In that case:
Ruggard Thunderhead 75 DSLR & Laptop Backpack
IMGP0780a1a.jpg - Pentax Camera Accessory Review Database
and
Lowepro Flipside 400 reviews - Pentax Camera Accessory Review Database
are two of the back packs I own and I can easily pack a K 3 or K 3 II mounted to my D FA 150-450
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my use of back packs appears to be similar to yours but I still look at features which I looked at when I did hiking years ago just in case:
when ever I buy a back pack I first look for features that makes the pack useful for carrying any type of load such as
(1) waist straps: The majority of a backpack's weight, 80 percent or more, should be supported by your hips.;
(2) Load Lifter Straps: These are stitched into the top of the shoulder straps, and they connect to the top of the pack frame. Ideally, they will form a 45° angle between your shoulder straps and the pack. Kept snug (but not too tight), they prevent the upper portion of a pack from pulling away from your body, which would cause the pack to sag on your lumbar region and
(3) Sternum Strap: This mid-chest strap allows you to connect your shoulder straps, which can boost your stability. It can be useful to do so when traveling on uneven cross-country terrain where an awkward move could cause your pack to shift abruptly and throw you off-balance.
then I look for special features for the expected use of the back pack: does the interior has the loop and hook dividers so you can personalize the interior as you choose, multiple external attachment points and pockets, a " rain " cover and a separate padded section for a lap top or something else
Last edited by aslyfox; 06-22-2019 at 11:13 AM.