Macro Lens question

[archaic0]

I've just started my trek into macro photography and see a long and fun time ahead!

To save some money though, I bought an extention tube to begin with until I can afford a full macro lens. I'm unsure about the depth of field though. I'm using a Canon 28-135 IS on a Digital Rebel XT with a Canon 25mm extention tube II.

My depth of field right now is VERY narrow. I think I remember something about this being the case with extention tubes, but right now I'm unable to find the information I found a while back. It seems not like the depth of field is narrowed, but eliminated completely. Is this normal for the range I'm working at?

Attached is a picture of a cricket corpse. In it, you can see the sides of the cricket body are in focus, but the top is not. That's only a couple millimeters of working focus distance. Certainly not enough to work with live subjects and really not even good enough for dead ones if I can't get their whole body in focus.

In shopping for a new lens, I've found Canon's 100mm f/2.8 macro in the $450 range, but wondered if that's what I need to target? I'm at 135mm now and enjoy the level of magnification I can get. Is the focal length of the lens what I need to focus on for the magnification? As in, if I get a 60mm macro lens, I will back up from where I'm at now, right?

I also have Canon's 70-200 f/2.8L lens and the 28-135 out performs it in magnification simply because of the distance to focus is not shortened enough. Are there other 200mm lenses that might work well?

Thanks in advance for your input!

[Loupey]

Hello, archaic, and welcome to the site!

You pose a lot of good questions. First of all, the image you posted looks quite normal - sure the DOF is going to be a lot shallower than you're used to, but that is going to be the case with any dedicated macro lens too.

In terms of the relationship between magnification and DOF, there is no difference between a "tubed" lens and a dedicated macro lens if shot from the same distance and yielding the same magnification. I think where a lot of people forget is that a normal lens may often get used wide open or nearly wide open so when they stick an extension tube, they think they can still shoot it like that. Dedicated macro lenses are slower (f/2.8 and f/3.5 for Canons) so people already know it's slower and seem to take more effort into "stopping down" the lens. That being said, macros are generally shot with medium to small apertures (f/8 to f/32) to gain the necessary DOF. I don't know what you shot your images at.

Using tubes with zooms can be done but there is a lot going on. You can get more magnification if you zoom to the shorter end of the zoom while you have an extension tube on. BUT, you subject distance will decrease dramatically as will your DOF.

The reason why your magnification with your longer zoom is less is because you're using the same extension tube. The longer the lens, the more extension you need to maintain a given magnification.

As for the difference between the 100mm macro and 60mm macro, the main one is the camera-to-subject distance. They both will yield a 1:1 (lifesize) magnification, but the 100mm can do it from farther away. And the 180mm macro can do it from even farther.

Zooms with tubes can cause significant distortion around the edges of the frame. Using primes will produce much better results. If you think you'll need a fast prime in the future (like an 85mm f/1.8 or 100mm f/2), you can have it do double duty by using tubes with those instead of buying a slow macro and a fast prime later.

[archaic0]

Thanks for the reply. I've actually been here for a while I think, I just haven't been active in a long time. I don't remember this site layout, but the URL was in my favorites. Did a facelift happen some time in the last year?

The image I posted was taken at f/9 and with the cricket nearly touching the lens. It was taken at the long end of my lens, 135mm. I tried some to swing the apature closed, but it didn't seem to help much with my DOF. And while I expect a smaller DOF, I guess I just hoped I could get at least an inch or two rather than a millimeter or two. 'small' DOF is subjective, are there any numbers to show me what a lens gets at a given focal length and apature and just exactly how a tube changes that? Because I would certainly use that number in my buying decision if say one lens could achieve a 6 inch DOF at 100mm f/11 vs another that could only get 1 inch.

Can I use my image as something to go by when shopping for a dedicated macro lens, or is the extention tube throwing things off? What I mean is that if I wanted to get that subject at that end size, but from say 12 inches away, do I need to look higher than 135mm? How much higher? 180 isn't much above 135, so realistically could I expect to get a couple inches of distance or a couple feet with that change?

Unless the extention tube is throwing things off a little, it seems like the 100mm dedicated lens wouldn't satisfy me. At least not with insects as my subjects.

Does anyone here shoot macro of insects and other such things at 12 inches or more away? And what equipment do you use to do it? Post some images?

And my 12 inch mark isn't anything special, I just figured if I was roaming around outside trying to catch live things I might be able to do that at 12 inches, but certainly wouldn't get them to stick around if I touched them with the lens.

[Loupey]

... are there any numbers to show me what a lens gets at a given focal length and apature and just exactly how a tube changes that? Because I would certainly use that number in my buying decision if say one lens could achieve a 6 inch DOF at 100mm f/11 vs another that could only get 1 inch.

