Can you use a screw-on apodization filter, or does it need to be inside the lens?
Asked 4/2/2017
5 views
2 answers
0
I’ve read about lenses that use an apodization element to smooth out out-of-focus highlights. Since it seems like a circular graduated neutral-density filter, could a similar effect be achieved with a front-mounted screw-on filter if some vignetting is acceptable? If not, is a DIY apodization filter near the aperture likely to work reasonably well?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
2 Answers
4
Going into my favorite resource again, Smith, Modern Optical Engineering, we find
Apodization is the use of a variable transmission filter or coating at the aperture to modify the diffraction pattern. Coatings which reduce the transmission at the center of the aperture tend to “favor” the response at high frequencies; coatings which reduce transmission at the edge of the aperture tend to favor the lower frequencies.
Now, what often happens with telephoto lenses is that the entrance pupil (aka aperture stop) is well in front of the physical lens. That makes mounting the apodizing element difficult, to say the least. You'd need the full lens prescription to know where the aperture stop is, and build an extension mount to hold the filter.
The Sony lens mentioned (I'm guessing) must have an internal relaypoint which reimages the entrance pupil, and that's where their apodization filter is placed. There's no guarantee that any given lens has such a relaypoint, so even if you did open up your lens, there might not be an appropriate place for the filter.
Originally by user25396. Source · Licensed CC BY-SA 4.0
user25396
9y ago
0
Generated from our catalog & community — verify before relying on it.
A front screw-on apodization filter generally won’t work the way a true apodization element does. Apodization is a variable-transmission filter placed at or very near the aperture stop so it changes the light distribution across the pupil and therefore the blur rendering and diffraction behavior.
On most lenses, especially telephotos, the effective aperture stop/entrance pupil is not at the front of the lens and may be located deep inside the optical design. That means a screw-on front filter is in the wrong place and will mostly just add vignetting rather than produce the intended apodization effect.
In principle, a custom filter placed very close to the actual aperture can produce some apodization-like results, but doing this properly depends on the lens design and the exact position of the stop. Without that information, it’s difficult to implement well. So: yes, it may be possible as a DIY experiment near the diaphragm, but no, ordinary screw-on filters are not a practical equivalent to a true apodization lens element.
Recommended products
UniqueBot
AI9y ago
Your Answer
Related Questions
What does an apodization filter do for bokeh, and is it worth it?
What would translucent aperture blades do to image quality and bokeh?
Can you use a square graduated filter with a circular screw-in filter system?
Can I use a screw-in variable ND together with graduated ND filters in a holder?
Can you use a screw-on variable ND filter with a Cokin Z square filter holder?