Lens hoods advice

[Helen Bach]

Here is an old APUG thread about lens hood design geometry. I have linked to the last page so that you are spared the 'discussion'. Just scroll down to the bottom of the page - the summary is in the last few posts. The first page has a summary of the method and reasoning, though I would use the entrance pupil in the calculation, for better performance.

Good luck,
Helen

[BrianShaw]

Even a screw-in rubber shade is better than nothing,

At the risk of embarassing myself in front of family, friends, the nation, and the world... no matter how much I read about the physics and theory of lens hoods (and I must admit that I simply LOVE these discussions), this is the answer I keep coming back to when not using a compendium on a view camera OUTDOOR.

When shooting indoor, I generally use the cheap and easy screw in rubber filters for easier access to the shutter. Even getting "one size larger" adapters is too fussy in my experience.

[rdenney]

Rick,
the sharpness of the hood mask doesn't play any role on its optical effect (is minimal) and is not the reason why shades are made longer.

I may be wrong on the reason but I'm confident of the results, being a wide-angle nut on many formats and struggling with flarey lenses.

Consider these two shades:



(Images linked are on Trevor Allin's excellent website for Pentacon Six cameras.)

Both shades are mounted on a 50mm f/4 Carl Zeiss Jena Flektogon for the Pentacon Six camera. The first shade is the one provided by the factory. The second is a Hasselblad shade for their 50/2.8, mounted in front of a thick UV filter (which makes it vignette, as it happens). The lens has an 86mm filter ring--this is a large lens intended for the 6x6 format--bigger than many large-format lenses. The shade on the left is quite huge--over five inches square on the front.

The shade on the left is more effective, for two reasons. One is that it is longer, which requires it to be wider as well. The second is because it is (mostly) square rather than round. Both shades are tight and will vignette when using a filter.

As to the degree of focus, you may be right. I've compared the effect of shades at different apertures, and wider apertures will see vignetting when narrower apertures won't (or will more clearly), but that's more a depth of field issue than a focus issue. I haven't tested enough to back up my statement, so I'll leave it at that. Clearly, though, a long shade makes it easier to get that large-diameter piece of glass out of view of, say, the Sun than using a shorter shade. There have been times I could not find a way to shade the lens with my hand without seeing some effect of my unfocused hand on the ground glass, while parking in the shade of a fortuitously placed tree provided the shade and still stayed outside the frame. It may not be focus--it may just be the relationship of the distance of the shading edge to the size of the front element, given that the goal is to shade all of that front element from a strong light source.

Rick "noting that particular Flektogon is rather flarey and thus rewards meticulous shading" Denney

[chris_4622]

Here is an old APUG thread about lens hood design geometry. I have linked to the last page so that you are spared the 'discussion'. Just scroll down to the bottom of the page - the summary is in the last few posts. The first page has a summary of the method and reasoning, though I would use the entrance pupil in the calculation, for better performance.

Good luck,
Helen

A few years ago George did the calculations for my lenses. I made the shades and they worked very well, as long as I didn't use any movements. I am now thinking about how to make a version with barn doors using the measurements he gave me. I would make one for each lens but as long as they fold up I can fit them in my pack.

chris

[rdenney]

When shooting indoor, I generally use the cheap and easy screw in rubber filters for easier access to the shutter. Even getting "one size larger" adapters is too fussy in my experience.

One of the things I like about the Cambo compendium shade is that it swings away very easily or even unclips for fiddling with the shutter, though it doesn't get short enough for some lenses especially when using a recessed board. When using a Sinar bellows on a rod, I adjust the front of the bellows, and the push the back forward if the lens is long enough to allow it, for making adjustments to the shutter. With short lenses, I usually just pull the shade off. For a 65mm Super Angulon, the bellows I use for a shade are just about fully compressed, but still provide good access from the sides to adjust the shutter, given that the lens is on a flat board.

Rick "the camera itself dictates many of the options" Denney

[BrianShaw]

One of the things I like about the Cambo compendium shade is that it swings away very easily or even unclips for fiddling with the shutter...

Yes, that's the exact one I avoid using at times. Mine is the older type that clips on, rather than flips up. Maybe a flip-up would be a better option but I don't have noticable problem just using rubber screw-in shades for portariture in a studio environment.

[GPS]

I'm going abroad for an assignment now and I don't think I'll have internet access there. Have a good shade for your lenses!

[BrianShaw]

Good luck and safe travels, Geep!

[GPS]

Thanks a lot, Brian.

[Joanna Carter]

Rick "sometimes wondering why people argue about the difference in contrast between multicoated lenses and then use them without shades" Denney