Newbie with Exposure Calculation Question

Hi Folks,

I'm new to pinholing, and I have a question about adjusting exposure times to allow for reciprocity failure.

With the Pinhole Assist app on my iPhone, I can have it calculate a compensated exposure time by choosing from a list of predefined reciprocities. For HP5+, there's three to choose from: Ilford's own, someplace called WO Lenses, and one form G Gainer (with a link to his post here at APUG: (there was a url link here which no longer exists), which I read but had a difficult time understanding).

The times as calculated by those three are wildly different. Take a look:

(times in seconds for HP5+ and f/250)
[TABLE="width: 411"]

metered

Ilford

WO Lenses

G Gainer (APUG)



1.00

1.00

1.70

1.10



5.00

10.80

12.90

6.40



15.00

55.00

55.20

23.10



45.00

279.70

311.20

93.10



120.00

1,194.50

2,658.90

355.80



300.00

4,636.00

32,251.30

1,340.50



600.00

12,931.90

244,068.30

3,798.40



1,200.00

36,073.00

1,917,377.20

11,030.90



2,400.00

100,626.60

15,249,340.00

32,617.90


[/TABLE]

Which ones do I use?

Thanks for your help,

Adam

Take three shots one at each recommendation.

pinhole photography defies precision -- reciprocity changes the longer the exposure gets, how dim the light is to start, the color of the light, the phase of the moon and whether your wife was angry at you this morning.

But seriously, tables are just a guide, do what xmas said there -- bracket your exposures and then take one double what everyone recommends, just to see how it comes out. As you gain experience you'll get a feel for what works in what situation.

agree with Xmas...

I add that a good starting point for me was to use the free software Pinholedesigner >> http://www.pinhole.cz/en/pinholedesigner/
you can find good data for the most common films. Just insert F camera and choose the film!

If I have punched the correct buttons on my calculator 40 mins( last exposure) has a reciprocity failure that takes the exposure to almost 6 months under WO lenses!

Can this possibly be right? If it is then the other two exposures are so inadequate that the neg might be clear.:eek:

It had better not be a portrait of grandma in the garden on a summer's day unless it is Miami and the seat is very comfortable. Mind you the odd toilet break would be OK

Sorry for the levity but this is almost surreal

pentaxuser

Thanks for the replies, folks. I tried out a roll of HP5 and I'm not surprised about my conclusions. First, at shorter times, the differences are much less noticeable. Second, the folks who spent lots of time and money creating the film generally know what they're talking about. To my eye, the Gainer exposures are underexposed. The Ilford exposures are very nice. The WO Lenses exposures are almost as good as the Ilford, but at longer exposure times they become too long for me to use them.
So, I'll stick with the Ilford times for now.

Attached are the results. (Now I have to cut away at the part of the camera that's causing the vignetting.)

Adam W said:

The Ilford exposures are very nice. The WO Lenses exposures are almost as good as the Ilford, but at longer exposure times they become too long for me to use them.
So, I'll stick with the Ilford times for now.

Attached are the results. (Now I have to cut away at the part of the camera that's causing the vignetting.)

Click to expand...

The Ilford and WO lenses are similar until you get to the longer exposures where it is difficult to imagine that the Ilford and WO lenses exposures can be similar in terms of the negatives produced as the differences are astronomical.

I wonder how WO Lenses arrived at its exposures after about the first 4 mentioned?

pentaxuser

Hi,

I'm the creator of Pinhole, so I might add a few things. I fitted in Pinhole Assist all the curves I could find on the Web. I did not had the time to test them all (speaking frankly I only use photo paper and sometimes Fuji 160S).

First : One important thing is to press the (i) button the is present on each reciprocity curve: It will show you the detail of each curve, each element of the tables used, and a link to web source, so you can get more information.

Usually I find tables that relies on experiment, however with HP5 I only found formulas. The problems with formula is that I do not get a range a validity (with tables, I know when I and within the bounds of the table or when I extrapolate).

• All W/O Lenses comes from here : http://pinhole.stanford.edu/equations.html
• Ilford curve comes from here : http://www.greenspun.com/bboard/q-and-a-fetch-msg.tcl?msg_id=006PxQl. It is exponential but less than Gadget Grainer.
• You found Gadget Grainer post, this is also a formula. It goes up very quickly to the infinite.

Thank you for conducting the test. I will add a note to the reciprocity table, to favorite Gadget Grainer HP5 curve.

Henry63 said:

Hi,

I'm the creator of Pinhole, so I might add a few things. I fitted in Pinhole Assist all the curves I could find on the Web. I did not had the time to test them all (speaking frankly I only use photo paper and sometimes Fuji 160S). One important thing is to press the (i) button the is present on each reciprocity curve: It will show you the detail of each curve, and a link to web source, so you can get more information.
Usually I find tables that relies on experiment, however with HP5 I only found formulas. The problems with formula is that I do not get a range a validity (with tables, I know when I and within the bounds of the table or when I extrapolate).

• All W/O Lenses comes from here : http://pinhole.stanford.edu/equations.html
• Ilford curve comes from here : http://www.greenspun.com/bboard/q-and-a-fetch-msg.tcl?msg_id=006PxQl. It is exponential but less than Gadget Grainer.
• You found Gadget Grainer post, this is also a formula. It goes up very quickly to the infinite.

Thank you for conducting the test. I will add a note to the reciprocity table, to favorite Gadget Grainer HP5 curve.

Click to expand...

Thanks for the reply, Henry. I have another question: I have found Kodaks numbers on the data sheet for Tri-X 400, but how do I get that curve into Pinhole Assist?

Adam W said:

Thanks for the reply, Henry. I have another question: I have found Kodaks numbers on the data sheet for Tri-X 400, but how do I get that curve into Pinhole Assist?

Click to expand...

Never mind! The WO Lenses curve is close enough to the Kodak data sheet that I can use that one.