I recently purchased a 25mm lens for my Pentax 645 system. This is one of the new lenses designed for the digital 645D / 645Z cameras alongside the DFA 645 55mm and the DFA 645 Macro 90mm.
A few important facts about the lens:
At 25mm when used on the 645D it is equivalent to 19.5mm on a FF 35mm camera. This is one of the widest medium format lenses available. I also use the excellent 645 35mm.
It’s a heavy beast at 1040g and expensive US$ 4,996.95 at B&H (although still several thousand less than the Hasselblad 24mm). Occasionally they appear used on Ebay, which is where I purchased mine.
As with the 645D body, the 90mm, and 55mm, it’s weather sealed so can stand up to the elements. This really separates the Pentax system from other medium format digital systems which are more suited to a controlled studio environment.
The front element is curved, which means filters are designed to be inserted internally. The filters are 40.5mm and polarizers can be rotated with a nifty dial on the holder.
Interestingly, this is a DA 645 25mm F4 and not the DFA 645 25mm F4 lens I borrowed from Pentax a couple of years ago. This means it is not a full frame 645 lens unlike the DFA 645 Macro 90mm, the DFA 645 55mm, or any of the older 645 lenses.
There is some softness in the corners as is to be expected on such as wide angle lens. Chromatic aberration also occurs in the corners when there is high contrast (backlit foliage shows purple fringing) although this can be easily fixed in Lightroom.
It’s exactly one month before the release of the Pentax 645Z. If you are keen, or worried they’ll be in limited supply, you can pre-order the 645Z at B&H. The sensor in the 645Z is the same size as that in the 645D, but the higher resolution and overall jump in image quality (if the rumors are true) will mean that the latest digital lenses will really shine.