I've just done the opposite, on one of my bikes.
I have a rather wide spread 5 gear freewheel, 14,17,22,27,32

I needed a few more gears, so I went from a 52,40 chain rings,
to a rather close triple of 52,47,36.

I having to relearn how to shift, especially since I'm using
a backwards shifting, stem mounted, Suntour.

One of my preferred setups for pleasure riding on my Moto GJ is a 13-14-15-16-17-19 with 36-49-52 single step plus granny combo. Single step makes the shifting dead simple, which is nice for high speed pleasure riding on a friction shifted vintage bike.
On my commuting and other utilitarian bikes, I prefer a half-step plus granny combo, (with the same chainring progression as above) for the added flexibility, with a wider range rear, e.g. 13-23 up to 13-28. All my rides sport a short to medium cage RD to shift/wrap such combos.
I do use the 52T chainring on all my rides on all my bikes, i.e. in the 80+ gear inch range, and typically all the way to 108 (downhill, or at least with the wind, obviously ).

You're not making it easy asking for both a lower bail-out gear _and_ closer-spaced high gears. That's less easy than either/or, and hoping to do this without changing derailleurs and a whole bunch of other stuff is a tall order. You also haven't hinted at how low a low gear you think you need/want, so all we can do is talk about what we use, and spitball. It's hard to be specific without actual numbers. You will need to know the actual tooth count of the freewheel cogs.

Spacing your high gears closer doesn't impact derailleurs, but can you find the cogs/ratio you want? Like John E said, a corncob pretty much means single-tooth jumps all the way through, so a 6spd corncob would be 13-18. 13-23 is only a corncob if you're talking 11 cogs. Maybe you can find the right cogs for your freewheel to go 13-17+24, corncob plus a bailout. Maybe not. Maybe going from 6spd to 7spd will give you better choices.

Lower gearing is likely to impact ders, both to shift bigger cogs/smaller rings and to handle the extra chain. Going triple means extra chainring/bolts, longer bb at a minimum. Maybe new crankset, maybe new bb. Depending on how small an inner ring you want, possibly new fder. And likely new rder as well, if you want a really low low with a lot of chain to wrap.

Many possibilities. If your triple inner can go down to 24t, you can change your 42 to something bigger and get closer high gears. Go from 6spd to 7spd for closer high gears.

You'll want most of the high gear work on the two bigger rings, and use the small ring for the hills. But you have to pay attention to the gear progression. How many duplicate gears on 13-14-15-16-18-24 (for ex) and 42/52? 44/52? You've got 5 cogs from 13-18 for high gears, and 2 rings for 10 high gears, but if 3 or 4 are identical, or close to it, you've only got 6 or 7. And the shifting necessary to avoid the dupes might be a pain. Crossover makes easier shifting, but wider gear spaces; half-step maintains tighter progression, but shifting is considerably more complex.

This is one of the reasons, like it or not, that compact doubles with 9-11 cogs simplify gearing life. No dupes when you're only using the big ring for faster/flatter riding, dumping to the small ring for climbing. No double shifting to maintain a steady progression, easier A/B big/small shifting in the front, less muss, less fuss.

He said he is looking for a 1:1 ratio when on the granny gear and the largest rear cog.

I must have missed that. I'm only seeing two posts from him, neither mentioning a low gear target. All I'm seeing regarding low gear needs is: "I need a way to spin up these hills."

My apologies, there is another C&V thread on the same topic. I had the OP's confused.

No worries, wouldn't be the first time I missed the nose on my face!

If you're modeling gearing, this can't be beat: kstoerz.com | visual drivetrain comparison tool

I have a shimano tri color corncob on my touring bike, with an ovaltech triple. It ended up there by accident, after I broke the removal ears on the original freewheel. It was all I had on hand, so on it went. Since we don't have that much elevation here sans the occasional overpass, I rarely shift more than a gear or two. If I were to take it on a longer ride through the hills, I may wish for more gear, but that's what that granny gear is for. Sure I'll have to shift a few times to get everything lined up, but this bike isn't built for speed anyway.

To me, "corn cob" means 13-17 or 13-19, etc. IMO, 13-21 or above doesn't qualify.

Note Wide difference double like the 20t (28-48) in the 22nd post chart only has an overlap of a few gears

You could do that with a 86 BCD crank . or 2/3 of the 110/74 triple

What 8 speed 28 also gives you a 19-18-17-16-15 ? A 12-21 8speed with a 28-38-48 gives a nice climbing gear, close shifts all the way across the spectrum with no cross-chaining. If you are not a spinner , you might not appreciate it.

I run a Shimano 50/39/30 crank and a 14-25 9speed cassette I modified to 14-28. Nice tight ratio with less than 11% steps (except for the 28T bail-out), perfect for group rides in CO where all the rides start a 5000 feet and go up. Compact double riders are always double shifting on the flats, triple riders pick one of three gear ranges.

For a 5-speed, 13-17 or 14-18 would indeed qualify. For a 7-speed, yes, 13-19 or 14-20.

How about for a 9-speed? By the same single tooth progression logic, 13-21 would qualify, would it not?

My definition: TL-TH = N-1, where TL = low/large cog tooth count, TH = high/small cog tooth count, and N = number of cogs on the cluster/cassette.

I see your point, but I think it's worth keeping the middle ring for the improved chainline benefits.

Yeah, some of us are guilty of stretching the definition a little.

But I think the general thrust of the thread is (or has become) that a triple with a tightly-spaced FW/cassette can be really nice... and true corncobs are hard to come by in post-FW systems. Once you have one-tooth jumps out to the 17T or 19T, there are diminishing returns to those tiny jumps, so they move on to the two-tooth jumps. (The 13-14-15-16-17-19-21 "J" cassette I wish I had bought more of encompasses the classic 5-speed 13-17T corncob and adds to it.)

Depends on the number of cogs on the cogset. A 12-21 eight speed is the tightest eight speed cassette currently sold by Shimano. 12, 13, 14, 15, 16, 17, 19 & 21 qualifies as a corncob.

So would a 12-13-14-15-16-17-18-19-20-21-22-23-24-25-26-27-28 count as a corncob? Just askin'.

Heh. I guess so. I saw an article about 13-speed cassettes being on the way. Some sort of breakthrough is making it possible, though I don't remember what. Maybe it's material hardness at lower cost, to make everything narrower. It will be funny if we skip 12-speed cassettes.

13 speeds, FTW!

I am intriged by the idea of a 28-48 double, especially a 86bcd Stronglight 99. Does anyone have any pictures of a crankset like this? Front and rear photos would be great. Any personal experience using this combo. What FD would you use?

And here I was, betting it would never happen!

As I said earlier, the shifting pattern would be majorly annoying, at least for me. This is where electronic shifting could be an asset to me. Just hit the one shifter, moving it higher or lower. The computer figures out which derailleur or derailleurs to use and which way and how far. That could be an improvement. Already, I'm seeing the wisdom of 1x drivetrains for that very reason. Your only choices are up and down, no mixed shifts.