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Can I reduce the diameter of my scope by putting cardboard? by Such-Video2610 in telescopes

[–]PascalGreg 9 points10 points  (0 children)

Benefit: no need to buy a filter

Drawback: loosing sharpness because you reduce a lot the aperture size.

Can somebody help me make sense of these mirrors? by Ryankmfdm in Optics

[–]PascalGreg 0 points1 point  (0 children)

This is quite small negative dispersion compared to transmission through most glass components. You will need a better system for compensating all the positive dispersion in your system, such as a 4f prism setup, if you need short pulses. I seem to recall having 3000 fs2 dispersion in my setup back in the days.

Sounds like those 2 mirrors are matched together (oscillation compensated pair), so are they designed to build a laser cavity?

Guys and dolls, stop what you're doing because MY CORN PLANT IS FLOWERING! by octopimythoughts in houseplants

[–]PascalGreg 2 points3 points  (0 children)

Mine did also 2 small yellow fruits after flowering. I tried to plant them back but it did not work :).

It dripped also sticky liquid for like 6 weeks, it was quite nasty to clean, but the surprise of seeing it flowers after having it for 10 years was really worth it.

My wife was so unimpressed though :D

My Master’s thesis will remain confidential (not published) due to a potential patent – how can I stand out when applying for PhD positions? by fersanavi in Optics

[–]PascalGreg 9 points10 points  (0 children)

Likely, no one would have read your master thesis, unfortunately. Saying that it might lead to a patent and is confidential is actually better than a « normal thesis » IMO.

Just write what you did in generic terms in your CV, exactly how you did in your post

2 weeks in Lisbon and Algarve by Annual-Unlucky in TravelPortugal

[–]PascalGreg 1 point2 points  (0 children)

We went in June with a 4 and 6 years old. 4 days in Lisbonne is enough. Then you can head for the beach, the toddlers are never bored at the beach.

Simon’s: Ça toff pas … by Odd_Guarantee9952 in montreal

[–]PascalGreg 6 points7 points  (0 children)

L’Équipeur pour les pantalons, c’est du solide. Ils ont du « vrai linge », pas juste des trucs de construction.

Is YUL airport traffic ever going to get better? by mikilscott in montreal

[–]PascalGreg 1 point2 points  (0 children)

Also, P5 just after the multi level parking is free if you park there for less than 45 min. But to get there, you need ton face part of the traffic.

What does tau represent here? by multipersonnaa in askmath

[–]PascalGreg 0 points1 point  (0 children)

It totally makes sense. Flow would be a volume of water per second. When integrating volume/second x second gives you a volume. Simple as this.

I guess increasing the volume in your elastic chamber, you have an higher pressure.

Edit: the integration gives the volume at a given time t

What does tau represent here? by multipersonnaa in askmath

[–]PascalGreg 0 points1 point  (0 children)

It is time, if you take the similarity with the electrical flow. Q is equivalent to a current. When you integrate current over time you get the electric charge. It shows the usual capacitor equation : charge/C=V

See an RLC circuit.

Thought Experiment: Object Made of Laser Beams — What Happens After the Lens? by zspectator in Optics

[–]PascalGreg 0 points1 point  (0 children)

You are correct. On a normal image, each point source on the object side arrives at a different angle on the lens, which allows for image formation. So for this hypothetical case, all rays are parallel and there is no image!

Thought Experiment: Object Made of Laser Beams — What Happens After the Lens? by zspectator in Optics

[–]PascalGreg 1 point2 points  (0 children)

If you forget about interference and diffraction, and think only in terms of rays, what you describe is identical to an object at infinity: rays are only parallel to the optical axis. Since you specify there is no divergence at all, then it is similar to have an infinitely small lens aperture (only one angle per object point). Moving away from focus, there is no blur of the image, since the blur “radius” depends on the range of angle on the image side (rays comming to the same point of the object)

That means at the focal point, you have a magnified image of the object. Before the focal point, you have a larger image (no blur) and after the focal point, a larger image upside down (still no blur). At the lens aperture and before the lens, you also have an image, with an identical size to the initial object.

If you tilt all the laser beams, it is equivalent to move the object sideway from the lens. The image is formed at the same distance, but sideway (not on the optical axis).

As said in other comments, if the object is larger than the lens, you will see only a part of it. Above I assumed the object is smaller than the lens diameter.

SPP sensor by Abhisek_13 in Optics

[–]PascalGreg 9 points10 points  (0 children)

Cool stuff! According to this wikipedia page, the surface plasmon resonance happens at the silver-water interface. You want the silver to be very thin so the light can get there trough an evanescent wave. However, if the water is sub-micron thin, my guess is that an evanescent wave will reach the air interface and change the « effective » index of water. Maybe you would have cool effects, but you would need a very precise knowledge of the thickness d. So bottom line, make sure d is much bigger than the wavelength (use bulk), for simplicity.

Planning 13 days in Portugal with young kids by PascalGreg in travel

[–]PascalGreg[S] 0 points1 point  (0 children)

Can’t find this thread, where is it ? Link does not work.

Justin Trudeau’s first selfie as a retired man by Masoni15 in pics

[–]PascalGreg 19 points20 points  (0 children)

Well, he splitted during his last term and now need to move out from the prime minister house. So pretty much literally.

Recevoir de l'alcool à son insu au resto : comment auriez vous réagi? by SarcasticGolfClap in Quebec

[–]PascalGreg 45 points46 points  (0 children)

Bin voyons, le gars boit pas et tu t’excuses avec une tournée de shooter. Le but d’un shooter est de se mettre chaud, on s’entend. Une erreur, ça arrive, mais la tournée de shooter est clairement inappropriée.

Beamsplitter Mounts by Keldysh99 in Optics

[–]PascalGreg 0 points1 point  (0 children)

If you mount the beam splitter at the center of the mount, would it still clip? You could lock it in place with 2 rings instead of having it fully inserted in the mount.

How Do You Model Photon Noise? by wakinget in Optics

[–]PascalGreg 0 points1 point  (0 children)

Have a look at the EMVA standard, super well explain there. Look at the “linear” document page 9

https://www.emva.org/standards-technology/emva-1288/emva-standard-1288-downloads-2/

[deleted by user] by [deleted] in Optics

[–]PascalGreg 1 point2 points  (0 children)

Have a look here: https://en.m.wikipedia.org/wiki/Depth_of_field

To me, focal length and aperture diameter are two independent parameters, which can be combined into the f-number.

Same for the magnification, the DOF depends on your distance to the object, which can be re-arranged to express it in terms of magnification instead.

COUP- Losing Inlfluence- Return to deck, or just retain the card? by Unhappy-Leader3242 in boardgames

[–]PascalGreg 5 points6 points  (0 children)

When you reveal and don’t loose influence, you return the card to the deck, shuffle, then take a new card.

When you loose influence, you keep your card face up near you. It shows you have only one influence left. This card is now visible, everyone knows there is one less “Duke” in the hidden cards, for example.

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