[wadge22]

Sigma 135-400mm f4.5-5.6 and 120-400mm f4.5-5.6, as well as Tokina 80-400mm f4.5-5.6 all might fit the bill.

[MikeNArk]

Sigma 135-400mm f4.5-5.6 and 120-400mm f4.5-5.6, as well as Tokina 80-400mm f4.5-5.6 all might fit the bill.

I agree with these recommendations. I have the Sigma 135-400 APO and use it virtually every day with good results. The Tokina 80-400 lens is also one that I would consider, but it may be difficult to find for a Pentax camera.

[wadge22]

The Tokina 80-400 lens is also one that I would consider, but it may be difficult to find for a Pentax camera

It's definitely not one that comes up frequently, but there's one up on ebay right now, shipping from Japan, and purporting to be in near mint condition. No hood though, at least none pictured.

[UncleVanya]

I doubt 55-300 will work with 1.4xTC. Teleconverters are usually designed for fast high-quality lenses.

Doubt away… but there are numerous reports from forum users that claim it works ok in good light. I’m personally unlikely to use mine that way since I have the 60-250 and fa* 300 as better options for teleconverter use.

[Digitalis]

These lenses are profoundly uncommon however if you ever come across a second hand Sigma 100-300mm f/4 APO, GET IT!



Pentax KP - Sigma 100-300mm f/4 APO EX




Pentax K5IIs - Sigma 100-300mm f/4 APO EX


Also the Pentax FA*250-600mm f/5.6 is a beast, but when it comes to telephoto zoom lenses it is superb..


Pentax KP - SMCP-FA*250-600mm f/5.6

[m42man]

It might not matter if the body can read the focal length as much as you might think. Use the tool linked in the link mentioned in this thread to set an optimal single setting for manual zooms. There are multiple optimization choices that influence the decision, and the tool output gives you the info so you can decide what focal length setting is optimized for your use.

Setting IBIS on a manual zoom with SCIENCE! - PentaxForums.com

In the marketplace recently there were listings for a Sigma 120-400, a 50-500, as well as a 100-300 all of which offer the automation to inform the body of the focal length in use.

Hmm, the linked post states, from the article it's referring to: "IBIS for a 28-200 (per this paper) should be set to 75mm for optimal effect". This is bunkum, and should be ignored.

If you input a value which is greater than twice the actual focal length, the camera will move the sensor such that you end up with more blur than with SR turned off.

There are two formulae you can use though:

1. This equalises the blur reduction at each end of the zoom range, and is intrinsically safe (i.e. will never magnify blur): 2*min*max/(min+max)

2. This equalises the amount of blur at each end of the zoom range, so is better at the long end - but is only safe for zoom ratios up to 3:1 - just take the average, i.e. (min+max)/2

There's another, more sophisticated formula which optimises for random zoom settings, and this can be found over at dpr. You end up with a value somewhere between the two above, but be careful, as some (large) zoom ratios will end up with an unsafe value.

[UncleVanya]

Hmm, the linked post states, from the article it's referring to: "IBIS for a 28-200 (per this paper) should be set to 75mm for optimal effect". This is bunkum, and should be ignored.

If you input a value which is greater than twice the actual focal length, the camera will move the sensor such that you end up with more blur than with SR turned off.

There are two formulae you can use though:

1. This equalises the blur reduction at each end of the zoom range, and is intrinsically safe (i.e. will never magnify blur): 2*min*max/(min+max)

2. This equalises the amount of blur at each end of the zoom range, so is better at the long end - but is only safe for zoom ratios up to 3:1 - just take the average, i.e. (min+max)/2

There's another, more sophisticated formula which optimises for random zoom settings, and this can be found over at dpr. You end up with a value somewhere between the two above, but be careful, as some (large) zoom ratios will end up with an unsafe value.

The paper clearly discusses the pros and cons of the various settings and clarified why each might be best under what circumstances. It also clearly points out why using that recommended setting is probably best and leaves it up to the reader to decide which tradeoff they prefer.

[m42man]

The paper clearly discusses the pros and cons of the various settings and clarified why each might be best under what circumstances. It also clearly points out why using that recommended setting is probably best and leaves it up to the reader to decide which tradeoff they prefer.

Yes, I should have read the article - so you'd only choose the value of 75 if you weren't anticipating using FLs below 37.5mm (or at least were happy with blur magnification that would result if you did). Still, hardly "optimal".

[maw]

I have owned it for several years and it is an excellent zoom, for sharpness, focusing speed and weight,
I use it mostly on the K1 but also on the K3II, the only problem is finding one in good conditions, and price.

Sigma 170-500mm F5-6.3 APO DG Lens Reviews - Sigma Lenses - Pentax Lens Review Database

[straton]

The Vivitar 100-500 F/5.6-8 A Series 1 Lens is sharper than the Sigma 170-500 F/5.0-6.3 ASP APO in the foreground and as good at infinity. It is much lighter. I got mine for $170. For any long lens you will get better sharpness using a light-weight tripod, allowing you to use the K-1's mirror lockup (Live View), than you will on your mono-pod,

[gatorguy]

I have owned it for several years and it is an excellent zoom, for sharpness, focusing speed and weight,
I use it mostly on the K1 but also on the K3II, the only problem is finding one in good conditions, and price.

Sigma 170-500mm F5-6.3 APO DG Lens Reviews - Sigma Lenses - Pentax Lens Review Database

I was very surprised at how well it performs up to 400mm or so. At full-zoom it's a little soft, but nothing that can't be taken care of with a little sharpening in DxO or Topaz. For the price it's a real winner, recommended.