[BigMackCam]

As part of a project I'm working on, I need to photograph a number of lenses from the front, to show the markings on the trim ring and also the shape of the aperture at various settings.

In some early test shots (and not surprisingly) the equipment I've used to take these photos is reflected in the front element and any bright-work on the front surround of the lens. Would a CPL filter help to remove these reflections?

More generally, does anyone have any tips or guidance that would help in avoiding any reflections?

Many thanks in advance

[Not a Number]

You should be able to knock out most of the reflected hot spots if you put a polarizer on your light source along with the lens.

Successful Light Polarization Techniques | Edmund Optics

[photoptimist]

A CPL would only help if the reflections are at a shallow angle (like a reflection across a pond at sunset). As the reflection angle approaches perpendicular to the reflective surface, the polarization effect drops to nothing.

Two solutions:

1. Off-axis lighting: Use a telephoto lens to photograph the lens front and mount the light sources as far off to the side as possible. You might need 3 or more light sources to get decent illumination due to shading by the filter ring. Also this solution will still have some problems if the subject lens is a UWA with a bulbous front element.

2. Cross-polarized lighting: Add a polarizing filter to the light source (linear is easiest) and a CPL to the camera and turn the CPL to cancel all the reflections. You'll only need one light source. You might notice a faint blue or purple reflection of the light source depending on the quality of the two polarizers.

[BigMackCam]

Thanks you both for the replies and advice -very much appreciated. It's a slightly trickier problem than I'd anticipated Seems I have some experimenting to do...

[pepperberry farm]

the handful of times I've attempted this, I've used offset lighting for best results; I need to set up my light-box and give it a go...

here's a couple of examples that have turned out for me:





backsides, too

[BrianR]

Do you have an example of what you've tried so far? Below is a pretty simple photo to show the aperture shape and size (also the dust and grime on the lens). Just a reflective umbrella up close with something light behind. Add more relatively large light sources around the front (more umbrellas or softboxes, or even use a light tent with the front curtain pinched in) and you can uniformly light up the front assembly, the reflections of the light sources won't obscure the aperture shape if the aperture is backed by white.

It depends on exactly what you're trying to show though (there's no detail on the aperture blades in my example). Another option is to use a couple sets of lights, one to show the front assembly, one to light the aperture and blades how you want. Two photos, one with each light setup and combine in post. This would be a fast edit, but might look odd if the viewer is paying attention to the lighting.

[dmr]

Back when SMC Takumars first came out (1970s) some of their ads had some very spectacular surface photos of the lenses, showing some rather brilliant color effects. You might look at some ads in 1970s-1980s Popular Photography and the like and try to reverse-engineer the lighting and technique.

[Kerrowdown]

Photographing the front of a lens - reflections?

Here's a thought... what about one of those wee diffused light tent/cube thingys... would that do it?

[BigMackCam]

Do you have an example of what you've tried so far? Below is a pretty simple photo to show the aperture shape and size (also the dust and grime on the lens). Just a reflective umbrella up close with something light behind. Add more relatively large light sources around the front (more umbrellas or softboxes, or even use a light tent with the front curtain pinched in) and you can uniformly light up the front assembly, the reflections of the light sources won't obscure the aperture shape if the aperture is backed by white.

It depends on exactly what you're trying to show though (there's no detail on the aperture blades in my example). Another option is to use a couple sets of lights, one to show the front assembly, one to light the aperture and blades how you want. Two photos, one with each light setup and combine in post. This would be a fast edit, but might look odd if the viewer is paying attention to the lighting.

Thanks, Brian. Unfortunately, I don't have the test shots I took - I wiped them while they were still in camera, before I sent the body off to the UK Tamron distributor to calibrate my Tamron 10-24 lens

I'm trying to show just the front of the lens (for the trim-ring markings), and the shape of the aperture at each setting, to demonstrate how that shape changes. A number of the lenses I'll be photographing have interesting star-like apertures when stopped down a little; others - mainly telephotos with a large number of blades - remain almost perfectly circular. It's of interest in terms of out-of-focus rendering.

I'm thinking the pinched-in tent with two flashes, each firing at a front corner of the tent (to fully light up the diaphragm) might be the way to go. I'll set my tent up and give that a try tomorrow, I think.

Here's a thought... what about one of those wee diffused light tent/cube thingys... would that do it?

Thanks, Kerrowdown... see above

[dmr]

Here's an example of the style I was talking about. Do any of these have the look you're looking for? This was from a 1981 PopPhoto magazine ad.

[BigMackCam]

Here's an example of the style I was talking about. Do any of these have the look you're looking for? This was from a 1981 PopPhoto magazine ad.

Those are great, but not what I'm looking for, alas

I want to avoid all reflections on the glass so the photos show the current aperture shape - almost as if the glass weren't there...

Thanks for posting this, though

[dmr]

Ok, I misunderstood.

What I would probably try is illuminating the walls (as neutral as possible) of a room from behind the camera with 2-3 floods and position the subject (lens) such that as little detail on the walls as is possible shows in the reflections in the lens. I might also experiment with some kind of a light source at the bottom of the lens to show the aperture in silhouette. I would also use a fast wide-aperture taking lens, focusing carefully on the image of the aperture.

[dmr]

I did a quickie proof of concept earlier this morning, not studio conditions, but lit mainly by reflected light from the walls. I positioned the subject to keep any speculars off of the lens surface.

Is this approaching the look you're going for?

[photoptimist]

The tent idea sounds good. I assume you'll be shooting through a circular hole in the roof of the tent so that the reflections on the curved front element don't have a distracting reflection of the camera, tripod, etc.

One issue is depth of field -- the markings of the trim ring and the edge of the aperture ring reside at significantly different depths. Even at f/22 both planes may not be in focus. You might end up needing to shoot a series with the first image focused on the trim ring and subsequent images refocused on the aperture blades. If you are ambitious, you could even use focus stacking to composite two or more images to get both the trim ring and lens internals in focus.

For bonus points, if you get the correct behind-the-lens lighting (and set the white balance), then light shining through the lens will give you an image that shows the color cast of the lens.

For extra bonus points you could also position a 45° angled mirror by the aperture ring so every image also shows the aperture setting. (Of course, the depth of field issues are even worse for that!)

Too much fun! Good luck!

[BrianR]

I'm thinking the pinched-in tent with two flashes, each firing at a front corner of the tent (to fully light up the diaphragm) might be the way to go. I'll set my tent up and give that a try tomorrow, I think.

Not a light tent, but my quickie with a similar idea is below. A minor obscuring of the aperture, but it shows up pretty well when backed with white. More separation of the white reflectors would move the reflections out more (open up the tent more). There are reflections on the left and right sides of the front ring with this setup, it this obscures text, carefully placed little black cards on either side would take care of it. This may be necessary in a light tent depending on how your lights are hitting it. My reflectors were vertical, but my subject lens was pointed upwards causing the reflections in the front element to be annoyingly non-parallel. Easy enough to re-align things