Shooting "in the zone"

I start at 30° fairly normally. It just works for my location.

Not every object I would like to collect runs high enough for me to limit myself to higher angles. Instead, I begin at my 30° limit and climb from there. (And 30° happens to clear the back fence well.)

Tonight, since everything is finally working as it should again, I’m imaging Bodes Galaxy in two different sessions, and the first started at 30° and is about to finish at ~45°. Then my second session will follow from 45° up to nearly 60° before it subsides.

The first is 100 images at 60 seconds each. The second will be 100 images at 180 seconds each. I think the 3 minute exposures will carry the rest of tonight.

Ah-Ha! It just switched from the first to the second. It’s doing the starting Slew, Center, And Rotate. Now the autofocus, and away it will go.

And me… away I go to bed and my CPAP. Tomorrow I should have two sets of files of Bodes to play with. Finally, things are working great again. Such a trying sport to play.

I bid you ado.

Hi Tony

As you know, seeing and FWHM is affected by altitude in a big way, once you get below about 35 to 40 degrees. Here is one example of data on this, but there are many others you can find on the web that show similar or even worse shifts. http://brucegary.net/ASD/x.htm

Personally, about 40 degrees is my absolute limit for RGB (I don’t do a lot of Luminance), but even then I can see bigger changes than expected. My local problem is that the city and houses, including my own house, is around me, so the lower you look the more you are affected by local heating effects from roads, roofs, even trees, which degrade seeing as well. So unless you have flat fields around you seeing will worsen even more rapidly than this chart shows at lower elevations.

The second impact on FWHM is refraction. Our atmosphere refracts light, it acts like a prism, the lower the altitude the bigger the effect. This is huge for planetary imaging where an ADC (Atmospheric Dispersion Corrector) is required for the very best images, especially at low altitudes. This is a prism or set of prisms that can help correct the problem when properly aligned with the horizon. This effect is also present for deep sky imaging, especially with larger apertures. Looking at Pellier’s book on Planetary Astronomy at 100 mm aperture, without an ADC, his suggested B,G,R and L lower limits in degrees altitude are: 45, 19, 12 and 55! Luminance is the very worst as it has the broadest range of wavelengths input, which I think is why you specifically mentioned luminance as the big problem. At 350 mm he gives minimum altitudes of 74, 51, 36 and 89!

By the way, while Pellier’s book is on planetary astronomy, it goes through the detailed advantages and disadvantages of different telescope designs and the effect of the atmosphere and local conditions on imaging, aw well as being totally comprehensive on planetary imaging, so an excellent book I think even for those that don’t do planetary.

Rick

I unfortunately don’t have the images easily on-hand to demonstrate this anymore, but with an LRGB image you can pretty substantially Gaussian blur your RGB data (more than you would think) without seeing much noticeable impact once you’ve added your luminance data in.

Not that I would recommend blurring your RGB data on purpose — I say this just to illustrate the point of how RGB sharpness matters much less than luminance sharpness. Because of this, I have my Target Scheduler plugin in NINA set up to prioritize shooting Luminance when my target is nearing meridian.