[Barry Pearson]

makes not much sense, because the lens is to slow. Better get an other zoom. There are a lot better options out there.

The Pentax D FA 28-105mm is the lens I have, and will continue to use, for this walk-about purpose on the K-1-series.
My 2 years of experience with it tells me that it has very high image quality over its natural optical range.

I'm currently testing this combination: K-1ii, D FA 28-105mm, Pentax 1.4x TC.
I set the camera to square crop mode, which eliminates the corner vignetting caused by using a converter that wasn't designed for FF, and this crop shows in the viewfinder.
So I'm just using 4912 x 4912 (24 MP) of the K-1-series sensor, and the best part of the lens field.
Initially at least, I'll use the lens wide open, hence an actual f/8.

I'll be running comparison tests on what image quality I can get, with the lens at 105mm, with or without the Pentax Converter, using Lightroom Classic CC to squeeze out the best image quality.

Pentax D FA 28-105mm lens: 440 grams
Pentax 1.4x Converter: 126 grams, and slips into a packet.

[clickclick]

That 50-135 result was unexpected. I'd love to find out more about a 60-250 with the baffle modifications too. Thanks for the quick report Adam. Being able to use the 50-135 as a full frame f/4 70-189 is a really nice surprise.

And I found with the full frame Pentax 1.7x AF/TC, my 50-135 fully covers the full frame. Of course, this is a bit different scenario since the Pentax 1.7x AF is full frame to start, but the simple translation is using a crop lens on a full frame TC has a good chance of expanding the crop image circle enough to fully cover the full frame sensor. Now, whether the IQ really is better than just resampling and enlarging the crop lens without any TC is a whole separate rabbit hole, and my results are a big "depends".

[angerdan]

BUT! I believe Pentax is making new teleconverters that are full frame compatible! They mentioned that during a recent interview..

FF TC - full frame teleconverter - PentaxForums.com
CP+ 2018 Pentax Interview - CP+ 2018 | PentaxForums.com

[Charben]

The Pentax D FA 28-105mm is the lens I have, and will continue to use, for this walk-about purpose on the K-1-series.
My 2 years of experience with it tells me that it has very high image quality over its natural optical range.

I'm currently testing this combination: K-1ii, D FA 28-105mm, Pentax 1.4x TC.
I set the camera to square crop mode, which eliminates the corner vignetting caused by using a converter that wasn't designed for FF, and this crop shows in the viewfinder.
So I'm just using 4912 x 4912 (24 MP) of the K-1-series sensor, and the best part of the lens field.
Initially at least, I'll use the lens wide open, hence an actual f/8.

I'll be running comparison tests on what image quality I can get, with the lens at 105mm, with or without the Pentax Converter, using Lightroom Classic CC to squeeze out the best image quality.

Pentax D FA 28-105mm lens: 440 grams
Pentax 1.4x Converter: 126 grams, and slips into a packet.

My original thought was to use the DA 1.4x converter on K1 using FF mode. I do expect some vignetting. But there are a group of DA lenses which will work on the K! with little or no vignetting. Was wondering if the converter is in this group.

Yes, using crop mode should result in images without vignetting just like using a DA series crop lens on K1. However, according to Pentax, the resolution will drop to 15.36 mp not 24 mp as noted. This resolution is lower than the APS C K3.

Please let me know how your tests turn out.. I expect it will work fine with respect to vignetting. But like to know the resulting resolution..

[Barry Pearson]

My original thought was to use the DA 1.4x converter on K1 using FF mode. I do expect some vignetting. But there are a group of DA lenses which will work on the K! with little or no vignetting. Was wondering if the converter is in this group.

In my experience, I always get vignetting with the Pentax 1.4x Converter when used on the K-1-series.

Yes, using crop mode should result in images without vignetting just like using a DA series crop lens on K1. However, according to Pentax, the resolution will drop to 15.36 mp not 24 mp as noted. This resolution is lower than the APS C K3.

I hope I always said "square crop mode", not just "crop mode". There are two different crops on the K-1-series.
"APS-C Crop Mode" on the K-1-series is about the same resolution as the K-5-series, and less than the K-3-series.
"Square Crop Mode" is about 24 MP: 4912 x 4912.

Please let me know how your tests turn out.. I expect it will work fine with respect to vignetting. But like to know the resulting resolution..

Vignetting is bad in the corners of the full FF sensor. But "square crop mode" is sufficient to eliminate the bad bits, and shows in the viewfinder.
There are other crops that work as well, but they rely on a bit of guesswork.

[Charben]

In my experience, I always get vignetting with the Pentax 1.4x Converter when used on the K-1-series.



I hope I always said "square crop mode", not just "crop mode". There are two different crops on the K-1-series.
"APS-C Crop Mode" on the K-1-series is about the same resolution as the K-5-series, and less than the K-3-series.
"Square Crop Mode" is about 24 MP: 4912 x 4912.



Vignetting is bad in the corners of the full FF sensor. But "square crop mode" is sufficient to eliminate the bad bits, and shows in the viewfinder.
There are other crops that work as well, but they rely on a bit of guesswork.

Thanks for the reminder on 1:1 square crop. Aside from wanting to know how DA 1.4x converter will work on K1, I do not use crop lens on my FF. The Crop mode is always set to FF. Forgot about the 1:1 crop mode completely.

There are a group of DA lenses that will work on K1 with little or no vignetting.. see this link RiceHigh's Pentax Blog: Compatibility of DA Lenses on Full Frame

I have the DA*300/4 for my K3. This lens is compatible with K1 and I have used it recently in FF mode. There were no vignetting..

[UserAccessDenied]

We have tested the following lenses with the TC:

DA* 300mm "red" - light vignetting wide-open, worsens as you stop down
DA* 200mm "green" - no notable vignetting
DA* 50-135mm "green" - soft corners only
DA* 60-250mm "yellow" - light vignetting throughout lower half of the zoom range (note: baffle was not removed)

TLDR, if reach is your objective, it will probably not deliver a FF image circle when you need it. But it really varies from lens to lens.

This is a legitimate question:
If reach is your objective, why shoot with a K-1 in the first place?

Wouldn't the benefits of the crop (K-3ii, KP, K-5iis) outweigh any benefits the FF would provide?

Maybe I'm missing something here... I'm a K-3ii shooter and primarily focus on wildlife, so reach is my main objective! I've just kinda stopped following the FF content as I assumed it would never be a place for me. The idea of losing that extra "reach" with the 1.5x crop factor has me thinking I'll stay APS-C forever. Am I missing something here?


Granted, yes the technology in the K-1 and K-1ii is beyond that of the K-3ii, but that's to be expected. Assuming the K-3ii successor has similar high ISO capabilities and AF speeds as the K-1/K-1ii, what are the benefits for long-reach shooters like myself to consider FF?


Cheers!
Logan

[clickclick]

This is a legitimate question:If reach is your objective, why shoot with a K-1 in the first place?

Pretty much agree. I've done a variety of comparison shots between my K-3II and K-1 with the DFA 150-450, and as long as I have good light, the K-3II wins, which makes sense - the crop area of the sensor on the K-1 that matches the FOV of the K-3II is about 16MP versus 24MP for the K-3II. The only time I reach for my K-1 when birding is when the light gets low, and I need to keep my shutter speed up. I feel like the noise at 1600 on the K-3II is about on par with the K-1 at 3200.