My policeman son would tell me: "Drive it like you stole it!" . Use the heck out of it and enjoy !

A Darwin Award candidate has been found?

If the spot does not affect images, then forget about it. If it does affect the final image then what solvents have you tried? I have used Xylene to remove gunk with no damage to coatings, but go slowly and gently, and under good ventilation, preferably outdoors. Hospital cotton swabs, and one pass then replace with another swab. No scrubbing action at all, no real pressure. Just dampen with solvent on the offending area and gently pass the swab over it again only hard enough to loosen the crud, also rotate the swab so a clean part of the swab makes contact every cleaning pass, replace them often. After that harsh cleaning do a normal lens cleaning solution then a bit of distilled water to finish up. I would only do that if the lens were indeed needing it, and there was no alternative. In that case the lens is junk, and in the worst case: if you destroy it then just buy a new one. Before an outcry is heard I have done this on maybe ten lenses, never lost one! I have collected/repaired used microscopes for years, and the objectives can often be found compromised by gunk.

If you are not shooting tons of images, then why not shoot raw, or better yet: both? When I worked as a pro doing weddings and events: I and most of my colleagues at that time almost always shot JPEGs. It was up to us to know how to craft good images without the use of raw. We watched our histograms carefully. So we knew when a RAW image was the wise choice. Though honestly, I think I shot RAW less than 1% of my images in a year. The added processing speed while working with JPEGs was a blessing when I had to go through almost 2000 images and get them culled down, retouched, and ready for the bride to see in a week or so. I became so much in the habit of shooting JPEGs that I feel more comfortable doing it that way, even though I am completely retired for five years now. So now I usually shoot both at once. I rough edit using the jpegs to save time, then dump the RAWs that are not needed. But when action requires continuous shooting at the fastest rate the camera can muster, JPEGs only all the way!

If there was a lens made that had a wide zoom range, fast constant aperture, and low price, every photographer here would own that lens, and never part with it, even to our grave! You saw some great recommendations in the wide to tele range of zooms. Just settle on a few, then look up some reviews on each of the lenses. Then decide, and make an informed purchase. You will have confidence in your choice because you did your own homework. Now if you want a sweet bokeh and something for rad street portraits, just get a lowly 50mm, as an additional lens, in a f1.8-1.2 range as budget allows. It will give you a fast 75mm equivalent view on your Dx camera, with bokeh galore. So a wide zoom to sweep the street views, and a tight fixed to get personal with. If there is a local photo club near you, say hello and you may find yourself taking test shots on your camera body with a slew of nice lenses. Even a faster f2.8 lens in the range of zoom you have now cannot duplicate what a prime fast lens can render. And most of the great brands of lenses have made stinkers, that burn the purchaser. So do the homework before you lay your money down.

Beautiful images, and congrats on the write up!

If you can afford a sturdy CF tripod get it. There will be no regrets. If money is a big issue, then look for a good used aluminum, and buy at least one step larger than you think you need. A lot of good Aluminum tripods are on the market cheap because of the many pluses of the CF models and sometimes just the previous owners craving to upgrade. Just look at the multi millions of great photos out there taken with aluminum tripods for the past 75 years. Carbon fiber is better for several technical reasons, but not essential to make a prized image.
I have both and prefer the big aluminum tripod for my beast lenses, because I cannot justify a beast sized CF pod, and my Al version does an admirable job still. But the smaller CF tripod is a blessing during a long hike.

Sigma, Tokina, Tamron, and etc make excellent lenses nowadays. In the old days Sigma was usually the cheapest and helped many amateurs on a budget get their feet wet, enough said? But I would not turn my back on them now, great stuff! I still have an older Sigma zoom stashed in my drawer amongst a dozen Nikkors.
By the way there was also a 500mm f8 version of the same lens we are talking about, also light, but harder to focus with that F8.

A T-mount lens fits any camera that you can buy a t-mount adapter for. The adapter can be had used for $5 or so. But remember these were from the film days. You must be very careful when attaching to your modern camera. Some digital camera mounts may not be compatible. I use Nikon and have not had problems using the t-mount with my camera body: a D750. I use a T-mount to take photo-micrographs, and astro photos.

If I recall they were T-mount so a fits all? The lens itself just has threads to accept a T-mount adapter, no auto diaphragm lever. That lens sold by many different names. I used to have one, at the time (1960?) it was OK compared to hyper expensive name brands like Nikon or Canon. They were preset lenses. That means you computed your exposure, and set the aperture manually. Then rotate the preset ring to open it up to focus and compose the shot. Then rotate back gently until you feel it stop and now expose your image. I see them on the used market now and then, and like someone said they are not worth a lot. The $20-50 range was being generous, and shipping would throw it way out of range for its value.

to reply to jccash:
I have a monopod, but never really used it much. I think the tripod is essential to what I do, my style of shooting. Though a monopod is way better to walk with, no question there. I became used to carrying a tripod back in my large format days. And a small tripod would not work with that type camera. Aluminum was the only lightweight material in those days. But now that I am older, and only using a DSLR, maybe the monopod will get used more? So far still carrying the tripod, old habits die slowly? But I did purchase a carbon fiber tripod! Baby steps. . .

I usually carry a tripod in my hand, use it like a walking stick when I can. Never liked to hang it off my shoulder as it seemed to beat me up to much when I did not keep my hand on it. Kind of annoying to hike and then make an odd move only to have the tripod swing around on a strap and give me some new bruises! So better to keep it in hand.

Yeah in the good old days I had 4x5 Arca Swiss, and a Sinar. Also had 8x10 Arca Swiss. But preferred the Arca 4x5 for field use. It had a customized split rail that made it so easy to transport in my backpack. The technical quality of images was superb. But the important thing that I took away from those years with the big cameras was slow down! The format made you think a lot before even setting up the camera. When the shutter release was pressed you knew how you were going to develop that piece of film to achieve the final image that was already in your mind! A lot of that process was due to the brilliant Ansel Adams whom I never met. His books on Zone System were the large format bible. He taught us to think more and shoot deliberately.

If the crossbar cannot support the ten foot span, then your crossbar needs an upgrade. I used to use a back ground twenty foot wide for large groups, and added two support stands, Spaced evenly, inside the two on the ends, to support multiple crossbars linked together to give me the twenty foot span needed. When using 9 ft seamless, or ten foot span, I never had problems when supported with two end stands and the crossbar. You can make additional crossbars using steel conduit piping.

If it is that three paneled model with black, grey, and white, then I can tell you it was marketed to wedding and portrait photographers initially. We would use it to set color balance and also make sure both ends of the scale was exposed properly. We dealt with white wedding dress and a black tux and wanted texture and detail at both ends. The early digital cameras were not great in scale capturing ability. And worst case: we needed to preserve the whites so the bride was happy. A simple grey card is all most amateurs ever need? And yeah they were not cheap, I got mine for around $100 with the 30 inch and small one as a package, maybe bought it 20 years ago at a wedding photographers conference. The little one was always in my bag for use when the lighting changed and I wanted to make sure I got the color balance right. I usually shot the big one with my first group shots in the church to use later when processing. And the reverse side was intended to use as a handy reflector to use for fill. Often had my assistant hold it while doing available light portraits. Retired now but still have the device and use it once in awhile too! Would I buy one now? Heck no, too pricey and cannot write it off either.