Light Meter - Technical Inquiry

[samerr9]

Hi all

I have a technical question that I couldn't solve by myself so I thought of sharing it in here. I am posting it in Fashion as most of you use studios and probable light meters.

In a previous post about the full body studio lens, most of us agreed that using a longer lens is better for distortion and it was noted that more light in needed when using longer lenses because the camera will physically be far more the subject and light needs to travel further. Here is my inquiry:

I have the Sekonic L308s. I place it next to the models chin and meter. I use the readings regardless of the distance between me and the subject. So if I am using a longer lens will the image be underexposed on those readins?

Thank you for resolving this for me

[ksgal]

Well, I don't think this is the case, an example... check out the settings for this moon shot

Near full Moon....

If more light was needed, you'd think they'd be shooting at f2.8 at 30 seconds or something, as far as that light traveled, from the sun, bounce off the moon, and down to the camera...

But best is to experiment and find out for yourself.

[Seawolf66]

Or you could think about a spot meter then you could do from the camera position: just my two coppers here

Originally Posted by samerr9

Hi all

I have a technical question that I couldn't solve by myself so I thought of sharing it in here. I am posting it in Fashion as most of you use studios and probable light meters.

In a previous post about the full body studio lens, most of us agreed that using a longer lens is better for distortion and it was noted that more light in needed when using longer lenses because the camera will physically be far more the subject and light needs to travel further. Here is my inquiry:

I have the Sekonic L308s. I place it next to the models chin and meter. I use the readings regardless of the distance between me and the subject. So if I am using a longer lens will the image be underexposed on those readins?

Thank you for resolving this for me

[Onslow]

Originally Posted by samerr9

Hi all

I have a technical question that I couldn't solve by myself so I thought of sharing it in here. I am posting it in Fashion as most of you use studios and probable light meters.

In a previous post about the full body studio lens, most of us agreed that using a longer lens is better for distortion and it was noted that more light in needed when using longer lenses because the camera will physically be far more the subject and light needs to travel further. Here is my inquiry:

I have the Sekonic L308s. I place it next to the models chin and meter. I use the readings regardless of the distance between me and the subject. So if I am using a longer lens will the image be underexposed on those readins?

Thank you for resolving this for me

The highlighted portion of your question doesn't make sense to me. What I have found is that it is the flash to subject distance that is important. The further away the flash is from the subject, the more output is required due to the inverse square law.

Once the light is reflected to the camera, it doesn't matter if the camera is 1 foot or 1 mile away from the subject, the same quantity of light from the subject will enter the camera.

[kgior]

Originally Posted by samerr9

it was noted that more light in needed when using longer lenses because the camera will physically be far more the subject and light needs to travel further.

Absolutely incorrect. Flash to subject distance will change your light reading.

Originally Posted by samerr9

I have the Sekonic L308s. I place it next to the models chin and meter. I use the readings regardless of the distance between me and the subject.

Yes

Originally Posted by samerr9

So if I am using a longer lens will the image be underexposed on those readins?

No

Originally Posted by samerr9

Thank you for resolving this for me

Your welcome

[Sailor Blue]

The light needed for the subject doesn't change with distance even though the light spreads out more as the subject to camera distance increases.

The reason is that if you use the same focal length lens at different distances the image on the sensor becomes smaller, concentrating more light on each pixel. This concentration exactly compensates for the loss of light intensity with distance.

If you use a longer focal length as you move away from the subject in order to keep the subject the same size on the sensor the aperture will increase with focal length, which keeps the amount of light from the subject on the sensor constant.

This makes sense if you remember that the aperture number is actually the ratio of the focal length of the lens divided by the physical diameter of the aperture. At f/8 the aperture of a 50mm lens is 6.25mm, 10.6mm for a 85mm lens,and 12.5mm for 100mm lens.

[poloman]

Kgior and Sailor Blue are correct.

[Bobby Deal]

Bottom line, take your reading and shoot that reading regardless of subject to lens distance the exposure will be the same. The only time your camera settings need to change is when subject to light changes.

The comment that was made in the other thread was misleading in that the poster was referring to a situation whereby you would need wider apertures to maintain the same DOF as you back up. However as you are shooting on white DOF is of no real concern as you will be shooting F/8-F/13 judging by the light chart you have shown us.

[samerr9]

Thank you all for clarifiying.

I was confused because of that post but it is clear now. I really appriciate your help and this forum as I am learning valuable things every now and then.