|
|||||||||
![]() |
|
Thread Tools | Search this Thread |
![]() |
#1 |
Regular Crew
Join Date: Jan 2004
Location: Europe
Posts: 180
|
Focal length and filter distance from lens
Hi,
I was looking at some sunshades/filterholders and matteboxes that could be used to mount a few contrast reducing filters in front of my PDX10. It has a focal length of 3.6mm at the widest angle of view. This 3.6mm wideangle (~50mm equiv.) - or should we call it "narrowangle" - is quite unusable for certain shots, so a wideangle adaptor must be applied. Now after that the focal length is 0.7x or 0.5x so it becomes: f=2.52mm or f=1.80mm With wideangle shots there are often contrast problems, at least in my shots, so I need some filters. *** What happens if I put some filters in front of the lens and the distance between the lens and the filter(s) is greater than or equal to the focal length? *** Problems? What kind of problems? Focusing on the filter? Picture quality degradation? Is there a way to circumvent those problems? At least the Chrosziel filterholders are rated as follows: f=7.8mm -> max 3 filters f=5.2mm -> max 2 filters f=4.5mm -> max 1 filters so f=2.52 or f=1.80 looks really bad :( I kind of guess why the Sony lens hoods only allow a single filter to be used... |
![]() |
![]() |
![]() |
#2 |
Retired DV Info Net Almunus
Join Date: Dec 2001
Location: Chicago, IL
Posts: 6,943
|
Two issues can arise, although I cannot say how they relate to specific focal lengths. One, depending on the nature of the mounts, the corners of extremely wide shots might become clipped by a deep stack of filters.
Second, given the depth of wide-angle frames, focusing on a filter (and any dust of smudges on it) can become an issue. I believe that these are probably the key matters at issue.
__________________
Lady X Films: A lady with a boring wardrobe...and a global mission. Hey, you don't have enough stuff! Buy with confidence from our sponsors. Hand-picked as the best in the business...Really! See some of my work one frame at a time: www.KenTanaka.com |
![]() |
![]() |
![]() |
| ||||||
|
|