D40 Body - small button

<p>This maybe a silly question but I have limited experience with DSLRs. On the Nikon D40 body there is a small button beside the lens mount (photo attached)<br /> <img src="http://i327.photobucket.com/albums/k446/revngo/lensmount02.jpg" alt="" /><br>

<img src="http://i327.photobucket.com/albums/k446/revngo/lensmount02.jpg" alt="" /><br>

Could anyone please tell me what the purpose of this small button is?</p>

<p>That's the release button that unlocks the lens from the mount so that you can remove it.</p>

<p>No not that button its on the opposite side, lower left as you look at the lens mount</p>

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<p>I think that is the button that lets the camera know that the lens is at it's narrowest aperture. Only for non-G (no aperture ring) lenses. This is needed so the camera can have the full range of apertures available.</p>

<p>That little switch detector is on all AF Nikon SLRs that have no aperture follower tab; i.e. the one that cannot meter with lenses that have no built-in CPU. On Nikon lenses that have an aperture ring, there is a little post with the fancy name "EE Survo Coupling Post." When the lens is set to its minimum aperture, that post will press on this little switch to inform the camera. Otherwise, the camera would display the Fee error. The switch is useless with G lenses since they have no aperture ring and is automatically set to the minimum aperture.</p>

<p>On Nikon bodies that have the aperture follower tab so that they can meter with no-CPU lenses, there is no such switch, e.g. the D200, D300, D700, etc.</p>

<p>Cannot believe I beat shun with an answer, but only by a few seconds, haha.<br>

And your answers is also a lot more elaborate.</p>

 

<p>Sjoerd, it is 4am here in California. Gimmy a break. :-)</p>

<p>Thanks very much guys for clarifying that, my curiosity is satisfied.</p>

Good question, and good answer, Shun. I never thought this small tab is all it takes for the lens to tell the SLR that it's at the smallest aperture. I thought it involved a complex protocol using the 7 data contacts.

<p>Here is an image comparing the D100 vs. D200 mounts. You can see the aperture follower tab in the 1 o'clock position on the D200, while the D100 has the little switch in discussion here in the 7, 8 o'clock poition.</p>

<p>You may also notice the different mirror size. The D100 was an early DSLR, converted from the Nikon F80/N80 film body so that it retains the mirror for a film/FX SLR. The D200 was designed from scratch as a DX DSLR so that it only needs a small mirror.</p><div></div>

<p>Well now here's an interesting question. Why do some bodies (D40/D60 etc.) have a switch that doesn't bind up on a non-AI lens and others (D100/D80 etc). have one that does?<br>

Is it just that the D40/D60 etc. is newer? What is like on a D90?</p>

 

<p>I don't know, but it is very annoying, i had to convert my 105mm F2.5 to AI myself to be able to use it on my D90. It is just 'leaving out' some plastic on the camera to make it fit.</p>

<p>Are you still up, shun?</p>

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<p><em>Why do some bodies (D40/D60 etc.) have a switch that doesn't bind up on a non-AI lens and others (D100/D80 etc). have one that does?</em></p>

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<p>Different mechanics involved. Why that came about, you'll have to ask the Nikon engineers that designed it.</p>

<p>On the D40/D60, the EE post on the aperture ring pushes the switch IN when the lens aperture ring is set to minimum aperture. Mounting a non-AI lens with an extended aperture ring rear skirt does essentially the same thing mechanically. No harm done.</p>

<p>On the D50/D70/D80/D90/D100, the EE post pushes the switch SIDEWAYS when the lens aperture ring is set to minimum aperture. Mounting a non-AI lens with an extended aperture ring skirt does NOT do the same thing (see above). Eventual harm done.</p>

<p>I think the current bodies (except for the D90) all have the newer design found on the D40?</p>

<p>D200/300/700 and D1/D2/D3 bodies don't have this little switch, but they do have an AI meter indexing tab/ring that also moves radially, not in/out, so mounting a non-AI lens will also cause eventual harm/damage.</p>

<p>You can add the D3000 to that list. We just received our sample D3000 from Nikon USA. It looks very similar to the D40, and that little switch also gets pushed in.</p>