Optical View Finder is not accurate.

[andi]

Hi guys, on the back of my post in this thread - I've run into a problem with my camera that I was hoping you could help me with.

I have a Canon 6D with a 35mm F2 IS. The issue is that what appears to be as in focus in my optical viewfinder is different to what autofocus/live view sees.

1. Camera is setup on a tripod
2. I have an object with text in front of the lens
3. Live view + auto focus brings the text in focus
4. Trigger shutter
5. Review image, text is also in focus

6. Without changing or moving anything, view the object through VF
7. Text appears out of focus, manually focus until text appears in focus through VF
8. Trigger shutter
9. Review image, text is out of focus

10. Without changing or moving anything, view the object through VF
11. Trigger auto focus, text appears out of focus through VF
12. Review image, text is in focus
13. View the object through VF, no dioptre adjustment brings the text into focus

What is confusing is that I can see a perfectly sharp image through the VF, but why is it so misaligned to what LV/autofocus reports?

Thank you in advance.

Cheers,
Andy

- - - Updated - - -

Should also mention that I'm using the standard focus screen, aperture was set to 3.2, shutter speed was set to 1/640.

[Filter]

Step 6 - Is the Dioptric adjustment set right?

[Lance B]

Some cameras allow adjustment of the focus screen under the optical VF with shims. I had to do this with one of my Pentax cameras a few years back as it was out of adjustment. You may need to do this with your Canon 6D if it can be done.

[arthurking83]

A point to note with the dioptre adjustment is that, if the vf is appearing OOF when the subject is actually in focus(ie, confirmed via LV or AF), then the text and other info in the viewfinder should also appear slightly OOF too.
That is the dipotre adjustment adjusts focus(for various human sight differences). It adjusts everything within the viewfinders view point.
Normally(but not strictly for every situation), as the dioptre is an adjustment for regulating human vision issues, if it's OOF, adjusting it doesn't necessarily line up any other alignment issues.
The primary purpose of this adjustment is to clarify the information available in the viewfinder .. not the image of the scene(what's usually called the aerial view).

From my experience with this type of issue, it's almost certainly an issue with the primary mirror.(or as Lance said a possible shim misalignment).

There are two mirrors within the mirror box of an AF DSLR.

The big one you can easily see inside the camera is the primary mirror. This is the one that gives you visual feedback into the vf.
The AF mirror is a secondary smaller mirror within the main mirror.

That can be(or should be) adjustable separately. In Nikon cameras I know this .. I have no idea about Canon cameras.

I've adjusted both my D300 and D70s back in the day to make manual focusing easier through the vf. (never done or needed to do the D800E tho)

I can't offer any advise re a 6D tho, but FWIW, in a Nikon camera there is a easy to reach primary mirror adjustment screw. It's a hex(allen key) headed screw which is easily reached and turned to adjust if needed.
This primary mirror adjustment is usually called the manual focus adjustment screw, as all it does is adjust the mirror associated with the primary view through the vf.

If you do research any info on how of if such an adjustment is available in your model Canon(which it really should) then just be aware that if you attempt to DIY just to have the exact spot on correctamoondo tool to so it.
** again FWIW I think the allen key tool required for the D300 and D70s was a 1.5mm allen key .. not an imperial equivalent!! this can be vital because if you use 2/32 equivalent allen key tool, which seemingly fits, but has the potential to slip while effecting the adjustment .. the only way to unscratch the primary mirror is with a new one!.

if you're not confident to do the adjustment yourself, a Canon service place should be able to do it for you in a couple of minutes.

I've done this, and I can tell 'ya it's as easy as pie. The only reason for this is because of the Lv feature in your camera.

[andi]

Thanks for the response guys.

Unfortunately I can't find anything about a mirror adjustment screw for the 6D. Not really sure what to do now.

I could rely on auto focus and just use the VF for composition, but I won't have the join of MF now.

[arthurking83]

Al the cameras I've seen so far seem to have this eccentric allen key just inside the mirror box towards the front.
Mind you all of the cameras I've experienced tho have been Nikons, and one obscure Topcon SLR from the 60's.
It's basically a rest stop for the mirror in the down position.

The more critical and important AF mirror adjustment is much harder to both see and access. Obviously if you muck about with the AF mirror stop you risk mucking up the AF(which you definitely don't want to do!).

I just did a search for a Canon 6D image to locate any images of the mirror box.
I found one which I can clearly see a small round tab looking thing which corresponds to the MF mirror stop on all the Nikon's I've seen.
With the mirror down, you can't see it, but if you raise the mirror(with a clean hand will do) you may see it.
It's on the RHS as you look into the camera(not as you hold it for use).

