M42-adapter-lens-aperture pin

[michael_przewrocki2]

<p>Optixpcb has m42-eos-adapter in two versions. one of them seems the have a hole to fit the pin.<br />one of them is: Black without width edged<br>

But i only understand it for m42-cams where cams lever will hit that pin an close aperture.<br>

it seems there are three different m42-versions. read somewhere but i cant remember details<br>

Thanks</p>

[bobatkins]

<p>Some general info here - http://bobatkins.com/photography/eosfaq/manual_focus_EOS.html</p>

<p>For M-42 lenses with a pin and no switch between auto and manual operation, the adapter has to depress the pin in order for you to change the aperture. M-42 lenses with an A-M switch can be used without the pin depressed when they are in the M(anual) mode. There are also some older lenses without a pin and which always have manual aperture control.</p>

<p>Some adapters are designed to depress the pin, some aren't. If the lens has no pin, you can use any adapter. If the lens has an M(anual)-A(uto) switch you can use any adapter. If the lens has a pin and no M-A switch, you need to adapter that depresses the pin</p>

<p> </p>

[jim_service]

<p>Michael - I'm guessing you are talking about a M42 lens to EOS body adapter. I have one to use my old Pentax lenses and accessories on my Canon body.<br>

I take it you're asking whether to get the adapter with a hole in it for the auto-diaphragm pin.<br>

The auto-diaphragm was introduced over 50 years ago and it enabled photographers to make their exposure settings (shutter and aperture) and yet continue to work the composition and focus while at full aperture. That pin closed down the aperture when the shutter was released. This concept is on all SLR/DSLR's today, and the better cameras have a preview button so you can view the effect of your chosen depth of field.<br>

To answer your question I'm assuming that all M42 lenses with auto-diaphragm work like those from Takumar (Pentax), that is, the lens is wide open till that little pin is pushed. Then the diaphragm shuts down to the aperture you had set.<br>

If you're using this on an EOS body, there is no mechanism to push this pin, the EOS body does does this electrically, not mechanically. So the pin will stay out, the lens will stay wide open and you're stuck with a shallow depth of field always.<br>

My advice is to get the adapter w/out the hole. The pin will be depressed when the lens is screwed to the adapter. The diaphragm will follow the setting you make on the aperture ring ->all the time<-.<br>

The drill is: open wide to do your focusing and composing, stop down to choose the depth of field that suits your needs, then find the shutter speed that yields the right exposure.<br>

Welcome to the world of fully manual photography, just like Ansel and Henri and Eugene.<br>

Actually, the EOS body will do that last step (shutter speed) for you.</p>

[paul_wheatland]

<p>I use the m42 to EOS adapter made and sold by fotodiox USA. The adapter pushes the pin in to allow f stop changes.</p>

[michael_przewrocki2]

<p>I still dont understand why optixpcb offers both versions. The one with hole i dont understand.<br>

my m42-lenses all have M/A-ring. i also have p6/M42.<br>

so lets compare both: <br>

M/A: M/A-difference only working when pin is pushed. In Auto-aperture set-one can quickly switch to fully open.<br>

The only "advantage" of that hole is leaving the spring untouched. permanent pressure could weaken it.<br>

Just have found out that one of my two Vivitars M42 had oily blades and i can see how slow mechanisme is.<br>

Super Takumar 50/1.4 was hardly ever on an adapter and wonderfully working.<br>

So the hole in adapter has two advantages:<br>

a) left in automode no pressure on spring<br>

b) switching from M to A opens aperture quickly<br>

So i will get one with hole.<br>

Where is the advantage of having NO hole pin always pressed? accidental switch to A and fully open lens? </p>

 

[michael_przewrocki2]

<p>I am now understanding it:<br />if pin is pressed the inner diameter is 36.55mm.<br>

m42mm-ring has approx. 40mm.<br>

so the adapter which should not touch the pin "without wielded width" must be about 38mm inner diameter.</p>