Ouroboros

Not sure if this counts but looked out the window in the wee small hours to be treated with lovely views of Venus, a crescent Moon towards the east and Orion in all its magnitude towards the south. Tempting though it was I slunk back to bed.

As for my elongated guide stars, a quick google this morning suggest this is quite a common observation with OAGs. I understand it is due to picking off stars at the edge of the image field where distortion will be most apparent. I didn’t adjust the position of the prism when putting the set up together. I just checked the prism wasn’t vignetting the main image in daylight. Regardless of stretched stars the guiding looks good to me, and I haven’t even fiddled with any of the settings.

@pipnina Yes, I’m pleased with what I see, but then I don’t have the experience to know whether it is what I should expect. That’s why I would appreciate comment from experienced ‘opticians’. I also don’t really know what to measure.

Took delivery of an Askar FRA 300 telescope and OAG last week. I’ve had a humdinger of a cold the last four days but decided tonight I just had to try it out before the weather deteriorated in the south as forecast. The skies were misty which didn’t really matter for some tests. Here’s a couple of single subs - 120s and 300s respectively. The stars look pretty round right across the field, although towards the corners there is clear evidence of chromatic aberration. This surprises me a little because the ASI2600 is an APS-C sensor and the 300 is supposed to be designed for full frame cameras. I want to analyse the images properly in Pixinsight. These are just screen shots. Any thoughts on the quality of the stars anyone? Zoomed into a corner …. I found the Askar OAG quite easy to set up. And the guiding seems quite good. I was a tad surprised how elliptical the guide stars looked. More like a streak. Is that normal for OAGs?

Struth! Not cheap these things are they?

Funnily enough it was the frustration of drop-outs using direct, wired USBs in PCs and Macs over ten years or so that led me to the ASIair which I have found to be (mostly) far more reliable.

I have only just realised this having just acquired and fitted (though not tested) the Askar M54 OAG. It hadn’t occurred to me before. I guess you have to make sure you’re happy with framing first, then calibrate. I think I tended to do that anyway.

Yes, very good. S@N did a prog on the VLT recently. Still available on iPlayer.

Well done, Kostas. It’s an excellent image and cleverly arranged.

The nice post lady brought another goodie today. I got it all connected up and the main and guide cams co-focused. Well, kind of anyway. It’s tricky when they’re not actually looking at the same thing. I’ll have to wait until I get some stars to focus properly. This is my first OAG, so I’m interested to see how well it performs.

Small and perfectly formed. Askar FRA300 and Askar filter drawer. It was sent by FLO inside a box, inside a box, inside a box, inside a box. I can’t say it was under packaged. Brilliant to have it redirected to a pick up point too. So I didn’t have to wait in all day or worry about it being left on the doorstep. I’ve ordered the Askar OAG too.

“Press and guess” I like that phrase. Sums up my workflow. Actually I’m pretty much OK until I go nonlinear, then I feel I’m flaffing around in a multidimensional space of possibilities. I’m not quite sure where I’m going or how to get there. I always do get somewhere. I end up with an image. But I often feel there’s a better image lurking in the data if only I knew how to get it out.

That’s an extraordinary image, @Clarkey, irrespective of whether it’s your first go in PI. It took me a moment to recognise it was the NAN because it’s such a wide field. Isn’t there a lot going on there in the region? Wow! I’m very interested to see how you progress with this image because I am hoping to do some dual band Ha + OIII imaging myself having only done OSC up till now. I have been watching some videos to try and get my head around how processing of dual band differs and I have to say I as yet don’t have a clear idea of how to go about it. Hoping people will suggest a few more tutorials in response to your post. What briefly was your workflow to get that image?

I decided to have a look at some of my subs to see how many pixels they shift between subsequent shots. The was data obtained with a 910mm FL main scope and 176mm FL guide scope. Focal lengths determined by the ASIair. Anyway there's a x5.2 multiplier between the two. The pixel sizes between the main and guide cam are identical. I had set the dither to 5. Presumably that's +/-5. I'm not sure whether the 5 pixel dither referred to is measured along the x and y axes, or whether along the hypotenuse. Anyway it doesn't matter a lot because of the large difference in focal lengths. I do get some odd measured dither values ie more than 5 but much less that 5 times 5. I think the maximum dither was 13.5. But most were less than 5 along the hypotenuse. The over size ones are probably down to a shift in pointing or something. Odd because my stars were (mostly) round. Anyway, I think this confirms what ZWO told @Jim Smith ie dither is main camera pixels.

Oh, yes. Sorry. You did say.

I really like that, @kirkster501. I like the way the galaxy core is large and misty. Quite often the core of M31 looks too small and intense in images. I also like the subtle saturation in the white bits of the galaxy and the additional ‘highlights’ of colour on the disk’s edge. That’s coming on nicely. Perhaps for my taste the yellow stars are a tad too yellow, but it’s all down to personal taste. I don’t know whether you find this but if I process an image for too long I can’t assess it anymore. I have to leave it and come back to see it (almost) afresh.

I know where everything is. It’s here somewhere …. errr …. errr ….

Nice. Lots of detail in the Ha. What were the imaging details, telescope etc?

Yes, good point. I’ve never bothered to measure it. I set it at 5 pixels. The maximum is 10 isn’t it? Can’t remember. Anyway as long as I’ve see it shift a bit between subs I have accepted it as working OK. I am also uncertain just how it important it is to dither with a CMOS camera in my case given that I use a master dark. I started using dither back when I used a DSLR to avoid having to take darks after imaging.

Thanks for doing that.

Oh, @FLO … and something I should have asked earlier …. how is an ASIair best attached to the handle? It looks like direct connection is not possible unless the slots in the handle happen to be separated by 20mm - the distance between the threaded holes on the underside of the ASIair.

@FLO. Brilliant! What lovely people you are! Thanks.

How does the filter holder work? I can’t find any pictures or videos of that. That’s mounted filters presumably?

I feel I ‘know’ it’s guide cam pixels from knowledge lost in the mists of time. You have to multiply by the focal length of the main scope divided by the FL of the guide scope to get the dithered distance on the main camera. That assumes both camera pixels are identical in size. If not you have to further multiply by the ratio of the guide cam pixels to main cam.

Absolutely superb.