Packard shutter hole sizing

[Fragomeni]

I’m getting ready to search for a Packard shutter but would like clarity on how to determine what size hole I need. This will be for a Carl Zeiss Apo-Tessar in barrel which has a 3.5 inch rear diameter (the barrel, the glass diameter is smaller). It’s currently flange mounted on a 6x6 Deardorff board with a 3.5” hole. Do I just need a Packard with a 3.5 inch hole (same size as lens board hole/outer diameter of the rear barrel body) or is it better to oversize the hole relative to the lens mounting hole? If oversizing is good practice, by how much should I aim? Or since I know the rear glass is smaller than 3.5 inches in diameter (relative to the hole in the lens board), should a 3.5 inch Packard hole be good?

[j.e.simmons]

You also have to consider the size of the shutter itself.
http://packardshutter.com has the dimensions.

Probably a 3 1/2 inch hole would be good enough if you don't plan to get larger lenses in the future. 3 3/4 might be better, but the shutter itself is larger and might not fit.

[Jody_S]

The shutter will mechanically vignette the image if it is the same size as the rear element and it is placed behind the lens. Whether that will matter or not depends on the coverage of the lens and the format you're shooting. If it's an 11x14 lens you're shooting 8x10, there will be no effect. If it's an 11x14 lens you're trying to use for 8x20, then that few millimeters might be important.

[Fragomeni]

You also have to consider the size of the shutter itself.
http://packardshutter.com has the dimensions.

Probably a 3 1/2 inch hole would be good enough if you don't plan to get larger lenses in the future. 3 3/4 might be better, but the shutter itself is larger and might not fit.

Fitting the board isn't an issue. This is for a 20x24 that I've built and I can always change out the board size to fit the shutter if necessary.

The shutter will mechanically vignette the image if it is the same size as the rear element and it is placed behind the lens. Whether that will matter or not depends on the coverage of the lens and the format you're shooting. If it's an 11x14 lens you're shooting 8x10, there will be no effect. If it's an 11x14 lens you're trying to use for 8x20, then that few millimeters might be important.

Mechanical vignetting is exactly what I assumed could happen and want to solve for. Just not sure how to determine if it'll happen and how to account for it by sizing up. This lens covers 20x24 wide open at infinity and it's essentially a wide angle on the format. The rear element itself is 2.5 inches in diameter. A 3.5 inch Packard would then give an extra 0.5 inches all around (same as the lens board hole) but I'm not sure how to account for the extra depth of the Packard and whether or not it would cause vignette. Any sound way to work out what size hole I should get for this 600mm lens covering 20x24?

[mhayashi]

The larger the hole, the instantaneous mode speed or the fastest speed is slower, due to the size of hole and weight of the shutter blades.
My 5” hole packard shutter has 1/8 sec speed at instantaneous mode.
So you should consider your desiable speed at minimum against the packard hole size.
I’m sure Jon Gilchrist of Packard shutter company would tell you which shutter size suits your needs beside the vignetting issue.

I use the packard shutter for a lens with the rear element diameter larger than 75mm, the sinar copal shutter hole size.

I think 1/2 sec is controllable by a lens cap as a shutter, so using the packard shutter with larger than probably 6” would be meaningless just for speed.

The Sinar copal shutter is reliable having 1/60 at max speed with the half speed increments.
That is very convenient.

Another concern about the packard shutter is the shutter must be parallel to the gravity for the proper movement, not the case for the Sinar copal shutter.

I mount the packard shutter in front of barrel lenses due to the physical limitations of bellows against the shutter body size.

[Jody_S]

Any sound way to work out what size hole I should get for this 600mm lens covering 20x24?

Simple trigonometry. You need the angle of view, distance from the rear element to the Packard shutter blades, and size of the opening of both lens and shutter.

[Tin Can]

I almost always use my Packards with flash

My largest is a very old 4-1/2 inch Packard with DIY microswitch, flash eliminates shutter speed

I put the shutter as close as possible to lens rear, but that varies

My Tessor f9 900mm casts a narrow beam