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12-09-2010, 03:29 PM   #31
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The subject is drifting. Magnification has to do with the size of a captured image vs the size of the subject. If a subject is 10mm square, at 1x magnification its image will also be 10mm square, NO MATTER THE FRAME SIZE, whether 110-m4/3 or FF/135 or 5x9cm. A 50mm lens on 100mm total extension, focused on a subject, will deliver 1x magnification, NO MATTER THE FRAME SIZE.

If you fill the frame with an image, you will necessarily have different magnifications for different frame sizes. And the DOF will vary, but DOF is a complex function of photography, presentation, and perception -- it involves MUCH more than frame, focal length, aperture, and subject distance, which are what a photographer can control.

I had intimate experience with this back in my film days. I could put a T-mount Vivitar 50 on my Pen-FT 135/HF (half-frame, portrait aspect) SLR, or on a Nikon F 135/FF (full-frame, landscape aspect) SLR. APS-C is virtually the same size as 135/HF, with the same formatfaktor. (And we didn't speak of crop factors then.) I'd shoot the same subject from the same spot with the same lens on the two different cameras with the same film in the same light, then develop and print on the same paper with the same enlarger and lens at the same height. And if I chopped-off 1/4 from each side of the FF print, the two prints looked EXACTLY THE SAME. No DOF difference, no perspective difference, no magnification difference, nothing.

And that's all a smaller frame does -- it chops-off the margins of the image.

12-09-2010, 03:52 PM   #32
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QuoteOriginally posted by cyclone3d Quote
Those links are basically saying the same thing I am.
Not quite.

But let's ignore all the other details and focus (yes, pun very much intended ) on magnification ratio.

QuoteOriginally posted by cyclone3d Quote
It should work this way - I think - due to the crop factor.

I'll use the 24mm for the example.

You mutliply by 1.5 to get the effective focal length which gives you 36mm.

You should be able to focus just as close as you could with a full frame camera, so it should affect the effective macro the same way, except you divide instead of multiply.

So 2.7/1.5 = 1.8.
Say you use the 24mm lens with a full frame camera.

The max magnification ratio is 2.7. So if you're photographing an object 2.7cm long at minimum focusing distance, the image of this object projected on the sensor will be 1cm.

Now you change the full-frame camera body to one with APS-C sized sensor. Except for the size of the sensor now smaller, nothing (including the register or flange-to-film distance, the focal length, the focusing distance, ....) has changed.

What do you think the length of the image of the object projected on the APS-C sensor is? Yes, still 1cm.

The magnification ratio doesn't change, is still 1:2.7.
12-09-2010, 04:07 PM   #33
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QuoteOriginally posted by Class A Quote
Regarding the Tamron 90/2.5. It is a great lens but from my experience when combined with the 1:1 extender (which is just a 2x TC), the quality doesn't rival a great 1:1 macro like the Sigma 70/2.8. .
The 1:1 extender is not 'just a 2x TC' . It doesnt contain any glass. Image quality is not degraded by extra elements. You could, of course, use a 2x TC to get the same ratio, but you wont get the same image quality as using the glassless dedicated tube.
I've even used both, and shot @ 2:1 and still got a great quality macro shot, which does show this lens to be at the top of its game.
12-09-2010, 06:29 PM   #34
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QuoteOriginally posted by Squier Quote
The 1:1 extender is not 'just a 2x TC' . It doesnt contain any glass.
Sorry, you are right. It is an extension tube. I didn't look properly and mistook it for the 2x TC I tried the Tamron 90/2.5 with. I didn't like the results but others may do.

As I said the lens itself is great and I believe it will stand up to the extra magnification of the extension tube very well, but using such a tube will cost light, stand-off distance and is a bit of a hassle with the Adaptall system.

12-09-2010, 06:36 PM   #35
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yes, there's something to be said for buying a true ( 1:1 ) macro lens without the need for adding extras to achieve 1:1, but the penalty is price. For the price of the 90 f2.5, compared to the price of true 1:1 macros right off the bat, its a no brainer.
In the right hands, you wouldnt be able to tell the difference between a 1:1 shot with the 90 f2.5, and any macro costing twice the coin
12-09-2010, 08:32 PM   #36
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QuoteOriginally posted by SOldBear Quote
Not quite.

But let's ignore all the other details and focus (yes, pun very much intended ) on magnification ratio.



Say you use the 24mm lens with a full frame camera.

The max magnification ratio is 2.7. So if you're photographing an object 2.7cm long at minimum focusing distance, the image of this object projected on the sensor will be 1cm.

Now you change the full-frame camera body to one with APS-C sized sensor. Except for the size of the sensor now smaller, nothing (including the register or flange-to-film distance, the focal length, the focusing distance, ....) has changed.

What do you think the length of the image of the object projected on the APS-C sensor is? Yes, still 1cm.

The magnification ratio doesn't change, is still 1:2.7.
Of course the magnification from the lense doesn't change, but because of the crop factor you are going to have less subject data on the same number of sensor pixels provided both the full frame and APS-C cameras have the same pixel count on their sensors.

Then, when you view both at 100%, 50%, or whatever, the one from the APS-C camera is going to look like it was on a longer lens.
12-09-2010, 08:45 PM   #37
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QuoteOriginally posted by cyclone3d Quote
Of course the magnification from the lense doesn't change, but because of the crop factor you are going to have less subject data on the same number of sensor pixels provided both the full frame and APS-C cameras have the same pixel count on their sensors.

Then, when you view both at 100%, 50%, or whatever, the one from the APS-C camera is going to look like it was on a longer lens.
I rest!

Edited to add:

To RioRico: I now agree with you - the term "crop factor" is not only confusing. It sucks. I knew that it was a bad concept but I didn't know that it could do that much damage. BTW, as part of the home-schooling curriculum, I taught my son, then 11 yr old, photography using a bunch of different cameras: Minolta 7Xi and Pentax Super A, Pentax 110, Canon Elph 370 (APS film), Yashica D (6X6 TLR), Canon G5, Canon SD700IS, and Pentax K10D. I did not mention the term "crop factor" or "effective focal length." When he read about them somewhere and asked me, I explained to him why the terms came into existence, but told him that he could not use them in my "class."

Last edited by SOldBear; 12-10-2010 at 01:12 AM.
12-09-2010, 09:17 PM   #38
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QuoteOriginally posted by cyclone3d Quote
Then, when you view both at 100%, 50%, or whatever, the one from the APS-C camera is going to look like it was on a longer lens.
You're right but the thing is that the term "magnification" is defined in terms of "size on the sensor" and in this case it doesn't matter how much sensor is around the projection of a particular subject. In other words, you are not allowed to count the higher enlargement factor of APS-C towards "magnification".

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