Fair Season

[Brian_A]

Hey All,

I just thought this might be an interesting thread to start, seeing as it seems to be Fair season. Ours just ended here, but here is a scene I made two images of. Playing with the whole reciprocity thing, I think I was waaayyy off on my exposure, but I dug out what I could in Photoshop. (Maybe someone could PM me a good way to meter in this kind of difficult lighting condition.)

Both images were made utilizing a Horseman Woodman 4x5 with DaYi 6x17 back, Nikon 150mm f/5.6 lens, on a Gitzo tripod & head combo and metered with a Sekonic L-558R. First exposure is 25sec @ f/5.6 and second is 30sec @ f/5.6. Ilford Delta 100 film.

Enjoy!

-Brian

[Brian_A]

Hmm after some thinking, I like these cropped versions better. These are slightly larger than 6x12 now that they are cropped... What do you think?

Thanks,

-Brian

http://www.akersonstudios.com/lfforum/fair1_6x12.jpg



http://www.akersonstudios.com/lfforum/fair2_6x12.jpg

[argos33]

In these situations I find it helpful to have a small digital camera (with some manual features) handy to meter with. I use the digital to help get a good idea of the exposure, and then compensate for reciprocity for the given film. It may take some experimenting to find the right compensation, but studying the fact sheet for that film is usually a good starting point.

http://www.ilfordphoto.com/products/product.asp?n=8#
Click fact sheets, then go to professional fact sheet.

I like the cropped versions better too, definitely brings back some memories.


Evan

[Brian_A]

Evan,

Well, I usually have my D200 with me, but I was trying to run with a lighter load that night. Plus that bag just wasn't big enough for my D200 and 4x5. I've recently purchased a new bag that fits the whole shabangabang, though. (Boy is it heavy when it's loaded. Fun, I tell ya.)

Oh and I did study that fact sheet along with other sites. One site had a great formula that matched very well to Ilford's curve..

Y = X + 1 ^ 1.465

I don't know how mathmatically correct that is stated, but what I'm getting at is, Measured Time (X) + 1 to the power of 1.465 equals Adjusted Time (Y). Anyway, like I said, I used that and compared it against the given times in the Ilford datasheet and it was pretty accurate. That's good for both Delta 100 and PanF 50. I haven't checked to see if their other films use the same curve or not.

Anyway, enough with this math stuff. I like the croped versions too. The other ones just didn't have anything worth while to keep all that dead space in there. Thanks for the input!

-Brian

[al olson]

Something is missing here. One raised to any power is still one.

[BarryS]

Something is missing here. One raised to any power is still one.

I'd guess Brian meant Y = X ^ 1.465. I have some software that will try to generate a best fit curve for any set of points and I used to generate reciprocity formulas to put on a calculator. Now I just look at the chart and wing it--same results. :)

[mrladewig]

I'd guess Brian meant Y = X ^ 1.465. I have some software that will try to generate a best fit curve for any set of points and I used to generate reciprocity formulas to put on a calculator. Now I just look at the chart and wing it--same results. :)


I believe the correct notation would be

Y = (X+1)^1.465

[BarryS]

I believe the correct notation would be

Y = (X+1)^1.465

You may be right, although the difference between X and X+1 raised to 1.465 is going to be marginal at reciprocity length exposures.

[Brian_A]

mrladewing had it right... Sorry about my inability to put that into a proper layout. Math obviously isn't my strong suit :D Anyways...

If you had metered a shot for let's say, 120 seconds:

1125.33 = (120 + 1) ^ 1.465 - 18.75 Minutes

1111.73 = 120 ^ 1.465 - 18.53 Minutes



So now you've moved from a 2 minute exposure to a 18.75 minute exposure - versus about 18.53 minute exposure. While it may seem marginal, it goes along closer to Ilford's curve. Don't ask me, I just read it somewhere, tried it and it worked... I don't have too much experience in the long exposure category, but wouldn't that 12ish seconds would make a large difference? Please, correct me if I'm wrong as I'm still trying to learn this stuff.

-Brian