[MaineNative]

My vote is the 18-135, 10-17 and the 55-300. I have all three lenses and they are fairly compact. This is the combo I normally take on travel with my K-5. The 55-300 would pretty much be just for wildlife.

The 10-17 is “fishy” at 10 mm, but it makes some neat shots due to the wide view. Just pay attention to what you want to keep straight and put it in the middle of the lens.

[K-Three]

I just got back from a trip to Mt. St. Helens, similar car trip and day hikes with the family, 5 days worth.
I had a small shoulder bag with K3, 18-135, 55-300 and 15mm in it. Also had my big LowePro backpack with K5, too many other lenses and other stuff in it. Never touched the big bag. mostly switched back and forth between the two zooms. Got lots of scenics, wildlife, some wild flowers, and the family.
Had tripod and monopod with me too, they stayed in the car.
If I was by myself, I would have carried more as I could stop and work with it, with the family I was time constrained, no one else is a photographer, they don't understand.
YMMV,

[seventysixersfan]

all of these comments were super helpful, thank you so much! I definitely have some considerations to think about.

Tonight I put out all the different combinations (assuming I stick strictly to my "3 lenses only" plan) and it was helpful for me to visualize the lineups as follows:

#1 the all zoom option: (aka the @Rogerstg option)


#2 the fisheye zoom alternative to option one above (aka the @MaineNative option)


#3 the DA 15 limited alternative to option one and two above (aka the @stevebrot option)


#4 the highest image quality, and lightest/most compact option but most frequent lens changes needed (aka the @Gianclaudio option)


#5 the no overlapping focal lengths option (aka the @northcoastgreg option)


#6 the "specialty lenses" combination that is the least flexible option (nobody suggested this)


of course, there are other mixes and matches that I left out, but you get the point. I'm currently leaning towards either options 1, 2, or 5.

[suraswami]

We have reached the Climax, which 3 stooges are going to win?

I vote 1

[Paul the Sunman]

I'm a big fan of the DA 10-17 ... in moderation. As a sole UWA on an extended trip though, I think you'd get very sick of the smell of fish long before the end. The 15, 18-135, and 55-300 would be my choice.

[microlight]

My normal travel kit is another variation on this, as seen in my signature. We were in Sequoia National Park a couple of years ago - enjoy!

[aslyfox]

A serious note, be watchful and careful of your surroundings

no taking a step backwards to perfectly frame your image and falling off of the cliff


________________________
I would cheat and take 4


the 15mm isn't big and it is a limited:

Diam x Length 63 x 39.5 mm (2.5 x 1.58 in.)
Weight 190 g (6.7 oz.)

Read more at: SMC Pentax-DA 15mm F4 ED AL Limited Reviews - DA Prime Lenses - Pentax Lens Reviews & Lens Database

the 10-20 mm

Diam x Length 8.6x8.9 mm (3.4x3.5 in.)
Weight 520 g (18.3 oz.)

Read more at: Sigma 10-20mm F3.5 EX DC HSM Lens Reviews - Sigma Lenses - Pentax Lens Review Database

the 100mm is a very sharp short telephoto ( I have the non WR version ) and gives you macro if you wish

Diam x Length 65 x 80.5 mm (2.6 x 3.2 in.)
Weight 340 g (12 oz.) w/ Hood: +38g ( 1.34 oz. )

Read more at: SMC Pentax-D FA 100mm F2.8 Macro WR Reviews - D FA Prime Lenses - Pentax Lens Reviews & Lens Database

and the PLM

Diam x Length 76.5 x 89 mm (3.01 x 3.5 in.)
Weight 442 g (15.6 oz.)

Read more at: HD Pentax-DA 55-300mm F4.5-6.3 ED PLM WR RE Reviews - DA Zoom Lenses - Pentax Lens Reviews & Lens Database

[MetalUndivided]

I'd go with either #3 or #5.

[microlight]

Some samples from my non-overlapping travel trio, from last year' New Zealand trip:

The Pa at Pa Beach on Great Barrier Island - 10-17 Fisheye at 11mm, de-fished in ACR.
Waikato river at Huka Falls, North Island - 20-40 at 20mm.
Lonely yellow-eyed penguin, sunset at Cape Saunders, Otago Peninsula, South Island - PLM55-300 at 300mm.

[WPRESTO]

Been there, photographed those places and the #2 or #1 kit as pictured above is the way to go for maximum range and compact, light to carry.
1) 18~135mm for general shooting
2) 10~17mm and defish*, as recommended above. There are close-quarters places where you'll want either this or the Sigma 10~20mm, but the Pentax is more compact if you want a small, light kit.
3) 55~300mm, there is wildlife, both birds and mammals, you'll want the reach.

RECOMMENDATION, if possible, get an achromatic close-up filter for the 55~300mm, very useful for flowers, insects, lizards and sometimes a snake with a noisy tail. My original version of the 55~300mm worked well with a Nikon achromatic close-up lens (now discontinued, but clean copies almost always available on EBAY), Canon still offers a range of achromatic close-up filters and there are also units from Marumi in two diopter values and many thread sizes.

ALSO RECOMMENDED: A monopod or very lightweight tripod, not necessarily carbon fiber.

