Exposure times

[Chairman]

My S2 has an f2.7 lens. I have another camera which has an F3.5 lens. Those are both when zoomed right out.

How much would I theoretically have to increase the shutter time for the f3.5 lens to get the same exposure as the f2.7 lens ?

Thanks
Gary

[BowerR64]

couldnt you just calculate that on the S2? put it in Av mode and set it to 2.7 then hit the shutter, then move it up to 3.5 and hit the shutter again.

[Chairman]

Ah, of course I can. Never gave that a thought !

Hmmm ...
1/8th on the fast lens, 1/5th on the slow lens.
1/3rd on the fast lens, 1/2 on the slow lens.

That's a huge difference - the slow lens needs about half as long again !! :eek: :eek: :eek: :eek: It explains a heck of a lot about some comparison shots I was taking.

Thanks for that :)

Gary

[BowerR64]

What ISO? that seems like alot.

I tried my S2 on 100 ISO and both stops need 1/60 shutter.

Your ISO must be on 50? with no flash indoor?

[Chairman]

That is on 50 iso, yes, pointed into the corner of a room at 4 in the morning :) The actual shutter speeds I got aren't important, I was only interested in how far apart they were so I could work out how long to fire the nikon for to get the equivalent of a 15 second exposure from the canon. I think it's about 23 seconds, so I'll use 30.

Cheers
Gary

[BowerR64]

So your gona do some compairison shots? or what are you doing?

[Chairman]

It's been raining solidly here for about 12 hours and I've been playing with long exposure night shots of shiny wet streets and buildings. :)

With a total lack of success. :mad:

I hauled out the nikon dslr to try that (man that feels so HUGE and HEAVY after getting used to the S2 !) but everything came out black, which I can now put down to me not exposing it for long enough.

So I might try again.

Or I might go to bed. :D

Cheers
Gary

[BowerR64]

I took this one with a slow shutter and a street light. I think 5-10 seconds somthing like that.

http://i5.photobucket.com/albums/y191/BowerR64/Camera/Thisoldhouse2.jpg

These were long exsposure with a very faint street light it looks like 20 watts or less and the side of the church has another one. I tried every w/b setting wich looks the best?

http://i5.photobucket.com/albums/y191/BowerR64/Camera/TheChurch4.jpg

http://i5.photobucket.com/albums/y191/BowerR64/Camera/TheChurch3.jpg

http://i5.photobucket.com/albums/y191/BowerR64/Camera/TheChurch2.jpg

http://i5.photobucket.com/albums/y191/BowerR64/Camera/TheChurch1.jpg

Its weird how the ligh tlooks green. :confused:

[Chairman]

I've done some more playing about tonight, and finally got some good results from the dslr.

So far as I have managed to work out, the problem was that while both cameras were in their version of "whole scene evaluation" for metering the nikon is a lot more thorough about it.

I had them both in shutter speed mode. There was a streetlight in a top corner of the shot and some bright building security floodlights in the (distant) centre which the S2 blithely ignored and gave me a decent enough shot using 1/15th @ f2.7. The D100 which was set to 30 secs thought "oooh, lights!" and took the shot using 1/30th @ f22 - giving me something that has been exposed for twice as long and came out almost black :eek:

After I threw nikon into full manual it went off at 1/30th @ f3.5 and gave me something that was waaaay overexposed. I brought the shutter speeds down step by step until I was down to 1/15th, same as the canon with its faster lens, and was getting shots that were brighter than the S2's but which also looked about right.

So now I have a camera with a faster lens and a camera with a slower lens, for the same shutter time and more or less the same aperture the camera with the slower lens gives a brighter picture. Could that be because the lens and/or CCD is physically bigger ?

Gary

[BowerR64]

post both pictures, can you take one with the S2 how you like it then match the exsposure with the nikon? list the basic settings too. time, Fstop ISO

[Chairman]

I'll post the shots tonight if I have time, I think the main 'problem' now is sorting the white balance. The canon shot looks more natural and I can't recreate it in the nikon shot, although I will got there eventually - the nikon I shot in raw format so I can do anything I like now with the white balance / colour temperature.

I did another comparison thing - I found that my S2 teleconverter will fit the front of my big nikon zoom, so on it went. 300 zoom, x 1.5 tele = 450 zoom, x 1.5 conversion factor = effectively a 675 zoom. Unfortunately though no image stabilisation. I stuck it on a tripod, pointed it at a distant sign, and used the self timer to fire it. On the best of the resulting shots I could make out the big words but not the fine print.

Then I put the teleconverter back on the S2 (432 zoom x 1.5 tele = 648 zoom), pointed it at the same sign handheld with no timer and pressed the button. On that shot I could easily read every word on the sign. I guess the lesson is that at the longer zooms IS becomes more than just "useful".

Gary

[XaiLo]

So now I have a camera with a faster lens and a camera with a slower lens, for the same shutter time and more or less the same aperture the camera with the slower lens gives a brighter picture. Could that be because the lens and/or CCD is physically bigger ?

Gary

Slower lens = greater exposure time = greater amount of light, hence brighter picture.

[Chairman]

Slower lens = greater exposure time = greater amount of light, hence brighter picture.
Logical enough as far as it goes, but why would a slower lens give a brighter picture than a faster lens if the shutter speeds / apertures / ISO's / metering etc are the same ?

Gary

[BowerR64]

Because the sensor is bigger.

The larger around the lens is the more light it can get. Its the same with the pixals on the sensor. The larger SLR sensors have larger pixals so more light can get in it faster thats why they are better in low light.

I bet eventualy P&S cameras will be using older SLR sensors. The a series of the future will be using rebel size sensors. :D

That would be sweet huh?