Are there super-macro lenses for getting "inside"?

Question

As a follow-on to the question How can one capture gun bore shots? I'm wondering how we can get a wide perspective inside a very small space. For example, I like this shot of a .45" barrel with a true macro lens. But if you lengthen the subject barrel or shrink its diameter you'll end up with something more like this shot of a .38" barrel taken with a 300mm.

I'd like to be able to capture a shot of the inside of a longer and narrower tubes from a very close distance: something like a pinhole camera placed 1 inch from the tube end. That would give a striking tunnel perspective from even a very tight tube, and in the limit the full length of the tube would be in focus.

But I don't shoot with pinholes, I shoot with DSLRs. (I did consider a DIY/true pinhole but evidently those don't produce sharp images.)

So what are real-world options for approaching that "pinhole" extreme? And what are the physical tradeoffs and limits I have to consider?

Clarification: I don't mean I want to literally get a lens inside the hole. Rather, I want to capture a perspective that looks like it's just outside the hole and magnified enough that even if it's just a quarter-inch diameter tube that quarter inch can almost fill the frame.

Answer 1

Yes there are "super" macro lenses available. A macro lens usually provides up to 1x magnification, i.e. it can focus close enough to project an image onto the sensor that is life size. Super macro lenses go beyond 1x.

The most widely available off the shelf super-marco is the Canon MP-E 65mm which offers up to 5x magnification.

Using this lens on an APS-C DSLR you will be able to fill the frame with a quarter inch (6.35mm) hole at a magnification of 2.5x, which is comfortably inside the lens's maximum 5x.

An alternative to buying a dedicated super macro lens is using extension tubes to increase the magnification of a 1x macro lens (you might just get to 2.5x this way if the lens has a short focal length) or you can use a reversed wideangle lens, for more information see: What are the biggest differences between Reversal Rings, Extension Tubes and Macro Lenses?

At 2.5x magnification depth of field will be tiny, so focus stacking will be required if you want to see the rifling all the way to the back of the barrel.

See: What software is available for macro focus stacking?

Answer 2

Following further research and testing: Here is the result of focus stacking, using Zerene Stacker, 15 images taken with a 60mm macro lens on an APS-C camera at f/16. The subject is a 12"-long .310" diameter rifled barrel.

Answer 3

Your best bet would be a fiber-optic camera. Depending on your budget, you might be able to get a crappy one on ebay for around $100 or you could spend upwards of 6k at

http://www.gradientlens.com/Flexible-Borescopes/Hawkeye-Pro-Flexible.aspx

Answer 4

There are a few routes I think you can go with this but extension tubes, ring lights, and focus stacking are probably the most practical for your constraints (i.e must use DSLR).

http://www.diyphotography.net/the-comprehensive-guide-to-macro-photography/

In the past, I used a fiber optic light to tightly control my light source. I used an older variant of the product shown in the link below

http://www.coleparmer.com/Product/Cole_Parmer_Fiber_Optic_Illuminator_115_VAC/EW-41500-50

Also, in regard to the gun barrel, I remember that Zorin Denu said that he polishes his barrels to get the light to more readily bounce around and fill the small space. So I think even if you can't get the light source to be collinear with the barrel, you may get enough.