ulf Posted March 22, 2021 Share Posted March 22, 2021 Last Update: 03 Aoril 2021 agb/labelFinalized: Work in progress.Bushnell 21mm f/3.8 Automatic Manufacturer: BushnellLens Label: Bushnell Automatic f:3.8 f=21mm No.<serial number>Currently manufactured: No Lens type: Manual focus, Prime, Ultra Wide-angleFocal length: 21mmAperture range: f/3.8 – f/16, Manual / Automatic with pin-actuation , 6 blades,Design: TBDFlange Focus distance: Mount dependableMount: M42 x 1.0**, others?Sensor format/coverage: up to 24mm x 36mmFront filter: 72 mm x 0.75 mmIntroduction year: TBDS/N of test object: 7000206**Mount of test object Image of test object: Transmittance SummaryDefinitions of the parameters belowRange: The Bushnell 21mm f/3.8 Automatic lens transmits 1-55% in an increasing slope from 354nm to 400nm.TVISmax (%) =74%T400nm (%) = 55%T365nm (%) = 15%This rather low percentage is an indicator for a longer exposure time under typical UV-pass filtration peaking around 365 nm.λUV HMvis(nm) = 378nmλUV HM400 (nm) = 371nmλUV Zero (nm) = 354nmThese three values indicate that the lens is working best for UV-A photography with filters with a good transmission closer to 400nmSpectral transmission graphs:UV-NIR, Bushnell 21mm f/3.8 AutomaticThe transmission measurement accuracy into the end of NIR range is less good due to limitations in the light source. UV, Bushnell 21mm f/3.8 Automatic UV-Log, Bushnell 21mm f/3.8 AutomaticNumerical Spectra Data available: Pending Filters and how to use them on this lens:The front filter thread is 72mm standard filter thread. A step-up filter ring and bigger filters will be needed to avoid vignetting with a filter stack.This wide angle makes it unsuitable using front mounted dichroic filters, causing a big colour shifts towards the corners.It might be possible to use such filters rear mounted instead ti decrease the problem. (tbd) It is possible to use rear mounted filters, either in lens mount adapters for mirrorless cameras like Sony A-series etc, or placed directly in the camera. An alternative, if space in the camera allows, is to putty-mount a filter directly against the lenses rear flat parts.The rear lens element is recessed and thus safe and the ring provides a good reference plane for orienting the filter normal to the optic axis. My Omega 330W80 Improved Ø25mm, is mounted in a 27mm-filter ring and would work well to mount as it is.Handling and focussing:This lens has a focusing helicoid that smoothly turns almost a full turn for focus from infinity to around 0.3m. Flare and sun-stars: TBD Sharpness: TBD Lens distortion:TBD Chromatic Aberration / fringing in UV:TBD Link to comment
dabateman Posted March 22, 2021 Share Posted March 22, 2021 Ulf did you have the rear filter glass issue that Cadmium posted: https://www.ultravioletphotography.com/content/index.php/topic/1626-bushnell-21mm-vs-nikkor-18mm-uv-transmission-test-comparison/ Link to comment
StephanN Posted March 22, 2021 Share Posted March 22, 2021 Would it be worth noting that the same lens probably also goes by other names, e.g. the Soligor 21mm f/3.8 (https://www.ultravioletphotography.com/content/index.php/topic/4169-soligor-21mm-f38/ ) looks pretty similar? Link to comment
ulf Posted March 22, 2021 Author Share Posted March 22, 2021 Ulf did you have the rear filter glass issue that Cadmium posted:https://www.ultravio...est-comparison/No I did not.This is a different type of lens with f/3.8 while Cadmium's lens is a f/4.5.They do not share that problem. Link to comment
ulf Posted March 22, 2021 Author Share Posted March 22, 2021 Would it be worth noting that the same lens probably also goes by other names, e.g. the Soligor 21mm f/3.8 (https://www.ultravio...ligor-21mm-f38/ ) looks pretty similar?Yes I saw that when writing about the Bushnell-lens.Except for some external differences like the focus ring design they appear very similar.That made me glad when I got the Bushnell-lens as your images look sharp.Frankly I have not used it at all. I have been more into close-ups of flowers.However I like the wide angle perspective and after getting a FF Sony A7 III that lens makes more sense to use like you do on your Canon 6D. Link to comment
OlDoinyo Posted March 25, 2021 Share Posted March 25, 2021 This could be another decent lens in the 20-21mm range; there are not a lot of those (The Tamron and Asahi offerings are similar, but with slower maximum aperture.) Now if there were only a 14mm that is usable in UV.... I suspect rear-mounting dichroic filters will also lead to problems. These old wide-angle lenses have small rear elements and high corner divergence angles in the rear. Stick to alternatives if possible. Link to comment
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