Size calculation for MPE65 photos

[davholla]

I thought the way you calculated the magnification was to look at the magnification and then multiply it by the crop factor.
So if you take a photo with the Canon 7DMKII at 1.0 Magnification the magnification is 1.6 times.
Like this photo below

EF7A1267mosquito by davholla2002, on Flickr

However I have been told that I am wrong which I admit is possible. Can anyone clarify this?

 

[tirediron]

There is no magnification inherent in the crop factor; all the crop factor is, is an approximation of how much your field of view is reduced. In other words, if you place a 50mm lens on a 1.5 crop sensor camera, then the field of view will be equivalent to a 75mm lens placed on a full-frame body, BUT... the subject(s) will not be magnified.

 

[john.margetts]

Surely the magnification depends on the display size?

 

[KmH]

The MP-E 65 has a maximum magnification of 5x life size.
How much it magnifies is adjustable from 1x to 5x.

+1 to what John said, the crop factor just indicates the field of view is smaller than a full frame (135 format(35 mm)) and provides no magnification.

 

[Ysarex]

Surely the magnification depends on the display size?

Magnification is typically defined as magnification-in-camera and is calculated to express the relationship between the size of the object photographed and the size of the recorded image. So assuming a magnification of X1 we should be able to place the original object onto the sensor and the object and it's image should align as equal in size.

An example from 35mm film days: A US quarter was the same diameter as the width of 35mm film and so an X1 magnification photo of a quarter using a 35mm camera would produce an image the same size as a quarter.

Joe

P.S. Tirediron is correct that crop factor is unrelated.

 

[davholla]

The MP-E 65 has a maximum magnification of 5x life size.
How much it magnifies is adjustable from 1x to 5x.

+1 to what John said, the crop factor just indicates the field of view is smaller than a full frame (135 format(35 mm)) and provides no magnification.

I thought if with the same lens at the same magnification you took a photo of e.g. a bee with a Canon 6D and 7DMK II the image would look bigger on the 7D MKII?

 

[Ysarex]

The MP-E 65 has a maximum magnification of 5x life size.
How much it magnifies is adjustable from 1x to 5x.

+1 to what John said, the crop factor just indicates the field of view is smaller than a full frame (135 format(35 mm)) and provides no magnification.

I thought if with the same lens at the same magnification you took a photo of e.g. a bee with a Canon 6D and 7DMK II the image would look bigger on the 7D MKII?

You'd have two different images such that the image from the 6D would contain more surrounding material -- more of the flower the bee is on -- but if you did in fact take the two photos with the same lens and magnification then you should be able to overlay the two sensors and have the same size image of the bee on both. The 7D image would be cropped-in compared to the 6D image.

Joe

edit: Here's an illustration that should help:

It may also help to understand that magnification is a function of lens focal length and distance to the subject. If you don't change either of those then you can't change magnification. Changing the size of the recording medium has no effect.

 

[Overread]

Magnification is typically stated as 1:1 or 3:1 etc.. where
Size of the image reflected on the sensor by the lens : size of the subject in real life.

Now sensors vary in physical size; but if you've a photo taken at a known magnification and you've got the physical dimensions of the sensor you can work out the real size of the subject by dividing the photo into equally spaced segments to the same number as its dimensions.

However its important to note the DSLRs and lenses are not scientifically accurate. The lens has markings on the barrel but in reality they are not perfect. Furthermore magnification can change a little depending on the focusing distance (not an issue for the MPE as it has no focusing setup; only increase and decrease of its magnification). But still manufacture tolerances are not to strict scientific standards as they don't need to be .

As a result whilst it can give a good rough estimation of size; if you want accurate measurements you need a ruler or similar measuring stick of known value in the photo with the subject at the time of the shot.

 

[davholla]

So are my calculations for this correct?
EF7A1826Harvestman by davholla2002, on Flickr

Harvestman leg length in the original (this has been cropped) 55 mm, body length 17 mm. This is how I worked it out. I measured an uncropped body length as 331 mm in an image size of 1930.4. I then used this formula (sensor size/magnification)* (image size/body in image) = (22.4/1) *(1930.4 *331). This is a cropped image so please don't try to check my maths as it will not be the same