Louis D

Rather than a prism arrangement, the Foveon sensor (introduced 20+ years ago) had stacked photodiodes of differing spectral sensitivities at the wafer level. As you can imagine, the red channel being at the bottom of the stack had the lowest sensitivity and highest noise of the three, which is unfortunate for Ha imaging. However, it does get rid of the Bayer anti-aliasing filter which reduces resolution. On the flip side, the article mentions color noise at low light levels, which is exactly what DSO imaging is. Perhaps it might be more promising for solar system imaging where the light levels are generally quite high, and enabling one-shot color without an anti-aliasing filter might be advantageous.

Someone on CN seems to have done the measurements.

Been there, except with tequila.

Just did a google search on tablet holder with clamp and came up with plenty of options to hold a table on the end of an arm which has a clamp at the other end to attach to a tube or similar. I've seen plenty of videographers' run and gun rigs with tablets attached in various ways to the superstructure so they don't have to keep their eye mashed into a viewfinder peephole, so I know there are good solutions out there to be had.

Yes, but not the same local time. That was my point about being a slave to UTC when comparing the local views at the same time. Taken to the extreme, you might be asking why is it so bright out when it's UTC 00:00 (midnight Greenwich) in New Zealand. It's the same time, so the sky should be the same, right?

BTW, does anyone know why the current popularity of unboxing videos exists? I find them completely uninteresting. At the end of the video, I still have no idea if the item is any good for its intended use. I only include images of the packaging in my reviews to satisfy those who find that sort of thing essential to a review.

Do both of you always swap views after focusing for infinity using distance vision eyeglasses or contacts? If not, it is unreasonable to expect the eyepiece/telescope combination to be focused at the same distance for two observers that have native eye focus at different distances. If you are focusing for infinity with other eyepieces and both observers have distance corrected vision, I'm not sure why you needed to adjust focus with those other eyepieces and not the ES-92 17mm.

Why would you use UTC instead of local time? If you had used 19:00 local time (assuming both consistently use Standard or DST/Summer Time), then Mars would have indeed been much higher in Cyprus.

I only use prism diagonals for correct image viewing. For everything else, I use GSO dielectric mirror diagonals. I've never felt the need to upgrade from them. On this topic, I have a vague recollection that some folks have noticed that prism diagonals correct chromatic aberrations in certain scopes, but I can't recall the details. Does anyone else recollect this or is my mind on <insert illegal drug name>?

As others have said, I use nebula filters for some nebula observing. I've tried various filters on Jupiter and Mars with marginal success. Of course I use a solar filter or wedge with the sun. I tried some vintage color line filters for solar, but didn't notice much improvement. All of the above work with any scope. However, for my fast achromats, I have been extensively trying out various combinations of yellow/long-pass/minus-violet and cyan/short-pass/blue-green filters on Venus and the moon to block unfocused violet-blue and red light to vastly sharpen the image at higher powers. You end up with a pale lime-green color cast. I've also tried various light green filters which achieve similar results over a narrower passband and lower transmission.

Don't. I've twisted plenty of Chinese/Taiwanese sourced screws completely in two just using finger pressure. Some others took using pliers to twist them in two. Once twisted in two, you'll need to drill out the portion stuck in the device and retap larger threads.

Not completely true. You can shift the individual RGB channels relative to each other in post, not the frequencies within each color band. Blurring within each band cannot be corrected in post. Here's an image from a rather thorough article about ADCs showing the improvement an ADC can make over doing the shifting in post:

You might not have enough back-focus to insert the ADC in the focuser. If you have one of those Synta focusers with the high-hat 1.25" adapter, you could probably substitute it with the ADC with the proper low profile adapters to hold it in the bare focuser opening. I only have 25mm of back-focus on my Dobs due to undersized secondaries and low profile focusers, so an ADC is not an option for me.

