Bee with extension tubes

[scitch]

I finally got my extension tubes and reversing ring with step up adapter. I played around for a few minutes today.

First is an old, dirty, dead bee with 32 mm of Kenko extension tubes and a Tamron SP Di 90 mm F/2.8 macro lens. I didn't stack deep enough, so the ocelli and the antennae are not in focus. It's a stack of 8 images ZS PMax. I hate not having live preview on the Sony Alpha 200. I can't see in low-light conditions through the viewfinder.

I also got a new external flash and diffuser and used it here.



Here is the same bee, but with the full 68 mm of extension tubes and same macro lens and flash/diffuser. I'm pretty happy with this one except for the glare off of the eye. I tried using PS CS5 to fix it, but have no PS skills. This is 9 images ZS PMax.



Finally, a couple of questions:
When I reversed the macro lens on the extension tubes, the image got smaller. Is that supposed to happen? I zoomed all the way in and out and could still see the entire bee in the field of view.

Also, the alpha/maxxum lenses have a mechanical aperture control, so when it's reversed, what's the best way to adjust the aperture? I usually stick a Q-tip in the track, but then it's either wide open or full closed.

Here is a side-by-side of the lens mounted reversed (left) and normal (right). Of course the subject was different distances from the lens in order to focus it. On the left, the aperture was very small. That picture is with room lights, illuminator, camera flash, external flash, ISO 400, 4 second exposure. On the right is ISO 200, 1/2 second, only external flash.

So, did I do something wrong or am I expecting the wrong results from reversing the lens? These are single images, not stacked.



Mike

[NikonUser]

I have an older model Nikon 105mm manual focus Macro that focuses to one-half life size.
I use it non-versed on bellows extensively for insect shots.
At full bellows it gives me a 3.4x magnification.
EXAMPLE HERE HALF=WAY DOWN PAGE
I'm sure with more extension I could get higher mags.

My point is: your Tamrom should be excellent non-reversed with extension.

[rjlittlefield]

When I reversed the macro lens on the extension tubes, the image got smaller. Is that supposed to happen?
...
So, did I do something wrong or am I expecting the wrong results from reversing the lens?

I think it's the wrong expectation. I tested just now with my Sigma 105 mm macro, and it behaves very much like you describe.

Don't feel bad about missing the prediction. Even when you know all the theory, making an accurate prediction depends on lens characteristics that are never published. Those characteristics can be measured and then used to make further predictions, but the initial measurement is done by setting up a test very much like you did and seeing what the magnification turns out to be. Essentially, you need to run the test to get enough information to "predict" what the test would show.

From a practical standpoint, I agree with NikonUser. With this lens, the best approach is probably to use it in its normal front-forward arrangement, and add extension to get more magnification. There may be (probably is) a slight loss in optical quality that way, but the gain in convenience frees up time and energy to work on other issues like lighting and stepping that are more important at this stage of the game.

Judging from your single-frame shots, the glare on the bee's eye would be difficult or impossible to fix in post-processing.

What you need is a diffuser that covers a wider angle of space around the bee. My favorite technique is to place a large piece of tissue paper close to the subject, even wrapping around it, and then flash from far enough back that all the paper gets illuminated. NikonUser accomplishes the same thing using styrofoam cups. Morfa has an elegant "Simple modular diffuser for field work" that uses the same principle.

The purpose of the wider-angle diffuser is to imitate the lighting that you might see outside on a completely overcast day, where the sky is equally bright in all directions. This spreads out the glare over a much larger area on the subject, in exchange for which the glare becomes less intense so that you still see the subject through it. The tomatoes shown HERE illustrate the idea. The lighting you currently have is more like the first tomato shot, where what you'd like to have is more like the last one, or even farther.

--Rik

[scitch]

Thanks Rik and NU. This is the diffuser that I was using: http://www.bhphotovideo.com/c/product/6 ... fuser.html

Rik, with my lack of theoretical knowledge, experimentation is my only option. I just thought I had remembered people on this forum showing that reversing a lens gave higher magnification. I seem to gravitate towards insects, so the extension tubes with the Tamron looks like it'll work just fine. I do enjoy compound eyes, though, so I was hoping that reversing would let me zoom right in on the eye.

NU, I would be VERY happy if I could get images that look like the 3.4X that you linked to.

Would it be feasible to use this setup (extension with Tamron) in the field or should it be considered for studio stacking only? It seems like the working distance, light gathering, and depth of field were pretty good.

Mike

[rjlittlefield]

This is the diffuser that I was using: http://www.bhphotovideo.com/c/product/6 ... fuser.html

Again, the goal is to make the light source cover a wide angle around the subject. That diffuser sits very near the front of the flash and is not much larger than the flash itself. To make it cover a wide angle around the subject, you will need to position it very close to the subject, like just outside the field of view.

I just thought I had remembered people on this forum showing that reversing a lens gave higher magnification.

With some lenses, it does. One common example is to reverse a normal 50 mm lens like you'd find on old film cameras. Mounted normally, those lenses will focus from infinity to 18" or so -- very low magnification. But pop one onto a reversing adapter, and suddenly it gives close to 1:1. Other lenses behave differently, as you've seen.

