कला
सुन्दरता र कल्याण
हस्तकला
संस्कृति र इतिहास
मनोरञ्जन
वातावरण
खाना र पेय
रिभर्स इन्जिनियरिङ
विज्ञान
खेलकुद
प्रविधि
पहिर्न मिल्ने
Retrofocus Wide-Angle Lens
Reflex cameras put a mirror between the lens and the film, and a conventional wide-angle lens needs to sit closer to the film than the mirror allows. Pierre Angénieux in Paris reversed the telephoto idea: a diverging group in front, a converging group well behind it, so the lens's focus lies further back than its focal length.
**US 2,649,022**, "Wide-angle photographic objective lens assembly", Angénieux, filed 29. July 1950, granted 18. August 1953, describes an objective whose "distance along the axis between the back surface of the last lens and the focal plane … is relatively very large with respect to the focal length". (His US 2,649,021 of the same day is a different lens - a large-aperture projection objective.)
**You build one on the bench**, measure its back focus against its focal length, and fit a mirror in the room it leaves.
शुरुआती
90 minutes
निर्देशनहरू
1
1
Two lenses, reversed
Two lenses, reversed
Front: concave about -50 mm, facing the scene. Rear: convex about 50 mm, 60 mm behind it. Aim out of a window.
यस चरणका सामग्री:
अवतल लेन्स1 टुक्रा
उत्तल लेन्सको सेट1 सेटचाहिने औजार:
प्रकाशीय बेन्च र पाटो
लेन्स अड्याउने सेट2
2
Find the focus
Find the focus
Move a tracing-paper screen until the distant scene is sharp. Measure rear lens to screen: the back focus. Measure the height of one far feature on the screen.
यस चरणका सामग्री:
नमुना सार्ने कागजको मुठो1 पाना
मास्किङ टेप1 रोलचाहिने औजार:
फलामे रुल3
3
Compare one lens
Compare one lens
Remove the concave lens. The +50 mm lens alone focuses about 50 mm behind itself; measure the same feature's height.
चाहिने औजार:
फलामे रुल4
4
Fit the mirror
Fit the mirror
Put the concave lens back. Stand a small mirror at 45 degrees between the rear lens and the screen position and turn the screen to catch the image from the side - a reflex viewfinder. With the single lens there is no room.
यस चरणका सामग्री:
समतल ऐना1 टुक्रा5
5
Back focus vs focal length
Back focus vs focal length
Jupyter नोटबुक लोड हुँदैछ…
6
6
History & Context
History & Context
**What the patent specifies:** a diverging meniscus front element and a converging group far behind it, giving a back focal distance large compared with the focal length. **Modern build (derived):** two stock lenses and a mirror.
Angénieux sold it as the Retrofocus; nearly every SLR wide-angle since uses the layout. Its limits: the asymmetry brings barrel distortion, and the big front element makes the lens larger and heavier than a symmetric design.
सामग्री
5- 1 टुक्राप्लेसहोल्डर
- 1 सेटप्लेसहोल्डर
- 1 पानाप्लेसहोल्डर
- 1 रोलप्लेसहोल्डर
- 1 टुक्राप्लेसहोल्डर
सम्बन्धित ब्लुप्रिन्ट
यी ब्लुप्रिन्टहरूले ज्ञान साझा गर्छन् — प्रविधि, सामग्री वा सिद्धान्त
CC0 सार्वजनिक डोमेन
यो ब्लुप्रिन्ट CC0 अन्तर्गत जारी गरिएको छ। तपाईं अनुमति नसोधी प्रतिलिपि, परिमार्जन, वितरण र प्रयोग गर्न सक्नुहुन्छ।
ब्लुप्रिन्ट मार्फत उत्पादनहरू किनेर सिर्जनाकर्तालाई सहयोग गर्नुहोस् सिर्जनाकर्ता कमिसन विक्रेताले तोकेको, वा यो ब्लुप्रिन्टको नयाँ संस्करण बनाउनुहोस् र आम्दानी बाँड्न आफ्नो ब्लुप्रिन्टमा जडानको रूपमा समावेश गर्नुहोस्।