<p>Absolutely:
<span class="math-container">$$\theta = \frac{4GM}{c^2b},$$</span>
where <span class="math-container">$\theta$</span> is the angle of bending, <span class="math-container">$G$</span> is the gravitational constant, <span class="math-container">$M$</span> is the mass of the star/blackhole/whatever, <span class="math-container">$c$</span> is the speed of light, and <span class="math-container">$b$</span> is the "impact parameter", the distance from the light ray to the center of the mass on its closest approach if it was NOT deflected (i.e., <span class="math-container">$b=0$</span> for an impact).</p>

CC BY-SA 4.0
2019-09-18T13:34:37.320Z
This is the weak field approximation. The question was asking about strong lensing.
TimRias
CC BY-SA 4.0
2019-09-18T18:46:28.517Z
This is a weak lensing formula that doesn't address the question asked.
ProfRob
CC BY-SA 4.0
2019-09-19T13:45:12.657Z
I do not recall the bold term being there when I answered it!
Maury Markowitz
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2021-04-05T11:00:48.470Z
@MauryMarkowitz that's right, I put it in boldface because apparently you didn't see it.
ProfRob
CC BY-SA 4.0
2019-09-18T10:40:20.133Z
2019-09-18T11:07:36.800Z
2019-09-18T11:07:36.800Z
Maury Markowitz
<p>I was reading about gravitational lensing. I was just curious to know if there are any formulae or methods to find the angle at which the light deflects due to <strong>strong</strong> gravitational lensing? </p>

<p>And how far should that massive object be present so that we can observe multiple images of the observing object? </p>

CC BY-SA 4.0
2019-09-12T06:50:21.443Z
Hi Ishan, it's a great question, but on this site you're expected to have done a little research yourself before asking, i.e. at least read the [wiki](https://tinyurl.com/yye89tv9), have a look at related SE questions (e.g. [here](https://tinyurl.com/y6tdzv3y), [here](https://tinyurl.com/y2feh8ev), and [here](https://tinyurl.com/y5ajzboe)), and maybe have a look at the first few Google hits, like [this](https://tinyurl.com/yxgp34rq) and [this](https://tinyurl.com/yxqoxe32). I suggest you take a look at those links and come back with more specific questions to things you don't understand :)
pela
CC BY-SA 4.0
2019-09-18T18:45:39.223Z
@Pela (and upvoters) None of those links provide anything like a quantitative answer to this question.
ProfRob
CC BY-SA 4.0
2019-09-18T20:20:19.557Z
@RobJeffries Yeah, you're right. The question was a bit different when I wrote this comment, and seemed to me like the OP simply wanted more general knowledge on strong lensing.
pela
<gravitational-lensing>
Gravitational lensing
ISHAN KAUSHAL
# Gravitational lensing

(Asked by: username_0 on 2019-09-12)

I was reading about gravitational lensing. I was just curious to know if there are any formulae or methods to find the angle at which the light deflects due to **strong** gravitational lensing?

And how far should that massive object be present so that we can observe multiple images of the observing object?

**Tags:** gravitational-lensing

> **Comments:**
> **username_1**: Hi Ishan, it's a great question, but on this site you're expected to have done a little research yourself before asking, i.e. at least read the [wiki](https://tinyurl.com/yye89tv9), have a look at related SE questions (e.g. [here](https://tinyurl.com/y6tdzv3y), [here](https://tinyurl.com/y2feh8ev), and [here](https://tinyurl.com/y5ajzboe)), and maybe have a look at the first few Google hits, like [this](https://tinyurl.com/yxgp34rq) and [this](https://tinyurl.com/yxqoxe32). I suggest you take a look at those links and come back with more specific questions to things you don't understand :)  
> **username_2**: @Pela (and upvoters) None of those links provide anything like a quantitative answer to this question.  
> **username_1**: @RobJeffries Yeah, you're right. The question was a bit different when I wrote this comment, and seemed to me like the OP simply wanted more general knowledge on strong lensing.  

---

## 1 answers

### Answer by username_3 on 2019-09-18. Score: 3

Absolutely:
$$\theta = \frac{4GM}{c^2b},$$
where $\theta$ is the angle of bending, $G$ is the gravitational constant, $M$ is the mass of the star/blackhole/whatever, $c$ is the speed of light, and $b$ is the "impact parameter", the distance from the light ray to the center of the mass on its closest approach if it was NOT deflected (i.e., $b=0$ for an impact).

> **Comments:**
> **username_4**: This is the weak field approximation. The question was asking about strong lensing.  
> **username_2**: This is a weak lensing formula that doesn't address the question asked.  
> **username_3**: I do not recall the bold term being there when I answered it!  
> **username_2**: @MauryMarkowitz that's right, I put it in boldface because apparently you didn't see it.  

---

