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Old Apr 1, 2008, 8:29 PM   #11
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Nagasaki wrote:
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Not all cameras show the effective aperture so the Minolta may not have changed or it may have changed and the camera continued to show the set aperture rather than the effective aperture. I believe Canon cameras work in this way while current Nikon cameras show the effective aperture.

As a matter of interest I tried this with a Sigma 50mm macro and that does not change aperture it stays at 2.8 throughout the focusing range.

Ken

My Minolta experience is limited to the Maxxum 7000, Maxxum 7 and Sony A100. All three cameras displayed aperture values as expected. A prime lens always displayed a constant aperture. The apertures for a non-constant aperture zoom would vary as the focal length of the lens was changed. The 100mm f/2.8 Macro was used on all three bodies and I don't ever recall anything that suggested that the aperture was varying with focusing distance.

Thanks for the info on your Sigma 50mm Macro. It sounds like you truly have a constant aperture lens.


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Old Apr 1, 2008, 8:32 PM   #12
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rjseeney wrote:
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That is correct. Remember though, the physical aperature is not changing. The effective aperture is what is changing. The camera shows the effective aperature change so the photographer can make adjsutments to exposure. As you focus more towards infinity (away from the closest focusing distance)the aperature changes less.
Thanks for the reply RJ. As you have probably figured out already I have never seen this behavior before. I initially wondered if I had a faulty lens but from what I read here this is perfectly normal for certain lens designs.
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Old Apr 2, 2008, 8:32 AM   #13
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FrankD wrote:
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rjseeney wrote:
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That is correct. Remember though, the physical aperature is not changing. The effective aperture is what is changing. The camera shows the effective aperature change so the photographer can make adjsutments to exposure. As you focus more towards infinity (away from the closest focusing distance)the aperature changes less.
Thanks for the reply RJ. As you have probably figured out already I have never seen this behavior before. I initially wondered if I had a faulty lens but from what I read here this is perfectly normal for certain lens designs.
It's actually normal for all lens designs. It's only really apparent with Maco lens due to the magnifications involved. This effect occurs with all macro lens...it's just that Nikon bodies account for it and show the effective aperture. Physically, the aperture is constant and stays the same.
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Old Apr 2, 2008, 10:14 AM   #14
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rjseeney wrote:
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This effect occurs with all macro lens...it's just that Nikon bodies account for it and show the effective aperture.
This does not occurs will all macro lenses: My two macro lenses never did this and so does Nagasaki Sigma's... Frankly I'll be quite upset if I bought any f/2.8 lens and found out it effectively lose more than 1/2 its brightness depending on where I focus!
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Old Apr 2, 2008, 12:11 PM   #15
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NHL wrote:
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rjseeney wrote:
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This effect occurs with all macro lens...it's just that Nikon bodies account for it and show the effective aperture.
This does not occurs will all macro lenses: My two macro lenses never did this and so does Nagasaki Sigma's... Frankly I'll be quite upset if I bought any f/2.8 lens and found out it effectively lose more than 1/2 its brightness depending on where I focus!
You previously mentioned that you have a Sigma 150mm f/2.8 macro. What is the other macro that you have?

BTW: I'm losing two stops with the Tamron so I'd say that was 1/4 the brightness.
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Old Apr 2, 2008, 2:05 PM   #16
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NHL wrote:
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rjseeney wrote:
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This effect occurs with all macro lens...it's just that Nikon bodies account for it and show the effective aperture.
This does not occurs will all macro lenses: My two macro lenses never did this and so does Nagasaki Sigma's... Frankly I'll be quite upset if I bought any f/2.8 lens and found out it effectively lose more than 1/2 its brightness depending on where I focus!
Again, I don't claim to be a physicist or completely understand the how's and why's. But from everything I've read, this effect does occur regardless of design. Examples I've come across:

Here is a review of a Sigma 105 macro that discusses reduction in effective aperature at close focus
http://www.shutterbug.com/equipmentr.../0899sb_sigma/

A discussion in another forum that provides mathmatical formulas and why this effect occurs
http://www.nikonians.org/forums/dcbo...topic_id=13313

A review of a canon macro lens that discusses effective aperture
http://photo.net/equipment/canon/mp-e-65


I've spent alot of time looking over this and at this point feel my comments are correct. I don't believe everything I read, but when I consistently read it many times from many sources......Google it yourself, and you'll find many more examples that discuss this and confirm the statements I've made.

If Nikon bodies didn't account for this with some lenses (nikons Micros, and apparently at least the tamron that was mentioned), most people wouldn't even know that this occurs.

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Old Apr 3, 2008, 1:14 AM   #17
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rjseeney wrote:
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Again, I don't claim to be a physicist or completely understand the how's and why's. But from everything I've read, this effect does occur regardless of design.
Me neither all I'm saying is at least the two macros that I have tried on my camera: the Sigma 150mm and 70mm f/2.8 EX their aperture (in Av) do not change as I focus...



Quote:
Here is a review of a Sigma 105 macro that discusses reduction in effective aperature at close focus http://www.shutterbug.com/equipmentr.../0899sb_sigma/

IMO this is not a good example example because: However, the effective aperture does reduce in size in extreme close focusing because of light loss due to extension (the lens barrel increases in length).
-> Whereas the difference with the 150mm is its lens barrel stays constant in lenght...



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A review of a canon macro lens that discusses effective aperture http://photo.net/equipment/canon/mp-e-65

Another bad example IMO as this lens design increases its lenght as one varies its ratio between 1x and 5x
-> An illustration of this is would be using two pipes with the same diameter: A longer pipe is darker as one look through it as opposed to a shorter pipe...
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Old Apr 3, 2008, 9:04 AM   #18
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Sorry to jump in here with a silly question, but what does focusing to infinity actually mean?
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