Canon 500D Close-up lens vs. extension tubes for magnification.

[Ronald Zigler]

Given that the Canon 500D Close-up lens will provide greater magnification on the Canon 300mm f4 than perhaps two extension tubes, is there any benefit or advantage one could imagine to recommend using the extension tubes rather than the 500D Close-up lens? Image quality?

[Mike Milicia]

Hopefully, some of the macro gurus will chime in but here's my two cents ...

Since the 500D adds another optical element, there could theoretically be some image degradation but I don't think it's anything you would notice.
The biggest difference between using tubes and the 500D is the maximum working distance. With the 500D, your maximum working distance becomes 500mm or about 19.7".
I'm not sure about the exact formula for computing maximum working distance with tubes but I think you will find that the 300 f/4 with 50mm of extension will give you about
6 or 7 feet of working distance. So the tubes give you greater versatility and also have the advantage that the same tube can be used with any lens. But if the maximum working
distance limitation is not an issue, you may be better off with the close-up lens. One other advantage of the close-up lens is that there is no light loss like you get with a tube.

[Roger Clark]

Hopefully, some of the macro gurus will chime in but here's my two cents ...

Since the 500D adds another optical element, there could theoretically be some image degradation but I don't think it's anything you would notice.
The biggest difference between using tubes and the 500D is the maximum working distance. With the 500D, your maximum working distance becomes 500mm or about 19.7".
I'm not sure about the exact formula for computing maximum working distance with tubes but I think you will find that the 300 f/4 with 50mm of extension will give you about
6 or 7 feet of working distance. So the tubes give you greater versatility and also have the advantage that the same tube can be used with any lens. But if the maximum working
distance limitation is not an issue, you may be better off with the close-up lens. One other advantage of the close-up lens is that there is no light loss like you get with a tube.

I haven't chimed in because I do not know the answer. But my experience with the add-on lenses has not been as good as with extension tubes.

One clarification. Extension tubes do not lose light. Exposure becomes longer because of added focal length with the tube which gives more magnification. With more magnification, you spread the light that comes through the aperture over greater area. Same with an add-on lens. So for a given magnification, whether tubes or added lenses (either front lenses or TCs) the exposure will be the same (except there is some added loss due to transmission of the added lenses).

Roger

[Mike Milicia]

If I take an incident meter reading of the light that is hitting my subject and shoot at the indicated exposure using an extension tube, the image will be underexposed. The amount of underexposure will depend on the size of the tube relative to the focal length of the lens. For example, if I use a 25mm tube on a 50mm lens, the image will be underexposed by about a stop. If I use the same tube on a 300mm lens, the image will be underexposed by about a third of a stop. If I shoot at the incident reading using the 500D instead of a tube, the image will be exposed correctly. In other words, to expose the same subject in the same light correctly with an extension tube will require either a slower shutter speed, larger aperture, or higher ISO than I would have to use with the 500D. That is what I meant by a "loss of light".

[Ronald Zigler]

If I am understanding this correctly, then while the 500D close-up lens on a 300mm lens will give you greater magnification, one would need to get closer to the subject in order to maximize the advantage of this lens; on the other hand, 50mm of extension tubes will give less magnification, but allows you to remain further away from your subject. Canon lists the magnification of the 300mm f4 lens with the 500D as 0.82x-0.59x and the magnification with a 25mm extension tube as 0.37x-0.09x. Would 50mm of tubes double this? If I am not mistaken, I think Roger may have published a formula for determining magnification with extension tubes? I suppose it is possible to calculate the precise magnification possible with 50mm of extension tubes on a 300mm lens. Correct?

If I take an incident meter reading of the light that is hitting my subject and shoot at the indicated exposure using an extension tube, the image will be underexposed. The amount of underexposure will depend on the size of the tube relative to the focal length of the lens. For example, if I use a 25mm tube on a 50mm lens, the image will be underexposed by about a stop. If I use the same tube on a 300mm lens, the image will be underexposed by about a third of a stop. If I shoot at the incident reading using the 500D instead of a tube, the image will be exposed correctly. In other words, to expose the same subject in the same light correctly with an extension tube will require either a slower shutter speed, larger aperture, or higher ISO than I would have to use with the 500D. That is what I meant by a "loss of light".

[Mike Milicia]

Yes, with the 500D, you cannot focus if you are more than 500mm (19.7 in.) away from your subject. You MUST be very close in order to use it.
Extension tubes give you a greater maximum working distance. I don't know the exact formula but this table :

http://www.bobatkins.com/photography/eosfaq/closeup.htm

indicates that a 300mm f/4 with an EF25 gives you a maximum working distance of 3649mm (about 12 feet).

[Charles Glatzer]

I haven't chimed in because I do not know the answer. But my experience with the add-on lenses has not been as good as with extension tubes.

One clarification. Extension tubes do not lose light. Exposure becomes longer because of added focal length with the tube which gives more magnification. With more magnification, you spread the light that comes through the aperture over greater area. Same with an add-on lens. So for a given magnification, whether tubes or added lenses (either front lenses or TCs) the exposure will be the same (except there is some added loss due to transmission of the added lenses).

Roger

Roger,

Internal focusing lenses with added magnification lenses?

Chas

[Roger Clark]

Roger,

Internal focusing lenses with added magnification lenses?

Chas

Chas,
I'm not sure what you are referring to.

Roger