Wikipedia:Reference desk/Archives/Science/2024 October 4

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October 4

Lens

Suppose a camera had lenses and one of them was a lens that was flat on one side and convex on the other, and you reversed it so the flat side was in the other direction. What would happen to the focal length? RJFJR (talk) 02:58, 4 October 2024 (UTC)

It would be like a minute change of a zoom objective. The direction of the change depends on the original orientation of the lens. That is because in this case the optical position of the lens is slightly beside the mechanical position. And the shift occurs because the direction of the difference goes to the opposite. 2A02:3032:305:F2EF:616E:4B30:D3CA:B0AE (talk) 09:55, 4 October 2024 (UTC)

Reversing the lens also affects the optical aberrations, which is why we sometimes want an asymmetrical lens. PiusImpavidus (talk) 15:08, 4 October 2024 (UTC)

The OP describes a plano-convex lens. The Focal length of the lens is the distance at which a beam of collimated light will be focused to a single spot and is given exactly by the lensmaker's equation. For most purposes this thin lens approximation can be used: ${\frac {1}{f}}\approx \left(n-1\right)\left[{\frac {1}{R_{1}}}-{\frac {1}{R_{2}}}\right].$. Philvoids (talk) 19:00, 4 October 2024 (UTC)

I have read the article about lenses. The thin approximation is mentioned three times or so. But the real formula is not at all. 176.0.164.84 (talk) 11:28, 7 October 2024 (UTC)

nevermind. Found it. Don't know how I could overlook it. 176.0.164.84 (talk) 11:32, 7 October 2024 (UTC)

Physical Conditions where childhood development is essential to diagnosis

As I understand it, when someone is assessed for autism they are asked questions about their childhood behaviour and development as well as their behaviour now, even if they are well into adult life. This means that two middle-aged men with identical behaviours could receive different diagnoses if one displayed signs of autism as a child and the other didn't.

If that is right, and sorry if it isn't, then are there any examples of physical conditions which are diagnosed the same way? Where displaying symptoms as a child is an essential part of the diagnosis, and two patients displaying identical symptoms in adult life may be diagnosed differently?

81.106.106.219 (talk) 12:43, 4 October 2024 (UTC)

Not an expert by any means, but our autism article says it is a neurodevelopmental disorder that is manifest in early childhood, and therefore a history of the condition is highly pertinent. Alansplodge (talk) 20:16, 6 October 2024 (UTC)

Correct. When even fairly young children are being evaluated, their earlier childhood gets questioned. When I inquired about this, I was told that the reason is to see what the behaviour of the person was like before they starting autistic masking. So, presumably, any other situations where masking (personality) can come into play would also form part of the OP's answer. Matt Deres (talk) 18:37, 10 October 2024 (UTC)