Smiling Wasp

[abpho]

Ichneumon Wasp (I believe).

35 frames at 5:1 at f/4, ISO 100, 4 seconds. Used three LED lamps through a sheet of paper towel for my lighting source.

Studio Shot with MP-E on a 7D. Couldn't get a decent 7:1 (ish) shot on full frame so went down to 5:1 on crop and got slightly better results. MP-E at 5:1 is stretching it. I am thinking of going with an objective here more and more.

Played around a bit with the lighting. Managed to reduce the hot spots by moving the lights further away form the subject / diffuser. Still can't illuminate that dark spot on the eyes. I think this is where the lens sits. No amount of finagling can get rid of that section. Any suggestions?

I did not spend a ton of time in post. The subject was really clean. Schmutz on right compound eye too extensive for cloning so left it alone for the most part. Final image comprised of DMAP stack with a pinch of PMAX.



Thanks for looking.

[rjlittlefield]

Looks good from here. I guess you must be seeing soft at actual pixels?

Still can't illuminate that dark spot on the eyes. I think this is where the lens sits. No amount of finagling can get rid of that section. Any suggestions?

Yes, that's the reflection of the lens, also known as the "black hole". It's very hard to get rid of. What you have to do is to either hide the lens or make it go white, as seen from the standpoint of the subject. That means some sort of beamsplitter setup, either putting the lens behind a semi-reflective mirror or pumping light out through the lens using a beamsplitter behind it. There's an example of the first approach HERE that might be workable for your application.

Be aware that at higher magnifications, there's a significant amount of image degradation from shooting through that slanted piece of glass. Thinner glass and smaller apertures reduces the degradation. It's possible to buy really big cover slips (at correspondingly high prices). Their thinness would make them ideal for this situation.

--Rik

[abpho]

I've seen plenty of shots without the "black hole". I will have to ask around on how they deal with that problem. I checked out your link. Interesting, but for now I will just tuck it into the back of my mind.

Thanks Rik.

[rjlittlefield]

I've seen plenty of shots without the "black hole". I will have to ask around on how they deal with that problem.

Perhaps if you point to some, we can explain how the shot worked. Typically shots appear without the black hole when either 1) there are no shiny surfaces facing the camera, or 2) the illumination did not come from two sides. If you find another easy way to eliminate it with a specimen shaped and posed like yours, there will be great interest in hearing the method.

--Rik

[abpho]

I am reminded of the pictures that Yousef just posted. Namely the compound eye of an Ensign Wasp. Here. But on closer inspection the black hole is there as well. Just very well hidden. In the Red Eye Bug picture it is very hard to make out the black hole.

I thought that perhaps is had to do with my short working distance. I wanted to see if a greater working distance would allow more light to get past the lens, therefore reducing the black hole effect.

Now that I am shooting some stacks with live view enables I can better see how the light affects by subject. I will keep improving.

CheerS!

[rjlittlefield]

Thanks for the examples.

In the Ensign Wasp, the black hole is huge and intense, but it's not so obvious because it's positioned off-center near the bottom of the eye and there's not much light coming from below.

The Red Eye Bug is an interesting case. Each of its shiny facets is surrounded by a non-shiny area that is more or less uniformly bright regardless of the angle. If you look at the small circular dark areas, those are the shiny facets, and actually you can see a clear image of the ring of the lens reflected in those.

Both the White Weevil and the Metallic Parasitoid Wasp show black holes very much like your own, and for the same reasons.

I thought that perhaps it had to do with my short working distance.

Short working distance can make the problem worse.

Certain lenses are also particularly bad, especially ones like the MP-E 65 with big black areas surrounding the glass.

One of the nice things about Mitutoyo objectives is that their glass almost fills the front of the barrel, so in their case the black hole is only as big as it really needs to be, given the lens aperture.

With other lenses, the black hole can be reduced by wrapping a diffuser around the subject and shooting through a hole that's just big enough to pass the entrance cone of whatever aperture you're actually shooting at. That may require also the use of a black cone lens hood, narrow end toward the subject, to keep stray light from getting into the lens. The setup HERE, bottom left of the first panel, will illustrate that idea.

None of these tricks will eliminate the black hole, only make it smaller.

--Rik

[DQE]

From Rik:

Certain lenses are also particularly bad, especially ones like the MP-E 65 with big black areas surrounding the glass.

