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Very interesting answer from Leica on 35mm 1.4

tashley

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Jamie Roberts

Jamie Roberts

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Hi Jamie! Daft question but if the effect is gone by f5.6 due to DOF then what effect are you seeing?

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Hey Tim--

 

What I mean is that by 5.6 (ish) the field of focus begins to be more normal. As I said earlier, wide open, the point of focus is near the back of the (thin) focal field; stopping down moves the field forward (a lot) to the point where round about f4 the point of focus is near the very front of the field.

 

If the calibration were off, then the lens would backfocus at f4 (even if you couldn't see this wide open).

 

By f5.6 (and afterwards) the focal field is much more normal; beginning to get to 2/3 back 1/3 in front which you can see by f8. I'm guessing the increased DOF at 5.6 helps this along.

 

By f8 the field is what I'd expect entirely.

 

Make sense? There is definitely a field shift.... but the focus point is still good throughout (or so slightly off that I can't see it in a print--and I've gone 30 * 40 now with these images).

 

Distance also makes a difference; if I'm 15 or 20 feet away I can usually get good (not perfect) focus guessing from the hip.

 

(FWIW, I find this "shooting from the hip" actually pretty easy with all the M8 lenses; the 75 1.4 is the hardest, but even it's possible due to the 1.3 crop and increase in depth of focus).

 

Tim--it might actually be worth it to send one of your M8s along with a 35 1.4 here! You never know. Of course, it's harder to drink beer that way ;)

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carstenw

carstenw

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I tested a 35 Lux Asph in the Leica Store in Berlin, and the focus shift was bad enough that when sharp at f/1.4 (according to viewfinder focus), at f/4 it was very soft. This is not dependent on the aperture setting, since you don't look through the lens. This was on a tripod, and with the staff watching as I did it. They were as surprised as I was.

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tashley

tashley

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I tested a 35 Lux Asph in the Leica Store in Berlin, and the focus shift was bad enough that when sharp at f/1.4 (according to viewfinder focus), at f/4 it was very soft. This is not dependent on the aperture setting, since you don't look through the lens. This was on a tripod, and with the staff watching as I did it. They were as surprised as I was.

 

 

Welcome to my weird world...

 

:-(

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tashley

tashley

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Tim--it might actually be worth it to send one of your M8s along with a 35 1.4 here! You never know. Of course, it's harder to drink beer that way ;)

 

Hmmm... return postage plus appropriate insurance, approximately £280.... return air fare starting at about £250... which leaves around £30 for beer...

 

I feel a Homer moment coming on...

 

:0)

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ChrisC

ChrisC

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Hmmm......, approximately £280.... return air fare starting at about £250... which leaves around £30 for beer...)

 

So that's another session for Zenfolio booked I take it?

 

[Are you sure 30 quid for beer is enough to get the full effect out of a wobbly focus lens?].

 

...........Chris

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magd0328

magd0328

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I attach an extract from Optics (Hecht, 2nd edition). This explains the focus shift, but does it explain everything?

And one more thing: this effect is (of course) not specific to the M8. I have experienced it with my M6.

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tashley

tashley

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So that's another session for Zenfolio booked I take it?

 

[Are you sure 30 quid for beer is enough to get the full effect out of a wobbly focus lens?].

 

...........Chris

 

 

After 30 quid's worth of beer, who cares?!

 

:cool:

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tashley

tashley

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I attach an extract from Optics (Hecht, 2nd edition). This explains the focus shift, but does it explain everything?

And one more thing: this effect is (of course) not specific to the M8. I have experienced it with my M6.

 

That sounds about right. Lord, if I could get a lens with the same DOF wide open as your flatbed scanner, I'd be in heaven!

 

;-)

 

Tim

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Jamie Roberts

Jamie Roberts

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After 30 quid's worth of beer, who cares?!

 

:cool:

 

Exactly!!!

 

Tim--given the costs--come by here! You can stay and we can do beer-aided lens testing.

 

Honestly, more and more the 35lux is my go-to lens on the M8. I've really wanted to see it fuzzy in the center at f4--honestly--but it just isn't! It's tack sharp, actually, all through the aperture range till diffraction beyond f8.

 

You guys have me so scared I won't even send it in to get coded! Time for a DIY job. Gotta go buy some nail polish!

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Jamie Roberts

Jamie Roberts

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I attach an extract from Optics (Hecht, 2nd edition). This explains the focus shift, but does it explain everything?

And one more thing: this effect is (of course) not specific to the M8. I have experienced it with my M6.

