RD1s with Elmarit 28mm f2.8 ASPH Focus Shift

[akk2]

I just got my 28mm f2.8 ASPH from B&H today.
When I mount it on my RD1s, I got back focus at 0.7m. :bang:
it aligned to infinity in VF.
I have no problem focus my CV 35/1.4 SC at 0.7m and 50/1.1 at 1m, both wide open. 😎
And a little bit front focus (about 3mm) on my 50/2 heliar.
It is a focus cam problem or the lens? What should I do?

 

[LCT]

...I got back focus at 0.7m. :bang:
it aligned to infinity in VF...

1. Do you mean the focus patch does not align and/or the camera gives blur results at 0.7m?
2. Do you get sharp results at infinity?

 

[ampguy]

Do other lenses focus accurately at min focus distance? How did you measure the shift?

Here is how I measure - min distance, focus on Tabasco, each figurine to left is 1.50 cm closer to lens, and to right of bottle, 1.50 cm away from lens. Camera on tripod, focus ring never moves, only aperture ring.

focus test images for Nokton 40/1.4 @ min. focus distance

 

[akk2]

The other lenses focus accurately at min distance. I put camera on tripod and focus on flat copy to test it if i have to. But i care more about real world condition. the 28/2.8 asph need to move the focus patch about 1/3 the patch to the right, so it will be sharp. (I keep it @0.7m and move the camera)

I just send it back to B&H and exchange for other copy of the lens and try again. If it happens to shift again, I would wait until I get my M9 (still waiting) and see what happen.

 

[Philip Whiteman]

In my experience, you have to make an allowance for certain lenses based on experience – recalibrate yourself as it were, rather than the R-D1.

My 50/2 and 35/2 Summicrons focus like a dream on mine, as does my 28/1.9 Ultron – at least when used wide open. However, unlike the other two, the Ultron progressively focusses further back as it is stopped down (a problem with aspheric lenses, some have claimed, although I am not sure I believe that's the fundamental reason for it). It's irritating, and I was at first tempted to adjust the rangefinder or even return the lens, but I now know to focus a tad in front of the subject as I stop the thing down.

I also find the R-D1's rangefinder is prone to hanging up, especially with those lenses like the Ultron that have a non-rotating rangefinder drive cam, rather than a ring that rotates with the focus grip or tab. With the R-D1 it's a good idea to rack the focus in and out as you zone in on the right setting.

I hope your M9 is an improvement on this, akk! Certainly, the super-precise and stiction-free rangefinder on my old M6 makes the Epson's look distinctly downmarket…

 

[LCT]

...unlike the other two, the Ultron progressively focusses further back as it is stopped down... I also find the R-D1's rangefinder is prone to hanging up, especially with those lenses like the Ultron that have a non-rotating rangefinder drive cam…

What you describe here looks like focus shift. I did not know that the CV 28/1.9 was affected by that. Focus shift is not related to aspherical surfaces AFAIK. Some asph lenses like Summilux 35/1.4 have this problem, other non-asph like CV 35/1.4 have it as well. Fortunately, many asph and non-asph lenses are free from it like the Elmarit 28/2.8 asph and almost all Leicas.
What do you mean by the Ultron having a non-rotating RF drive cam by the way? All focus cams rotate don't they otherwise the rangefinder could not work. Just curious.

 

[LCT]

...I also find the R-D1's rangefinder is prone to hanging up…

If you mean that the R-D1 is slow or otherwise difficult to focus with i will have to disagree with you. I own both a R-D1 and a R-D1s and i have no focussing problems with them as long as i stay within the accuracy range of the rangefinder. My 28/2 and 28/2.8 Leica and Minolta lenses are very easy to focus with specially. I might have to adjust a slight RF misalignment from time to time though (R-D1).

 

[Philip Whiteman]

Sorry, LCT; I've been otherwise occupied.

Yes; I was talking about what seems to be a focus shift with the 28/1.9 Ultron. The lens appears to focus correctly at full aperture. However, as you stop down, the actual plane of focus seems to shift backwards – to stuff behind the thing you've aligned the rangefinder on (for example, you've focused the camera on the subject's eyes and in the image it's the ears that are sharp). This is most problematic at apertures around f4, but is masked by stopping down further to f8 - f11, where depth of field gives adequate sharpness in the apparent plane of focus.

