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Very soft corners on Flektogon 25mm f/4
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PostPosted: Thu Jun 29, 2017 3:10 pm    Post subject: Very soft corners on Flektogon 25mm f/4 Reply with quote
Hi!
This is my first post. I love this forum, I love manual lenses both on digital and film. Smile

I currently own a mint Flektogon 25mm f/4, marked as "Aus Jena" for export. I am using it on a Sony a6000 with a Roxsen Speed Booster (a clone of the Mitakon Lens Turbo) MD-NEX with a MD-M42 ring: I noticed that at all apertures the borders and the corners are... soft...? No, almost bokeh! If I stop at f/11-16 the corners do have some improvement, but nothing to say about. This is pretty strange, because I have others 24mm and 28mm which are pretty sharp on the focal reducer. In addition, I had the possibility to try a Flektogon 20mm f/4 Zebra on my camera for a week: it performs very very very very better on my Speed Booster than the Flektogon 25/4.
Ok. That's my question: is this a normal behavior of the Flektogon 25/4 of my copy has some problem?

P.S. sorry for my English, I am Italian and I am not very fluent in that language Wink

This shot is taken at f/5.6:



This is a crop of the previous one:



PostPosted: Thu Jun 29, 2017 3:57 pm    Post subject: Re: Very soft corners on Flektogon 25mm f/4 Reply with quote
Aiez wrote:
Hi!
This is my first post. I love this forum, I love manual lenses both on digital and film. Smile

I currently own a mint Flektogon 25mm f/4, marked as "Aus Jena" for export. I am using it on a Sony a6000 with a Roxsen Speed Booster (a clone of the Mitakon Lens Turbo) MD-NEX with a MD-M42 ring: I noticed that at all apertures the borders and the corners are... soft...? No, almost bokeh! If I stop at f/11-16 the corners do have some improvement, but nothing to say about. This is pretty strange, because I have others 24mm and 28mm which are pretty sharp on the focal reducer. In addition, I had the possibility to try a Flektogon 20mm f/4 Zebra on my camera for a week: it performs very very very very better on my Speed Booster than the Flektogon 25/4.
Ok. That's my question: is this a normal behavior of the Flektogon 25/4 of my copy has some problem?

P.S. sorry for my English, I am Italian and I am not very fluent in that language Wink

This shot is taken at f/5.6:



This is a crop of the previous one:



PostPosted: Thu Jun 29, 2017 4:38 pm    Post subject: Re: Very soft corners on Flektogon 25mm f/4 Reply with quote
Aiez wrote:
Hi!
This is my first post. I love this forum, I love manual lenses both on digital and film. Smile

I currently own a mint Flektogon 25mm f/4, marked as "Aus Jena" for export. I am using it on a Sony a6000 with a Roxsen Speed Booster (a clone of the Mitakon Lens Turbo) MD-NEX with a MD-M42 ring: I noticed that at all apertures the borders and the corners are... soft...? No, almost bokeh! If I stop at f/11-16 the corners do have some improvement, but nothing to say about. This is pretty strange, because I have others 24mm and 28mm which are pretty sharp on the focal reducer. In addition, I had the possibility to try a Flektogon 20mm f/4 Zebra on my camera for a week: it performs very very very very better on my Speed Booster than the Flektogon 25/4.
Ok. That's my question: is this a normal behavior of the Flektogon 25/4 of my copy has some problem?

P.S. sorry for my English, I am Italian and I am not very fluent in that language Wink

This shot is taken at f/5.6:


Welcome to the forum!

I see nothing wrong with the photo. The other ship is too far away, you need to fill out the frame with a subject where everything is in the plane of focus. To be unoriginal, a brick wall photo for example will show you if something is wrong.


PostPosted: Thu Jun 29, 2017 4:56 pm    Post subject: Reply with quote
A 20mm would have much deeper depth of field than a 25mm, that might explain it.

Its possible also that the speed booster increases field curvature, but all else being equal this would be less apparent at shorter focal lengths.

As blotafton says, the best objective test is the old brick wall.

But photography isn't all about being objective. Your results are truly judged by subjective standards.
If it looks good anyway, in spite of flaws, its good.


PostPosted: Thu Jun 29, 2017 7:01 pm    Post subject: Reply with quote
the speed booster ruins the corners in the shoots. try without it.
I got one a year ago and make the same soft corners ( the left more than the right in fact ) so i sell it


PostPosted: Thu Jun 29, 2017 7:43 pm    Post subject: Reply with quote
I agree your focus is on the boat in front. Notice that the sidewalk is sharp. Focus acuity drops the further back in the photo you go. Do you have other examples?


PostPosted: Fri Jun 30, 2017 7:21 am    Post subject: Reply with quote
Quote:
Its possible also that the speed booster increases field curvature, but all else being equal this would be less apparent at shorter focal lengths.


This is absolutely true, I noticed that behavior with other lenses too.

Quote:
But photography isn't all about being objective. Your results are truly judged by subjective standards.
If it looks good anyway, in spite of flaws, its good.


And that's also a wise thought, I am in fact happy with my Flektogon, for reportage work: it's just perfect for street photography and live music stuff. But sometimes I shoot some landscapes or architecture and I am not happy with that Wink

And now, some other pictures: I can't find any brick walls here in my city (yeah, Trieste is pretty strange), but I photographed the beautiful view from my apartment, which is perfectly flat Laughing

You'll see that it is sharper on the right side than the left side, which is pretty strange: my others wide-angle lenses are equally sharp on both sides...

