Help!!! Cannot get my flats to work with H18 !!

[RobH]

Hello all.....like it says above, I simply cannot get my flats to work with my Stalight Xpress H18

I have wasted hours and hours of data trying to get this darned thing right, and am not far from giving up with the thing and sticking to my trusty 16HR.

This is new data taken at F10 with my Edge 11.....great detailed data that I was really looking forward to processing which is utterly unusable due to the flats issue. :mad:

The flats were taken the morning after the imaging session, and to make absolutely sure that there was no movement when the filter wheel initialised, I disconnected it.

Flats were done with an EL panel and set at around 24000adu.

New blobs have appeared, and the plethora of tiny dust particles are not being removed when the flat is applkied....there in fact seems to be overcompensation.

I'm also seeing halos around some particles

Flats were bias subtracted.

I'm completely at my witsd end with this....try as I may, I can't cure it and it means the camera is unusable unless I can get to the bottom of the problem.

Here are 3 images (stretched to display the problem)

The master flat, an image with no flat subtraction, and one with subtraction.

Help!!!!!!!!

Rob.

[robbieince]

Hi Rob

Looking at your flat, the edge marks seem to show signs of chip moisture - my atik does this sometimes. The haloes are a give away for me.

Presumably everything else is constant - I would look at chip temperature and potential for dew or ice on the chip.

Did you let the camera come to a steady temperature before you did the flats the morning after?

Don't despair I am sure you will sort it - it will end up being something trivial.

[SteveP]

Rob

I suggest your problem lies with the master flat itself. If you look carefully, the flat contains a galaxy-like artefact at the bottom-middle which accords with a similar artefact on the light. After applying the flat, this artefact disappears in the calibrated frame as you'd expect. However, those weird raindrop type artefacts around the edge of the flat have just been reversed on the calibrated frame which suggests to me that these artefacts aren't a permanebt feature in the optical train.

Have a look at all of the individual flats and see if there is anything strange on any of them

Steve

[RobH]

Hello Rob.

Yes, I did allow the camera time to get settled before I started the flat run.

The problem is though, with the H18, that when a sub is downloading, the setpoint cooling stops functiioning, so maintaining an even temperature is impossible.

I tried to program in a 15 second delay between each frame, but although everything was setup for this, for some reason it didn't happen.

Still, temperature changes shouldn't make any real difference to the way the flat applies, and this seems to be a big issue.

What sort of ADU are others using when shooting flats with an 8300 chipped camera?

Is there another way of applying the flat frame...in photoshop for example, where it is possible to adjust the effect it has?

Cheers

Rob

[ollypenrice]

This cooling issue was affecting a guest with the 15mm square chip version of the Starlight camera as well. I only mention this to widen the net of the thread. I'm really sorry you are having this hassle Rob. Do you think the filterwheel might not have been behind earlier problems after all?

Olly

[RobH]

Steve....there are differences between the individual flats, especially the artifacts at the edge. However, the small particles that are wrecking the image of the galaxy itself are common to all the flats, so are in the imaging train, but are being overcompensated, which is mindnumbingly frustrating, as they are too numerous and too deep in an important section of the imasge to clone out.

Olly.....the wheel was also the problem previously as it wasn't returmning to the exact same position, but because of that, this time I made sure that didn't happen by shooting through luminance only and then locking the wheel in place.

I was also seeing these moving artifacts before too, so it looks like a two pronged problem.

I have to say, it's driving me nuts, and I'm a hairs breadth away from getting rid of all my SX gear with the exception of the Lodestar, and simply buying another 285 chipped Atik, or an Atik 4000 (I assume you aren't having these issues Olly)

Cheers

Rob

[Ant]

I really cannot help much as you guys know so much more about this sort of stuff than me.

And I only have a small chip cam (H9). But I always seem to have issues when adding the flats into the processing. One minute I would have great results with 36k ADU then I wouldn't...

So I've started talking three sets of flats (flats don't really take that long) at 16k, 26k and 36k and processing using each set in turn and seeing which one works best.

Apologies if this doesn't add anything useful to the thread.

Cheers

Ant

[ollypenrice]

The Atik 4000s seem to be pretty painless. In fact almost entirely painless. Not as fine a chip as the 285 but so much bigger and I have come to like the square format because it maximises the use of the flat field and reduces the options (hence agonizing) on how to frame a target. Darks and flats are a piece of cake with a Neumann panel and set point cooling.

I occasionally get misbehaviour on the part of the coolers. They just go AWOL for a bit. But restarting is the answer and it only happens about three times a year. So, yes, pretty happy.

Olly

[Helen]

Can I just pick up the point about the filter wheel? Is there a problem with the SX filter wheel?

Thanks

Helen

[SteveP]

Rob

Does the H18 have a shutter? The reason I ask is that I recall somebody on another forum - it may have been CN or Yahoo - was describing a similar problem and that there was a build up of frost on the protective glass behind the shutter which left a residue as it defrosted. It could be a similar issue

Steve

[robbieince]

I still suspect it's thermal moisture. When you do your flats the duration will be pretty short and so you don't really need cooling - have you tried making flats without cooling at all?

[martin_h]

I get exactly the same effect on the QHY9 - sometimes, and its down to moisture/icing on the chip face, I usualy give thr CCD a blast with a hairdryer before I use it and change the dessicant before I switch on the cooling. I also now only cool it to -20C

I shoot my flats at about 22000 ADU

[adamsp123]

My money would be on moisture/ice Rob

[FraserClarke]

I occaisonally see stuff similar to the main problem on the bottom right on an SBIG ST8. In that case, it is icing on the chip. I fix it by warming back up to ~10C until all the ice is gone, and then cooling down slowly in steps of 5C every 5--10 minutes. Takes an hour to get down to temp, but it seems to stop the ice forming on the chip (I presume it forms instead on some other part of the camera which is colder than the chip).

I also take as the sign that I need to regenerate the desicant plug in the camera (does the SX camera have the option?)

[RobH]

Thanks all.

I emailed Terry Platt last night and he confirms that the issue is moisture and icing and has asked me to return the camera, which I will do today.

Robbie.....although I've moved the camera since taking the images, I'm going to shoot a new set of flats with the cooling turned off, as any particles on the optical window/chip surface should still be in the same place, and larger donuts shouldn't be too hard to remove in processing....if I can get rid of the multitude os small donuts in the spiral arms I'll be happy. as I can then use the data .

Helen....yes, I have had a problem with the filter wheel not returning to the exact same position. I now have a new wheel which seems better so far but that I still need to thoroughly test.

Obviously, without exactly the same position when shooting flats, you end up with issues.

Pleased as punch with the Edge 11 though, and very happy with the fact that I can get good results at F10.

Cheers

Rob

[Helen]

Thanks Rob. Its useful to be aware in case of problems with the filter wheel/flats.

I'm glad SX are sorting you out...

Helen

[RobH]

I've done a new set of flats without the cooling on, and have no icing issues.

However, they are still not applying properly, and are leaving all of the small donuts over the galaxy.

I did 2 sets. one at 24k ADU, and another at 16k.

Both give the same result.

Having looked in detail at individual subs, it seems that these donuts have appeared after I took the lights, probably as the result of moisture.

I'm determined to salvage this data if at all possible, so will have a bash at making a false flat, and using the clone tool rather a lot I think!

Rob

[robbieince]

Hi Rob

Glad you have at least zeroed in on the problem. I agree if you clone out the new dust on the non cooled master flat you should be ok - i guess trial and error is the only sure way.

Sorry I missed you at sgl6 it would have been nice to have caught up.