*Defishing primarily loses the corners where there is rarely something that will be missed. I use LR and defish using the the distortion slider. If that's not quite enough, I send the image file to PS, then back to LR and the distortion slider is back at midpoint so it can be used again to remove even more distortion, if desired.

[UncleVanya]

Been there, photographed those places and the #2 or #1 kit as pictured above is the way to go for maximum range and compact, light to carry.
1) 18~135mm for general shooting
2) 10~17mm and defish*, as recommended above. There are close-quarters places where you'll want either this or the Sigma 10~20mm, but the Pentax is more compact if you want a small, light kit.
3) 55~300mm, there is wildlife, both birds and mammals, you'll want the reach.

RECOMMENDATION, if possible, get an achromatic close-up filter for the 55~300mm, very useful for flowers, insects, lizards and sometimes a snake with a noisy tail. My original version of the 55~300mm worked well with a Nikon achromatic close-up lens (now discontinued, but clean copies almost always available on EBAY), Canon still offers a range of achromatic close-up filters and there are also units from Marumi in two diopter values and many thread sizes.

ALSO RECOMMENDED: A monopod or very lightweight tripod, not necessarily carbon fiber.

*Defishing primarily loses the corners where there is rarely something that will be missed. I use LR and defish using the the distortion slider. If that's not quite enough, I send the image file to PS, then back to LR and the distortion slider is back at midpoint so it can be used again to remove even more distortion, if desired.

This! The Raynox, Nikon, or Canon is a good idea. Light and easy to use.

I own all of the except the Sigma and the Plm version of the 55-300 (I have the DA version). I adore my DA 15, and if you plan sunrise or sunset pictures with the sun in the frame... there the glare resistance of the DA 15 may be a major benefit over the 10-17. The defished 10-17 is overwise an excellent choice.

[DeadJohn]

Summarizing my thoughts: consider bringing just 2 lenses, the 18-135 and 10-20.

You said you wanted to reduce lens changes, which makes the 18-135 an obvious choice for your main lens.

I always like having something wider than 18mm on APS-C size sensors like the K-50. The DA 15 is a contender for size, contrast, and flare resistance. Your 10-20 is also a contender due to zoom versatility. If you do indeed only bring 2 lenses I think the 10-20 versatility wins.

You might not need the 55-300. 135mm is already a great amount of reach for landscape features. Only bring the 55-300 for wildlife, which might be tricky to photograph while 2 kids are with you. It's a personal decision, based on your family's patience and whether you might have opportunities to photograph while they do something else.

[WPRESTO]

SUREST THINGS ARE: You'll regret not bringing something and you'll never use something you do bring.

[The Squirrel Mafia]

#1 the all zoom option: (aka the @Rogerstg option)

#2 the fisheye zoom alternative to option one above (aka the @MaineNative option)

I'd have a hard time picking between the 10-17 & 10-20. The 10-17 has it's charm & the 10-20 is rectilinear. You can get some very interesting photos with the 10-17 & even get some semi-rectilinear photos at 17mm. I think I'd lean towards the 10-17 by a hair & use the 18-135 as your widest rectilinear lens when you need to.

I have a feeling that you're going to end up using the wide & long tele zooms the most & probably not going to use the 18-135 much. That's what happened to me the last time I was in Japan. I used the 10-20 the most followed by the 50-200.

[seventysixersfan]

Thanks for all your excellent comments. And yes, I will definitely watch out about trying to get the perfect selfie— I have heard about people in Yosemite falling to their death this year doing just that.

So I went back to pictures I took from my 2018 and 2017 trips to Acadia National Park in Maine and Olympic National Park in Washington State, to get a sense of what lenses I most often used. I’m now thinking I might not need the 55-300mm zoom, assuming I take my 18-135, because I agree with @DeadJohn - in my circumstances in traveling with a 8 and 5 year old, I don’t have time to change lenses all that often in the field — so it’s more likely I will pick a lens for a particular day and leave the others back at the hotel or in the car. I did use my DA 70mm a fair amount while in Acadia and got some awesome candid shots of my kids scrambling around on big rocks and on the beach. I also used my DA 15mm in Olympic a lot, though my 18-135 was the true workhorse of that amazing trip. I actually took my DA 10-17 and Sigma 10-20mm to Acadia and used both, though I seem to recall that the DA 10-17 shots were more contrasty and of course had the punchier Pentax colors. Plus DA 10-17 is a lot lighter and smaller. I also took my DA 55-300 PLM to Acadia but ended up using it just for a few shots. I guess I’m not really a wildlife shooter, or the 135mm end of the 18-135 is good enough. I think I’ll leave the 55-300 at home in the interest of keeping my camera bag as light and small as possible.

So... I’ll probably pack the DA 10-17 fisheye for wide angle and creative shots (though I might swap it for the Sigma 10-20 at the last minute when I’m packing). Then I will also take the 18-135 for use as my primary walk around, and finally, my favorite lens DA 70 for a fast telephoto prime that will give me the sharpest pictures. That’s a pretty nice group of 3 lenses given my particular circumstances, shooting preferences, and where I’m headed.

I love this forum! Thanks for the great advice.