 

Um, isn't this why a lot of Leica's lenses are aspherical in design? Just curious!

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rami G

rami G

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You guys have me so scared I won't even send it in to get coded! Time for a DIY job. Gotta go buy some nail polish!

 

 

I must say that I am very worried about the coding issue. I have had my 35lux asph and the 28 cron coded, and they got all the issues described here, of focus shift, etc. Had DAG trying to adjust as much as possible but things are not easy. the 35 has a clear focus shift and all shots at 1.4 are sharpter than at 5.6 unless I front focus intentionally. The 28 focuses fine at f/2 close to mid range, but longer to infinity it is a mess. at infinity I can get more information from the VC 15 than from the 28 cron at any aperture inspite of the wider field of view (that is, read sign-posts from a given distance, etc)... Presently, I am pretty confident that I am not going to send my perfectly focusing 21 asph for Coding. I am worried weather this whole issue is related to the coding process (I know it was discussed but I apologize if it was covered and refuted already somewhere along this very long thread, or elsewhere).

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tashley

tashley

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Interesting stuff coming out here - your description of the 28 cron behaviour is exactly why mine got returned and I'm currently awaiting its replacement.

 

With your 35 cron, try the following: at a distance to subject of around 2 metres and with a flat subject exactly parallel to the camera and with lots of fine detail, good light, low ISO and a tripod, take shots at F2 and 4. Then at F4 still, pull focus a tad closer. Now check out the results on screen at 100%.

 

What I get is:

 

F2: bit soft everywhere but pretty good for wide open

F4: somewhat soft in the centre (softer than at F2 by far) but perfect at the edges

F4 with focus pulled forward: perfect in the centre, bit soft at the edges.

 

In other words, the focus shift has a spherical component on mine at least, which means that short of hitting F5.8 or eight AND pulling focus forward a touch, there's no way to get the sharp-across-the-frame look I thought I would get from the lens.

 

Now what is really really interesting here is that Jamie's is uncoded and that yours were ok until they got coded. Which heavily implies that it's some difference in the coded lens mounts that's at the root of this.

 

After 15 pages of this, I STILL don't think we've gotten to the root of it!

 

Tim

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tashley

tashley

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Exactly!!!

 

Tim--given the costs--come by here! You can stay and we can do beer-aided lens testing.

 

Honestly, more and more the 35lux is my go-to lens on the M8. I've really wanted to see it fuzzy in the center at f4--honestly--but it just isn't! It's tack sharp, actually, all through the aperture range till diffraction beyond f8.

 

You guys have me so scared I won't even send it in to get coded! Time for a DIY job. Gotta go buy some nail polish!

 

It's a deal, I actually think I will do this sometime! Between us we will boldly go where no beered up lens testers have gone before. Blimey, and I thought when I bought m8 first M8 that I would travel the world with it but I didn't quite realise why!

 

;-)

 

Tim

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rami G

rami G

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That sounds very disappointing. I actually have the 35 lux, but I will try that. I sent my 28 back to DAG to see if there is any way to improve it. The interesting thing I find about the M8, which is totally uncomprehensible to me, is that it is easier to focus perfectly using longer lenses (50mm, 75mm) than with the 28, 35. The attached image (not for artistic purposes, thought), for example. I took it with the 75 lux @ 1.4. I just don't get anything close to that with my 35 lux @ 1.4. usm 70/1/0

 

Interesting stuff coming out here - your description of the 28 cron behaviour is exactly why mine got returned and I'm currently awaiting its replacement.

 

With your 35 cron, try the following: at a distance to subject of around 2 metres and with a flat subject exactly parallel to the camera and with lots of fine detail, good light, low ISO and a tripod, take shots at F2 and 4. Then at F4 still, pull focus a tad closer. Now check out the results on screen at 100%.

 

What I get is:

 

F2: bit soft everywhere but pretty good for wide open

F4: somewhat soft in the centre (softer than at F2 by far) but perfect at the edges

F4 with focus pulled forward: perfect in the centre, bit soft at the edges.

 

In other words, the focus shift has a spherical component on mine at least, which means that short of hitting F5.8 or eight AND pulling focus forward a touch, there's no way to get the sharp-across-the-frame look I thought I would get from the lens.

 

Now what is really really interesting here is that Jamie's is uncoded and that yours were ok until they got coded. Which heavily implies that it's some difference in the coded lens mounts that's at the root of this.

 

After 15 pages of this, I STILL don't think we've gotten to the root of it!

 

Tim

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