Have MD Rokkor X 50/1.4, can you check...

motleypixel · Joined: 12 May 2010 Posts: 135 Location: Austin, TX USA

Hey gang,

If you have a Minolta MD Rokkor-X 50/1.4 then can you tell me about how much focus throw travel you have from infinity to minimum focus distance? The distance the elements move.

I'm a rookie at fixing these lenses but I had a rough focusing one and having about 5 50/1.4 breakdowns under my belt I thought I'd try it on this lens. Here's the deal...I had a hell of a time getting the full focus throw to work w/o it getting hung up as I approached MFD (min focus distance)...it was painful and was due to my lack of experience with the focus ring on this lens. It's hard to explain but I think I have full focus throw on this lens but oddly enough it doesn't represent this on the distance indicator.

Right now on the stop of infinity the rear of the lens (metal element housing) I have about 1/2mm protrusion and it certainly seems this is the correct spot compared to an untouched MC Rokkor-X 50/1.4. Now as I focus to MFD it stops about 1/2 way between 1.75 and 2 feet (should be 1.5ft) on the distance scale (this is the hard stop). Unlike infinity I think it's not the focus ring hard-stop tab, rather it's the max out of the lens group screwing into the helicoid.

My total focus throw from infinity to MFD (again shows half way between 1.75 and 2) of the front lens group (as measured on the element shroud) is 5.5mm My other untouched MC Rokkor is about 7mm of element group travel.

Can some who has this lens tell me what they have at infinity (lens barrel protrusion out the back) and the total focus throw front lens movement distance?

Thanks,
Roy

motleypixel · Joined: 12 May 2010 Posts: 135 Location: Austin, TX USA

Okay here's a clearer explanation. Sorry for the long cut ~10min but just wanted to throw this video together. The changing EV is due to the sunlight shifting because it's a bright part cloudy day today.

http://www.youtube.com/watch?v=u9sK-iDytms

motleypixel · Joined: 12 May 2010 Posts: 135 Location: Austin, TX USA

And more detail: http://vimeo.com/12720515

Thanks,
Roy

rpress · Joined: 23 Jun 2010 Posts: 1

I have an MD Rokkor 50/1.4 which should be the same unit.

I noticed in your video that you didn't pay particular attention to where you started to thread in the helicoid, or did you? The helicoid has many positions it can be started in, and only one of them is correct.

Some measurements of mine:
The gap bewteen the focus ring and the DOF guide at infinity is 0.8mm.
The travel from infinity to minimum focus is 7.6mm.
The amount of the lens group protruding beyond the focus ring at infinity is 5.1mm.

You will need to try each start of the helicoid until you get the right lens protrusion at infinity.

If I recall it was 10.5 turns in on the fine thread part of the helicoid, to get the 0.8mm gap.

You should use moly grease (CV joints for cars) or teflon grease (for bicycles) because of the aluminum/aluminum helicoid. Otherwise it will be rough and the aluminum will gall causing permanent damage.

I used "Finish Line Premium Teflon Grease" for the helicoid, it was a bit too thick, so I thinned it with "Tri-flo" just a little and now it is perfect and buttery smooth.

Hope that helps.

motleypixel · Joined: 12 May 2010 Posts: 135 Location: Austin, TX USA

Thanks repress...I found out my problem...take a look at how I put the leading bar back in...all of the lenses I've seen, including the rokkor 58/1.4 have it such that the tab of the leading bar goes down (i.e. towards the front element) but in the case of this rokkor 50/1.4 the tab goes upward...works perfect now.

Thanks,
Roy