I suspect that this may be the same thing(but I don't know this!!).
one major visual difference is that: on the Nikons, you don't touch the physical mirror stop itself. there is a small hole in front of the Nikon version just in front of the actual mirror stop. It's recessed and can't be seen easily, but within this recess is the actual allen key to effect the adjustment .. ie. not the actual protruding mirror stop itself.

Obviously I can't offer any help with adjustment nor if you could find a way to do so, in which direction to adjust.

On my D300 and D70s, just after I started using the 50mm f/1.2, I had a lot of trouble finding the exact point(plane) of focus with this lens(the Nikon version is MF only!)

So I adjusted the D300 first, but not knowing which way to make the adjustment I simply guessed(and of course it was wrong ). With the D300 it wasn't an issue as it has Liveview. So with the help of liveview I readjusted the stop to give a more accurate focus plane indicator for the way I used the lens.
What was actually happening was that as I focused closer and closer to the plane of focus, with Nikon's a green confirmation light lights up to indicate focus.
It's not very accurate, but an OK guide. Problem for the way I shoot tho is that by the time I've got to this point as I shoot, I may overshoot the actual plane of focus by a mm or two .. so the image was almost sharp but not exactly.
So I reset the MF mirror stop so that as soon as the lens was focused from near to the plane of focus, it would indicate focus confirmation with the green light.
The end result was that I could achieve accurate MF with this lens(obviously with a very thin DOF) BUT only if I focused from near to far to focus. If I focused the other way(from infinity) instead, I'd always miss the plane of focus going by the green dot. The focus screen was way too coarse to visualise accurate focus with this lens.

So in effect, what I'd done was to deliberately misalign my D300's MF system to suit my shooting methods more accurately!

Once I was confident I knew what I was doing with the D300(if you could call it that ) .. I then did the same with the D70s. D70s doesn't have liveview, so confirmation of success was the old and tedious: adjust -> shoot -> transfer image to pc -> examine image at 100% -> adjust -> shoot -> transfer image to pc .... etc.

Later tho, I ended up getting a Katzeye split screen focus screen.
When I installed that, it clearly showed that when I used Lv to get accurate focus, even tho the green dot was still confirming focus was OK, and the image was in focus .. the split screen showed a misalignment of of the split screen .. indicating that focus wasn't spot on(through the vf).

So I went back into the mirror box and adjusted the mirror stop again to suit the new split prism focus screen.

In a word ..... easy!
Like I said the hardest bit was to figure out what sized tool to use, so I don't either round off the hex key, or worse slip and ruin the mirror.

The moral of that diatribe is that even tho I (deliberately) stuffed up a seemingly fine system, I did so to suit my purpose, and it was easier to unstuff it, because I now had the understanding of how to do it.


Like Lance said too tho there may also be shims under your focus screen.
The katzeye screen came with two(plus I still had the original Nikon shim too.
Initially I added another of those shims that Katzeye supplied but it made the entire image OOF with no way to focus at all. Seeing was completely abonimable unless you like nothing but blur.
While the shims are easy to do(but harder in a Nikon than the mirror stop adjustment), in effect they are only a one way adjustment and a lot more coarse compared to the fine tuning a mirror stop allows.

Oh yeah!... just a note that I am a habitual tinkerer type!

Here's a link to the 6D images I found:

I'll describe what I think is there compared to the Nikon equivalent.
Large round protrusion at the front on a Nikon is the mirror stop. I can't see any way to adjust this protrusion, as the face of it looks smooth. On a Nikon there is a small recess towards the front of the camera where the allen key is placed to adjust the protrusion.
Look further inward towards the sensor and you will see a similar but smaller looking protrusion as well, higher up in the mirror box too.
On a Nikon this rear most protrusion is the AF adjustment stop. Again I can't make out any way to adjust it on a Canon(and better!) and on a Nikon there is a similar recess with an allen key to adjust that one too.
On a Nikon tho, even tho I can get an allen key in there, there is just no room to make any adjstment as the travel of the allen key too is completely restricted .. once again better as I won'[t find myself in adventurous tinkering mode and stuff that one up.

if I can locate the hand drawn diagram that describes the entire system I'll reply again with it which makes it much easier to visualise the mechanics.

hope that helps.

[Sargimuss]

I'm not sure if you've solved this yet, but I'll add a bit in anyway...

Just above the video mode switch on the 6D is a small focus adjustment wheel. this is the Diopter Adjuster (As Filter mentioned)

Set your camera up again and set focus through the LiveView or Auto focus, when focus is achieved (and without adjusting the lens at all), switch back to VF again and while looking through the VF, scroll this small wheel either way until focus through your eye is achieved.

Hope this helps if you haven't found an answer yet