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Archive 2014 · What causes MFD to go off?

  
 
Cableaddict
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p.1 #1 · p.1 #1 · What causes MFD to go off?


Hey folks.

I've got an inexpensive (but well built) lens that is not even CLOSE to having its correct MFD.

The lens is an Oly 75-150 f/4. (I want a cheap, light-ish walk-around lens in this aprox FL)

It's listed as having a 5'2" MFD, and this was just confirmed by an FM'er.
I'm getting slightly over 8', and I've tried four different brands of EOS adapter.
This lens also focuses past infinity, though just a tad.


The lens itself looks to be in virtually as-new physical condition, in every way. Weird. Any thoughts on what could be SO off, on a lens that seems OK?

Do you think the infinity adjustment will also change the MFD?, ad to that extent? If so, any idea where the adjustment screws are on this lens? (Prolly under the grip, if they exist at all, but I don't want to mess with that until I know for sure.)


-thanks.



Apr 15, 2014 at 11:32 PM
LightShow
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p.1 #2 · p.1 #2 · What causes MFD to go off?


Cableaddict wrote:
Hey folks.

I've got an inexpensive (but well built) lens that is not even CLOSE to having its correct MFD.

The lens is an Oly 75-150 f/4. (I want a cheap, light-ish walk-around lens in this aprox FL)

It's listed as having a 5'2" MFD, and this was just confirmed by an FM'er.
I'm getting slightly over 8', and I've tried four different brands of EOS adapter.
This lens also focuses past infinity, though just a tad.

The adapter is probably too thin(to guarantee you can reach infinity with your lenses) so it focuses past infinity, the amount you need to turn the focus ring to get to get back to infinity is unfortunately lost at the MFD, infinity adjustment may or may not help.
Some adapters are screwed together, those can be taken apart and shimmed.
For one piece adapters, you are stuck, there are a few options, infinity adjustment of the lens, asking the adapter seller if they have any with the correct thickness, or in some cases you may be able to shim the lenses mount by removing the mount and adding a shim, just keep in mind that any modification to the lens will cause it's infinity to be unreachable on the proper mount(eg film body)



Apr 16, 2014 at 01:10 AM
Dudewithoutape
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p.1 #3 · p.1 #3 · What causes MFD to go off?


Because its a zoom, the MFD may be different. Are you getting 8' with both sides of the zoom?


Apr 16, 2014 at 01:45 AM
Cableaddict
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p.1 #4 · p.1 #4 · What causes MFD to go off?


Dudewithoutape wrote:
Because its a zoom, the MFD may be different. Are you getting 8' with both sides of the zoom?



That's a good point.

- but yes, it's the same at both ends.



Apr 17, 2014 at 06:15 PM
JonPB
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p.1 #5 · p.1 #5 · What causes MFD to go off?


5'2" to 8' doesn't seem like a huge distance, as far as the mechanical distance that the lens might move to make up that range. (I once had a 28-80 zoom that focused as close as 19 feet, and taking it apart showed that it was only a matter of about two millimeters to get it down under 2 feet.) I agree with LightShow that it is probably the adapter.

Here's what I'd do: put the camera on the floor with the adapter, shim the adapter with aluminum foil, maybe several layers of it, then place the lens on top of that setup at MFD. (Don't try to secure the bayonet, as you don't want to stress the hardware too much. This means that there may be light leaks as well as some tilt, but that's not what we're testing.) See if it focuses closer than 8' above the floor. If so, you know you're moving in the right direction.

Hope this helps,
Jon



Apr 17, 2014 at 07:17 PM
DaveOls
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p.1 #6 · p.1 #6 · What causes MFD to go off?


You could just get an extension tube if you need to focus closer.


Apr 18, 2014 at 09:13 AM
Cableaddict
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p.1 #7 · p.1 #7 · What causes MFD to go off?


DaveOls wrote:
You could just get an extension tube if you need to focus closer.



That's a good thought. However, I would only ever use this lens as a convenient walk-around lens, so swapping-in rings would not make sense.

Also, this is a good GENERAL technical question, so finding the answer should be helpful to many folks, with many lenses.



Apr 18, 2014 at 06:19 PM
Cableaddict
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p.1 #8 · p.1 #8 · What causes MFD to go off?


JonPB wrote:
I agree with LightShow that it is probably the adapter.......



I'm starting to think so, too, although I've tried four different adapters. I have one more coming and of a different manufacture, so fingers crossed. No need for you test idea since of COURSE that would make it focus closer.

I guess it makes sense that if it's focusing PAST infinity, it would also not focus all the way to MFD.

------------------------

Anyway, in case the new adapter doesn't help (or just "to know" ) again:

Does anyone know if this lens has helical stop-screws, and where they are?

- And would there be 2 sets, one for 75mm and one for 150mm?





Apr 18, 2014 at 06:24 PM





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