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M82 C-11 QHY8


darditti

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I put quite a lot of exposure into this: 3.75 hours to be precise with an IDAS filter. I think it is a fair result, but the flat fielding hasn't worked that well, as so often. I find the dust bunnies move between sessions if I remove the camera from the scope, so unless the flat is taken in the same session, at dusk or dawn, it is not right. I could leave the camera on the scope, in the run-off shed, but I find then it frosts when in operation. I find it has to be kept in a heated house. This seems to be specifically a problem with the QHY8.[br]

David[br]

M82-09-01-21IDAC11QHYLR.jpg

(click to enlarge)

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Hi David,

Lovely result - you should be pleased with that!

As far as flat-fielding, thats the way of it - you cannot move focus, move the camera, or do anything which changes the imaging train at all for them to be valid. The only thing you can do is shoot the flat-fields after you've done your imaging.

Cheers,

Richie

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Well, I Look past the bunnies at a very nice Image of M82.

I'm sure you will resolve the Issues with the camera.

I'm sure SteveL cured his QHY8 problems with heat band David, but perhaps a discussion with him would be better.

Ron.

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Nice image.

Lovely round and natural looking stars, great detail, and a few other fuzzies showing too.

Re. flats, I tend to use the same imaging train for long periods of time, because of the issue of having to shoot new flats every time you change it.

Cheers

Rob

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I like the image David, the detail around the core is great, and the scale through the big scope is lovely. Everything is spot on except the dust bunnies. I have the qhy8 and I know exactly what you mean. Flats for a single image have to be taken during that session I find.

Here is my technique, it seems to work well most times.

Store QHY8 inside in an airtight box packed with silica gel sachets.

Keep sensor clean. This helps to stop ice forming on the marks. I have seen a fingerprint pattern though come through once, and it certainly wasnt MY finger that put it there!

When fitting IR filter, I heat both filter and Qhy8 with a hair dryer and keep the warm air blowing through them until the last second. Same goes the the next filter, CLS in my case. Biggest mistake is to undo the combo after this.

I wrap a 2" eyepiece heater around the filters and nosepice too, but im not sure it makes much difference. If it should happen to freeze up during a session, I use a hair dryer again. Ice on the chip will graduallyt melt anyway, you just have to hope it doesnt leave too dark a mark.

What about layering an emphasised red channel section over the core to bring out the red emissions?

Thanks for posting

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Very impressive! And especially so at your location - looking forward to more galaxies from your direction! Was the seeing better that night, than when I came over on Friday? As for dust bunnies, I can't see them!

[edit] well I can if I take your image and stretch it to utter destruction - but not as you've presented it, not on my monitor...

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Thanks for these comments and suggestions, most helpful. I think the bunnies are probably not on the filter, as that is so far from the chip it probably would not produce visible ones, they are more likely on the cover glass of the camera. One possibility is to leave the camera in place and arrange for an "always-on" heater to keep it dry outside. Another is to make a light box so I can take flat fields any time rather than having to wait for dawn or dusk.

Seeing was only average on this night - but I was able to image M82 through the meridian, so it was very high. This is a very simple processing (one of the things I like about the QHY is that you don't need to do much to the images), but I may try TJ's suggestion with the red channel.

David

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What a gorgeous image. I've rarely seen an M82 with such fine core detail. The absence of Ha makes it all the clearer although that might be the next stage of the project.

I don't think it is as important to keep the imaging train intact as people often suggest esp if the vignetting is even. I just keep the filter wheel/drawer in place, on the camera, when removing from the scope. Even then, dust bunnies on the filters are nothing like as intrusive as those on the chip. It doesn't matter what orientation the camera is on the scope, it isn't going to effect the alignment of the dust. If you keep the camera sealed it's unlikely that that new dust will get on the chip.

I use a Gerd Neuman filter drawer with my QHY8 which works very nicely. It isn't airtight so you still need to use the QHY8 nosepiece unless you glue a plain 2" filter into the drawer. Some people have done this and it works very well.

When my QHY8 has been blighted by icing and left a load of marks I have resorted to this quick and dirty trick. With the curves tool up, click inside the dust bunny and just outside in an unaffected area. On your image I got a reading of 4 and 8 respectively. I put these points on the curve and then set the output of the lower point to 7. The curve above the upper point then needs straightening and the dust bunnies have vanished. 2 minute job

12058_normal.jpeg

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That's a neat trick Martin! I'll have to remember that one.

I do something along these lines.

Copy the layer, then change the blend on the top layer to "Soft light". The result is a little dark, but by lessening the opacity you can strike the balance. The detail stays, and the background is preserved. 45 sec job :(

I'd be interested to see how you get on with the lightbox David. At the moment I use a propped up artists canvas with a battery fluorescent light behind to get the flats, but it is far from ideal, although the results are reasonable. Ideally something which suited all my scopes would be great. Are there any plans around for them? How does one ensure that the light is evenly distributed, I imagine with bulbs it would be tricky not to get brighter areas, even with barely opaque perspex??

Thanks

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Both these are considerable improvements on my processing. Thanks! I think Martin's is the best of all. A good tip.

There was an article in Martin Mobberley's column in AN at least a year ago on how to make a light box with perspex and bulbs etc. Trouble is, you have to make one for each telescope you use, and I use several.

The solution to the flats problem I am pursuing at the moment is instead to keep the camera on the telescope and keep it slightly heated all the time, 24 hours, with a dew strip, so hopefully it will always be dry. Then one master flat taken in twilight should continue to be valid until I start imaging with another scope. We shall see.

David

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