Canon100mm macro vs 60mm, Issues

Hi, I’m new to the forum (at least posting) and was wondering about a few technical questions about macro photography. I have the 30d, with ds125 strobes.

1. I have the EFS 60 mm macro, and I have a very hard time hitting focus on a regular basis notwithstanding the varying aperture settings. I have tried AF One Shot and after locking focus, obviously the slightest distance change ruins the sharp focus. The AF Servo seems to work a little better at tracking moving objects but seems slow to react. I am curious as to what others are doing. I have tried focusing lights, which seem to help some, but the LCD ones with diffusers don’t seem to be strong enough. Likewise the modeling lights don’t seem to work well. The zenon ones leave spots. I was wondering, people who have both the 100 and the 60mm, if the 100mm has the same sluggish focus problems (slow, low contrast, low light) as the 60, because it has the limiter (which I don’t know how far out, it locks).

2. Secondly, if theoretically, we were shooting the same object with both lenses, we would have to move the 100mm back away from the target to get the same image size on the sensor. After doing this to achieve the exact same size on sensor, would the depth of field be the same using the same aperture, or would the 100 have a larger one. Similarly, same scenario, we move both lenses back away from the target (say 1 inch to make the math easy) the same distance without adjusting focus, would the 60mm be more out of focus because the ratio of the change to the target distance would be greater? EG:100mm lens is 24 inches from target, 60 mm is 14 inches from target (or whatever it is to make the image size the same on sensor). 100 lens would only change 1/24 of the distance or about 4%. The 60mm has moved 1/14 of the distance or about 7%. The question is, is the slight amount of movement that actually occurs underwater while taking the photo, more critical with the 60 mm, as one has to get almost twice as close to get the same image size.

3. With all lenses, there is obviously a drop off in resolution (MTF charts) and contrast at around f16 and smaller; the question would be when is too small of an aperture to increase DOF, really creating diminishing returns, as far a picture quality (image sharpness vs DOF).

4. Would there be any disadvantage using the same port for both of the lenses (so I don’t have to schlep so much crap around) even though there would be a couple of inches of air in front of the 60mm in the port. Would it throw off the focus?

I have a lot more questions, but don’t want to get overwhelmed all at once. Thanks for your feedback. Phil

Hi,

Good questions!

RE the focus - all macro lenses are sluggish to some degree, it depends more on the camera AF system or your technique to get faster focus lock. Some cameras have bigger/better af sensors than others. Also you need to understand that af uses contrast changes to find focus. You can NOT focus on a blank slate or a smooth patch of sponge, etc. You need to find a line, lock focus, then move around.

I use one shot AF for macro. You can use the star button as your AF button, then when you let go, move the housing in and out for your fine selective focus. Hit the shutter when you have it.

With the 100mm, you can get 1:1 from further back. Alternatively, you can use a diopter (on the lens or on the outside of the port) to bring the close focus even closer - if you want to go greater than 1:1

HTH

James

I can weigh in quickly.

Regarding question 2 - In macro work, for a given magnification (size of subject in the viewfinder) and aperture (f-stop), the depth of field is the same, regardless of the lens (of course, assuming the same camera, etc). However, the field of view will be different for each lens.

double posting wont help that much. I'm sure the team can merge the topics.

As for the last question:

It is possible, but..

I tried the 60mm in a 100mm size port I already picked up (havent got the lens yet). The field of view (at least above water) is narrow enough so that there is no port shade in the pictures. I suspect this will be even better under water. However, the 60mm focusses very close. If you use the longer port, it might focus on the inside of the port.

Gerard

For the DOF:

http://www.dofmaster.com/dofjs.html

1. People use powerful focus lights and many switch to manual focus. As macro lenses get longer, AF tends to work less well in my experience. James is right, all macro lenses are sluggish to a degree because their focus range is so great and you have to have good contrast for the AF detection to work. That means adequate lighting, patience, or MF. Even with MF a good focus light is important.

