HELP! A friend just gave me his old 4x5 pinhole. No idea what the Aperture is!

[Pinholethrowaway]

Hey LFP forum,

A friend just gave me his old pinhole camera. I'm not sure what his Aperture is on it. I'd like to shoot hp5 400 pushed at 640. Here are the camera stats, it's all I know about it:

Lens says .018" wide-angle 8x10, but he built it inside a 4x5 box.
The lens sits approximately 5 inches away from the film plane.

I'd love to know the Aperture of this LF pinhole camera so I could properly expose!!
Cheers

[BrianShaw]

Measure the aperture. I don’t think there’s really any other way to calculate the exposure.

[tonyowen]

Lens says .018" The lens sits approximately 5 inches away from the film plane.Cheers

Best guess is 0.5mm - which is a 'so called' standard pin-hole.
Next use the program 'Pin-Hole Designer' to give info on exposure etc
Regards
Tony

[Oren Grad]

Based on the labeling, the opening is presumably .018", or approximately 0.46mm. With a "focal length" of 5 inches (127mm), that makes an f/stop of about 276.

[Pere Casals]

You also may take a set of sewing needles, find one that passes and one that does not pass, than take a digital caliper to measure the neddles.

The calculator will tell you the aperture: https://www.mrpinhole.com/calcpinh.php

Anyway you may make a bracketing by removing the slide of the film holder in several steps during exposure, like if it was a test strip under the enlarger, just guess an f/ for the band in the middle, and find what under/over exposure is the right one for the f/ you guessed.

I did that to find the ISO for paper negatives...

[Pinholethrowaway]

Hey everyone, I just wanted to say thank you for all the wonderful responses!!!!

I can't wait to use this camera now!!

[Jim Jones]

Best guess is 0.5mm - which is a 'so called' standard pin-hole.
Next use the program 'Pin-Hole Designer' to give info on exposure etc
Regards
Tony

Rather than use a "standard" pinhole, the best pinhole diameter should be calculated for the intended focal length. This gives a noticeable improvement in sharpness over a more randomly selected diameter. Experience has taught me to use www.pinhole.cz/en/pinholedesigner with a user constant of about 1.5, although a somewhat larger constant may be better for ultra wide angle use. If the pinhole can be laid on a flat bed scanner and scanned at the minimum exposure that gives good clean edges, the pixels across the pinhole can be counted and the diameter accurately calculated. Overexposure gives an enlarged apparent diameter.

[Chauncey Walden]

If that size (,018 inch) is correct with your HP5 rated at 640 in bright sun I would try 1/2, 1 and 1.5 second exposures.

[Tin Can]

Jim,

Do you think this program is safe to install?

I just stopped the install as WIN 10 gave a warning.

Is that program significantly better than the online, http://www.mrpinhole.com/calcpinh.php which I used a few times.

I don't know what the 'constant' means as Mr Pinhole does not use that term.

Rather than use a "standard" pinhole, the best pinhole diameter should be calculated for the intended focal length. This gives a noticeable improvement in sharpness over a more randomly selected diameter. Experience has taught me to use www.pinhole.cz/en/pinholedesigner with a user constant of about 1.5, although a somewhat larger constant may be better for ultra wide angle use. If the pinhole can be laid on a flat bed scanner and scanned at the minimum exposure that gives good clean edges, the pixels across the pinhole can be counted and the diameter accurately calculated. Overexposure gives an enlarged apparent diameter.

[Jim Jones]

As I recall, Pinhole Designer can be downloaded from several sites. I've used it for a long time with never a problem with the download, but don't remember which site I downloaded from. The 'constant' in Pinhole Designer is a variable that lets the advanced pinhole maker to tailor the calculation to his own preference. The Rayleigh constant of 1.9 seems a little large to me, although a good compromise for wide angle cameras. I use about 1.4 or 1.5 for slightly sharper image centers.