I am using pinhole assist and find it helpful. Make sure you have all your settings in there correct, including whether you preflashed. But in general, with a digital camera, I tend to expose for the highlights in a scene and bring up the shadows in post-processing. With film photography, it’s generally recommended to expose for the shadows. I find this is definitely true for the Pinsta with harman direct positive paper, preflashed or not. I meter near a shadowy spot that I want exposed. If it’s a landscape, I usually also meter for the whole scene and make an exposure somewhere between the two numbers, but closer to the shadow exposure number. Unless you are using a filter, be prepared for your best exposures to lose detail in the sky.

I found it an interesting exercise to just walk around with the pinhole assist app open even without my camera and see how various settings register.

Yeah, unfortunately f stops don't work like that. To go from f/8 to f/16, you need to double it twice. It's two stops between f numbers that are twice the size. So, to get to f/256 from f/16 is 256x not 16x...

Hey! This is the constant fun of photography :) Firstly, yes, any averaging light meter will assume you want the scene to be 18% grey and will adjust accordingly. If you point it at a dark scene, it'll make that black look grey. If you point at a bright scene, it'll make those whites look grey. You can try to find a mid-tone to meter from, or notice that the meter is likely to be tricked and compensate accordingly.

I tend to use a digital camera set to ISO 100 f/16. As the Pinsta pinhole is f/229, I decided that this is near enough 256 for Rock n Roll :) Every 2 stops doubles the f-number, so f/16 to f/32 is 2 stops, or 4x the exposure time. Say we start with time x at f/16:

f/16 = x

f/32 = 4x

f/64 = 16x

f/128 = 64x

f/256 = 256x

so, to get from f/16 to Pinsta pinhole size, we need to increase the exposure time by 8 stops, so double it 8 times or multiply by 256.

Next, the ISO. The process I use (BW reversal) has an ISO of about 3, but Harman Direct Positive is usually around 2. Let's do the maths.

ISO 100 = y

ISO 50 = 2y

ISO 25 = 4y

ISO 12 (ish) = 8y

ISO 6 = 16y

ISO 3 = 32y (I'd stop here for my BW reversal, but we need around another half stop to get to 2)

ISO 2 = 32y x 1.5 = 48y (you may notice that this is about 50.... but there's a reason I've done it this way, which I'll explain in a minute)

so, to get from ISO 100 to ISO 2, we need to increase the exposure time by 5 1/2 stops, so double it 5 times, then multiply by 1 1/2, or multiply by 50.

Putting all this together, you can just take the exposure time and multiply it by 256, and again by 50 (which is the same as multiplying by 12800 in one go) or... (the reason I did it the long way):

you can do it in your head by progressively doubling the metered time 8 times, followed by 5 more times, followed by adding 50% :)

In other words if your metered time was 1/100 you could jump straight to a time of 128 seconds or you could go:

x = 1/100

double it 8 times:

1/100 --> 2/100, 4/100, 8/100, 16/100, 32/100, 64/100, 128/100, 256/100 (which I'd simplify to 2.5s)

double it 5 more times:

2.5s --> 5s, 10s, 20s, 40s, 80s

then add 50%

80s --> 120s

which is near enough :)

By the way, I picked 1/100s because that's the "Sunny 16" speed. In bright sunshine, that's roughly the time you'd want.

For this example, it's probably easier to jump straight to 128s, but for more complicated times I find it simpler to do the progressive doubling on my fingers!

Hope that was helpful and not confusing(!)