Magnification

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Harald
Posts: 614
Joined: Fri May 13, 2011 10:33 am
Location: Steinberg, Norway
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Magnification

Post by Harald »

Hi there,
I have a microscope with 4 objectives and a camera adapter to go with this. The camera adapter is 2x magnification.
If I use an 10x objective with the 2x adapter the magnification will be 20x..
But if I use my EOS 7D, whitch have a crop of 1.6, will the magnification be: 10x x 2x x 1.6 = 36 ??

I just love this forum and now I know I have a lot to learn..

I´ve recomended the forum to all my photofriends.
Kind Regards
Harald

Lier Fotoklubb / NSFF
AFIAP / CPS
BGF / GMV
http://www.500px.com/blender11

Mitch640
Posts: 2137
Joined: Sun Aug 15, 2010 1:43 pm

Post by Mitch640 »

Question, is the camera adapter one of those aftermarket ones that fit the EOS mount and has a 23mm tube to fit into a lens hole and has the 2x lens built in?

If it is, then the company claims it is 2x, until you read the fine print, where it says it is closer to a real 10-15x. I had one, and it did compare to the same magnification I got from using a 10x eyepiece lens in another adapter I had. :)

ChrisLilley
Posts: 674
Joined: Sat May 01, 2010 6:12 am
Location: Nice, France (I'm British)

Re: Magnification

Post by ChrisLilley »

Harald wrote: But if I use my EOS 7D, whitch have a crop of 1.6, will the magnification be: 10x x 2x x 1.6 = 36 ??
No, the optical magnification is still 20x and this is the value you should use in equations to work out the depth of field and the effective aperture.

'crop factors' are sometimes useful, to help people who grew up with 35mm film cameras imagine what field of view lenses will have on smaller sensors. But they can also be actively misleading, if the same conversion factor is assumed to apply to depth of field for example.

There is nothing magical or primordial about 35mm cameras, and it puzzles me why people continually feel the need to convert things 'as if they were using 35mm'. After all, they were originally the small, jumped-up alternative to large format and medium format 'professional' cameras. Some Zeiss literature still refers to 35mm as 'miniature' cameras, which I find amusing.

One place where the sensor size does make a difference is when using microscope lenses, since the eyepieces on a microscope assume a certain field of view (diameter of the image circle) - 20mm, 25mm, 30mm in some cases. Crop sensors are often a better match for this image circle than full-frame 35mm cameras.

And also, the smaller the sensor, the less optical magnification is required to fill it with a given sized subject. Using the whole of the sensor puts the maximum number of pixels on the subject so should catch the most detail.

Hope that helps, and welcome to the forum!

Harald
Posts: 614
Joined: Fri May 13, 2011 10:33 am
Location: Steinberg, Norway
Contact:

Post by Harald »

Hi and thanks for the reply..

Yes it´s one of those aftermarked adaptors for 23mm photoport... :P

I hope to get my microscope this week..

I have done macro for some time now and I will try some micro as well. I hope to post some images later. It is in the beginning of the insect season here in Norway now. A lot to look forward to.

Thanks guys :D
Kind Regards
Harald

Lier Fotoklubb / NSFF
AFIAP / CPS
BGF / GMV
http://www.500px.com/blender11

Charles Krebs
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Joined: Tue Aug 01, 2006 8:02 pm
Location: Issaquah, WA USA
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Post by Charles Krebs »

Harald,

Chris is correct. If the optics in the adapter do actually provide a 2X magnification, then it will be 20X onto the camera sensor (with the 10X objective) regardless of the sensor size.

But regardless of what the "specs" are, the best thing is to do a quick and simple test. For most accurate results you should use a microscope stage micrometer (very finely ruled slide). But you can get a fair idea using a simple ruler and a low power objective. Your 7D camera sensor measures 22.3mm on the long dimension. If you use a 4X objective and photograph a ruler marked in "mm" you should have about 2.75 mm (actually 2.79) imaged across the sensor at an 8X magnification on sensor (22.3 divided by 8 ).

If you have a ruler marked in 1/16 inch increments, then you should have 7 units (7/16) recorded along the longer dimension.

If it appears to be significantly different you can determine the magnification of your adapter with the following relationship:

m = "camera sensor long dimension" / "distance recorded in sensor"

with your 7D:

m = 22.3mm/distance recorded (mm)


Chris,
There is nothing magical or primordial about 35mm cameras, and it puzzles me why people continually feel the need to convert things 'as if they were using 35mm'.
I think at least for lens focal lengths it was needed at the start of the digital "revolution" since the vast majority of people moving to digital were using 35mm (24x36mm frame size) cameras. But it is less necessary today. Although with all the various sensor sizes it is useful to have some standard to use for comparison purposes. For example, if the lens on a P&S marked 4.9-18.6mm I would still lack sufficient information to determine how "wide" or "tele" the recorded view is, because I have no idea of the sensor dimensions. But if it is stated (in literature or "test" reports as a 28-105mm (35mm equivalent) it is immediately obvious. Well... obvious to me and many others :wink: . Today it is not uncommon to meet people who have never used a 35mm film camera... or any film camera for that matter! But with the wide range of sensor sizes used I think, at least as far as lens coverage goes, some reference standard is needed. It is less than a perfect system since there are sensors that do not have the 2:3 ratio of 35mm, but it is still pretty useful IMO.

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