Definitely go with a monopod. .Many have a wooden knob screwed to the top to make it double as a walking stick. At 74 it looks natural. At 83 mine works great and is less bulky than a tripod.

Bill de is correct. The F/stop is a ratio between the focal length and the physical diameter of the aperture. Purely a mathematical/ physical function. The actual light transmission will vary. Several factors come into play.
The number of glass elements within the lens. There is a small light loss within each element. The more elements the more loss. The physical length of the lens. The longer the travel path the more light loss. Every maker coats each element with an anti-glare/ anti-reflection substance to reduce loss and reduce flare. All manufacturers are not alike. Also in the manufacturing process, not all of the same lenses are identical. It is really beyond our control. Shoot picture and be happy.

David Busch's manuals are very good and seem to be printed in larger type for us senior shooters.

Nikon makes a living on selling cameras, After the D7500 they will want you to buy the D7600 then the D7700. Do you see a trend here??

Not knowing where or time of day that you were shooting I will offer this possible cause. Light, sun or man-made, grazing across your front lens element will fog your pictures. As you rotate toward the light beam you can notice in the viewfinder a brief angle that the view is fogged. Some lenses are more prone to this as their front element protrudes further forward than others. You might try installing a Lens Hood and trying a similar shot, same time, direction to see if this is indeed the problem. Also, remove the lens from the camera and look through it to see if the fogging is a problem within the lens itself.

ElNikkor,
I am sure you know that pointing the camera at the sun for prolonged periods can damage or even burn holes in your shutter and is tough on the eyes. Now about the white spots. For a long time, it has been known that viewing the sky in broad daylight from the bottom of a deep well. one can see stars. I offer no solutions but just a possibility that the white spots are indeed stars. Since your lens seems normal in other situations I submit this as a possible solution. Know any astronomy people??

First off, since the manufacturers are smart, they do not make DSLR's that are film friendly for us old film shooters. Face it we are dying out so that is a disappearing market. There is no real market there in the first place. "We are a dying market".
Secondly, you learned film, get off of your rear and join the twenty-first century and learn digital. There are dozens of book & manuals out there to give you a bump start into the real world. You will find that you can do anything you could with film and more, and easier in digital without breathing developer/ fixer fumes. So stop complaining and join us old dudes in the digital world.

Flickr and a few online sites are a great way to show the world your photography. Flickr not only stores your photos but keeps a running set of statistics on the number of viewers who have viewed your pictures, who has them as a favorite and comments. The membership is free and they also have a "PRO" membership at $25.00 a year which gives you a larger storage file. You can communicate with photographers all over the world.

If for no other reason, the lens hood is the bumper, shock absorber for your lens. The space that it takes up is minimal, but the cost of having to replace the lens due to a broken or scratched front element will make the space loss seem like a small sacrifice. I must admit that it does make using a polarizer difficult.

Another thought: Being a lens junkie I have over thirty lenses. We travel the world a lot. I have found the Sigma 18-250 is the lens for traveling. Fairly compact and not very heavy. I also have a Sigma 19-300 but it is very heavy and larger in diameter. If the sensor on your camera is an APS-C the effective range of the 18-250 is really 27-375. I also always carry a 50mm f1.7 and a Sigma 10-20. I almost can't remember what they look like. The 18-250 never comes off the camera. Have fun on your trip.

I'd take the 24-70. To still stay light consider a 1.4X or 2X teleconverter. Pocket size yet would help with some outdoor shots.

Adorama will quote you the market price then pay you about a third less.

I'm with you. Long streaks of white do not look like water flowing to me.

Don't give up on your lens. Hand holding, up close with a macro lens almost invites it to hunt. Go MANUAL and a tripod.

I agree with you.I know that if I went to the same spot, set all the same settings, I wouldn't get the same picture. So, I guess it helps fill another page for that months issue.