QHY10 first light and some questions

[Garbz (Chris)]

Well I got a QHY10 the other day from the classifieds forum. So far I'm quite happy with it. A single 2min frame of Eta Carina exceeded what I was getting even with several hours from a previous attempt. Anyway some great pictures are attached, great in the quality of the camera only, the telescope setup attempt was crap as you can see by the wonderful focus and the mirrorflop that wasn't corrected.

Anyway question. The pictures had 10 bias and 20 dark frames taken with the same offset and gain settings as the light frames, all stacked in DSS. When I open the images in PixInsight and do a basic stretch they come out VERY green.

So the questions I have is, where does the green come from and what's the best way to get rid of it?
The attached pictures were fixed using dynamic background extraction followed by SCNR to eliminate the residual green. Somehow I think the picture shouldn't have been green to begin with.

Any tips?

[E_ri_k (Erik)]

Hey Chris, great images! I can't see any green in your images at all really. My images with my QHY10 have a slight green tinge to them also, but it is easily removed in PI and/or PS.

Can you post a version where you didn't use the SCNR tool, just to show how bad it is?

As far as I know the green comes from the bayer film on the sensor. For every red or blue pixel there are two green ones.

Erik

[carlstronomy (Carl)]

Chris that first image is a cracker, great detail.
With everything set up just right you images should look really good. Cant help much as I am using a DSLR for my imaging.

Carl

[Garbz (Chris)]

I've heard this may be due to the beyer matrix before. In which case I'm also wondering if I'm removing the green correctly with dynamic background extraction or if I should be using some other method. SCNR is only really used to get rid of some residual green towards the end of the processing so I'm not worried about that, actually I used SCNR on the green channel with my DSLR too.

I've attached a picture of my workspace with the two images opened and an auto stretch applied.

If I open a single frame pre stacking and apply a debeyer the results are even greener indicating some of it was removed with dark frame subtraction.

[E_ri_k (Erik)]

That's pretty green Some of my images have been a bit like what you have there, but not quite as bad. Mostly only AFTER a stack though. Cant say I ever saw much green in a single raw frame? I haven't had anything that bad for a while though? SCNR or HLVG (in PS) always took care of it though. Maybe run SCNR a few times?

Not sure what's going on with your dark frames though?

If those tool takes care of it, like it looks like it has I really wouldn't worry about it.

A bit strange that the Eta Car is not as green as the Tarantula though?
Erik

[E_ri_k (Erik)]

Just for comparison, these are single un-calibrated frames, auto-stretched. The one on the left has not had SCNR applied, but the right has. Still not as bad as yours tough?

Erik.

[Garbz (Chris)]

Well they may actually be equally green. Eta Car and the Tarantula both have different stretches applied. As said it's just an autostretch and both targets have a different brightness.

Single frame Eta Car attached. Not as bad as yours. I wonder if this could just be unfortunate light pollution. I noticed my image autostretched doesn't appear to have as much contrast as yours, and eta car is close to the city centre from my perspective (not to mention it's full moon in a few days).

Sorry to bombard you with questions but how do you capture your images? Ezcap or nebulosity?

My results were 180 seconds with gain 17 and offset 123. I did my bias and dark frames with the same gain and offset settings and with the cooler temp set at -15degC. 10 bias (just zero second shots) and 20 dark frames.

[E_ri_k (Erik)]

Originally Posted by Garbz

Well they may actually be equally green. Eta Car and the Tarantula both have different stretches applied. As said it's just an autostretch and both targets have a different brightness.

True, perhaps light pollution and the moon is washing it out a bit, and it's being picked up as green?

My sub was 600 seconds. With this image I was playing with the Gain and Offset, I had a Gain setting of 0, and Offset of 122 (That's a different discussion though, I now use Gain 22)

All good, keep the questions coming I am using MaximDL to capture. I usually have the cooler at -20 and I also shoot calibration frames with the same Gain and Offset.


Also, I'm not sure if the DBE tool will remove the green, I thought it just neutralises the background of any gradients? Then use the SCNR tool after? Thats what I do anyway.

Erik

[h0ughy (David)]

just a tip - your sensor is not sitting in the focuser properly as there is a small focus problem, one side is in focus or near it, and the other has fat bloated stars. work on your focus as you get it right your data will be easier to process later. your well on the way.

[Garbz (Chris)]

Erik yeah could be the light pollution. If the light is white (moon) then the increased sensitivity to green of the camera may cause it to be picked up this way. I'm not confident in my guiding to get 600s frames.

My next investment is either a proper guidescope rather than a finderguider, or an OAG module.

DBE does remove the green just fine. It removes any "background" and in this case it picks up the background as green. I was more wondering if it's normal for them to be green to begin with.

Originally Posted by h0ughy

just a tip - your sensor is not sitting in the focuser properly as there is a small focus problem, one side is in focus or near it, and the other has fat bloated stars. work on your focus as you get it right your data will be easier to process later. your well on the way.

Yes I noticed that, though I thought it was the result of not knowing the software and inadvertently focusing on a star that was no where near the centre of the frame. My field is anything but flat, something that I still need to solve. I've got the camera directly threaded into an adapter and directly to the back of the scope so any lack of flatness is either my mirror or the QHY10 itself. Either way the QHY10 came with a tilt adjusting ring so I may make use of that.

[gbeal]

My comment is master the OAG.
Don't heap too muc blame on the finder-guider though, it is more than adequate, unless you are imaging at 2500mm plus, which I doubt.
In my case I use an old 6x30 finder, solid mounted.
Keep at it.
Gary

[Garbz (Chris)]

It may be I haven't finetuned my settings properly but I have heard good effective guiding shouldn't exceed 10:1 focal length for really accurate guiding. My 50mm finder works well with my f/6.3 reducer but I see noticeably oblong stars when shooting prime at just over 2000mm.

Just read a thread about guiding through a guidescope so I'll have a play when the moon disappears and see if I can push my exposure up a bit.

[johnnyt123 (John)]

Going back to the green issue.
i get severe green subs with my camera

it is an Orion Starshoot Deep space colour ccd imager pro v2
I thought it was normal and just had to level it in PS.
So you are all saying it shouldnt be happening.....

the longer the exposure the more rediculously green the raw images are.....

John

[allan gould]

Sorry but this is a known phenomenon with the qhy10 in that it's due to the way the camera downloads the frame. It does red to the right and green to the left of the frame. Blue goes with the red (I think). Anyway that gives a weird colour cast to UNCORRECTED frames in that they have a green cast to them. It has to be corrected with bias frames which contain the same colour gradient. There is nothing wrong with the camera it's just the way the pixels are downloaded from the chip.
Hope this helps
Allan

[Garbz (Chris)]

Interesting. This is actually post correction. The bias didn't solve the issue. Or at least not completely.

In a slightly related note I've been working stupid hours for the last 2 months due to maintenance activities at work. So other than doing one more repeat of Carina a few days after the first post I haven't used it any further. Will rectify that as soon as we get clear skies again :-)

[allan gould]

I should have added that you will also need well done flats as well to correct this as well.
Allan

[Garbz (Chris)]

You just got me thinking. I always though flats were used as a lightness map only?

I've typically pointed the telescope at the ceiling and fired off a shot after an imaging session. This works nearly perfectly for vignetting. I've also heard of people shooting at dusk to get their flats which in theory would give them a major blue cast.

If what you're saying is true then my room lighting could be contributing to the green. Mind you I've proved it to be quite correctable so I wasn't too fussed.