Tolerances for a Summicron 28mm

[t024484]

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I have just acquired a Summicron 28mm.

Since I have the right to return this lens within a week, I did some measurements to be sure everything is O.K.

To start with, Infinity seems to be O.K.

But measured with tripod from a distance of 90cm, without touching the distance setting in between, I have the following results.

 

f2.0 – 14mm front focus

f2.8 – spot on

f4.0 – 7 mm back focus

f5,6 – 14 mm back focus.

 

My question is, is this front/back focus shift within the tolerance for this specific lens, or is it far too much.

With my other Leica lenses, I have hardly any measurable focus shift when changing the diaphragm.

 

Hans

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[colonel]

I have just acquired a Summicron 28mm.

Since I have the right to return this lens within a week, I did some measurements to be sure everything is O.K.

To start with, Infinity seems to be O.K.

But measured with tripod from a distance of 90cm, without touching the distance setting in between, I have the following results.

 

f2.0 – 14mm front focus

f2.8 – spot on

f4.0 – 7 mm back focus

f5,6 – 14 mm back focus.

 

My question is, is this front/back focus shift within the tolerance for this specific lens, or is it far too much.

With my other Leica lenses, I have hardly any measurable focus shift when changing the diaphragm.

 

Hans

 

I am curious as to the focus chart/test you are using

 

Also, is the focused spot within the DOF ?

[TomB_tx]

I don't have the 28, but I have seen similar shift on my 60's 50 Summicrons. At f2.0 indicated focus is at the back edge or just beyond the DOF, with the sharpest range shifting back as you describe while stopping down. Even so I don't see the impact in actual "live" pictures, just in careful tests.

[t024484]

I am curious as to the focus chart/test you are using

 

Also, is the focused spot within the DOF ?

 

This 100% crop was taken at f 2.0

 

Hans

 

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[ho_co]

I've never seen this chart. You photographed it with the camera vertical, right, focusing with the rangefinder spot on the heavy line at 0?

[farnz]

Superb 'Rising Sun' moire.

 

Pete.

[jaapv]

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A bit of a stress test, I would say. I struggle to find a situation where I would focus a 28 down to 90 cm at wide aperture in daily photographic practice.

[t024484]

A bit of a stress test, I would say. I struggle to find a situation where I would focus a 28 down to 90 cm at wide aperture in daily photographic practice.

 

So your advice would be, don't worry ?

B.t.w. the same ratio is visible at 4 meters distance. Spot on At f2,8 and 6 cm frontfocus at f2,0.

 

Hans

[t024484]

I've never seen this chart. You photographed it with the camera vertical, right, focusing with the rangefinder spot on the heavy line at 0?

 

Rangefinder on the heavy line, angle between testchart and camera 45 degree.

 

Hans

[IkarusJohn]

Here's mine showing 30 mm front focus at a similar distance (actually about 700 mm, as I couldn't see the chart otherwise).

 

I found no evidence of focus shift.

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Simply register for free here – We are always happy to welcome new members!

[jaapv]

So your advice would be, don't worry ?

B.t.w. the same ratio is visible at 4 meters distance. Spot on At f2,8 and 6 cm frontfocus at f2,0.

 

Hans

Well yes. You have demonstrated focus shift, probably normal for the lens. (I did not know this lens had it). Obviously you can have it optimized at your favorite aperture, but for general use I think this lens should be fine. 6 cm max @ 4 m? DOF is 2.68 meters @ 2.0... I don't think you would see that on a real photograph. Even at 90 cm DOF is 12 cm.

[ho_co]

Very interesting result, including the repeatability at greater distance.

 

If the lens behaves as you say, it sounds as if its focus is reasonably adjusted. But that seems to me to be quite a bit of focus shift in a lens that isn't known for focus shift.

 

In addition, according to E Puts, Leica lenses at open aperture are supposed to match the rangefinder.

 

I would ask Leica Technical Support whether, based on your description, the lens is behaving as expected.

 

I take it the line you're focusing on is approximately perpendicular to the long side of the frame? And I'm sure, since you're checking this lens this way, you've tested other lenses as well, and you're satisfied that your rangefinder is accurate?

[k-hawinkler]

I have just acquired a Summicron 28mm.

Since I have the right to return this lens within a week, I did some measurements to be sure everything is O.K.

To start with, Infinity seems to be O.K.

But measured with tripod from a distance of 90cm, without touching the distance setting in between, I have the following results.

 

f2.0 – 14mm front focus

f2.8 – spot on

f4.0 – 7 mm back focus

f5,6 – 14 mm back focus.

 

My question is, is this front/back focus shift within the tolerance for this specific lens, or is it far too much.

