Reverse Lens vs. Extension Tubes

[Tim Spencer]

Which will provide more magnification: a reversed lends or extension tubes? After extensive reading on this forum and experimenting at home, I'm still confued!

Also, which lens would work better - a 50mm or a 75-300?

Thanks,

Tim

[daft_biker]

Can you reverse the 50mm on the tubes?

[Tim Spencer]

Originally Posted by daft_biker

Can you reverse the 50mm on the tubes?

I'm still in research mode so I'm open to anything!

[Cambyses]

It all depends on the focal length of the lens you are reversing, the length of extension tubes, etc., and yes, you can do both. I think you would find your answers here:

www.peterforsell.com

Also if, like myself, you enjoy equations and diagrams, I have just started reading this book, and I certainly recommend it (and it has a chapter on magnification):

Amazon.com: Science for the Curious Photographer: An Introduction to the Science of Photography (9781568815817): Charles S. Johnson Jr.: Books

[Tim Spencer]

Cambyses - thanks - good info! Have a question though from your link: for reversed lenses, the author indicates the stacked lens cannot be a zoom. Do you know why? I've got a Canon 18-55 and a Canon 75-300. Looking to use those if possible...

I also have an old manual Pentax 50mm that I could use with an adapter.

[Cambyses]

I have never used reverse lens myself (not too comfortable exposing the rear element of my glass outdoors). That said, I cannot think of any technical reason why a zoom lens cannot be reversed, so not sure why the author says the stacked lens cannot be a zoom lens. However, I can understand that reversing a zoom lens would not be ideal. First, when you reverse a lens, the magnification you get would inversely be proportional to your focal length. So it makes much more sense to reverse a wider angle lens. Second, when you reverse a lens, you will lose light such that your effective f-number will inversely be proportional to the so-called pupil ratio of the lens (the ratio of the exit pupil of the lens divided by its entrance pupil). Prime lenses typically are symmetric with their pupil ratio equal to 1, and wide angles typically have pupil ratios larger than 1. Zoom lenses, on the other hand, are typically not symmetric and have smaller pupil ratios. This means that you will lose even more light if you reverse a zoom lens versus a symmetric prime lens.

As to your specific lenses, I am not familiar with Canon lenses. One thing to note though is that I think any lens you want to reverse should have an aperture ring on the lens, or else, once you reverse it, you will lose control of the aperture. It seems to me that your best option may be to put your 75-300mm on the camera, reverse your 50mm and stack it up onto your 75-300mm (assuming you can find the right reverse coupler/adapter).

[Tim Spencer]

Thanks - I'm going to try the 70-300 plus the Pentax 50 - appreciate your input!