ollypenrice

Now there's a thought! Not more ideas!!! Oh no... One crisis at a time is the trick when getting a RASA to work. I do normally pull halos down in post processing but this was a quickie and I also felt they helped define the cluster as the subject of the image. lly

I just recently borrowed a Polemaster from one of my robotic observatory clients, which is the ideal solution when you're observatory based and only want to use it once! I used it a few nights ago and was impressed. Everything worked as per the instructions and the result, according to PHD, was a one arcmin error which is what the makers claim. I quite fancied buying it from its owner but, really, I've no excuse for doing that. If I were building up and tearing down all the time I'd go for it. Normally I drift align. I followed this U-tube video and found it entirely accurate. Olly

I agree that concrete is good. However, I also think that square is bad! Well, yours is a pretty small square section but we have four square piers with square tops here and all users are fed up with them. When I became a user I cut the corners off. Round is less likely to snag cables or collide in meridian flips. You can buy round concrete cylinders for making fake Greek temples etc (something I do all the time...) and these make good piers when filled with concrete and rubble. (Use some rubble to mix less concrete!) But, yes, concrete makes great piers. It's very rigid and has lots of mass to absorb vibration. Olly

Yes, it's the edge of a jam jar lid with the flat middle cut out! It does slope up slightly as it is now from camera to dewshiled edge so, as you say, forming an ellipse. I can easily modify it to be parallel with the corrector. Good point. The dewshield doesn't extend far at all above the top of the camera. Maybe 50mm. Making the dewshield short like that arose from a discussion with Goran who found no dewing issues since the camera is warm and draws air in from the back before blowing it out of its sides. The idea is not to trap too much of the cooler's warm air output in the dewshield. There was certainly no dewing issue on the RASA on a morning which saw the guidescope lens very wet. I think an elongation on the side of the cable circle makes sense. Olly

It is, but it's a good deal larger in aperture than the corrector plate so shouldn't be seen by the optics or camera. Still, worth a look. I also rather wish the camera were black since reflective things close to the light path are never to be approved of. Olly

What we have at the moment, except for a change in its orientation... Olly

Yes, you're right. Another good test! I also wondered about the cables, since the stars themselves look round and CCD Inspector is happy with them. A diffraction artifact from the looped cables could well be a smeared out diffraction artifact and the orientation is plausible. I could always try a different cable route in front of the corrector. The present USB3 camera cable is also a thick one. A flat one, edge on, might be a better bet. I'll have a think about a semi-automated Photoshop fix as well but, even 'as is,' this is not the kind of thing to bug me. Like the Takahashi 'Inverse lighthouse beams,' I don't worry about them. Edit: A quick wipe with the Burn Tool (set to mid-tones at 6%) over the 'long' side of the halos seems to dispense with most of the effect. It's only necessary to my eye on the brightest stars. Olly

I could persuade myself that I could see this but I cropped a few stars in centered square frames and I can't really find anything. Olly

After making a tilt-test optical jig for the ASI2600 camera and tuning out a bit of tilt, it went back in the RASA 8 last night for a test. It was a disaster, worse than before. We then rotated the camera 90 degrees from landscape to portrait and, for the first time since we started all this, we had perfect corners. Ours is not to reason why. CCD Inspector gave great values for FWHM, tilt and collimation so... if it ain't broke, don't fix it. Portrait it is. We stacked 10x3 minute subs with no calibration files and I processed the stack in PI and Ps. I was expecting to give the corner stars a cosmetic tweak here and there at 100% but there was nothing to fix. Bliss! (Note: a smaller chip would have been performing well some time ago. The APSc we are using is more demanding of tilt and collimation at F2.) Olly

Possibly of interest to fast F ratio imagers since tilt isn't tolerated by steep light cones... Olly

What a charming spot! lly

Here's my take on this helpful video - - seen recently in a link on here. In our case the scope is a RASA 8 which has the camera sitting on a flat circular plate, so a simple re-orientation was in order to do away with the equivalent of a draw tube in the video... The laser holder is just a bit of alloy angle with one side cut off to allow it to bend at the bottom. Cable ties hold the laser on and a loose cable tie slides over the button to keep it lit. You can just bend the bracket till it moints to mid-chip. Three slim wooden plates 120 degrees apart stop the camera moving when rotated but for best results I pushed the camera holder away from one of these three and towards the other two when rotating it. A strip of masking tape round the camera let me number the tilt adjustment screws so I could keep a record of each tweak I made. It worked like a charm, assuming I picked the right laser reflection to track while turning. Initially it described a small circle but just the second tweak had it rotating on the spot. Will this improve our corners? We hope so! The whole thing was rustled up out of offcuts, the only expense being the 44mm hole-maker to let the laser see the chip. Olly

