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Question about infinity focus for m4/3 cameras
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PostPosted: Wed Oct 31, 2012 8:31 pm    Post subject: Question about infinity focus for m4/3 cameras Reply with quote
I have FOTGA adapters for 10 different mounts to m4/3 and on all lenses infinity focus has been reached at 3m mark. I checked with Nikon F, Konica AR, Minolta MD and M42 to m4/3 body and all of them are reaching infinity at shortly before mark of 3m.

Now, are those adapters to thick or to thin?

The camera I am mounting to is Olympus Pen E-PL1. While my plan is to get OM-D E-M5 at some point and stick with mirrorless m4/3 system I like to get right adapters or get them fixed. It doesn’t bother me to much while I know where the infinity focus is, and almost all prime lenses I have acting the same way (shortly before 3m mark on the lens) reaching infinity however I want to understand this how it is working.

Can anyone explain this in detail?


PostPosted: Wed Oct 31, 2012 9:18 pm    Post subject: Re: Question about infinity focus for m4/3 cameras Reply with quote
RAART wrote:
Now, are those adapters to thick or to thin?

The adapters are too thin. What you need is a kind of mini extension tube. For the theoretical Background have a look here (first good source I found for "lens infinity extension tubes theory"): http://forums.dpreview.com/forums/thread/3100295


PostPosted: Wed Oct 31, 2012 9:21 pm    Post subject: Reply with quote
The adapters are all too thin. This is deliberate as it is better to make the adapter too thin and focus beyond infinity than too thick and make it only focus to a few meters. High quality adapters will be designed to be only about 100 microns too thin. A good cheap adapter may be 200 microns too thin. Some adapters I've bought recently (from Big Is who has always been good in the past) have been as much as 500 microns too thin, which is pretty poor IMHO.

I suggest you try shimming the adapters to the correct thickness. Unscrew the mount ring and place a ring of ordinary paper under it. One or two thicknesses of paper will likely reduce the thickness error to the level at which it is not bothersome.

Mark


PostPosted: Wed Oct 31, 2012 9:34 pm    Post subject: Reply with quote
The interesting thing is that with longer focal length this changes. I tested first with different 50mm legacy prime lenses while I had a more then one and repeated this with one 300mm tele I had and almost focused exact at infinity, just slightly before...

I guess if I want to use same adapters for telephotography then I have to leave it otherwise I wouldn't be able to have infinity focus. I am wondering what if I mount 400mm or 600mm telephoto lens if it will focus at infinity or not. Unfortunately I do not have those focal lengths but i really like to know.


PostPosted: Wed Oct 31, 2012 9:39 pm    Post subject: Reply with quote
RAART wrote:
The interesting thing is that with longer focal length this changes.

That's normal. Extension tubes for macro photography have less effect the longer the focal length. It's the same for your too thin adapters. Longer focal length, less effect, more accordance with the focus scale.
RAART wrote:
I am wondering what if I mount 400mm or 600mm telephoto lens if it will focus at infinity or not.

It will reach infinity if nothing is wrong with the lens.


PostPosted: Wed Oct 31, 2012 9:47 pm    Post subject: Reply with quote
Then the most logical thing to me is to get more adapters and customize each one to specific lens and leave it permanently there.

I guess that if I go with aluminum foil, thin or heavy duty it will be better while humid/damp environment won't be having any effect or any kind of thin plastic. Maybe aluminum or any othertape to prevent sliding is better and I can tape them how many times I want...


PostPosted: Wed Oct 31, 2012 9:55 pm    Post subject: Reply with quote
RAART wrote:
Then the most logical thing to me is to get more adapters and customize each one to specific lens and leave it permanently there.

The specific shim thicknesses for specific lenses result from manufacturing tolerances only. If all lenses focus to infinity for their native mount you only have to calibrate each adapter once for all lenses with that mount. Infinity is infinity is infinity.


PostPosted: Wed Oct 31, 2012 10:01 pm    Post subject: Reply with quote
Sorry I do think that I misinterpret myself here...

What I wanted to say to have adapters customized to focal length of the lens, speak example for M42 adapter if I have this customized to infinity to work with all 50mm lenses but what about M42 135mm or 200mm lens. I think that in this case I will need another M42 adapter customized to other focal length.

Correct?


PostPosted: Wed Oct 31, 2012 10:04 pm    Post subject: Reply with quote
RAART wrote:
Correct?

No. If you shim your adapter to the correct thickness, all lenses will focus to infinity at their infinity mark no matter of their focal length (if the lens itself is calibrated correctly).

Edit: Otherwise you would require different register lengths for a single camera for different focal lengths...


PostPosted: Wed Oct 31, 2012 10:10 pm    Post subject: Reply with quote
I understand now. I just took a look at those formulas again.

In a a fact with smaller focal length is just more pronounced then with longer focal length while lenses should be already manufacturer calibrated to infinity.

Right?


PostPosted: Wed Oct 31, 2012 10:13 pm    Post subject: Reply with quote
RAART wrote:
Right?

Right! Cool


PostPosted: Wed Oct 31, 2012 10:17 pm    Post subject: Reply with quote
Laughing Dankeschoen Holger! Einen wuenderschoenen abend wuensche ich dir...

Thanks to everyone for a reply!


PostPosted: Wed Oct 31, 2012 10:21 pm    Post subject: Reply with quote
Gern geschehen! Schönen Abend. Very Happy


PostPosted: Wed Oct 31, 2012 10:47 pm    Post subject: Reply with quote
Those FOTGA adapters look a bit different to the ones I normally get, but I've never had issues with infinity being at the 3m mark on a 50mm lens wiht the ones I use.
It seems to me that the FOTGA adapters are a bit thinner than the majority of the micro4/3 adapters.


PostPosted: Wed Oct 31, 2012 10:53 pm    Post subject: Reply with quote
SXR_Mark wrote:
The adapters are all too thin. This is deliberate as it is better to make the adapter too thin and focus beyond infinity than too thick and make it only focus to a few meters. High quality adapters will be designed to be only about 100 microns too thin. A good cheap adapter may be 200 microns too thin. Some adapters I've bought recently (from Big Is who has always been good in the past) have been as much as 500 microns too thin, which is pretty poor IMHO.

I suggest you try shimming the adapters to the correct thickness. Unscrew the mount ring and place a ring of ordinary paper under it. One or two thicknesses of paper will likely reduce the thickness error to the level at which it is not bothersome.

Mark


+1


PostPosted: Wed Oct 31, 2012 10:55 pm    Post subject: Reply with quote
I do not know about others but the fitting on the lenses is very good also the fitting on the body is very good too.

I adjusted only M42 Fotga adapter to be on center and it was very easy while it had 3 tiny screws (accessible with allen/hex key size 0.050), just loosen them and turned with lens mounted to match red dot on the adapter itself and center focus mark on the lens. I heard that many people have this off center.

So far they are good...


PostPosted: Thu Nov 01, 2012 4:02 am    Post subject: Reply with quote
I use an adapter per lens on the hunch that cheap chinese adapters will probably be using soft steel on the lens mount side.
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