Cannon 100mm Macro

newby said:

I have this Cannon 100mm Macro. I would expect to close up on an
object such that the image is 1:1 full size as the sensor on my
20D. But in fact,
the closest I can get is about a flower of about 2 to 3 inches
across. Is this to be expected or is there anything wrong with my
lens? I saw on the web many macro pictures as close in as the head
of a dragonfly occupying the whole picture. Was that achieved by
severe cropping, or with another attachment such as an extension
tube or another closer up lens?

I would like to be able to take the picture of a small object the
size of a dime or a stamp that occupies the whole screen. How can I
do that with the 100mm Macro without further attachments to it?

Thanks.
--
newby

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mschecan said:

Strange,

I get much closer. Did you try both MF and AF? Here are two watch
shots with the 100mm macro. These may indicate the the highest mag.
but I'm not sure since I wasn't checking for it. The canon spec
says the magnification is 1 (or 1.6 for the 20D I guess), still
larger than what you aere getting. For a dragon fly's head you may
need an extension tube or a closeup lens though.

Hope this helps.

marq

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Ali said:

There is a switch that lets you choose between 1x and I think
0.25x. It's there so that autofocus can be faster when you're not
concerned with macro. Maybe that switch isn't set right?
Ali

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David@mybitoftheplanet said:

mschecan said:

Strange,

I get much closer. Did you try both MF and AF? Here are two watch
shots with the 100mm macro. These may indicate the the highest mag.
but I'm not sure since I wasn't checking for it. The canon spec
says the magnification is 1 (or 1.6 for the 20D I guess), still
larger than what you aere getting. For a dragon fly's head you may
need an extension tube or a closeup lens though.

Hope this helps.

marq

Click to expand...

Marq,

It doesn't matter what camera you are using, a magnification of 1:1
is going to remain the same, it's just that you get a smaller area
covered on a 20D than a full 35mm frame while a medium format
camera will record a much bigger area. On all three formats the
resulting image size of an object 1cm long will be exactly the same
size - 1cm.

The smaller sized sensor simply crops the image. It does not
magnify it.

The 100mm macro should focus down to 1:1 and at that magnification
will fill the 20D frame with an object that measures approx
22.5x15mm (the sensor dimensions), although you have to remember
that when you look through the viewfinder you will only see some
95% of that. In other words, if you focus manually on a ruler set
across the frame with the lens at 1:1, you will see nearer 21.4mm
while the recorded image will show the full 22.5mm.

newby, if you are unsure that your lens is focusing that close, try
drawing a rectangle that is about 21x14mm , set your lens manually
to 1:1 focusing and move the camera towards the rectangle until it
is clear in the viewfinder. It should only just fit in!
--
Best wishes,

David Jones
-UK Garden Wildlife Diaries at http://www.mybitoftheplanet.com

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