K-1: What to expect from your APS-C-lenses - a look through the FF-viewfinder

Having pre-ordered the K1 (without kit lens) I was wondering how my existing lens lineup would work with it. With my FF-lenses - both Pentax and third party ones - I of course have to wait until I get the K-1's body in my hands to really find out. But I thought: What about my four APS-C lenses, for instance my beloved DA10-17? Will they be of any use on the K-1?

So I dug out my old Ricoh XR-7 to check the image circles projected by my four lenses on it's viewfinder - an easy way to see basic vignetting and such. I mounted the DA 10-17, DA 16-45, DA 18-55 and my Tamron 18-250 on it and got some interesting results - thought I would share my "looks through the viewfinder" here with you.

Since it's not that easy to get a good picture of a "viewfinder view" be warned - not all the pics are perfectly sharp, but I think you'll get some interesting info from them anyway. In spite of quality issues involved I invite you to have a look at them at the full size presented here - I downsized them to 1200 px width for easy viewing.

Here's what I did: I mounted the aforementioned lenses on the XR-7 and did a sample shot at every marking of the zoom ring of every lens. On the DA10-17 I did an extra shot at about 15mm.

1. DA 10-17

Let's start with the DA 10-17:

The DA17-10 seems to have a large enough image circle for the full frame from 17mm up to 15mm. At 14mm you see rounded corners, at 12mm not even a 1:1 crop seems possible, at 10mm you have only a central part of the frame filled - but hey, 10mm is almost a circular fisheye, and this also doesn't fill the frame! Apart from that I hope to use the DA10-17 at the 17mm setting somewhat successfully on the K-1. Maybe a useful WW lens for it after all, even if used only at the long end!

2. DA16-45

With the DA 16-45 you get usable results from 45mm down to 28mm. At 20mm very prominent corner vignetting is obvious, at 16mm the frame isn't filled any more - to any side. The DA 10-17 definitely is the better option at this focal length. And since I have a FF Tamron 28-75 I probably won't bother using the DA16-45 on a K-1 - it should cover the usable 28-45 range of the DA 16-45 well enough.

3. DA 18-55

The DA 18-55 AL WR is okay from 55 to 35mm; at 24mm corner vignetting is visible, but not too bad IMO. On the other hand at 18mm even a 1:1 crop might be stretching it a bit ... Probably won't use it on the K-1, same reasons apply as stated for the DA 16-45.

4. Tamron 18-250

The Tamron 18-250 is my most used travel lens, and boy, Tamron has certainly been economical as far as the size of the image circle is concerned. You don't get a full frame picture at any length - not at the long end, and it really get's worse until you reach the final 18mm. Not a lens to consider in any way for the K-1. That's why I'm getting it's FF friend, the Tamron 28-300 (it will be far from a stellar lens on the K-1, I strongly suspect, but I really am a friend of the versatility of travel lenses like these, I have to admit).

Okay, that's about it. Didn't have any more APS-C lenses to test.

If you're interested here the setup for the viewfinder shots:

The XR-7 was directed towards a neutral background with a small Pentax Q7 piggy-backed on its viewfinder (for the DA10-17 the whole setup was moved much closer to the background to get the frame filled):

Here a closer view of the two cameras:

Here you can see how close the Q7 (with the close focusing 04 lens) sat on the XR-7's viewfinder:

As you can imagine focusing was a bit tricky - and I discovered a bit late in the process that re-adjusting focus after each single shot was a very good idea.

Any thoughts on my findings?

Phil