Need help with a macro problem

[Roger Clark]

Hello,
I need to get images at as high a magnification possible of a subject about16-inches or greater from the front of the lens. When I say as much magnification, I mean 2x (minimum), 5x (better).
I've tried combinations like (canon lenses and bodies):

180 mm f/3.5 L macro lens:
180mm + 2x TC 16-inches from front of lens = 1.0x

300 mm f/4 L IS:
300mm +25mm extension tube + 25mm extension tube + 2x TC =1.0x at 30 inches (the closest I can focus the lens.

I could buy more extension tubes; if I can get the 300mm down to 16 inches,, I could
approach 2x magnification.

Further, I'm looking through a window (at some ice samples at about -400 degrees F, -250 C).
My resolution on the target will become diffraction limited (60mm aperture) as I increase magnification and I may not resolve more on the subject.

I've been using a 20D, but will likely switch to a 40D to get live preview for focusing.

So, does anyone have any advice on how to achieve the magnification I need?
Another lens, in the 300 mm range with closer focusing ability? I obviously
do not need a wide aperture lens, nor AF, so other brands will be considered.
But I can't get closer than 16-inches.

Roger Clark

[Roger Clark]

I tried a 70-200mm f/4 L IS + 25mm extension + 25mm extension + 2x TC + 1.1x at 19 inches.

Roger

[Roger Clark]

Well, to look at it another way, 16 inches = 400 mm to the subject, and a little more
to the principle plane of the lens, so lets say 450 mm. To get 2x magnification, I need (450*2=)
900 mm back focus. The 200mm lens + 2x TC is only 400 mm (plus extension tubes),
thus explaining my 1.1x magnification. So I guess I need a 400 mm lens with very
close focus and a lot of extension tubes! So does a 400 mm camera lens with 0.4 meter
close focusing distance exist?

I could also use two 2x TCs to get my 200 mm lens to 800 mm, but image quality
is suffering (I've tried it).

Any ideas? (I suppose I'll have to build it.)

Roger
(pushing the limits ;-)

[Robert O'Toole]

So you need to be 16 inches or more away right?
The solution is a Bellows (Novoflex (http://www.adorama.com/NVCAB.html) makes one) set, if you need even more extension, you can use the adapters and use almost anything, even PVC pipe as extension.

Also try adding extension between the lens and Extenders, not just after the extender as this usually magnifies the effects.

I normally use lens stacking, a 300 or 400 with a 100 or shorter lens reversed on the front. I have used this to make headshot images of ants but at a very short distance from the front lens element.

Robert

[Roger Clark]

Robert,
Thanks for the info. The Novoflex looks very interesting. Do you think it could handle a 300 mm f/4 lens?

I tried extension tubes both between lens and TC and between TC and camera.
I agree that extension tubes between lens and TC produces the highest magnification.

The reversed lens idea is good for getting really high magnifications, but aren't you limited to about the flange to
camera film plane distance on the reversed lens? That would be about 44 mm for Canon cameras,
so far short of my 400 mm.

Roger

[Robert O'Toole]

Glad my info was of interest.


Robert,
The reversed lens idea is good for getting really high magnifications, but aren't you limited to about the flange to
camera film plane distance on the reversed lens? That would be about 44 mm for Canon cameras,
so far short of my 400 mm.



As I mentioned in the first line of my reply, I was not sure if you needed less than 16 inchs or more. So I thought I should mention it is case the answer was less than 16.

All I can say is that in the field using stacked lenses the focus distance really feels like you have to be literally on top of the subject. 44mm, less than 2 inches sounds possible.

Robert