I've been thinking about how to make such a chart for some time. But it would be a fairly complex sliding rule considering all the factors.

You must take into consideration everything that changes even with just one lens. Consider the 100mm shot at f/11, you could have a 6" DOF but that would happen at around 5 feet away I imagine. Now that same lens at the same f/11 but with a subject only 1 foot away would produce a DOF only a fraction of an inch.

A macro shooter must consider only two main factors: 1) magnification, and 2) shooting distance. Calculate the magnification that you think you'll be shooting the majority of time. Is it the size of an index card? A postage stamp? A sheet of paper? Once you calculate the magnification (for me it's around 0.25x and 0.35x), match up a lens that has that magnification with a minimum focusing distance that you can live with. Canon's website used to have a better lens chart that had all that info rather than the condensed one they have now. I have a PDF of their old chart - if interested I can email you it.

If bugs are what you're after, the 100mm might be a bit short. Generally, you need all the distance you can get so you don't startle them. My 180mm macro is good but my 300mm with extension tube is even better. A lot of what's shown on my website is with the 300mm/tube combo with a shooting distance of about 4'.

On the other hand, if you think you'll be doing more "studio" type indoor work with multiple lights, reflectors, etc., a shorter lens will keep you closer so that you can hold some of the lights, reflectors, etc. in your left hand.

[archaic0]

OK, that makes a lot of sense.

What size extension tube do you use on your 300? what might I use on my 200 to get similar results?

I have a feeling that I'm stuck with studio shots of dead stuff for the time being and I need to back up a little to increase my DOF. That must be my primary problem right now, the fact that my subjects are sitting on the lens basically so my DOF is paper thin.

I might experiment with taking several shots and compositing them for a larger DOF. I've done composite work before, but not anything as complex as that I don't think. I imagine that combining 3 or 4 images along a DOF plane will be a little intensive. I'm a vet in photoshop though, from a web development chair though, and photo work like this is still a little new.

Thanks for hanging with me. I really appreciate the input.

[Loupey]

What size extension tube do you use on your 300? what might I use on my 200 to get similar results?

When I use my 300mm for macro shooting, 70% of the time it is with the 36mm tube. Then 25% of the time it is with both the 20mm and 36mm tubes. The remaining 5% would be with all three tubes. But keep in mind that my 300mm is already close focusing by itself (4.9') so using tubes is truly supplemental for macro work on this lens. I believe the 70-200mm has the same close focusing capability so you should have similar results.

As for making a composite image for increasing DOF - I don't think I've ever seen that. Composites for combining action sequences and exposure values, but not for DOF. I think that you would get some strange ghosting due to OOF DOF around the periphery of the subject. I would be curious to seeing it if you try.

At the moment, I have the same 28-135mm lens. I did some tests earlier in the week with the tubes. I might post those results here.

[archaic0]

I'll have to play around some more. I hadn't put my 25mm tube on my 50mm f/1.8 prime yet, but I'm going to this week and see what it can do for me as compared to the 135. A quick test shows I can fill the frame with a postage stamp.

My 70-200 has a 1.5m min focus distance, and them zoomed to 200mm it makes nice closeups for some things, but not insects. I haven't measured it, but the 25 tube brings it in closer, but still not nearly as close as the 135 with the tube.

I just need to keep playing and see what results I can get with what combination of things. I just wish I had someone close by with a 300 that I could play with. I used a tax return last year to buy my 70-200 L lens and I'm not sure that I'll be able to drop another $1200 on a new lens anytime soon.

I've read a few people saying they've done the composite thing, it'll just come down to technique I think. If I can find some good subjects to photograph this weekend I'll post some images to this thread. It's quite cold here now though, so the pickins are slim for bugs and flowers. Maybe something else can stand in for now.

[Squidward]

I will preface what I'm about to post by saying that I do not own any Canon photographic gear so forgive me if what I'm about to suggest cannot be done here.

I love shooting macros with non-macro lenses by reverse mounting them in front of an extension tube. The wider the angle the greater the magnification and the less the depth of field. You think your cricket picture has little depth of field, try having less than 1mm of DOF. At about a 3X magnification my DOF is about one half of one millimeter. In the attached photograph, this spider, which measures about 1/4" long on the body, has his sides in focus but nothing else. This is the best shot I could get from about 15 shots taken of him because just breathing could pull me out of focus and back. I was turning blue in the face just holding my breath to get this shot. Nikon D70 with a reverse-mounted 35-70mm f/3.3-4.5 at 35mm at f/4 or so and 1/60 second with a 27.5mm extension tube sandwiched between the lens and body.