Using the Canon 100mm and a 500D close up lens

Hi folks,

In preparing for a trip to Florida and a couple of days at the bridge, I'm testing different macro setups in the pool. I put the 500D on my 100mm after some minor surgery to remove a few thousandths so it would fit in my S&S port. I was very impressed with the image quality and the corners looked great. I was expecting some falloff based on what I have read. I didn't see any real difference with the Auto Focus either. This would seem to be a great setup for a known macro dive. Am I missing something?

I'm not understanding how the working distance is affected my adding the Close up lens. Can somebody check my math please?

I'm using a 100mm macro lens with a 1:1 ratio if used on a FF camera. When I'm using it on the 40D this now becomes the equivalent of 1.6:1, so a 22mm object will fill the frame? OK so far? Now I put on the 500D which is a +2 diopter with about a 1.2:1 magnification factor? (Based on my simple testing) So now we have a mag factor of 1.92:1? Am I thinking about this correctly? Seems almost too good to be true, almost a 2:1 factor with no loss of light. So I'm giving up working distance on the lens by adding the 500D. I'm now limited to a max of about 500mm or about 19.5 inches of focal length?

What really surprised me in the pool tests was the minimum focal length came so far in. I knew that it was supposed to do that, (it is a close up lens after all). My land testing showed the min focus was at about 11 inches with the stock 100mm. I got much closer than that on a few images messing around in the pool and they are remarkably sharp. How do I calculate the min focal length for the combination? How close can I theoretically get?

I'm sure there is a thread here where this is discussed but three days of searching turned up nothing on this combination. Please excuse my ignorance and correct my terminology if I've got something wrong. I'm coming from years of shooting with extention tubes and framers so I never had to think about it. Any help really appreciated.

Cheers,

Steve

Looking forward to see if someone has the answers. Thinking about buying exactly that for my trip to Wakatobi.

Hi Steve,

The easiest way to solve this is testing. Do a test on dry land and photograph a ruler w/ the 500D fitted. What is the result? I wouldn't worry too much about the min focus distance - because who cares as long as it's at least around 2 inches from the port tip or so?

Underwater you have refraction of water due to the flat port interface. Through testing Craig and I discovered that there is no 4/3 magnification due to the refraction - rather the working distance gets longer and you get the same magnification. So for example if you were able to shoot a 22mm subject at 10cm working distance you'll now get a 22mm subject at 4/3*10cm working distance. This really helps if you're using a diopter.

Cheers

James

Thanks James,

I took your advise and rigged up a simple test in the pool. It turns out my old Seiko is exactly 36mm wide, so I put it in the pool on top of an old measuring square that was already rusted. Here is the setup;

So using the 100mm lens with the 500D installed, I took the 40D is the S&S housing and set the port different distances from the watch face. Camera was setup with AF on, single shot. I set the face of the watch on about a 30 degree angle so I could see the DOF. All the distances I'm quoting here are approx. due to the geometry of the setup. Turns out I get the equivalent to a 1:1 image at about 8 in. from the front of the port;

Moving into to about 5 inches I get a measured 2:1. Problem is I don't think it's practical to use the AF this close. It started hunting pretty badly inside of 6 in. I was using my FIXLED48DX focus light with the clear diffusser on and there was plenty of light. I was doing this at night with no ambient light. Oh yeah, it was raining. (My wife is now convinced that the guys in the white coats are clearly in my future)

Any way, what does this all mean? Image quailty was reasonable throughout the range of my simple test. Inside of 6 in I start to run into problems getting the strobes in the right position. It would seem that 2:1 is doable but I'd go with manual focus. I'm starting to think that a real plus of adding the closeup lens is the improved ability to use AF for the 1:1 range of shots. I hadn't thought about this before but since the lens isn't at it's focusing limit it just snapped right in outside of around 7 in. Does that make any sense?

Steve

1. Empty wallet

2. In the pool, with camera, ruler and watch...when its raining

3. taking photo of said watch and ruler

4. Expounding on DOF, focal distance and size ratio

My wife is now convinced that the guys in the white coats are clearly in my future

Steve....I can't imagine why?

BTW, I can't imagine a diopter making AF easier. It should theoretically give you a shorter working distance and shallower DOF. The lack of DOF should make focusing a little more challenging...but what do I know.

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BTW, I can't imagine a diopter making AF easier. It should theoretically give you a shorter working distance and shallower DOF. The lack of DOF should make focusing a little more challenging...but what do I know.

Thanks Gary,

That what I was thinking too. But for a very specific range (the distance around the 1:1)the AF was easier with the closeup lens than without it. I guess what I'm seeing is that the lens has trouble focusing at minimum distances. So when we put on the 500D there is more margin( + and - around 1:1). I making these assumptions on only an hour or so in the pool so I could be completely wrong headed about this. I'd love to hear some other people's experiences using the combination.

Cheers,

Steve