English is not my native language either, but I have managed to write a tutorial on this matter in English. I don't know if you have seen it yet.

My guess is that you have not made your font align and snap to a grid in Illustrator that is compatible with FontLab. If you don't do that your glyphs will be distorted when you copy it over bacause FontLab will snap every node to it's grid.

The article is here: http://font.is/?p=48

Good luck.

Thanks for your reply siguram. :)

I probably didn't express the problem clearly enough, sorry for that.
The issue is present ONLY in the screen and ONLY in small sizes (below 12pt).
In print (at any size) or in large sizes on screen it displays fine.
Also I have taken care of the alignment and the glyphs were not distorted as I copied them at a really large size (I read in a tutorial that the bigger the size of the glyph in AI, the less the distortion at FontLab and it actually worked)
So its probably not an alignment or distortion issue. Its something else I have no idea about (like hinting for instance, or some setting I guess)

Yes, it's because of hinting. If you want typefaces to look really good on screen at very small sizes, you will probably have to hint them manually.

Hi Quincunx. Thanks a lot for your reply.
Do you know of any comprehensive article/tutorial on hinting?
I tried to read FontLab's manual about it but it seemed quite confusing :/

If things are not aligning vertically at lower resolution, the usual cause is missing or incorrect alignment zones. These are horizontal regions placed (usually) near the baseline, cap height, x-height, ascender height and descender height (negative, below the baseline). Typically, the zones should enclose any points above or below these places that should align at low resolution. For example, if you have an alignment zone near the baseline, any points that are off the baseline but inside the alignment zone will "snap" to the baseline at lower resolutions. An alignment zone works sort of like the "snap to" distance in drawing programs.

You can create alignment zones manually or have FontLab create them for you (using the little green gem icon button) in the Font Info dialog box under Hinting Settings.

Read up on hinting in the Fontlab manual. Then install the awesome AFDKO and use the Adobe auto-hinter to make your fonts look fab onscreen.

Note: Even if you use the Adobe auto-hinter, you'll need to make alignment zones.

Thank you all, you are great!

I'll look into the alignment zones thing and if I get in trouble I'll ask you.
I have a strong feeling that this will solve my problem.

Does anyone know anything about the second problem I mentioned with Illustrator and ligatures?

Can you post the code for your liga feature?

Sure, here it is:

feature liga {
sub e s s by e_s_s;
sub f f i by f_f_i;
sub f f by f_f;
sub f r by f_r;
sub e s by e_s;
sub s s by s_s;
sub kappa lambda by kappa_lambda;
} liga;

and while we're at it, any idea why the last one isn't working (its the only greek ligature)?
That last question isn't very important, so feel free to ignore it if its not simple.

Thanks again!

Strange. It looks like it should work (although I haven't had any experience with Greek, so I have no clue about the last question). Not necessarily relevant, but I find it odd that you have a ff and ffi ligature, but not a fi ligature.

What do your languagesystem statements look like? For a good example see Miguel's post here.

@Mark: I'm planning to create an fi ligature as well. In general, I plan to add lots more ligatures when I solve the other issues I have with the font, as I love them :P

By the way, the Illustrator ligature problem was present before I added the greek ligature, so its not because of it.

@k.l.: Whoa that looked quite confusing but I'll study it in more depth when I find more time, it seems helpful. Thanks.

By the way, I tried to add alignment zones, I even made the one at the x-height very loose (602-650 when my font's x-height is 626) but it doesn't seem to work at all :(
Also, I tried to define a standard stem for hinting (as my font only consists of 1 stem width) but I still get issues with some thicker stems in small characters (I guess that's because the standard stem setting is for Type 1 and not TT? Is there something similar for TT?). However the alignment zones issue is more important, as the stem width problem occurs only on a small amount of glyphs, so I could solve it with manually hinting them I guess.
This issue is driving me nuts :'(

Thank you all again, I would be desperate if I hadn't found this forum. :)

YES, YES, YESSSS!!!!!
I finally managed to get aligmnent zones to work!!!!
I think I had been setting Type 1 zones instead of TT zones previously, and this is probably why they didn't work.

Also, the AI ligature problem is mysteriously solved, so it probably was a one-time thing. :D

Just thought I'd share my happiness with you :D

I have lots of problems to resolve still (stem widths, unicode ligatures) but these were the most annoying ones and they are finally SOOOOLVED! :D

By the way, the greek ligatures problem was solved when I added language EL; before the greek ligatures. :)