By 'focus cam' I mean the ring at the rear of the lens that drives the rangefinder roller on the camera body. On the Ultron, this ring does not rotate as the lens is focused: the R/F mechanism in my own R-D1's body has a small amount of 'stiction' – once in while the rangefinder freezes as you continue to focus the lens closer. This happens more with the Ultron than it does with my other Leica and Voigtlander lenses, all of which have rotating focus cams. I suspect the minute degree of vibration imparted by the R/F roller turning on the focus cam of these lenses is just enough to stop the R/F arm sticking.

I didn't mean to suggest that the R-D1's rangefinder is slow or difficult to focus. I very much appreciate the R-D1's 1:1 finder but, like many others, mine example suffers a slight (and non-fixable) angular misalgnment. You just don't see this kind of problem in Leicas – and I've used Ms for decades without ever having to reset their vertical or horizontal R/F alignment. Leicas offer superior reliablity, but at a price…

Ultimately, there's little point in getting too worked up about what are minor, although sometimes irksome deficiencies in Cosina/Voigtlander's lens range or the Espon camera. Both CV's lenses and the R-D1 camera are very welcome additions and indeed extensions to the rangefinder armory. They offer astonishingly good value for money and do 90% of the job quite brilliantly – but they are built down to a price and it sometimes shows.

 

[Ljós]

Back focus, no focus shift

Back focus, no focus shift

Oh, looks like there is an inofficial "back focus/focus shift"-festival going on at RFF these days...
More to the point: from the OP's description, this is a clear case of a "simple" back focus... as he stated in the text of the post. The title is misleading though: the reason for his dissatisfaction has nothing to with focus shift.
If all his other lenses focus correctly at .7m, as stated, then it is indeed likely that the Elmarit APSH is off... (it is still POSSIBLE that the brand new Elmarit is spot on, and that the combo of his camera and other lenses is "spot on", though they are "out of spec" taken by themselves. Just not likely.)

 

[LCT]

...By 'focus cam' I mean the ring at the rear of the lens that drives the rangefinder roller on the camera body. On the Ultron, this ring does not rotate as the lens is focused...

Pity that i don't use this lens as i don't see what you mean sorry. If the ring (focus cam) does not rotate, the roller cam does not move and the lens cannot be focused accurately. Or do you mean that the focus cam moves without rotating?

 

[Philip Whiteman]

That's right; the Ultron's focus cam simply moves in and out without rotating.

Some of the long-focus Leica lenses use a cam mounted on the end of a rod that is attached to the focusing head.

If the focus cam is of the more common type that rotates with the focus ring as the lens racks in and out, the roller on the end of the rangefinder operating arm spins round. If the lens focus cam is of the non-rotating type, the roller barely turns: this shouldn't matter – the cam will still push the roller back and forth – but if the action of the rangefinder suffers any friction or the return spring is weak, a lack of even the mildest 'rumble' from the spinning roller may be enough for the operating arm to stick as the lens is racked out for close focus.

The rangefinder cannot stick or hang up as you focus the lens further away, because in this case the roller is being driven inwards forcibly by the lens cam.

I said the Ultron SEEMS to shift focus because I am not sure I fully believe it myself (perhaps somebody expert on lens design can explain if such a thing can really happen and if so, why!)

The problem is that the R-D1's rangefinder is just not accurate enough, even when it doesn't stick, to focus consistently. If anyone doubts this, try focusing almost any lens on a medium-close object first from infinity and then from the closest limit: you will see a difference on the scale. Try the same on an M Leica, and that difference will be vanishingly small.

Of course, the other difference is that we can all chimp and fret over digital images endlessly, whereas the delay between shooting and developing film images allows one to relax and forget about such issues…

 

[LCT]

That's right; the Ultron's focus cam simply moves in and out without rotating...

Interesting indeed. None of my 30+ M lenses behaves like that. Thanks for this info.

 

[Philip Whiteman]

30+ M lenses? And I thought I was a GAS victim!

 

[LCT]

30+ M lenses? And I thought I was a GAS victim!

There are worst cases. I know a guy who owns a dozen R lenses as well let alone some Nikkors, Rokkors and Zuikos. :angel: 😀