Lens shade help

[chris_4622]

Anyone here have a formula or want to help me design two efficient lens shades? It's for a 300mm lens on two formats 5x7 and Whole Plate. Since they will only be used for portraiture they can be fixed and efficient and don't have to allow for movements.

I'm not looking for any compendium ideas or even barn door type shades. I will make them so they attach to a filter ring and screw that into the front of the lens. I just need to know the 3 dimensions for the two rectangular shades, L, W, H.

chris

[B.S.Kumar]

I don't have a mathematical formula, because that involves trigonometry = headache
The easiest way to figure out the required size is:
1. take a small square cardboard box
2. fit it to the filter ring
3. see if the shade vignettes at your focusing distance at the taking aperture
4. if it doesn't, increase the depth until it starts to vignette
5. if it does, reduce the size as necessary
6. paint it black inside.

The most efficient is one tailored to your format, so use a proportional mask in front, and move it until it just starts to vignette. That is the correct depth for the shade, for that distance and aperture.

An even easier option is to find a shade like the Sinar or Cokin type that allows additional rings to be attached to increase or decrease the depth as required.

The absolute best shade is the Sinar bellows with the roller blind mask in front that allows very precise masking, tailored to the exact photo that is being taken.

If you want a simple, inexpensive compendium type shade, send me an email.

Kumar

[Nodda Duma]

I know the math and what Kumar suggests is way easier.

[Leszek Vogt]

A goosneck with a 3-sided shade....clipped to the camera or tripod. It can be used on other lenses too.

Les

[B.S.Kumar]

The gooseneck 3-sided shades should be used carefully. They have a tendency to droop, and are easily moved. Also, if the ground is reflective - think snow, a beach or close to water, they may not be fully effective.

Kumar

[chris_4622]

All i have left to do is glue the step up ring on and screw it into the lens.
I used some "chemetal" aluminum i had left over from a countertop job. I put the shiny side inside and lined it flocked paper.

[ic-racer]

Anyone here have a formula or want to help me design two efficient lens shades? It's for a 300mm lens on two formats 5x7 and Whole Plate. Since they will only be used for portraiture they can be fixed and efficient and don't have to allow for movements.

I'm not looking for any compendium ideas or even barn door type shades. I will make them so they attach to a filter ring and screw that into the front of the lens. I just need to know the 3 dimensions for the two rectangular shades, L, W, H.

chris

I'd go with a compendium in case you want to focus your lens.

[mdarnton]

Chris- Clever. I've been pondering this but never thought of cutting it from one sheet!

[chris_4622]

ic-racer, once I epoxy the step-up ring on the back of the shade it will screw into the lens. Then my hands will be free. While the shade is efficient there is some room for minor movements and since this is for portraiture I won't be using much anyway.

mdarnton, thanks. It works well once you have your size figured which I did using a small cardboard box. You really only need two sides to the box forming a right angle. If you have a second person it's easier. Bending the aluminum to get nice corners without the proper tool is a challenge but I did it using wood blocks and clamps.

[Greg]

The absolute best shade is the Sinar bellows with the roller blind mask in front that allows very precise masking, tailored to the exact photo that is being taken.

Agree.... I use Chamonix view cameras. If you mount the Sinar roller blind mask in a Norma Auxiliary frame and mount the whole thing in one of the female threads in the base in front of the lens, you have one of most efficient shades out there.