calculating long exposure

hi,

does anyone has a calculator (an excel table, html page, java for mobile etc) to calculate long exposure shots. What i exactly mean is that, i've read some forums posts that to take a long exposure shots (double digit minutes or even hours) that are correctly exposed, some professional photographers fist take very high iso shot with large aperture (small f number) shot to get preliminary exposure time (up to max that your CAMERA allows (eg 30sec)). Then they make some calculations to get right exposure time at lowest ISO they can use in camera and at desired F number (eg 8 or higher).

So, it would be great to have such calculator in the phone, where you first insert your high iso and large aperture settings and then change the iso and f-number to level you like and the calculator gives you the right exposure. Then you set up your self-timer remote according to the settings you calculated and then take a shot (eg long exposure night shots for star trails).
--
http://www.hundiurg.eu

If you're out in the field with just your camera, you can use this little trick:

Compose and do a test shot at ISO 6400 at your desired aperture. Note the number of seconds for a correct exposure. Then, for the real photograph, change the ISO to 100 and expose for the same number of minutes as there were seconds in the test shot. For example, if the test shot was 90 seconds, expose the real photograph for 90 minutes.

Voila! A correct long exposure, within 7-percent or so!!
--
Stephen Von Worley, Santa Cruz, CA
Gallery: http://www.vonworley.net/
Blog: http://www.weathersealed.com/

You can probably figure it as fast as you can enter it into your iPhone. I personally just count it on my fingers. I can usually figure it out myself in about 10 seconds. But I guess it would make a nice little iPhone app anyway.

At least with digital we don't have to worry about film reciprocity, which really used to throw things off. Then if you had to figure in bellows factors it could be a real headache. Plus now you can see instant results right after you make the exposure. Beats having to wait for the lab to process it to see if you got it right.

well, if planning to take a 6 hours night shot of star trails, it means you can take only 1 shot per night

iPhone.. not for me. the app should be in some more common format that can be used in different phones. So, in my opinion it should be html file, excel table (with no macros, formulas only) or java or .jar file (if it's not the same). I personally use Nokia E71. So it would be great if i could use my phone as exposure calculator.
--
http://www.hundiurg.eu

Yes, that's definitely true about the six hour exposure! Well, if you don't find an app for your phone, the old meters with dials like the LunaPro work good for calculating one exposure to another. I used to use it for that in the old 4x5 days. Man, I must sound old!

Call I1, S1, F1 the ISO, shutterspeed and f-stop from the "test" measurement (high ISO, using your camera lightmeter). I2, S2, F2 the same for the actual shot. S2 is the thing you want to know, as I2 and F2 you decide yourself.

S2 = S1 * (I1 / I2) * (F2 / F1)^2

Since it's literally 3 minutes work, I've put an Excel sheet with this at http://www.wormeester.nl/exp_calc.xls

Have fun.

edit: The sheet has some example numbers filled in already to demonstrate what goes where.

Thank you so much GideonW!

Today i got so bored at the lecture in university so i took a piece of paper and a pencil and i think i found out these formulas as well..but in much longer way. On paper things worked fine. But i haven't put them into excel yet. Just for curiosity i'll try to insert my formulas somehow into excel as well to see if i get same results as you did (yours work is definitely easier (only 1 formula!) than mines on paper and mines work only with full stops both in terms of aperture and iso).

once again, thanks for excel!
--
http://www.hundiurg.eu

risto40 said:

Then they make some calculations to get right exposure time at lowest ISO they can use in camera and at desired F number (eg 8 or higher).

Click to expand...

Uh, just double the time every time you cut the ISO in half. Click click click click done.

Jeffrey

------------------------------------------------------------------------------------
Jeffrey Friedl -- Kyoto, Japan -- http://regex.info/blog/

The process your describe is just as I have explained many times here. The last part is really simple.

Just remember how your stops work. 3 clicks on the aperture is a stop (typically, for most cameras). You can jump through iso's in whole stops typically. And similar for shutter speed, just count in 3's, 3 clicks to a stop.