===============

Would the flat black Canon lens hood for the MP-E 65 lens help this situation?

I find it to be useful for reducing flare from my MT-24 flash in many situations, although a simple (and cheaper) DIY substitute would probably work as well.

[rjlittlefield]

Would the flat black Canon lens hood for the MP-E 65 lens help this situation?

Yes, but it's not nearly optimal.

That particular hood is hampered by the need to not intrude into the entrance cone for all magnifications from 1-5X on a full-frame sensor. Much smaller holes can be used under most other conditions.

Putting this in concrete terms, at 5X on an APS-sized sensor the cone of light accepted by an MP-E is only about 13 mm diameter at the front of the barrel even when the lens is wide open. At f/4 it shrinks to about 9 mm. The cone you need to stay out of varies linearly from that diameter at the front of the barrel down to the 5.4 mm field diameter in the plane of the subject

So, if you're willing to optimize for 5X and f/4 then you can get by with a hood whose front diameter is 9 mm or less, versus the 38 mm that I measure from advertising images for the hood.

--Rik

[dbur]

I have considered a disc that is white on the front and black on the back with a small hole that goes just in front of the glass to fill in the big 3" black face of the lens. Does that sound like an idea that would work?

[rjlittlefield]

It will help some, but I'm not sure how much. Imagine yourself outside, looking up into a sky full of nice bright clouds. Above you are two opaque disks: one black, one white. But they're both opaque, so their bottoms are heavily shadowed. It's true that the white one will look a lot brighter than the black one, but I think that even the white one will still be pretty dark compared to those clouds. If the lights are behind the lens, then the MP-E 65 with its black front is like that black disk with clouds behind it. Replace black with white and leave it in shadow, I'm not sure how much improvement there'll be. Let some of the illumination shine directly onto the white disk and it seems like things will get better. But I'm still not sure how much!

How about running the experiment and sharing with us what you find out?

--Rik

[abpho]

Thanks for the discussion. I'll have to try that next time I pull out the MP-E.

PS: That lens designation sounds so military. Like an MP-E assault rifle or something.

[johan]

Probably a pointless aside, but the talk of comparing black and white discs against the sky prompted me.

I noticed something odd about black the other day. If you have 2 squares equal size black and white on a monitor with a background colour, and focus on them, as you focus away from the monitor the white gets more dominant/larger and the black gets smaller.

There's probably a perfectly logical explanation but I hadn't seen it before, just thought it was interesting.

[DQE]

Would the flat black Canon lens hood for the MP-E 65 lens help this situation?

Yes, but it's not nearly optimal.

That particular hood is hampered by the need to not intrude into the entrance cone for all magnifications from 1-5X on a full-frame sensor. Much smaller holes can be used under most other conditions.

Putting this in concrete terms, at 5X on an APS-sized sensor the cone of light accepted by an MP-E is only about 13 mm diameter at the front of the barrel even when the lens is wide open. At f/4 it shrinks to about 9 mm. The cone you need to stay out of varies linearly from that diameter at the front of the barrel down to the 5.4 mm field diameter in the plane of the subject

So, if you're willing to optimize for 5X and f/4 then you can get by with a hood whose front diameter is 9 mm or less, versus the 38 mm that I measure from advertising images for the hood.

--Rik

Thanks for the very detailed reply.

I just measured my Canon MPE lens hood with an ordinary ruler, and the opening is cone-shaped with an exterior (the hood's light entrance) diameter of about 35 mm and an inner (the hood's light exit) diameter of about 25 mm. The cone's inner surface has many concentric, finely constructed anti-flare ridges. This lens hood projects about 12 mm beyond the exit plane of the MT-24 flash adapter that I use. In other words, this lens hood is threaded and screws surprisingly deep into the flash adapter, reducing its tendency to intrude excessively into the photographic scene, etc.

I never measured its flare suppression abilities quantitatively, being satisfied that it clearly and visibly reduced the problem I was having with twin-flash created flare with many scenes. I think the flash guns may have sometimes been rotated too much inwards, towards the central axis of the lens when I was having flare issues, but this definitely wasn't the only flare issue.

I would be glad to post a few functional but inevitably poor aesthetic quality photos of the Canon lens hood if it would be of interest or just for the forum's online information. Also let me know if I've left out any important dimensions that are of interest.