Along with parallax errors, non-ideal lens distorsion is a pain for stitching images since not all distorsion follow a nice a,b,c distorsion correction model, resulting in some mismatch between frames.
Going into Pentax forum in depth lens review or ephotozine test results, we can compare lenses on how much optical distorsion they produce. With the idea of reproducing a 4x5 exposure area by stitching multiple exposures from a Pentax K1, the "crop" factor between 4x5 and full frame being about 3x, for a wide angle shot I'd need to use a focal length of 100mm (more or less depending on the final FoV of the stitched composition).
-> Pentax D-FA24-70 f/2.8:
- Pentax forum test: -0.1% @ 70mm
- ephotozine test:
"70mm gives +1.45% pincushion distortion"
-> Pentax D-FA28-105 f3.5-5.6: -3.26% @ 28mm, -0.941% @ 35mm, +1.05% @ 50mm,
+1.55% @ 70mm, +1.6% @ 105mm
-> Pentax D-FA70-200 f/2.8: 0.9% at 70mm,
-0.6% @ 135mm, -0.5% @ 200mm ; problem with the DFA70-200 is the nodal point moves a lot from near front of the lens at 200mm to back of the camera at 70mm, very sensitive to the focal length and a pain to adjust in the field.
-> Pentax D-FA100 f/2.8 macro:
- comment from PF review
"This lens is designed as a macro lens with a flat field of focus and no distortion and we were definitely not able to detect any distortion."
- ePHotozine/Imatest:
0.07%
-> Pentax D-FA50 f/2.8 macro:
- comment from PF 50mm lens comparison:
"We are happy to report that none of the Pentax 50mm lenses had any measurable distortion."
-> Pentax D-FA50 f/1.4: comment from PF :
"Most 50mm lenses don't have significant issues with geometric distortion, and the HD Pentax-D FA* 50mm F1.4 SDM AW is no different"
- ePHotozine/Imatest:
0.01%
Is this a property of macro lens designs, or 50mm lens designs, to produce zero optical distorsion?
Are there any other lenses around that produce zero distorsion around 100mm focal length?
Last edited by biz-engineer; 02-19-2020 at 02:44 AM.