Old lenses only sharp in the centre?

[ffureel]

Ok now I have your attention.

I have a helios 40... Only sharp in the very centre at f/1.5, no surprise, and I like it.

How about the flektogon 35mm 2.4? I am wondering what the general performance of this lens is?

my one is only really sharp in the centre maybe 50%, at all apertures. Is this lens supposed the be sharp corner to corner?

[peterqd]

I think there must be something wrong with your lens. This was taken with the Flek 2.4/35


[edit: better example]

[Orio]

Unfortunately the Flek 2.4/35 depends much from copy variations.

A good copy should have good corners, except wide open where corners are a little weak - I am speaking of full frame camera, on an APS-C camera you should not notice that.

If your copy has poor corners at all apertures, then it is an unlucky copy, I am afraid.

Would you like to post samples with 100% crops of the corners? Of course that would help us in giving an opinion.

[peterqd]

Yes, but even a poor copy would improve as the aperture is closed wouldn't it? Does it look like the lens may have been dismantled? (e.g. paint missing from screwslots etc)

[Orio]

[Orio]

I wanted to add, about the very subject, take a look at the corners of the Canon L wide zooms (those costing many hundreds, or even a thousand), you will see that bad corners are not exclusive "quality" of old lenses

[ffureel]

Ok here is the full image, resized so you can still see what is going on. No need for 100% crops as you can see what is going on. This is shot on 5d, flek at 2.8. Lens it self looks in good condition, may have been took apart carefully. Who knows.

[ffureel]

The forum board made the file smaller than I intended. Though, it is not even the corners, if you look at the edges too. On the plane of focus, sharpness drops off really quick from the centre.

[Orio]

Very bad copy, no doubt about it.
I'm sorry

You can resell it (but you will get little money because of the fault), or, you can give it to a lens laboratory for fixing, but with the risk that you might have to spend money and they may not be able to fix the problem satisfactorily.

Unless you know a very good and trusted lens doctor, I suggest to sell the copy and add the little money that you get from it, to another money, and buy another copy of the lens, preferably from a trusted seller like Attila.

[maddog10]

Here is a full frame version (resized for web) from the copy I got from Attila. This is stopped down a step or two.

[ffureel]

Really, oh man.

I have been using it for a good while. I guess it helps that I do not shoot landscapes or anything that really requires more than just the centre in sharpness.

What would the problem be? Any chance I could take it apart and fiddle with some screws?

I mean this is from the same lens, and in this example looks good.

[Orio]

It most probably is a glass misalignment.
If you are not sure, make more tests, set the camera on a tripod, focus to infinite and make 3-4 shots at different apertures, then focus on a near subject and make again 34 shots at the same apertures than before.

[estudleon]

[quote="Orio"][quote="peterqd"]Yes, but even a poor copy would improve as the aperture is closed wouldn't it? Does it look like the lens may have been dismantled? (e.g. paint missing from screwslots etc)[/quote]

A really poor copy would not. I had a terrible Flek 2.8/20, it was muddy in the corners even at f/8.
Corners became acceptable only at f/11 but then the centre would start to lose detail due to refraction.
Needless to say I sold it immediately.
It is really a matter of good or bad luck with Fleks, especially the most recent ones (black barrel with orange writings) have lots of copy variance.
My current copy of Flek 2.8/20 is excellent (although I still prefer the 4/20)
Older Fleks (pre-zebra) seem to be the best, I have five 4/20 (one orange, two zebras, one leatherette, one with bumps), and the best one is the oldest one (with the bumps).[/quote]


Orio, I agree with you.

I have an old 20/4 Flekt. (no. 6.893.021) leatherette with fungus in the interior surface of the external lens, with billions of lines in the external surface - back lenses OK., and is sharp at F/11 and 16, may be F/8 too - corners so-so at F/8.
My wife had a 20/4 too, a zebra ones, and mine match her lens.