Would it be feasible to use this setup (extension with Tamron) in the field or should it be considered for studio stacking only? It seems like the working distance, light gathering, and depth of field were pretty good.

This should work fine in the field, especially if your extension tubes maintain coupling so that the diaphragm stops down automatically.

--Rik

[scitch]

Thanks again. The extension tubes do support the auto functions. Even though I don't use it on auto when doing macro, I can set the aperture electronically and focus and set exposure manually.

I was playing around again today trying to find which technique I like the best. I saw someone mount an objective on the front of a camera lens and I gave it a try. I literally duct taped an objective mounted in the lid of one of the objective shipping tubes with a hole cut out of it onto a UV filter and screwed that on. It wasn't even centered perfectly. I was surprised that it worked at all. What do you think in comparison to the pictures above? This was a Leitz 10X EF objective on the OEM Sony Alpha 200 general purpose lens.



I think it has some potential. I did not work on the lighting at all since I was just testing the idea. I was using external flash without any diffusion. I think I see some stars in the bright areas. Do I remember correctly that this is an indication that the objective was not centered or not straight?

When I photograph this way, does it not matter what the aperture of the camera is because the objective's is much smaller? Or is the objective aperture larger than the camera's and so the camera's aperture can make a difference? I guess some more experimentation could answer that. In this case, the aperture happened to be set at F16.

Mike

[rjlittlefield]

I was playing around again today trying to find which technique I like the best. I saw someone mount an objective on the front of a camera lens and I gave it a try.

The pictures you saw were using an "infinity" design objective, which has its aberrations corrected specifically to work well in this arrangement. The objective you are using is probably a "finite" objective that is corrected so that it will work better on bellows. Check the labeling to be sure. If it is a finite objective, it will carry some designation like 160/0.17, meaning that it is designed for use with a "tube length" of 160 mm and a cover glass thickness of 0.17 mm. An infinity objective will carry a designation like <infinity>/0.17, where <infinity> refers to the 8-on-its-side symbol.

Both types of objectives will work in the other configuration, but they won't be as sharp as they should be.

I literally duct taped an objective mounted in the lid of one of the objective shipping tubes with a hole cut out of it onto a UV filter and screwed that on.

There is no shame in duct tape. I've used it myself.

I was surprised that it worked at all. What do you think in comparison to the pictures above? This was a Leitz 10X EF objective on the OEM Sony Alpha 200 general purpose lens.
...
I think it has some potential. I did not work on the lighting at all since I was just testing the idea. I was using external flash without any diffusion. I think I see some stars in the bright areas. Do I remember correctly that this is an indication that the objective was not centered or not straight?

The cross-shaped stars indicate that the lens is astigmatic, meaning that it focuses radial and tangential features at different depths. At any single depth, this turns any bright spot into either a sharp radial line, a sharp tangential line, or some elliptical blur. The PMax stacking process preserves both of the sharp lines, leading to the cross-shaped features. If the lens is centered and straight, then the crosses will appear symmetrically in the image captured by the camera. Crosses that appear asymmetrically in the image suggest that the objective was not centered or not straight.

When I photograph this way, does it not matter what the aperture of the camera is because the objective's is much smaller? Or is the objective aperture larger than the camera's and so the camera's aperture can make a difference? I guess some more experimentation could answer that. In this case, the aperture happened to be set at F16.

Usually the objective's aperture will be smaller. It is safest to leave the telephoto lens wide open, since this will minimize vignetting and will avoid misleading the camera's exposure metering system. The latter aspect is because most cameras meter wide open and assume that when they stop down the image will get dimmer. But when the objective is establishing the aperture, that assumption is wrong and the image is likely to end up overexposed. If this was auto-metered, I think you got lucky because a) the camera's aperture setting is not too much different from the objective's, and b) you did not get significant vignetting, despite (a) which often causes problems.

Notice that despite the crosses indicating astigmatism, the objective's image reveals more detail about the subject than the macro lens does. The increased magnification more than makes up for the larger astigmatism in this case. But you would do better still by using the objective in its designed configuration. If this is a finite objective, use it on bellows. If it is an infinity objective, then figure out how to center it better.

--Rik

[scitch]

Thanks, Rik;

It was a finite objective, I don't have any infinite. So, is the astigmatism a characteristic of this type of objective or is there something wrong with this particular one?

I did get some vignetting, but I cropped it off. Not too bad, though.

I'll keep playing around and find which method I like best. I got some sorbothane the other day to help reduce vibrations.

Mike

[rjlittlefield]

It was a finite objective, I don't have any infinite. So, is the astigmatism a characteristic of this type of objective or is there something wrong with this particular one?

Astigmatism is not typical of any objective when it is used as designed, meaning at rated tube length and within its nominal field. Change the tube length or try to use a larger field, and all bets are off. Because this is a finite objective, you should definitely be using it on bellows, not with a telephoto. See HERE for illustration of how a good finite objective becomes bad when used on telephoto.

--Rik