Jitin Rajan , Sep 05, 2010; 02:45 a.m.
Hi, I had just bought MK-II with kit lense of 28-105mm f/4. Today i was trying to shoot some macro with revesal technique but could not handle the errors. i.e.
1- With Mk-II kit lense attached i place my analog 100-200mm pentax lense touching head to head, but could not get the focus right even keeping it on infinity. I took the other lense in my had and tried to place it away fro the attached lense to a limit where i could get the focus right. But in that case get lot of wide open space around my main subject.
please suggest where am i going wrong with the calculations. I was doing this by placing pentax 100-200mm lense zoomed to 100mm keeping the manual aperture to the max f-4, in front of attached 28-105mm canon lense with body MK-II 5D
Sample pics are attached .
Drop
Joseph Wisniewski , Sep 05, 2010; 03:10 p.m.
Oh, where to start...
The biggest mistake people make when macro coupling is not understanding that the lens closest to the subject, the reversed lens, is the one that's doing most of the work. I used to refer to that lens as the "front" lens, but its function is so important in a coupled lens picture that I decided that calling it the "main" lens is more accurate.
The lens on the camera doesn't really do all that much. You can replace the camera's lens with a plain old tube the same length as the focal length, and the main lens will still work. The only thing the lens on the camera does is to provide an "artificial infinity" to allow the main lens to operate in a flatter field, less distorted part of its range. So, "camera lens" or "rear lens" doesn't really describe it. All it is, is an extension tube with infinity compensation. Let's call it the "coupling" lens.
Macro coupling works best when the main lens is short. It should be both "relatively short", as in "shorter than the coupling lens" and "absolutely short", as in a normal or wide.
- You want a normal or a wide because reversing a telephoto literally doesn't do anything useful. The magnification is the ratio of the main lens's focal length to the coupling lens's focal length. You've got a 100-200 main lens reversed in front of a 28-105. That means the largest magnification you can have is 1.05x (the 100-200 set to 100mm, the 28-105 set to 105mm). You can have less magnification, all the way down to 0.14x (the 100-200 set to 200mm, the 28-105mm set to 28mm). There are lots of ways to get magnifications in that range that will give you much better results than coupling the lenses you're using.
- Macro coupling always gives you a "working distance" (distance from the lens to the subject) of about 39mm. That's great at high magnifications, but a pain at low ones. If you managed to extend the 100-200mm lens 100mm, you'd get that same 1x magnification, with a great 200mm working distance, instead of an awkward 39mm. If you only extended the 100-200mm 50mm, you'd get 0.5x magnification, with a huge 300mm working distance.
Aside from that, you're trying to control the aperture with the coupling lens. If you think about that lens as a "fancy extension tube", you see why that doesn't make sense. Like an extension tube, it's dealing with more parallel light, so all reducing its aperture does is narrow the optical path, causing vignetting. Control the main lens, instead. There's also techniques for placing an aperture between the two lenses, but we won't get into that, here.
Joseph Wisniewski , Sep 05, 2010; 03:40 p.m.
You really need to tell us more about what you're trying to shoot. You've got some idea of that, in your head, but you've not shared it. Instead you've shared your particular solution, and are asking us to fix your solution, when it might be a lot easier to look at the problem, instead.
I took a look at your photo.net portfolio, you've got two macro images, both bee on flower. That's low magnification, long distance. Some of the ways to do that:
- Extend your 100-200. Get an extension tube or three (the Kenko set of 12, 20, and 36mm is popular) and a Canon to Pentax adapter. The 36mm is probably just right for bees. And you get to stay 300mm from them, which is great, since bees are weird about people close to them. Yes, it's manual focus, but that's all we do at that sort of magnification, autofocus is nearly useless.
- Get a used or "off brand" 150 or 180mm macro lens. The results will be better (sharper, better contrast, less distortion), which won't matter that much for those bees, but will help with flowers, and those "industrial" shots you mentioned in a different post.
Something to consider, I'm not sure what you meant as "industrial". That's often low magnification, low distortion work that can be done with a simple, manual focus macro lens. I've used a Nikon 55mm f2.8 (about $100-200 used) and it can cover about 70% of what I call "industrial". And again, you can get an adapter for the 5D II. Or, you might already have a Pentax 50mm f2.8 macro around. Great lens on a Canon adapter.
And you might be looking to do some higher magnification work. That's where the coupling comes in. Got a 50mm f.14 Pentax normal? That's 1-2x coupled to the 28-105 (you really want to keep the 28-105 up in the 50-105mm range when doing this), and 2-4x coupled to the 100-200mm (get that Pentax adapter). A 35mm f2 or a 24mm f2.8 can take the magnification even higher.
Want something wild? Here's a 20mm f2.8 "main" lens, reversed on the front of a 200mm f4. The cactus flower stamen is only about 1/16 inch (or about 2mm) long. This wasn't easy, it took a lot of time and work, but it's an example of why one would try coupling. Like I said earlier, coupling always gives you about 39mm working distance. In comparison, I have an amazing 18mm Zeiss Luminar, a very exotic macro lens, that has to be used on a bellows. At 10x, it has a working distance of about 15mm, less than half what the coupled 20 and 200 give me. The working distance helped me set this up and get the light right.