2. Matt is right, the DOF is the same. For the second half of that question, moving in and out will result in equal changes in focus; the fractions don't matter. Because the 100mm has a narrower field of view, camera shake will be more noticable.

3. That is dependent on how you will view the image and how critical the extra DOF is. Certainly, most would say f/27 is beyond the limit and f/16 is likely to be OK. For some cameras and applications, even f/16 may be questionable. The beauty of digital is that you can afford to experiment. Practice on obtaining critical focus rather than using extra DOF as a crutch. Try some pool experiments. A 5D user will give you a different answer than a 30D user will.

4. The extra port length will gobble up your working distance. You need some distance to obtain good lighting on your subject and the 60mm is already pretty short on that. Using a port that is too long will effectively reduce the amount of magnification you are able to obtain so if you want to shoot small subjects it would be best to use the right port.

Thanks for all the good info. Sorry about the double posting; i didnt know where to put it-new to forum. Davichin, thanks for the DOF finder-that's great, and proves question 2. Interesting.

What kind of focus lights do you guys use. It would seen a really powerful led (5000k) with a diffuser would be ideal. When the 60 mm hits focus about f/11 to f/16, it is as sharp as a tack. Does anyone use the AF Servo mode while trying to track moving objects (small fish etc)? Obviously this would be close up, not macro.

Segal: I dont understand why the field of view would be different if the image in viewfinder is the same. For example, the 100mm has 16degree FOV which makes a 6 in. object fill the screen at 21 inches (Cotangent of 16degrees /6in) and the 60mm has a 25deg.FOV which makes the same 6in objectfill the screen at 12.8 inches. Keeping the same relative distances as per magnification, i dont think the FOV would change.

Good observations on the longer port with short lens, as for diminished working distances and possibility of even worse focusing becase of lens trying to focus on end of port.

Thanks for all the great comments and any more tips, comments would be appreciated.

Phil

For a real-world example...

Source: The-Digital-Picture.com - Canon EF 180mm f/3.5 L USM Macro Lens Review

The focal length also affects other macro photography aspects. Longer focal lengths require more distance to acquire the same subject framing. The result is a change of perspective - the telephotos compress/flatten the subject features more than short focal lengths. The wider angle of view of the short focal length macro lenses mean that more of the background will be in the picture - and that the background will be less-diffusely blurred. Picture what I am talking about ...

The pictures above were taken with three macro lenses (180mm L, 100mm and 60mm). They are identically framed using the same aperture setting (f/16) and have identical subject to background distances. DOF (Depth of Field) is not different (same framing, same aperture = same DOF until closer to the hyper-focal distance), but perspective/compression and angle of view are very different.

 

The 180mm lens shows only a small physical area of background subject that is compressed/enlarged to magnify the blur. Background subjects in the 60mm picture appear to be more in focus. They are not - they are just about as blurred, but they appear much smaller in the picture - and there are more of them because of the 60mm's angle of view. This gives a less diffuse looking background blur. If you are using a backdrop (such as rolled paper), the background blur aspect might not be important to you. It is easier to find a pleasing background for a 180mm macro picture because there is less background in an identically-framed shot.

Dang Matt - that's cool! Great example.

Cheers

James

I dont understand why the field of view would be different if the image in viewfinder is the same. For example, the 100mm has 16degree FOV which makes a 6 in. object fill the screen at 21 inches (Cotangent of 16degrees /6in) and the 60mm has a 25deg.FOV which makes the same 6in objectfill the screen at 12.8 inches. Keeping the same relative distances as per magnification, i dont think the FOV would change.

As you pointed out, the FOV is indeed different. 16 degrees vs 25 degrees!

The angles of view are different. At the subject plane the field width is the same but behind the subject the background composition varies.

What kind of focus lights do you guys use.

Fisheye FIX Light HG20DX.

Comparison article here.

Visual comparison here.