Fast lenses, and High ISO

Started 4 months ago | Discussions thread
EinsteinsGhost
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Re: "fast" is relative
In reply to bobn2, 4 months ago

bobn2 wrote:

EinsteinsGhost wrote:

bobn2 wrote:

EinsteinsGhost wrote:

bobn2 wrote:

EinsteinsGhost wrote:

bobn2 wrote:

Fine. That's what I said too. What determines how fast a shutter speed?

"Sensitivity" of the media, scene brightness and aperture. Nothing to do with media size.

That's a strangely abstract way of determining your shutter speed. Do you have a table of available shutter speed against media, scene brightness and aperture? As I remember, my camera allows me to set 1/8000 for any scene brightness, 'sensitivity' and aperture, why should I not?

Glad that you have a camera you know how to turn dials of. Now, let us try something more with it. For that matter, let us use one of your images with EXIF:

So, why did your camera, or you, choose 1/250s, f/4.5 at ISO 100? Your response will help you get my point, on why you can't just turn the dial to 1/8000s just because you happen to have it.

Can't remember why I chose that exposure at that time. I was just trying out the camera anyway. But if I reconstruct my thinking. I aim for the largest exposure that I can get, subject to my pictorial constraints. This was hand held, and I was trying to avoid shake, so I set a shutter speed of 1/250 for 85mm and f/4.5 is the largest aperture that lens has at 85mm. Does that answer your question?

That wasn't a question. It was a step to help you understand what you (and/or your camera) do when it comes to exposure.

I already know what my camera does when it comes to exposure. I don't think that I have anything to learn from you.

That is what you think. But your arguments suggest the opposite.

In this case, if you can't remember, or tell, chances are, it was probably your camera's decision-making in the process.

Chances are it wasn't, since I generally use 'M' mode.

With Auto ISO?

And that is perfectly fine. NOW, I have questions:

1-You speak of "large exposure". Could you explain how your idea of: "since I have 1/8000s, I could use it", fits in? In other words, you could have just as easily used 1/8000s shutter speed, right?

1/8000 would have given me a smaller exposure than 1/250 and I didn't need any faster than 1/250 to avoid motion blur, so I wouldn't have chosen 1/8000s.

It is time to revisit a funny argument you made which brought up this to begin with:

bobn2 wrote: That's a strangely abstract way of determining your shutter speed. Do you have a table of available shutter speed against media, scene brightness and aperture? As I remember, my camera allows me to set 1/8000 for any scene brightness, 'sensitivity' and aperture, why should I not?

So, why should you not? Perhaps, you should, but then you think it will give you "smaller exposure". Wrong. You can get the same exposure at any shutter speed, but you can't because you end up hitting certain limitations. A shutter speed of 1/8000s is five stops from 1/250s that your image shows. You have several combinations that will give you same exposures, whether you can achieve it all depends on your lens (how large it can go, or how much you're willing to go) and ISO setting.

In other words, that is not the only combination you could have had for the same exposure.

2-Would your selection of a different shutter speed guarantee a change in exposure?

If I had used a different EV in the same lighting conditions, it would have course resulted in a cange of exposure.

Only if you had forced it to over or under expose. But you had SEVERAL combination to get identical exposure. For that matter, why do you think the exposure would have changed with f/3.2 and 1/500s at ISO 100? With that, you go one stop larger aperture and that speeds up the shutter speed by a stop but you get same exposure.

3-What makes 1/250s, f/4.5 the "largest exposure" that you could?

1/250 was the longest shutter speed that I wanted for the reasons of camera shake, as explained. Twice the FL of the lens is a decent guide at 36MP, that gave 1/170, 1/250 is the nearest whole stop above that. f/4.5 is the largest aperture at that FL on that lens. hence, I couldn't have had a larger exposure and met my pictorial constraints, to do with shutter speed in this case.

You're talking Exposure Triangle. Can't argue against that. You couldn't go larger aperture due to your lens being as fast as it could get. You didn't want to increase ISO to speed up shutter speed either. But, where is this consideration for sensor size in all your considerations? If you were using a 1" Sony RX10, what would be your exposure values? (Base ISO 125).

4-What would be the issues with 1/8000s shutter in this particular scene?

I would have had five stops less exposure and thus a lot more noise.

Not if you were able to compensate with a faster lens. It is that you couldn't do to keep the same exposure. This is why your argument about "my camera can do 1/8000s, so why shouldn't I" was so amusing.

That was my original post. With high ISO do we need lenses with larger apertures just to allow more light when high ISO can achieve it for you with lesser light.

The only thing 'ISO' achieves is applying a given exposure to brightness function so that the image taken with your chosen exposure looks right at the end.

Which is the point of exposure, to achieve a specific brightness level.

But, you can achieve that specific brightness level with a different exposure just by setting the ISO differently. Does that make exposure pointless?

Yes, you can. In fact, I recall that being a major issue with a collective that I've often argued against.

You keep on saying this, but I can't remember myself or the 'collective' ever having an issue with setting the ISO differently.

The issue wasn't setting the ISO differently, but how ISO has no relevance in determining exposure was this collective all about. And I am fairly confident, more of it just might show up soon.

If you'd said that, I'd have understood what you are getting about. Choosing ISO first is a back to front way of going about selecting your exposure, and will sometimes lead to getting a smaller exposure than you could have had. If a suitable UI were made for cameras, you wouldn't have to do it.

I assume UI you speak of and use today is called "Auto ISO". Assuming that is what you did in that image, here is the kicker: your exposure was determined around it. If your camera had a base ISO 200, you'd have seen a faster shutter speed as a result (again, exposure determined by that).

But, keep going, I think we're heading in the direction I was alluding to, and you weren't willing to trust me.

But, since you seem to believe that you can't take ISO out of the equation when considering exposure, would you prefer lowest possible ISO if you can use it? Or, does it not matter?

As I said, I aim for the maximum exposure that I can, subject to my pictorial constraints.

Define "maximum exposure",

Most lux seconds at the image plane. The maximum you can used is either defined by your pictorial constraints or by what your camera can take.

Your camera can take something completely dark because of settings chosen, doesn't mean that is "maximum exposure". An exposure is what a light meter (built-in the camera, or an external one) provides, to as closely mimic a scene as possible. Whether you want slight under or over exposure is something else (and independent of format).

and please do tell how the aperture and shutter speed combinations provide that,

Both of those controls affect the amount of light and thus the exposure.

This is why I asked you to define maximum exposure. Which of the two is "greater exposure" on your camera at base ISO:

f/2, 1/1000s

f/2.8, 1/500s

and that the same exposure would have been impossible at any different speed.

Don't know what you mean by that. Maximising the exposure means largest aperture and slowest shutter spped, but there are competing reasons why you'd want to put limits on that (mainly motion blur and DOF requirements, sometimes using the lens' optimum aperture).

You will know when you answer the question above.

Which ISO is your particular favourite?

Base.

Quite often motion blur is more destructive than noise.

Says someone who thinks that exposure should not be based off ISO setting in the camera. Your words from above: "Choosing ISO first is a back to front way of going about selecting your exposure, and will sometimes lead to getting a smaller exposure than you could have had"

Now, you're worried about motion blur? Even more amusingly, assuming that favoring photography at base ISO equals motion blur? Amazing!

Try looking at your own collection of images, and tell me if you avoid base ISO from that fear. Or, you prefer using high ISO because motion blur can be more destructive.

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