[need advice] 35/2 Asph: focus shift, how much is too much?

[edwardkaraa]

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I agree with Wilson. The biogon is better than the cron at every aperture except at f/2. However, the biogon does have focus shift, just like the cron. The trick of Zeiss is that they calibrate it for f/2.8 which is enough to cover focus shift at all apertures except f/2. That is why most users think it is worse than it really is wide open, due to additional front focus on top of spherical aberrations. If you give the focusing ring a little nudge after focusing with the rangefinder, the wide open performance will surprise you (but still not as good as the cron).

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[Steve McGarrett]

I update this old thread as the lens is just came back from Wetzlar, after 2 months.

I can't do extensive testing yet, because it's raining heavily since a couple of days here, but apparently nothing has changed at all.

 

Lens seems to be still spot-on at f/2, slightly soft at f/4-5.6 (focus point shifts further away from camera) and acceptable by f/8.

Indeed, if I focus a bit shorter than what rangefinder says, then sharpness is better from f/4 on.

[lct]

Only way to be sure is to use your lens with a live view camera.

[Steve McGarrett]

Yes, if you read the topic back, you'll see I've made extensive testing, even with live view, in past months, before sending lens to Leica service.

[lct]

Yes i remember that but you wrote above "if I focus a bit shorter than what rangefinder says, then sharpness is better from f/4 on". Hence my comment above.

[Steve McGarrett]

lct, on 08 Dec 2016 - 15:21, said:

Yes i remember that but you wrote above "if I focus a bit shorter than what rangefinder says, then sharpness is better from f/4 on". Hence my comment above.

 

Yes, that was the same behaviour than before: LV said that lens needed to be focused shorter than what rangefinder said (at f/4-8), while at f/2 both LV and rangefinder were coincident.

 

Even if this was a lens I've never seen before, if focus is spot-on wide open, on rangefinder, and shifts away at medium aperture, that would be focus shift without needing of further testing. A fortiori, here we're speaking, instead, of a lens I have tested extensively two months ago, dozens of pictures with LV, tripod and so on, so it's not take very much to see if something has changed or not.

 

Anyway, I'll do further testing when weather will improve.

[NoctiluxM240]

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I have sold my Summicron 35 ASPH, too much focus shift ... Instead I bought the last type Ultron 35mm 1.7, lens that surprised me with its performance,  so impressive crisp at all apertures, focus spot on, and no focus shift.

[edwardkaraa]

Hi Steve, I guess my previous advice still stands. The way I see it, you've got two options:

 

1. Keep it as is, calibrated for wide open. This way you can use it either at f/2 or at f/8, which is how most owners use it anyway.

 

2. Send it to an independent repair shop, with clear instructions to calibrate the focus at f/2.8-4. This way you will get correct focus at all apertures except wide open. With some practice you will be able to compensate for the shift on the fly and it becomes second nature.

 

Good luck with whatever you decide.

[jaapv]

I agree with Wilson. The biogon is better than the cron at every aperture except at f/2. However, the biogon does have focus shift, just like the cron. The trick of Zeiss is that they calibrate it for f/2.8 which is enough to cover focus shift at all apertures except f/2. That is why most users think it is worse than it really is wide open, due to additional front focus on top of spherical aberrations. If you give the focusing ring a little nudge after focusing with the rangefinder, the wide open performance will surprise you (but still not as good as the cron).

Just out of interest: why do you use "Cron" for Summicron and not "Gon" for Biogon?

[Gregm61]

You don't know?

 

Zeiss lens will start focus shifting if you abbreviate their names, much like Leica lenses do, LOL...

[edwardkaraa]

Just out of interest: why do you use "Cron" for Summicron and not "Gon" for Biogon?

Actually it should be bio for biogon.

[pop]

Actually it should be bio for biogon.

In that case it should be "sum" for summicron, should it not?

[edwardkaraa]

In that case it should be "sum" for summicron, should it not?

No, because you have a summilux, summicron and summarit on the Leica front, but on the other side, you have biogon and distagon.

[pop]

Yes, and how would anyone not familiar with all those product names cope and make sense of our discussions?

[edwardkaraa]

Yes, and how would anyone not familiar with all those product names cope and make sense of our discussions?

Good point

[Exodies]

Just picked up my marron today. Not a chestnut but a tiny jewel.