long exposure shots

Hola

This is my first post here , i recently change to digital and i would like to know if someone here had experience with long exposure shots u/w

I will try to make some cave diving shots using a D70 on a tripod and want to know how is the best way to avoid the noise or any other problem related to digital handling long exposures/dark situations.

I already tried with film and the exposure time is about 2 minutes using "painting with light technique".

Will appreciate your comments

El buzo

Interesting question. There is not a lot you can do about long exposure noise while you are in the water. My only advice for in water is to shoot RAW. My advice is to use a low ISO - e.g. 200 as you have a tripod. Rather than increase the ISO. Others may disagree on that.

Then you are best placed to deal with noise in post processing. Some RAW converters allow you to smooth noise - Nikon Capture is good for this. Also by using RAW you can work in 16 bit colour depth in Photoshop when making adjustment, which will help maintain your image quality.

There are also quite a lot of dedicated noise reduction software out there. I haven't used it myself - but people who shoot in low light use it routinely on all their shots.

The other small problem with long exposures is getting hot pixels. Although newer cameras don't suffer with this. The best way to fix these is to view the image at 100% and then in Photoshop clean them with the clone tool.

Hope this helps.

Alex

Thanks

I will post my results after my "photo session".

El buzo

You should also turn on the camera's noise reduction feature. Nikon has a noise reduction feature that kicks in somewhere around 1/15th of a second, but you have to turn it on through the menu. It will take a little bit longer to write to the card but who cares?

Joe

The Nikon noise reduction feature doubles the time of the exposure. So if you are using 2 minute exposures this would lead to a 2 minute noise reduction phase. Total time for the picture 4 minutes.

This may not be possible or desirable with the time constraints of air and Decompression limits when underwater.

Saying that I have always had the noise reduction on when taking long exposures topside so can't say how much affect it has.

I've used it a lot with minimal impact to time. Albeit my shots were in seconds and not minutes so I can't say that I know for sure how long it will take. Nikon's manual says it will take "a little" longer to write to the card, but no specifics on how much longer.

Joe

The way it works is to take a picture of the same duration with the shutter closed. With no long exposure noise this should be pure black. However noise develops in a given pattern at a given temperature over a given time so on a long exposure noise will be generated. Therefore if you subtract the noise from the second black exposure from the first you should have a clean picture.

Hence the exposure must be the same length as the original or this will not work.

It may be possible to take a black photo and do the subtraction in software if pictures will be of the same duration and temperature will be constant (likely underwater). There is software available to do this but I am not sure what.

Mark

Well it sound too much complicated for me . My problem is that i only have basic knowledge about photoshop ( i am new to digital and i will just take a photoshop course starting next week ).

But also the photo that i want to make is in a total dark room deep inside a cave , the only way to do it is putting the shutter in bulb . I am not able to determinate the exact time of exposure because the room is quite large and it takes several strobe shots to exposure the area that i want . I did it on film and it took me around 2 minutes , but is very difficult because my friend ( lightning assistance ) needs to move all around the cave in the dark knowing were the camara is located in order to avoid ghosting images of himself.

Who said that u/w photography is easy !!

Anyway thanks for your input.

Saludos

El buzo

Aha, light painting!

Buzo: you can try this at home in a sealed room - set up your camera on a tripod and put it in bulb. Then light paint like you would do underwater.

If you don't have a camera already, see if you can borrow one. I'm intrigued to see your results.

Cheers

James

James

That is exactly my idea and that is why i want to make it with digital .

Attached you will find the only pic aceptable from 2 prior long sessions ( i deleted some partially gosht imaging )

Saludos

Is that you in the picture?

WOW, cool shot, once you got the exposure correct, you should try and add magenta filtering to the camera, this should help bringing back some warm colors, I'm too much of a wimp to go in these marvelous places , I definetly want to see more stuff from your trial and experience.

Regards

Alex :

No , it´s my buddy that was firing the strobes all over the room .

I was behind the camera/tripod .

El buzo

Jean :

Thanks for your suggestion.

We knew each other at Dema Miami on 2003, i was together with you and Mauricio in your booth . Glad to hear from you . Pls. say hola to Norma

Jose Alejandro

a.k.a El buzo