With my other Leica lenses, I have hardly any measurable focus shift when changing the diaphragm.

 

Hans

 

 

Hi Hans,

 

My 28mm Summicron-M ASPH shows a quite similar behavior.

Wide open front focus, then back focus.

Spot on halfway between f/2 and f/2.8.

I measured right at close focus distance.

 

However, the focus error divided by DoF appears to be at most about 0.1.

 

My 28 mm Elmarit-M ASPH is a little better.

 

Best, K-H.

[t024484]

Thank you all for the given responses to my question.

It seems that my findings have to do with the lensdesign, but on the other hand it does hardly harm in real life photography.

So I have decided to keep the lens.

One last positive remark on this lens: the rendering of this lens is one of the best I have ever seen with a Leica lens.

 

Hans

[t024484]

And I'm sure, since you're checking this lens this way, you've tested other lenses as well, and you're satisfied that your rangefinder is accurate?

 

Yes indeed, I have tested my all my other lenses. Starting with infinity and as a next step with this testchart.

All with perfect results, that is why I was a bit surprised to see a greater focus spread with the 28 mm Summicron.

But anyhow, it is a wonderful lens.

 

Hans

[t024484]

Here's mine showing 30 mm front focus at a similar distance (actually about 700 mm, as I couldn't see the chart otherwise).

 

I found no evidence of focus shift.

 

Did you focus from a tripod on the line "Focus here" with f2.0 and the result was 30 mm frontfocus ?

And after that you changed the diafragm to other values without touching the distance setting and the front focus remained at 30mm ?

 

Hans

[ho_co]

...

So I have decided to keep the lens.

One last positive remark on this lens: the rendering of this lens is one of the best I have ever seen with a Leica lens.

Keeping it sounds like the right choice.

 

I envy you.

 

 

 

Yes indeed, I have tested my all my other lenses. Starting with infinity and as a next step with this testchart....

Thanks, Hans. You seem to be a pretty thorough fellow. I just had to ask to be sure you had eliminated all the looks ends.

 

Again, congratulations on getting the lens. And thanks for a very interesting thread.

[Guest #12]

I have just acquired a Summicron 28mm.

Since I have the right to return this lens within a week, I did some measurements to be sure everything is O.K.

To start with, Infinity seems to be O.K.

But measured with tripod from a distance of 90cm, without touching the distance setting in between, I have the following results.

 

f2.0 – 14mm front focus

f2.8 – spot on

f4.0 – 7 mm back focus

f5,6 – 14 mm back focus.

 

My question is, is this front/back focus shift within the tolerance for this specific lens, or is it far too much.

With my other Leica lenses, I have hardly any measurable focus shift when changing the diaphragm.

 

Hans

 

Can I ask how you are reading the chart to get the 14mm? Thanks.

 

Did you make this chart?

 

I bought the same lens and it was front focusing to a similar degree. I did not think to check for focus shift. The lens went back to Leica NJ; meanwhile, I could not wait the 2 or 3 months it was taking to adjust the lens, so bought another. This copy was front focusing quite a bit more, so back to Leica for an additional 2 months. After the adjustment, the second lens was back to front focusing like the first lens.

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[t024484]

Can I ask how you are reading the chart to get the 14mm? Thanks.

 

Did you make this chart?

 

I bought the same lens and it was front focusing to a similar degree. I did not think to check for focus shift. The lens went back to Leica NJ; meanwhile, I could not wait the 2 or 3 months it was taking to adjust the lens, so bought another. This copy was front focusing quite a bit more, so back to Leica for an additional 2 months. After the adjustment, the second lens was back to front focusing like the first lens.

 

Sorry to hear that you had your share of focus problems. But at the end it must be one of the best lenses that Leica produces so I hope that the pictures you have made with the lens are amazing.

 

Number 30 on the posted image is about the point where the image is at it's sharpest.

This point happens to be 20 mm away from the intended focus point at 0.

Since the camera is looking under an angle of 45 degrees, the 20 mm on the chart are translating into sqrt(1/2)x20mm = 14 mm frontfocussing.

I did not make this chart, I just came across it somewhere in the past.

 

Hans

[thighslapper]

My 28/2 was all over the place .... infinity out as well.......

 

It's just back from Solms and I have yet to collect it.

 

I hope it will restore my faith in Leicas ability to adjust these lenses to the tolerances required on an M9 .....

 

So far I am not impressed .... all the second hand ones bar one I have are perfect .... and most of the new ones have enough errors to make them unreliable at wide apertures.... and as this is the main selling point for most of these lenses it makes it a bit of a joke to be honest.