[akash.srivastava]

I am thinking to upgrade to Full Frame from my Nikon D7200. Since, Pentax K-1 doesn't have a built-in flash, hence I will need to buy an external one. My requirements for flash usage is limited to occasional for family portraits.

What is the cheapest external flash available. I looked at ricoh site and found that AF 360FGZ (available for $109 at Adorama) is the cheapest and should work for my needs. However, I am unable to confirm whether it is compatible with Pentak K-1.

Also, are there any 3rd party flashes available?

[rawr]

Welcome to the forum.

Probably any flash with a standard ISO hot shoe will at least fire from the K-1.

The Pentax AF201FG flash should be a lot cheaper than the AF 360 FGZ II. And there are lots of third party flashes available that will work with the K-1 and support Pentax's P-TTL flash system, from Yongnuo (YN585EX), Shanny (SN600FGZ), Metz (26AF-2, M400, 44 AF-2, 52-AF1, 64 AF-1) etc.

Search B&H for 'Pentax flash', look at brands like Metz, Pentax and Sigma, and you will see that there is a decent range available.

[clackers]

However, I am unable to confirm whether it is compatible with Pentak K-1.

It is.

There are third-party flashes too, including by Sigma and Metz, but compatibility for each model is something you would need to research first.

[Paul the Sunman]

If you want P-TTL, I recommend either Pentax or Metz. The smallest one that can act as a master is the Pentax AF 360 FGZ II, which is very nice.

[kiwi_jono]

There are quite a few options. Might be beyond your budget but I agree that Pentax AF 360 FGZ II is a nice option. I have one (got for a good price second hand) and it works well with K-1, bit better build than previous model and is also weather resistant.
See: PENTAX AF 360FGZ II reviews - Pentax Camera Accessory Review Database

[C_Jones]

I have three Pentax AF360FGZ flashes that I use to do wireless shooting with. I have used them with both with my K-3II, which has no pop-up flash, and my K-5IIS, which has a pop-up flash. The off camera flash option using the built in wireless feature of the camera(s)/flashes is effective and simple to use. I resort to Manual mode when I use the flashes for off camera shooting, but the P-TTL mode is there if the user decides to utilize it. The AF360FGZ is very dependable and nicely built. The head does rotate up to bounce light off ceilings, but does not rotate left/right to bounce off walls/reflectors to the side of the subject. The left/right rotation would be handy, and it is available in the Pentax 540 units and other 360 (II) unit, but I have done well without it. Overall I would recommend the AF360FGZ unit along with any of the other Pentax 360 or 540 series units.

[Bob from Aus]

I got from B&H a $30 second hand AF200FG. I switched it to -1 Auto and it works a treat. It's still a bit heavy because it has 4 AA batteries.

[acoufap]

For family portraits IMO you don't need a big and strong flash. So for on camera usage or wired with a TTL cord I'd recommend the Pentax AF201FG. You can even use it outside in more wet situations because it's WR. To get a notion of the flashs size I added two images comparing build-in flash size of K-5 and AF201FG on the same K-5. It fits in every pocket and on the K-1 it also does a good job.

I wrote some additional informations about the AF201AF here. Maybe you find this helpful.

[akash.srivastava]

Thanks everyone for your valuable inputs. For now I have zeroed on Pentax AF 201FG.

[akash.srivastava]

Thanks everyone for your valuable inputs. For now I have zeroed on Pentax AF 201FG.

[Paul the Sunman]

Nice. The ability to tilt the head is a huge advantage over the 200FG. Just be aware that it doesn't rotate.