The rule of thumb for perfect kit is 60% of the new price in astro circles. Certain highly sought-after items go for more but it's a good starting point. Olly

I think that most good filters are parfocal but that most optics are not. That's to say that even a top quality apo has slight variance in focal length for different colours. I don't think we know what scope you are using, but even reflectors will be affected by coma correctors, field flatteners, etc. When I'm imaging for myself with Tak 106 or TEC140 I tend to focus in luminance and leave it there for RGB. When imaging with guests I do it by the book and refocus per colour. If I found it made any difference in my rigs I would, of course, do it by the book all the time... What does make a difference is regular refocusing with temperature change. I'm not much up on robotic focus but, if you use an offset, I assume it must be an offset from some focal point already defined in an initial focus. Wouldn't that mean that, if the focal position changed with temperature, the offset would now be wrong? High haze can look very like soft focus... If your file naming protocol is wrong, won't your offsets also be wrong? Olly

I'm in the South of France rather than the UK but I've spent considerable time imaging with both a TEC140 (0.9"PP) refractor and a 14 inch ODK (0.62"PP), sometimes on the same targets for comparison. I did an article in Astronomy Now on this comparison and also posted images for discussion on here. Many SGL members felt, as I did, that there was little to choose between the results though some felt the bigger scope had found a little more detail. I preferred the refractor stars, particularly on some targets where huge star spikes were intrusive. The ODK also suffered, on occasion, from flair from stars out of shot. However, to be fair to the ODK, the idea was to bin 2X2 on many occasions but the Starlight Xpress SXVH36 refused to co-operate, producing dark artifacts when binned. This robbed the big scope of much of its potential speed advantage. The 14 inch ODK project was set up in conjunction with a client. He, I think, would go for another 14 inch while I would stick with the large refractor. In short it comes down to personal preferences, probably more to do with peripheral factors like maintenance than the strict performance of the rig. It's worth noting, as well, that diminishing pixel sizes play towards shorter focal lengths or, at least, make shorter focal lengths viable for high resolution imaging. In the UK with relatively few clear nights I would also factor in the time spent fettling reflectors versus the plug-and-play aspect of refractors. Olly

It's very dark here. I don't have my head around the Bortle scale but our SQM readings sometimes hit 22. Olly

Getting there. Olly

As well as the size of the circle described by the star, we also need to think about the degredations of the atmosphere. If the celestial equator happens to be very low from your location it may be better to calibrate higher in more stable seeing. Olly

Single 3 minute sub, no calibration files at all, RASA 8 with ZWO 2600 one shot colour, all done with Paul Kummer in a joint venture housed in our robotic shed, the Observatoire Per Frejvall. We're not there yet on tilt and collimation but it's getting better in increments. The mount is an Avalon Linear Fast Reverse. This is astrophotography - but not as we know it! Olly

Nice to see you back! Yes, I've just joined the F2 brigade with a RASA 8, all in conjunction with Paul Kummer. Olly

Well, looking for the moon kept me out of trouble for a few minutes... 🤣lly

Probably best just to attach a JPEG. This link doesn't work for me. Olly

Ah, a different picture from that in the link. All is revealed! I've no idea whether or not the brightness of the moon would overwhelm the foreground clouds. I'll need to take a shot myself to find out. Olly

OK, you've all lost me. I can see no moon in the APOD-linked image from the first post. Where is it? (This is slightly worrying! ) Since this image states clearly how it was made and why, I can see no objection to it provided the camera was precisely relocated each time. (Important because the position of the moon is a natural phenomenon when the camera's position is constant.) Olly

No, you can just use the camera lens centered on the middle of the intended mosaic. Whatever the field curvature of that lens is, it will then define the curvature of the mosaic. You'll be using it as a template. At least, that's how I would do it using Registar for the mosaic construction. I'd take the lens shot then work out the size of the final mosaic and re-size the lens shot to that size. (You might consider making the final mosaic a little smaller since getting quality good enough for full size presentation can be difficult and time consuming at capture.) In Registar you can then register each panel to the template, discard the template and combine all the registered panels. There are other ways. I've post-processed a mega-mosaic captured by a client and using a template he made in Astro Pixel Processor from individual panels. APP did a good job of the template and field geometry but couldn't match up the panels seamlessly so I kept the template and then worked as above using Registar. Olly