[pschlute]

A good rule of thumb if you want to convert focal length equivalents from full frame to APSC, is to multiply the focal length by 1.5. For example, a 28mm lens on a full frame or 35mm film camera, becomes the equivalent of 42mm when used on an APSC camera like the K5iis (i.e. 28mm x 1.5 = 42mm). In other words, a 28mm lens on the smaller APSC sensor has the same field of view as a 42mm on full frame. This comes pretty close to being a normal lens then on APSC and not really a wide angle. At the longer end, that 105mm renders like a 153mm on the APSC. So your zoom range then becomes the equivalent of 42 to 153mm, as others have noted.

Hope this helps clarify things.

The OP has a K5 II. He does not need to convert anything to FF equivalents.

[DWS1]

I've used the D FA 28-105mm on a K70 and got great results. It's a great lens. It is not however a wide angle on APS-C. Closer to a normal lens.

[jim177]

OP, is there a special reason for wanting to use a D FA lens on the K5IIs?

If you intend going FF in the future it makes sense, otherwise not. Plenty of good DA lenses available.

I was interested in this lens as a good quality WR single lens for a variety of landscape situations. Also good for tourist travel, when we can.
I have the 50-200 and18-55 Pentax lenses amongst others.

---------- Post added 05-11-21 at 09:17 PM ----------

Thank you all for your very helpful answers! Seems that I need to relearn some basics on focal length and sensor size.
The HD DFA 28-105 mm might be the right choice for my all-in-one travel lens, but I'll do some more research.
Jim

[dbs]

Hi Jim

Use your 18 - 55 at 28 and see if that is wide enough for your ' travel ' shots.
I have/ use an 18 - 135 for a one lens option ( on a K5 ii ).
I do not own the 28 - 105


Dave

[Paul the Sunman]

The 28-105 is a great lens on FF, but on APS-C the 16-85 or 18-135 are more useful from my point of view because of the much wider short end. Even on FF, 28mm isn't very wide, and on APS-C it's much narrower still (42mm FF equivalent).

[caliscouser]

I was interested in this lens as a good quality WR single lens for a variety of landscape situations. Also good for tourist travel, when we can.

I'd recommend one of these:

DA 16-85 WR
DA 18-135 WR

The 16-85 will have slightly better image quality (but not by much) and gives you a little extra wide angle

The 18-135 gives you a little more telephoto and is cheaper

[clackers]

It's an excellent lens for APS-C, but of course you would also pack a wide angle lens as well, such as the DA15 or DA12-24 or DA11-18 or whatever.

[pentaxus]

It could be zoom range you like. I wouldn't like to use the 28-105 on APS C but my daughter prefers it. Sadly, none of us can tell you what you would like.

[othar]

As some pointed out: 28mm isn't particularly wide on your K-5ii, so when you mainly visit cities at your travels you should take a wide angle lens with you in addition to the 28-105mm lens.

If your interest is focused on hiking/mountaineering when traveling then 28-105mm has an advantage over some wider offerings in my opinion too. When taking snapshots of friends and family during hikes I tend to not bother that much about composition and perspective as I would with in general, because those tend to be fleeting moments that are over quick and I am aiming to create memories not art.
In those instances you might end up with some weirdly distorted pictures of persons when using the wide end of a 18 or 16 to something lens, while the 28-105mm lens forces you to exclude some of your surroundings it also helps to increase your keeper rate for those instances.

edit: my main walk-around lens on my K-3 is the F 35-70mm lens (hiking & mountaineering), for architecture I bring something wider with me too.
With lanscapes you can very often, very easily stitch multiple images together if your lens is not wide enough to photograph the whole scene at once

[mikesbike]

It is a fine-performing lens. I bought one at $100 off in a kit deal with my K-1 II, as an all-around moderate weight zoom lens having WR. Otherwise, I already have a number of other high quality FF zoom lenses. I never use it on my APS-C bodies, because in this case it provides no wide angle and I see no advantage compared to my excellent lenses which are designed for APS-C that do provide both wide angle and telephoto.

I like the DA 18-135mm as a high-quality all-around zoom lens on both my KP and my K-5 IIs. Its AF is impressively fast and sure on both cameras, and I get fine imaging from it and with an exceptionally useful zoom range. It is very well-built. It can even deliver quite fine close-ups, and it is very compact for such a zoom range. Due to its compactness, the built-in flash for grab shots works without a hitch, just be sure to remove the lens hood.

[Serkevan]

I was interested in this lens as a good quality WR single lens for a variety of landscape situations. Also good for tourist travel, when we can.
I have the 50-200 and18-55 Pentax lenses amongst others.

---------- Post added 05-11-21 at 09:17 PM ----------

Thank you all for your very helpful answers! Seems that I need to relearn some basics on focal length and sensor size.
The HD DFA 28-105 mm might be the right choice for my all-in-one travel lens, but I'll do some more research.
Jim

For landscapes 28mm on a K-5 might be wide enough. For travel... eeeeeeh I'd look into how much the lack of wide angle would affect you. Do you use your 18-55 at wider than 28 often? That's what you'd be missing on.

[Lowell Goudge]

Years ago, when I bought my first DSLR (*istD) it came with an FA-J18-35 mm lens, I supplemented it with the FA 28-105 F4.0-5.6 from my PZ 1 for quite some time as the two lens combo I would shoot with.

For the OP if he wants this focal length range, there are lots of legacy options, but I see no reason not to use the DFA 28-105, especially because it is a weather resistant lens.

The lens has the added benefit that being full frame he can move up to a K1 in the future without replacing lenses.

For years I used this strategy. The only cropped sensor lenses I bought were a sigma 10-20, and a Samyang 8mm fisheye.

The rest of my gear was full frame, which also allowed me to use it on my film bodies including my PZ1.

I ultimately replaced the FA 28-105 with a faster tamron 28-75 F2.8 lens, which has served me well, but I am looking to replace the Tammy with a WR lens at some point as I have had my K1 with the Tammy fog badly twice in humid conditions, once in Dublin and once in New Orleans. WR has a definite value when travelling because you can’t dictate the weather but you still want to go out and shoot, at least I do.

[Sandy Hancock]

DFA28-105 on the (crop) KP. I reckon it's OK

[jim177]

Hi Jim

Use your 18 - 55 at 28 and see if that is wide enough for your ' travel ' shots.
I have/ use an 18 - 135 for a one lens option ( on a K5 ii ).
I do not own the 28 - 105


Dave

Thanks. Good advice. I tried my 18 - 55 at about 28 mm and found it wasn't wide enough.
I'll rethink my options, but the 18 -135 is looking better now.

[dbs]

Hi Jim

The 16 - 85 seems to be the ' better ' option
Choices abound depending on what range and how many lenses you are happy to carry to get it.
Next week who knows what Pentax will bring to the table.


Dave