[peterqd]

[zewrak]

[ChrisLilley]

[Nesster]

Yes, you can always sell it as a super Lensbaby

It does seem like an element is out of its place or reversed.

[lauge]

...or bad case of fungus? Does it look clean when you look throu it?

[estudleon]

[quote="Nesster"]Yes, you can always sell it as a super Lensbaby

It does seem like an element is out of its place or reversed.[/quote]


I agree, but looking carefully the pics I chose the thesis that the element/s are reversed. If the element/s were out of place, not sharp focus in the center is possible. And if we name the misaligned element as "out of place", one border have to be sharp (or near it) and the other in front of the first border have to be more or minus in focus but not in the same way, depend of the + o - differences that the misaligned cause in the position of the element.

[ffureel]

So from the analysis I will assume a reversed element? it is sharp in the centre yes and the edges are equally blurry on all sides. There is no fungus, well what does fungus look like? Though I can definitely see the internal optics are really clear.

I have a suspicion that the lens is worse than when i got it. I can not be sure though. I never noticed this before. Then again i normally never take photos where I have everything on the plane of focus from right to left. Normally have a face perhaps in the middle, the rest is normally background blur.

What is the best way to test a lens sharpness? I will do that and post the results, the brick wall should probably work.

I really take care of my stuff, so the lens never gets knocked or anything. So how has this happened?
Are there any instructions on taking apart this lens, is it easy? Will i clearly be able to see a reversed element or anything?

[peterqd]

ffureel - below is a link to a site showing how to dismantle this lens. Compared to some others this one is not too difficult, but you need to be very careful, patient and methodical. There are tiny springs, screws and ball-bearings that want to jump out and across the room unless you're careful. I can't emphasise enough how important it is to put a cloth on the worktop to stop things rolling and bouncing. And get the right tools before you start - you'll need a set of jeweller's screwdrivers, a rubber grip for the front bezel ring (if necessary) and, in your case, a lens ring spanner.

Wear a pair of tight rubber gloves while you're working, and have a P&S camera, a notepad and pencil handy for taking notes and drawing sketches so you can see how to reassemble it.

You'll also need a diagram of the lens showing the curvature on each face of the different elements, so you can check if one has been put in the wrong way round. CZJ lenses often suffer from sticky aperture blades and I wouldn't be surprised if somebody has already opened this lens to clean them.

Good luck!

CZJ Flek 2.4/35 disassembly instructions

[ffureel]

Thankyou, I will give it a go.

Where can I find a lens diagram for the lens?

[Nesster]

I'd suspect the rear element first by the way, given the sample photos.

Try shooting a flat surface, a rough wall for example, to see how badly the edges go wack.

[ffureel]

Thanks,
Got it open.

And found this.
http://www.praktica-users.com/lens/mlenses/czjflek2.4_35.html

Now, is the first piece of glass and the third one at the back. Does it matter what way round they go? They look symettrical? Or is it slightly off?

[ffureel]

Took it apart, and got it all back together. Was fairly easy actually. From looking at the diagrams etc, all the elements were in the correct way round. I was not sure about the 1st and 3rdfrom the rear as they look symmetrical. Tried an experiment, flipping them over to see if any differences occured. the 3rd element could only be fitted one way around. And the very last element made very little if any difference either way around.

The only one thing I noticed is that the holder screw ring, that tightens down the 3rd element from the rear was loose. By a few turns. So am assuming that could have affected the results. I will post before and after crops.

It is shaper now, though still think it is pretty soft at the edges. Though I have little experience with these lenses, so have nothing to compare to.

Thing is, will I have to do this for every lens I buy? How will i know everything is properly aligned and tightened if I do not check? To be honest I am not going to check other lenses unless i feel something is wrong.

100% crop. Raw, no sharpening etc. Verdict?

f/2.4 before. centre

f/2.4 after. centre

f/4 before. centre

f/4 after. centre

f/2.4 before. right edge

f/2.4 after. right edge

f/4 before. right edge

f/4 after. right edge