Web Analytics RiceHigh's Pentax Blog: DA 18-55 on Full Frame

Tuesday, October 14, 2008

DA 18-55 on Full Frame

I have taken some test shots with the Pentax DSLR kit lens DA 18-55 on my (K)5D. Indeed, quite some Pentaxians have been wondering and questioning about how those DA lenses could produce if they are used on Pentax film SLRs. However, only just several Pentaxians had actually tried to do some tests and shot through the viewfinder or to scan exposed films and presented the effect(s) publicly before. Now, I think this series of my shots will show exactly how this Pentax standard kit lens will behave when it is put on a full frame (digital) camera. Look at the projected images below:-

@ 18mm (at f/4.5)

@ 20mm

@ 24mm

@ 28mm

@ 35mm

@ 45mm

@ 55mm (at f/8)

1. All images were taken with one f-stop closed down from wide opened;

2. All images were taken in M exposure mode with 1/8" Tv at ISO 800. As such, the tele images came out to be (at most 1.5 stops) darker, so as to exaggerate the vignetting effect at the tele side, for easy inspection.

Well, now you can see the contracted image circle(s) at the wide side of this digital kit zoom which is designed for the APS-C sensor format. As a side note, the infamous (de-)centering defect of (the DA/DA*) Pentax lenses has once again been verified. Just look at the images produced at the wider angles, it can be more easily seen that the projected image circles have been shifted to the right, that is, the optical center of my lens at those focals is actually yet mis-aligned to the left (when I am facing the back of my camera). But the even more strange thing is that when the lens is zoomed to the tele side, the de-centering is reversely shifted to the left (for the images produced, just look at the (positional differences of the) corner vignettings). In fact, the only symmetric image I could get is the one shot at 35mm. Huh? What? How come? Why?? :-0

So, some people may question if the sensor of my 5D and/or the mount/adaptor is/are just mis-aligned. But what I can tell is Not. It is simply because my Pentax F Fisheye Zoom produces symmetric images when at 17mm where a little bit of the built-in lens hood can be shot (for the technical reason for why it has to be, look here for the details). Just see this test picture:-


After all, the QC or simply quality difference(s?) between Pentax lenses that were made in Japan against those are / were made in Vietnam (or just nowadays) has yet been verified.

1 comment:

Anonymous said...

Gosh this is so very fascinating. Please investigate further and tell us the answer to this oh-so intriguing mystery.

Post a comment