OPT came under new management some years back. Their service was going downhill already when the pandemic hit. Their business model did not allow them to weather the storm, and they are now in liquidation bankruptcy. There are now maybe half a dozen dedicated astro vendors in the US.

Just make sure not to go to a cartel controlled part of Mexico unless you want to risk being kidnapped for ransom or just plain shot for being on their territory. Perhaps you know someone there who knows their way around and can keep you safe. The company my son works for just recently cancelled routine business trips to central Mexico to monitor their operations there. He himself did manage to take an uneventful pleasure trip to Mexico City and the nearby Aztec ruins this spring.

That probably explains why I let my NG subscription lapse in 2017. I had been noticing a significant change in the type and quality of the stories in those last few years. It wasn't the same NG I had grown up with decades earlier.

Definitely. As I wrote that, I was thinking about how many stars will never be seen throughout the year from any given point on the Earth's surface. You would need to travel to the opposite hemisphere and observe for a year there to catch all of the stars visible from both the northern and southern hemispheres. I think that's why the number I looked up was so vague. Even at the equator you would have trouble observing stars at or near the poles.

As a cynical American, I can say it's always all about the almighty dollar and the lure of a quick buck. These organizations are dealing with changing times and declining revenue, contributions, or state funding. They are doing whatever it takes to survive with little to no thought given to possible long term damage to their brands. These branding arrangements are generally judged to be low risk by their governing boards. In addition, merely getting their names out in front of the public is also seen as a form of advertising that may draw in new interest and funding. In particular, a form that costs them nothing except reputation.

It was probably distortion you were experiencing rather than field curvature. Field curvature causes the edges to go out of focus while on-axis is focused whereas distortion changes the placement of points relative to other points within the field of view depending on how far they are from the axis. FC is obvious without having to move the field of view across the sky whereas distortion is generally not visible until the FOV is moved. The exception is for extended objects like the moon placed near the edge. It may be stretched into an egg shape or flattened into an oblate sphere.

That amount of flex should be easier reproducible just by extending the focuser tube and pushing sideways on it. That seems excessive. Just adding a plate behind the focuser may just transfer the flexure further away. Ideally, you want a stiff reinforcing ring around the entire inside of the upper tube. Now I don't feel so bad having a Sonotube for my Dob's tube. It doesn't flex at all that I've ever noticed.

A few previous Heritage light shroud threads for more ideas:

And yet the Far Eastern optical shops have been cranking out consistently well figure parabolic mirrors for some time now. Why has this level of optical prowess eluded their refractive optics figuring lines of business?

That's very cool. I wonder if an IR-pass filter would work well? It doesn't seem like there's much scattered light in IR in a daytime sky.

Very cool. To translate to English, I just clicked open the Text Mode (OCR) tab on the left and right clicked in Chrome and selected "Translate to English". Not the best translation, but I certainly got the gist of most of the descriptions. It's obvious he had insufficient aperture to resolve even the showpiece GCs or to detect the faint nebulosity associated with some OCs. However, he was able to detect lots of galaxies that are mostly lost to light pollution in all but the darkest skies. It must have been an interesting time back then. Nice dark skies, but very crude and small instruments. It's also obvious he had no idea what he was looking at other than the star clusters. However, this source does provide the OP with an "authentic weblinks for the Messier Objects' Catalogue" as requested.

I actually bought both a used 6" f/6 KUO achromat and a used 6" f/5 GSO Newtonian and have compared them side by side on the same objects on the same night on my DSV-2B mount. The Newtonian with a GSO CC walked all over the refractor with a TSFLAT2 except for the spider diffraction spikes on all objects I observed. The lack of CA and SA really tipped the scales in the Newt's favor. It also weighs about half that of the refractor, making mounting much more stable. Crazily enough, the Newt cost 1/3 the price of the achromat! I would struggle to recommend the fast refractor over the fast Newtonian aperture for aperture. I'll have to find a tight double sometime to see if the refractor's lack of a central obstruction yields a better split or if the CA and SA negates that benefit.