MP-E 65 and dust

[gcflora]

This is strange and I have no explanation. When I shoot with the MP-E 65, there are more dust bunnies than using a different lens at the same aperture (shooting the sky or a white screen (my monitor) @f22 to test). Why would that be so?

Cheers

[Jules]

Is it the same dust bunnies as with other lenses Craig? I mean, is it dust bunnies on your sensor, or could it be dust on the rear element of the lens? (I'm totally guessing here.)

[mrDooba]

I think it's just the way the optics in MP-E work. I'm sure a more knowledgeable person will be able to explain but I know what you mean. It takes me for ever to remove all the buggers.

[gcflora]

Is it the same dust bunnies as with other lenses Craig? I mean, is it dust bunnies on your sensor, or could it be dust on the rear element of the lens? (I'm totally guessing here.)

That's what I am trying to work out. Could the dust that's showing be from the lens rather than the sensor? Some of the dust bunnies are the same, the others I don't know... they're obvious when using the MP-E but I can't really see them when using another lens

[Bear Dale]

I've found/find the same thing Craig.

When did you get it mate? I didn't know you had one.

[gcflora]

I only got it last weekend Jim Can't really use it very well at the moment

[Bear Dale]

Did you get a macro flash with it Craig?

[gcflora]

Did you get a macro flash with it Craig?

No, which is probably why I'm having so much trouble with anything over about 2:1

[Tricky]

This is strange and I have no explanation. When I shoot with the MP-E 65, there are more dust bunnies than using a different lens at the same aperture (shooting the sky or a white screen (my monitor) @f22 to test). Why would that be so?

Cheers

As you probably know, dust bunnies show up more with a smaller aperture (which is why sky/white screen tests to check for dust bunnies are usually done at the smallest available aperture).

With macro lenses, the aperture setting on the lens is affected by the degree of magnification (I think this is explained in the MPE 65mm manual, if I'm not mistaken):

Effective Aperture = (Aperture Setting) + (Aperture Setting x Magnification)

So, an aperture setting of f/2.8 at 1x magnification is an effective aperture setting of (2.8) + (2.8 x 1) = f/5.6.

By the time you get to 5x magnification, an aperture setting of f/2.8 is an effective aperture of (2.8) + (2.8 x 5) = f/16.8.

If you select f/16 at 5x, your effective aperture setting is (16) + (16 x 5) = f/96!!

If you're seeing more dust bunnies with the MPE, then that's probably because the effective aperture you're using is way smaller then anything else you've ever tried.

Of course, as you reduce the aperture in this draconian fashion, the amount of light getting through is tiny (plus any camera shake is greatly exaggerated by the lens' high magnification). Hence it is very hard to use the MPE with natural light alone... a dedicated macro flash is pretty much mandatory. Not surprised to read that you're struggling at even 2x magnification.

[AdamR]

Well answered, I knew there was a reason but couldnt remember it.

[gcflora]

Thanks Tricky! Perfect explanation