Helix - any advice for a newbie?

[Terere (Dom)]

So after lurking a couple of years I thought I'd post a picture.
Scope: Esprit 80
Mount: AZEQ5
Camera: Fuji X M1 (kind of dinky little mirrorless camera body)
ISO: 3200
Light frames: 112 x 30s exposure
Dark frames: 21
Flat frames: 21
Bias frames: 28
stacked in deep sky stacker. Some processing in photoshop

I still haven't got the sensor at just the right distance from the flattener, so the corners show some field curvature. Given I'm using a not so common camera I might need to get an adapter machined especially for this.

Not using guiding. I could probably get longer exposures unguided, but I don't have an intervalometer for this camera, nor an adapter to use the controls on the tripod (I didn't buy this camera for astronomy, but it's what I have).

I've never played much with flat frames before, but had a shonky go. I basically tied a white tissue over the dew shield and aimed it at some torch light.

I typically go too far processing these things, so I'm sure this is no exception, but I held back more than I normally do. The thing is, I had a play with trying to stretch it out and I notice this weird kind of streaking that I've not encountered before. I thought it might be the flat frames since I'm unfamiliar with them, but if I stack this without the flat frames the same streaks come in. You can see it if you zoom in on the image, but here's an exaggeration:


Any ideas what causes that?

[Atmos (Colin)]

Congrats on the image Dom, it's pretty good for 30s exposures and a DSLR!

As for the streaks, I think this is caused by the shorter exposures and you not hover coming the read noise of the camera. With my Nikon D700 I get similar but even worse noise with 30s exposures on my telescope. Longer exposures will increase the amount background exposure and decrease the read noise.

[thegableguy (Chris)]

Well done - I'm a bit jealous!!

I tried the Helix last night with extremely disappointing results, and that's using a much bigger telescope and a DSLR with intervalometer. Tried again tonight and couldn't even find it in the sky!!

Maybe my biggest problem is shooting at 8pm when it's still a bit low. What time of night did you take this?

[Terere (Dom)]

It was between 9 and 10 PM on Saturday night. It's a little dark where I am, but I still get light pollution from the Gold Coast to the east and Brisbane to the north. If I'd waited a few more hours it would have been in a better spot, but I was tired.

[Somnium (Aidan)]

Great stuff Dom. really nice first image post.

[sil (Steve)]

very jealous and a beautiful target

[casstony]

I had a similar streaking issue with the Helix recently after successfully imaging other targets on the same evening with exposures of a few minutes.

The sky was starting to get foggy and the Helix had my scope pointed more toward a source of light pollution (neighbours light) so I'm guessing the streaks are due either to the more intense light pollution or the descending fog.

[NorthernLight (Max)]

Hi Dom,

What you see is noise. I had the same and it looked like someone went through my nebulas with a rake. A clever man here on the forum enlightened me and told me hiwnto fix it. Never had it again afterwards. What you need is a process called dithering. It essentially means that you take each photo from a slightly different angle. So instead of keeping your scope dead Center on the target you Center each shot slightly different. The exposure itself of course needs to be made with the target remaining still. When you auto guide with Phd there is a function that performs the dither for you.
By dithering, the noise pattern ends up being always in the same spot whereas your target signal moves around. Since stackers like DSS lock on to signal from stars they automatically align the image so that signal sits on signal in the stack. The side effect of that is that the noise is now always in a different spot of your image and whilst the multiple exposure layers you are stacking keep building signal in the same spot it rejects the now randomly occurring noise. Works pretty well.