alignment I gave up and went with what I had and just guide out any errors. Well that was the plan. PHD wouldn't play and I couldn't get it to calibrate. No movement in the star!
So in the end just point the scope at M8 and took a series of sub.(thks Alistair)

27 x 1 min &
4 x 5 min subs.
+ 31 x bias,
27 x 1 min darks &
4 x 5 min darks.

After working out howto debayer in maxim and and getting the right offsets. Which I couldn't find much info on the x,y offsets. I settled on x=0,y=1.

Also attached is a 1 min and a 5 min sub. and a blue rendishion that I was working with till I found an image to compare it to and realised the debayering wasn't right.

I was surprised by the differance in the 2 subs. Didn't expect birds in the 5min sub, I just thought the trailing would be longer.

When I was packing up the next day I Noticed I hadn't attached the cam square to the focuser. :mad2:.

So to sum up. very happy with the cam and the result. Just have to get PA sorted. (cant wait to get obs finished) and work out what happened to my guiding. Using maxim DL to capture and process and find it pretty good to use.

Just need some warmer nights, (dont like the cold) and some clear skies.

Cheers

[stevous67]

Hey John,

You've got some great equipment to work with, so be patient, you'll get there. I have to recommend that you join a club. There your polar alignment issue will be resolved with some helpful assistance and advice - I have no doubt.

Your first images are great. There's a great potential there for certain.

Cheers

Steve

[scagman]

Hi Steve thanks for the encouragement. I think half my problem the other night was not having the finder lined up with the main OTA. I got a new right angle finder and think when I was lining the 2 up didn't realise that the 2 images were reversed. I had differant street lights centered in each FOV.:screwy:. I spent ages tuesday night getting the 2 FOV's centered, slew to another street light (We are up high and I have a good view to the west of the town below) and it wouldn't be centered in the main OTA, so after some head scratching i realsied my error. So now when I try to do an alignment I will be able to find the disired stars:D.

Just playing around with the gain and offset and the moment which I hope will reduce the saturated stars. More research/reading.

Regards

[alistairsam]

Hi John
I have the same bloated stars as well and as you say, it might be incorrect gain and offset
As we tried the other night, I'd suggest an eyepiece in your main scope for alignment and guide camera in the main scope for drift alignment only.
I didn't think of the image inversion.
Have you tried autofocus with maxim or focusmax? Not sure if it'll work with the distant street light, worth a shot, it'll save heaps of time
Even without autofocus, try focus control by software, that'll save a few leads.

[traveller]

That looks like a great effort John, keep it up.
Bo

[scagman]

I think I have to get the gain and offset setup right before I can get autofocus to work properly as I cant get the FWHM down to a low setting, its about 12-14 after a very short exp.

I have a few questions re setting gain/offset so I'll start a new thread.

Cheers

[scagman]

Thanks Bo, getting there slooowly.

[Poita]

Gain and offset should be around 14 and 17 for gain and offset 120.

There is a write-up here
http://www.stark-labs.com/blog/files/GainAndOffset.php

[alistairsam]

Hi Peter,

How bright should it be for this step "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". that's to adjust the gain.
I tried this indoors with the camera pointing at the ceiling FL. is this OK?

when you take a bias frame to get the value below 1000, would the gain setting impact at all? from the writeup in the link, you set the offset first, then set gain. so does it matter what gain you set when adjusting offset?

[Poita]

A light source like the ceiling light, or pointed towards the window during the day would be fine.

O n my QHY8 I have the gain set at 0 or 1 and it hits 65535 just pointing at my ceiling light.

Not sure if the QHY8L is the same, I am going from notes I made when I borrowed one and had around 14 for the gain, you mileage may vary!
Ann offset of 120 will do you fine, but if you want a more detailed procedure, then run through this one:
http://qhyccd.com/ccdbbs/index.php?PHPSESSID=dd8d6cda88c3caf 2538d2d2d816d8f2c&action=dlattach;topic=2671.0;id=273 4

Brendan also has the same document linked on his resources page under "QHY9 calibration" but it is valid for any camera.
http://brendanmitchell.net/?page_id=213

Lots of other useful stuff on Brendan's page too.

[scagman]

Hi Peter thanks for that I will try those settings tonight.
The settings I got last night was gain 0 offset 123 but found the street lights 20k's away were still producing FWFM of 12+ and a max value well above 65000.
I'm using one of Peter's(Exfso) light boxes which has an adjustable brightness setting. Having the brightness turned down below half and an exp. of 2secs my max values are very high. Using 1 sec exp they're well below 65000+ mark.

Alistair, reading the QHY8L manual it says to get offset then gain, then go back and check offset again to fine tune it.

So how long an exp. should you take and how bright. As adjusting either of these changes things.

[alistairsam]

Thanks,
That article by Todd and Felix was very good.
Can you view image mean values in Maxim?

[Poita]

Page one of the Todd and Felix article shows how to determine the minimum length of time to fill the pixel wells.
I'd have it bright enough to try and have that exposure time be under a second for your camera.

[Poita]

For Maxim, use the information command to get your averages, see this guide for details:
http://www.todman.id.au/astronomy/determining_qhy8_gain_&_offset.htm

[scagman]

Well after reading thru all the above links last night I went thru the exercise by Tod & Feix here http://qhyccd.com/ccdbbs/index.php?P...2671.0;id=2734 (http://qhyccd.com/ccdbbs/index.php?PHPSESSID=dd8d6cda88c3caf 2538d2d2d816d8f2c&action=dlattach;topic=2671.0;id=273 4) I ended up with a gain of 7 and offset 112 using the light box turned up to its brightest setting and an exp. time of 5.12sec. I dont have the data handy to get the exact numbers but the graph at the end looked similar except I have a very prolonged taper to reach the 65535 ceiling. I needed to goto .575- .6 sec exp. time to for the ave. to reach 65535, but the max value was getting there when the ave. was around the 40000 mark i think.

I will try tonight using the ceiling as the light source and see if that will allow me to get the exp. time down to under a sec. exp. time.

Why does everything always sound so easy when you read about it!!

Regards