om zuiko 28/3.5 front element

[aeolist]

hi everyone

i was wondering if anybody else has noticed that the front element of the 28/3.5 (and for that matter of the 35/2.8 as well - and any other zuiko lens that has a "flat" front element instead of a concave one) can be removed. It is being held into place by a round piece of metal that screws into the body of the lens.

So I accidentically removed the front element and my question is... is there a right way to put it back in? Or not?

is the lens biconvex or planoconvex?
http://en.wikipedia.org/wiki/File:Lens2a.png

Looking through it from either side the image is magnified. If it is a plano convex lens, then aberrations will show if it's put the wrong way, like in http://folk.uio.no/walmann/Publications/Master/node8.html

I guess it should be biconvex, I mean how would they know how to assemble it, even in the factory, if it was a plano convex lens?

Thanks!

 

[Prest_400]

The lens seems to be planoconvex, with the flat side out. This is a diagram of the lens:
http://www.mir.com.my/rb/photograph...pusom1n2/shared/zuiko/images/28mmf35optic.gif

How to reassemble it, no idea. Ask John of camtech. He is registered in his forums and his site is zuiko.com. If he sees this thread, I'm sure he will reply and give a word about it.

 

[Xmas]

I thought it was a positive miniscus but dont have mine to hand, but the flattest side should be facing out. Dont think the other wides are like the f/3.5.

You probably need a pair of cotton gloves to gat it back without finger prints, and the glass is delicate, it is not window glass.

Please dont torque down the ring holding the element in - if the lens and the recess are both cleanof dust etc the lens will be ok afterwards, i you are worried anout vibration after you screw the ring back a small dab of nail varnish across the ring and lens metal body, will holod, use bright colour so you can remove if needed.

Dont take lenses apart again, you will be well sorry if you need to send it for repair or it is scrap. I.e. you will seal in dust, dont try a 2nd time you need a clean room to avoid the dust.

Noel

 

[aeolist]

thanks for the replies

i am not worried about introducing dust or vibrations. going to try and feel the lens again for the flat side

anyway, i'm trusting my gut (and hands) and decided that one of the sides feels flatter, so put that facing outwards

actually it's much easier to judge if you try both side on the metal ring, one side is a better fit i think.

if mr. john saw and replied to this thread, that would be lovely

 

[John Hermanson]

As others have said, it's best not to take elements out unless you have experience. If you are going to do it, open quickly, blow dust out, reassemble immediately. In this lens, curved side goes in. John

 

[aeolist]

well I didn't open it on purpose
the ring was wobbly and I rotated it the wrong way

and it generally does get wobbly after a few weeks of use, and then i have to screw it again - not much of a problem

the lens is only slightly curved, kind of a challenge to actually see the curve.

anyway i think it's ok now, thanks for all these replies! you guys are fast!

 

[Greg Campbell]

Hold the lens so as to reflect a bright light. Looking at the image of the light source, you should see positive or negative magnification on the non-plano surface.

Did any spacers fall out?

Hopefully you haven't been eaten pizza before handling the lens! Blow off any dirt with an air can or brush.
If you absolutely need to remove gunk, try breathing on the lens in a humid environment, and then wiping VERY gently with a scent-free kleenex type tissue. (Test the tissue first on a window, etc. to make sure it's not saturated with baby oil or some other junk.)

-Greg

 

[aeolist]

all is fine, thank you

so I'm holding the lens and look at the idol of the lamp, i get a yellow and a purple idol actually

on side A they are identical in size
on side B the purple one is smaller, the yellow one is blown up

so side A should be the one that faces outwards? and side B faces the innards of the lens, yeah?

well makes sense that a plano surface presents no magnification.

 

[John Koehrer]

Use a ruler or straight edge & set it on the surface. It should be apparent which is flat.

 

[aeolist]

good idea, unfortunately only in theory

rulers have dirt on them (argh!)
and I actually couldnt tell the difference between the 2 sides

going to stick with the bright light thing!