Louis D

Most APOs have curved fields because the radius of curvature for most refractors is about one third of the focal length. There are some astrographs (4 or more elements) and Petzvals with designed flat fields. For the rest, you'll need to purchase a field flattener unless you use a really small imaging chip (planetary imaging) or buy a really long focal length refractor. The shorter the focal length, the shorter the radius of curvature, the worse the corners will look. Being an APO simply means really good control of false color. It does not mean complete freedom from chromatism as in a reflector or flatness of field.

How steady is the seeing in your area? If the atmosphere is turbulent, there isn't much point in increasing your magnification because all you'll be doing is getting a closer look at blurry details. Do stars twinkle at night or do they hang there in the sky like little Christmas lights on a tree? Do bright stars show color flaring that rapidly varies at modest magnifications? Those are signs of atmospheric turbulence.

When focus doesn't immediately change when focus direction is reversed due to slop in the mechanism.

There's also adapters from Vixen/Synta finder shoes to Quikfinder base if you have such a base already on your scope. I have one for my refractors, and it works great.

Generally about 1.3x. You can figure this out for yourself with a ruler or tape measure. Just measure the difference in width of the view without any barlow, with the barlow in the normal position, and with the barlow lens elements screwed into the eyepiece. For refractors and Newtonians, none. It's just acting as an extension tube. You'll have to rack your focuser inward to compensate. An extension tube can be handy for terrestrial usage when you want to focus closer than the stock focuser outward travel allows. For mirror focusing telescopes like SCTs and Maks, you'll be extending your focal length slightly to reach focus further back with the extension tube. This can also induce a bit of spherical aberration in the image because you're getting further away from the design intended focal length.

Dang, sorry to hear about your chronic pain. I can relate as I've had my share of back and neck issues over the years. I would probably lean toward getting an 8" Dob, have it setup in the backyard by someone with a good back on a leveled set of slightly raised pavers to protect it from ground dampness, and leave it there under a high quality telescope cover when not in use. That way, all you have to do is pull the cover off to observe. An 8" Dob is fairly easy to use while sitting and there are no tripod legs to have to work around. All you have to carry out is an eyepiece case. I would stick to smaller eyepieces because the weight of larger, premium eyepieces tend to add up quickly in a case.

I have 8x42 and 15x70 binoculars that I use for astronomy. The 15x70 are right at the limit of hand-holding if you can sit in a lawn or camping chair and hold them by the objective end while jamming the eyepiece end into your eye sockets. If I'm going to get out a tripod, I'll just get out a telescope with a binoviewer instead.

I keep my non-eyepiece accessories in a toolbox. I keep my Telrads in a relatively flat cardboard box with closed cell foam wrapped around each for protection. It frees up a lot of space in the eyepiece case.

I don't know if Europe suffers from the same issues, but you never know whether you'll need a metric or USCS/SAE/standard (not Imperial) socket or allen wrench when trying to loosen a threaded screw/bolt. Sometimes due to wear, neither set has a perfect fit. It gets annoying at times.

Here's how the Meade 5000 Plossl 40mm looks in a field flattened AT72ED f/6 refractor (top) and in a Synta (Orion/Celestron) 127mm f/12 Mak (bottom). The difference in scale is due to the difference in focal lengths between the two scopes. However, it's pretty clear that at f/6, things get ugly toward the edge, but at f/12, it looks pretty nice. You may need to select and expand the f/6 version to see the details.

Already been done nearly 2 years ago over on CN.

They are 5 element, 60 degree, positive only eyepieces except for the 5.5mm which has 6 elements and might be negative-positive design. They are very sharp in the inner 50% (30 degrees) and then get progressively worse to the edge in sub-f/6 scopes. It's been rumored that they were resurrected as the ES-62 line of eyepieces since all the focal lengths match up.

It probably has weather very similar to our Mount Washington in New Hampshire. Most of the times I've been to the top, it's been socked in with clouds.

By compressing the amount of existing light into a smaller image circle. The absolute amount of light remains the same, but the amount of light per unit area increases. Basically, it's a focal reducer that increases the focal length and exit pupil while decreasing the AFOV. TFOV remains the same (or close to it).

After a meridian flip, how big of a deal is it to get the spider vane spikes of stars realigned with images from before the flip when imaging with a Newtonian?

Not to mention it rhymes with slough in American pronunciation meaning a swampy drainage or marsh. We had one on our acreage that never dried out. Anything with wheels would get stuck in it when trying to traverse it. When I first heard about slew rate in electronics, I was mystified as to why you would use the same word for something totally unrelated. I had no idea at the time that the swampy usage wasn't spelled slew since that's the most obvious way to spell it, just like threw, brew, or shrew.

I was going to say, can't you use multiple frames to detect stars because they move in a deterministic manner within and between images? I'm not familiar with the 3D data set idea, but if all the comet data does end up in a single plane, it should be fairly simple to remove everything not in that plane (the stars). That, or squash them all into a single point each within the comet image plane so the stars are pinpoints instead of trails.

Mailman is probably it since postman is the formal as in the movie title The Postman Always Rings Twice. In your original sentence, we would have probably just said "Look what showed up in the mail today!" or "Look what showed up on my doorstep today" since we rarely see our postmen because our mailboxes are all centralized at the back of the subdivision, and because many packages arrive via UPS, FedEx, or Amazon delivery directly at our doors nowadays bypassing USPS.

Just looks like imager noise, so not a big deal for most viewers. I kind of like the effect of not having star streaks in the image distracting from the comet.

Off topic, but is postie a common nickname for a postman in the UK? I've never heard the term used anywhere in the US.

If you get a Telrad riser, how are you going to use the RACI without going around to the other side of the scope? It seems like it would be a wall between the focuser and the RACI. I use a GSO/Revelation coma corrector to good effect in my Dob. I had to add a 25mm spacer ring between the eyepiece holder and the optics section for best correction. It requires about 11mm of in-focus and adds 10% magnification. Your eyepieces also need to focus within about 5mm of the eyepiece shoulder for best correction. Only my 12mm NT4 required parfocalization since it focuses 19mm below the shoulder. It also made it so much easier to swap it in and out by minimizing refocusing.

I've got two Synta 127 Maks, one Orion branded, one Celestron branded, and neither has any focus backlash and both were well used when I bought them. I would return that scope straight away as that is not right to have focus backlash like you describe.

I'm able to reach focus with my Dob (low profile focuser) using the GSO/Revelation coma corrector. It's how I was able to take this photo of a Mercury transit at prime focus with a DSLR:

From what I know of Ben Nevis, you probably wouldn't want to be observing from its summit, either. You were higher than that when you were visiting the plains of northern Arizona!

The 25mm BST is not very good at f/6 from 50% out. It does have plenty of eye relief for eyeglass wearers. The 24mm APM UFF is much more consistent across the field and is quite usable with eyeglasses. If you expand the FOV image, you'll see that the BST tends to blur out sooner than the HD-60 and much sooner than the UFF.