So just look at what ISO you took that shot at. How ever many counts about 100 or 200 it is, change the other things the same. Use your fingers if you need to remember it was 5 stops. So if you then close your aperture 2 stops, your fingers will tell you you need 3 stops with the shutter still.

I'd worry about how a digital camera works with a long exposure.

The other day I looked at a terrible image from a D300 of the sky -- all red and blotchy.

The camera owner thought there was some kind of light leak in the camera; my thought is that he overstressedthe circuits. Sort of a digital equivalent to turing up audio speakers so high that they distory.

Sometimes film still has something going for it.

Anyway, try yourself a long test exposure, just to see if the picture loks any good.

BAK

pptphoto said:

Yes, that's definitely true about the six hour exposure! Well, if you don't find an app for your phone, the old meters with dials like the LunaPro work good for calculating one exposure to another. I used to use it for that in the old 4x5 days. Man, I must sound old!

Click to expand...

Yep, that LunaPro was incredible.

Does anyone remember what the "highest" ISO (ASA) that could be pre-set ???

I think when it was sold, ASA 400 was about the highest available, so I just wonder what the meter would allow since 6400 and even 25,000 was unconceivable at that time.

--l
Thanks for reading .... JoePhoto

( Do You Ever STOP to THINK --- and FORGET to START Again ??? )

vonvonvon said:

If you're out in the field with just your camera, you can use this little trick:

Compose and do a test shot at ISO 6400 at your desired aperture. Note the number of seconds for a correct exposure. Then, for the real photograph, change the ISO to 100 and expose for the same number of minutes as there were seconds in the test shot. For example, if the test shot was 90 seconds, expose the real photograph for 90 minutes.

Click to expand...

Great Idea.

I just wish 90 minute exposures were practical on digital.

BUT ... it seems to me that it should be possible for a camera to allow auto-stacking with an intervalometer that could shoot (all-night) at 1/sec, or 1/min, 1/hour, etc.

That should allow (all-night) star-trails.

(or maybe stacking 10/sec for 1 to 10 seconds for water-flow without ND filters)

Maybe the new Sony sensor used the the Sony HX1 or Casio EX-F1 could do it at 60fps ???

vonvonvon said:

Voila! A correct long exposure, within 7-percent or so!!
--
Stephen Von Worley, Santa Cruz, CA
Gallery: http://www.vonworley.net/
Blog: http://www.weathersealed.com/

Click to expand...

--
Thanks for reading .... JoePhoto

( Do You Ever STOP to THINK --- and FORGET to START Again ??? )

look no more, just search in iTunes for Exposure Assistant (i have no connections to the developper, and anything with this app, jsut the fact that i bought it)

This Little app is a must for anyone doing long exposures. No more tables needed, be honest in order to get a 30min exposure with iso 100 how many test shots did one waste? No more waisted test shots, take a test shot with highest iso your cam can do, put data in the current settings, put desired iso and aperture or shutter and the other value is calculated on the spot.

I can honestly say I no longer need to wait for the dark frame to be completed, I had a 42min exposure then went to the room and I didn't need to wait another 42min for the dark frame to be completed, went to bed and in the morning I saw the result, abs perfect!!!

Every time you close down the aperture a stop, double the shutter time. Then every time you halve the ISO, double the shutter time. That's it!

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http://101-365.com/

I can't remember the Luna Pro but my Ultra Pro's go up to ISO 8000!

They are still going strong - used one today to check the colour temperature of one of those old Multiblitz Diaduplicators.

I finally got a setup for copying colour negative film using a D700 + PB-6 bellows + 55mm micro Nikkor on a copy stand. Each copy takes about 20 seconds for a 12MP raw file! That beats the hell out of my Epson V700 doing 300dpi 6x4's !!! That was taking 2 minutes per image!

Despite spending all day testing two different lots of - + conversion software I've come back to using CS5 as the best solution.