F/4


F/5.6

[url=http://forum.mflenses.com/userpix/20176/big_10267__DSC1896_1_1.jpg]
[/url]
F/8

[url=http://forum.mflenses.com/userpix/20176/big_10267__DSC1897_1_1.jpg]
[/url]
F/11


F/16



PostPosted: Fri Jun 30, 2017 9:50 am    Post subject: Reply with quote
Some misalignment true. Quite common i think. Try using it in your favor (it looks very nice on first seaside sample).


PostPosted: Fri Jun 30, 2017 9:53 am    Post subject: Reply with quote
Aiez wrote:
Quote:
Its possible also that the speed booster increases field curvature, but all else being equal this would be less apparent at shorter focal lengths.


This is absolutely true, I noticed that behavior with other lenses too.

Quote:
But photography isn't all about being objective. Your results are truly judged by subjective standards.
If it looks good anyway, in spite of flaws, its good.


And that's also a wise thought, I am in fact happy with my Flektogon, for reportage work: it's just perfect for street photography and live music stuff. But sometimes I shoot some landscapes or architecture and I am not happy with that Wink

And now, some other pictures: I can't find any brick walls here in my city (yeah, Trieste is pretty strange), but I photographed the beautiful view from my apartment, which is perfectly flat Laughing

You'll see that it is sharper on the right side than the left side, which is pretty strange: my others wide-angle lenses are equally sharp on both sides...



If these images are taken without the speed booster the most likely explanation is that your Flektogon is decentered. The other answer is that the adapter is poorly made. Then the left side would be soft with every lens mounted on the adapter/speed booster.

I have many lenses with this issue. Zooms are more likely to have it. Probably because of the higher number of lens elements, but prime lenses can also suffer from decentering.

One of my worst offenders is a Vivitar 35-85mm f/2.8.

The best way to deal with it is to find a better copy.


PostPosted: Fri Jun 30, 2017 10:29 am    Post subject: Reply with quote
blotafton wrote:
Aiez wrote:
Quote:
Its possible also that the speed booster increases field curvature, but all else being equal this would be less apparent at shorter focal lengths.


This is absolutely true, I noticed that behavior with other lenses too.

Quote:
But photography isn't all about being objective. Your results are truly judged by subjective standards.
If it looks good anyway, in spite of flaws, its good.


And that's also a wise thought, I am in fact happy with my Flektogon, for reportage work: it's just perfect for street photography and live music stuff. But sometimes I shoot some landscapes or architecture and I am not happy with that Wink

And now, some other pictures: I can't find any brick walls here in my city (yeah, Trieste is pretty strange), but I photographed the beautiful view from my apartment, which is perfectly flat Laughing

You'll see that it is sharper on the right side than the left side, which is pretty strange: my others wide-angle lenses are equally sharp on both sides...



If these images are taken without the speed booster the most likely explanation is that your Flektogon is decentered. The other answer is that the adapter is poorly made. Then the left side would be soft with every lens mounted on the adapter/speed booster.

I have many lenses with this issue. Zooms are more likely to have it. Probably because of the higher number of lens elements, but prime lenses can also suffer from decentering.

One of my worst offenders is a Vivitar 35-85mm f/2.8.

The best way to deal with it is to find a better copy.


Ok, thank you very much! Wink

The Speed Booster seems to be ok, it works just perfect with other glasses. So it must be the Flekty... Here in my city there is a man which is very very skilled in repairing vintage lenses, he has a terrific shop where it has tons of old lenses! Maybe he can fix my Flektogon or it is not worth repairing?


PostPosted: Fri Jun 30, 2017 12:00 pm    Post subject: Reply with quote
Aiez wrote:
And now, some other pictures: I can't find any brick walls here in my city (yeah, Trieste is pretty strange), but I photographed the beautiful view from my apartment, which is perfectly flat


So you're from Triest, the most important city on earth for coffee lovers? Beautiful city. I like it very much and additional I like Hausbrandt, Illy, etc...

Sorry, I can't help you really with your problem. Generally the mechanical quality of such old GDR lenses is rather mediocre and I don't know whether it's worth to try to repair it.

Cheers,


PostPosted: Fri Jun 30, 2017 12:04 pm    Post subject: Reply with quote
A 25mm Flektogon is definitely worth repairing, they are not all that common and in good working order are very good lenses.


PostPosted: Sun Jul 02, 2017 12:00 pm    Post subject: Reply with quote
That fact that one corner is a bit softer than another could mean lens was disassembled before (for cleaning etc). And rear lens element could be located at wrong position. That's why you have such issue. The best way is to adjust It with collimator at the professional store.
Unfortunately It's quite common situation after dismantling the lens. I saw the same thing on Flektogon 4/20 and 2.8/20 lenses. You can try to resolve it yourself, but best way is to find good service.


PostPosted: Sun Jul 02, 2017 11:00 pm    Post subject: Reply with quote
My adviice? Professional service recommended for this lens. My criteria? Can I buy a better example on ebay for less than the service? Can I do it myself at minimal financial or time risk? If both answers are no, I pay the guys that know what they are doing. In some ways you are lucky. Very few top quality, and certainly no inexpensive options for lens repair in the part of the world I reside.
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