70-210 + 6T magnification

[benoit_deshaies]

<p>Hi, I have a Nikon AF 70-210mm f/4-5.6 and I am considering getting

a Nikon 6T diopter for taking close-up pictures. I was wondering how

much more magnification I could achieve with that setup? The lens can

currently focus as close as 4' (1.2m).

 

<p>I read <a

href="http://www.photosynthesis.co.nz/nikon/lenses.html#70-xx">on the

web</a> that this is a 1:4.5 magnification. On a D70 with a 24mm

sensor, this mean I can fill the frame with an object 24mm*4.5=108mm

wide. Judging by the bottle-cap example below, this seems about right.

 

<p>How much closer could I get with a 6T? How wide would an object

have to be to fill the frame? I couldn't find the math for this. Thanks.<div></div>

[benoit_deshaies]

BTW, sorry for the boring bottle cap picture :)<div></div>

[arnabdas]

I think the focal length of the 6T filter is about 330mm. The math for magnification at *infinity* is

 

Focal length of main lens /focal length of diopter

 

210mm/330mm = 0.64x life size on 35mm. (assuming zoom at longest FL)

 

On D70 APS-C sensor it will be 0.64x * 1.5 = 0.96x life-size, almost 1x.

 

As you rack the lens down to closest focus, you will get additional magnification. I know of no specific formula about this gain.

 

Now would someone please double-check me? Thanks!

[bill_chiarchiaro]

Magnification does not depend upon the size of the sensor or film (but field of view does).

 

The 6T has a power of 2.9 diopters, meaning its focal length is 345 mm (1000 / 2.9). So, if the camera lens behind it is set to infinity, then the working distance of the combination will be 345 mm from the 6T. This is regardless of the focal length of the camera lens. The diverging light rays from an object at 345 mm will be made parallel by the 6T. The camera lens will take those parallel rays and bring them to focus on the sensor or film.

 

Indeed, one formula for magnification is (image distance) / (object distance). Or, reproduction ratio is 1 : (object distance) / (image distance). In this example, the reproduction ratio would be 1 : 345 / 210, or 1:1.64.

 

The D70's sensor is 23.7 mm wide, so at that reproduction ratio, an object 38.9 mm would fill the width of the frame (23.7 * 1.64).

 

Note that the D70's "1.5x crop factor" didn't enter into this.

 

Also note again that the working distance mentioned above is measured from the 6T, in other words essentially from the front of the camera lens. On the other hand, the distances on the lens's focusing ring are measured from the sensor or film plane. You need to add the 345 mm to the distance between the sensor or film plane and the front of the camera lens (ignoring the thickness of the 6T to keep it simple) to make the distances comparable.

 

--Bill

[arnabdas]

ooops. I made a mess of the whole thing. Thanks Bill!

[bill_chiarchiaro]

Arnab,

 

Maybe we should give it a few hours, to see if anyone finds a problem with my analysis! We hear so much about the crop factor that's it's easy to assume it affects just about everything. Let's see, ISO 800 on the D70 must be equivalent to ISO 1200 on a 35mm film camera...

 

--Bill

[david_h._hartman]

The 6T is a 334mm, 2.99 diopter close up lens. Folks get

confused because the 4T is a 341mm, 2.93 diopter close up lens.

For practical purposes they are 3.0 and 2.9 diopters respectively.<br>

<br>

If you reverse mount a 105/4.0 Bellows Nikkor on a 200/4.0 AIS

Nikkor your get about 2x so Arnab got it right. I calculate 0.63x

using the 334mm figure from the Nikon instruction sheet. This is

with the prime lens focused to infinity and assuming that Nikon

didnt fudge the focal length of the zoom by 5%. The image

ratio should be close to 1:1 when the lens is focused to its

minimum but I think it may fall short.<br>

<br>

I must object a bit to using the 1.5x factor here. People use it

with lenses used at normal distance because they associate a

familiar angle of view with the focal length of lenses designed

for full format 135. This makes some sense though it's awkward and

one should outgrow this. With reproduction ratios 1:1 is 1:1

whether the camera is APS/DX or 8x10.<br>

<br>

If a photo has any scientific purpose youll need to know

the actual reproduction ratio. If filling the frame with a given

bug is the object then you need less magnification with APS/DX

than full frame 135. I liken this 1.5x factor thing to speaking a

new language by translating each word into ones native

tongue. One must think in the new language to become fluent.<br>

<br>

Im so tired I hope this makes sense.<br>

<br>

Regards,<br>

<br>

Dave Hartman.

[chris haake]

Dave, technically speaking, you're right about reproduction ratios. However, most photographers think in terms of <i>photograph size</i>, not strictly <i>reproduction ratio</i>. Therefore, what I get in a 4x6 will be about 50% larger with an APS-C-captured image than it would with a 135-sized negative, hence the assumption that there is some sort of "magnification" factor. Naturally there isn't, but as these sensors were designed to provide us with images to magnify anyway, there is a practical logic to this assumption.

[vivek iyer]

The crap factor does not change the focal length or the magnifications.

[david_h._hartman]

This comparison might be interesting to some...<div></div>

[vivek iyer]

The 1Ds Mk II is missing, Dave. Is it because the crap factor vanishes there?

[david_h._hartman]

Yes, the EOS-1Ds has a sensor size of 35.8 x 23.8mm and now

the Mk II has one of 36.0 x 24.0mm, this according to http://consumer.usa.canon.com.<br>

<br>

I wish the Nikon D2Hs had been a 19 x 29mm format or something

close especially with the same size and quality of pixel as the D2H,

just more of them.<br>

<br>

I noticed that the Nikon D2X, Canon 20D and Canon EOS-D Mk II all

have the same aspect ratio as 135 full frame so I added a

diagonal line to highlight this. I also added 135 half frame

because some object to the term full frame so I

though this might help them understand where the term full frame

came from. I don't know if there were half frame cameras before

the Olympus Pen F which debuted in 1963 but these terms are at

least that old.

[vivek iyer]

"I don't know if there were half frame cameras before the Olympus Pen F which debuted in 1963.."

 

Yes, there was a very limited run of a Leica (now very very very expensive if anyone finds one of these) that had film counter up to 72. Not an SLR.

 

There was a special order FM10 (made for some scandinavian traffic police?) that was half frame. But this was well after Pen F.

 

And, I don't know if the half frame TLR, Tessina precedes the Pen F.

 

More pixels? D2X (same puny "dx"sensor).