ZWO290M Ha DSO - at last

[JayPea]

I finally managed to try out my camera properly last night both with a DIY lens adapter and new DIY peltier cooler. Two of my last three attempts have ended with disappointment with washed out skys. Probably from a combination of excessive light pollution and not the clearest skys by the time I’ve set up (I was desperate to try it!). I’ve had the camera since May and apart from quickly testing it worked when I got it, last night was only the second time I’ve got a proper DSO image off it. 

 

Because of security lights, car park lights, street lights, soggy grass and a good view of the moon I was setting up in my north facing front drive rather than the back garden. It’s fine but I must remember to duck my head when I retreat to the garage. The bloody door tried to scalp me last night. I’m glad I had a thick woolly hat on.

 

As well as trying the DIY cooler (well, more of a slight chiller) I was also trying a Hydrogen Alpha filter for the first time. So I chose the Elephant Trunk IC1396 and surrounding nebula. I’d made an adapter to attach the camera to my Nikon lenses (last night using a 70-200 at 70). But now I have the cooler attached I need a lens with a foot for attaching to the mount. Therefore I couldn’t use my little 50mm which looked ideal. So I was expecting the image to not quite fit on the sensor.

 

For once things ran smoothly. I set up in the light and aligned finder scopes with lenses and checked it all worked. I went back out around 7:00 and polar aligned. Luck was with me and I could see both of the first stars through gaps in trees for a 2 star alignment. I don’t think I’ve ever had that before. Focus was a problem though. At 200mm I could see the Bahtinov cross pattern clearly but not when zoomed out to 70mm. So I judged focus by eye without the mask. I then slewed to the target and checked with online plate solving that it was looking at it and all looked OK. My DIY guide scope could see a few stars. I reduced the exposure to get less blobby stars and guiding worked straight away. Some frustration with the focus but otherwise all relatively quick and easy for once. Apart from the bump on my head I don’t think I’ve had such a painless set up.

 

I set the camera (ZWO 290 mono) to 60 seconds and a gain of 300. I’m not sure what the best settings should be as I haven’t had opportunity to experiment. By now the chiller had settled the sensor temperature to around -0.5 degC. I got it going for 35 shots and went inside for drink and telly. I ran a few batches of images off through the evening. Focus didn’t look to move. By the end I was getting the impression that the sky was less clear than when I started. Looking below Polaris it gets quite orange and starless, almost like a haze in the sky and Polaris is only just visible. So by 11:00 I switched to collecting darks and packed up at 12:00 just as the street lights went out.

 

Out of 225 lights I had 3 that showed obvious movement so I ditched them. A stack of the rest and a quick tweak in Lightroom produced the image below. I’m more than happy with that for a Saturday evening. Next plan is to get to grips with a star mask. I’m finding the stars are getting quite big by the time I’ve processed the image (although I guess that might also be focus in this case?).

 

I actually feel like I’m making some progress and Ha mono looks the way to go for my situation.

 

Cheers,

John

 

PS doesn't it look more like ET's finger than an elephant truck?

[Adam J]

Very nice considering the small sensor area you have to work with and the focal length you have got lots of detail. Will you add OIII, am interested in how that would turn out with the small pixels. 

[JayPea]

Unfortunately I don't have a OIII filter . If I was sure it could work well with light pollution I could be tempted.

With what little testing I've managed so far the small sensor and pixels (2.9um) have not proved a problem. But I've only used it with f2.8 camera lenses and the BSI nature of the sensor probably helps with the faster glass. I'm finding telescopes generally a bit long and slow for the FoV I think I need for the smaller stuff. I'd like a 300mm focal length f4 telescope if one exists. I'm considering an old Nikon 300/4 ASF prime (can't afford a 300/2.8!) as an alternative. But first I need a way of shoe horning a filter wheel in there and I think that's easier with a telescope than a camera lens.