(Possibly dumb) questions re: manual focus

[Mark24173]

I'm used to rangefinder manual focus, but less so with DSLRs. I know that medium format (or however people define it - bigger than 36x24) viewfinders are supposed to make it easier to focus manually if you don't trust the AF.

I know AF can be off if the mirror's not quite right or if there's something wrong with the AF module. What I don't know for sure is if the alignment (or not) of the mirror itself affects manual focus.

I got a chance to have a quick play with an H3D 31 ii with 80mm 2.8 lens today. I expressly set it to MF only to see how close I could get just by eyeballing it. I only got three shots off before the battery went out, so I took my CF card home to have a look. The one shot which came out OK is the one attached. I was aiming at the "Leica" logo, but the point of focus was a bit behind it on the eyepiece thing.

Now the most reasonable explanation is that I didn't focus it accurately enough, which is entirely possible (I knew the battery was running out so I was kind of rushing it). Also, the light down there isn't very bright, so I wouldn't be surprised a bit if this was user error. I programmed in a 100ms delay as well, so the picture's actually reasonably sharp. The focus though is definitely not where I intended it to be.

What I want to clarify, though, is whether manual focus is in any way affected by the mirror. If it is not, then I know that it just comes down to practicing more on my MF technique.

Thanks in advance for all words of wisdom.

[Conner999]

There are too many variables. I came from DSLRs to MF and tend to find MF on the H5 (in my case) much better due in part to the massive VF.

It is true that IF the lens-to-sensor distance is not identical to the lens-to-focus screen distance (via the mirror), you can get MF errors. The usual solution is to shim the focus screen.  It's not uncommon in DSLR world (I've had to do it), but I've not heard of much evidence of it in MF. 

It could be simple hand movement due to the mirror slap. While delay helps (even handheld), that's a BIG mirror flapping up & back.

I'd suggest re-scheduling the test and calling the store ahead of time to ensure the battery is fully charged and bringing (or arranging with them) use of a tripod. With a tripod you can AF then check VF to see if looks in focus or do the reverse. Get what you think is perfect MF then hit AF and see if lens barrel shifts to any degree.

You can download free focus test charts to put on nice laptop screen and when in perfect focus, you'll see a moire-like pattern all over it through the VF. Here is one of many. As would walk focus back-forth you see the pattern emerge, peak at perfect focus, then subside.

http://www.travelthroughpictures.com/wp-content/downloads/MFATarget.gif

In a perfect situation: grab a good FW800 cable (Hasselblad or tether tools work), download the free Phocus software and spend sometime shooting tethered to give you instant feedback. 

Good luck and welcome to MF world.

[NickT]

Also be sure to adjust the diopter on the side of the prism until the numbers in the lcd are sharp. I find the AF on Hasselblad always does a better job than I do, camera set to MF with user button set to AF drive.

[Conner999]

Completely forgot about diopter