Spiratone Plura-coat Minitel 100mm F2?

[Velectron]

Hi everyone,

I came across this Spiratone lens marked as Spiratone Plura-coat Minitel 100mm F2. Couldn't find anything on the net on this lens.

Does anyone know anything about this lens? Not sure if this is a Sigma or Tokina-made lens. Filter diameter is 58mm.



Another one in different mount

[hifisapi]

[Attila]

Welcome, nice to see you here! Must be rare I never seen it, my guess is Tokina and excellent stopped down. If you have it already please share photos taken with this lens.

[Velectron]

Thanks for helping to make the pictures show up. I tried to upload instead of using direct links but it seems to screw thing up worse.

I do pay attention to Spiratone lenses but this is the first time I have seen this lens.

I do not have this lens yet but may be able to update in a month or so.

Cheers!

[hifisapi]

what is the lens mount? Pentax K?

[simbon4o]

photos with it?

[luisalegria]

It does look more like a Tokina than a Sigma, but it could be nearly anything.
In any case this thing is certainly uncommon in any brand.
I have never heard of a 3rd party late 1970's 100/2.

[Pancolart]

Interesting!

[stingOM]

Wow. That's a very uncommon looking lens.

It is however listed here:
www.jcolwell.ca/MM/listFocalLength.pdf

http://camera-wiki.org/wiki/Spiratone

[Velectron]

I just realised it could be related to the Soligor C/D 100mm F2, which is probably made by Tokina.

Same filter ring size and about the same size, but the DOF scale looks quite different. [edit: sorry for the mistake, the DOF scale are actually the same]

[Velectron]

Just an update.

I managed to grab both lenses and just got them today.

One is Canon FD and another one is Pentax K-mount. But unfortunately....both had haze inside, on the 3rd element from the front

Managed to clean up the Canon but the Pentax one cannot be saved. The coatings are degraded. Strange to have both lenses having haze in the exact same surface of the same element!

And behold, these two 100mm F2 are the exact same lens as my Soligor MC 100mm F2, as I had guessed earlier! Same design, same construction, same lens elements. Probably made by Tokina.

More to update later!

[dimitrygo]

[luisalegria]

Degraded coatings aren't a huge problem.
The effects of coatings are cumulative on all surfaces.
So is the effect of lack of coatings.
So if just one surface has a problem, out of perhaps 8 surfaces in a 4-group lens, I don't think it would have much effect.

[Velectron]

Here are the pictures of the 3 lenses. Sorry for the quick snapshots.


Soligor at bottom. Serial number starts with 279xxxx. Does this actually means this is made by Sun Optical in 1979 instead of Tokina as I had though earlier?


Soligor is at the extreme left

Some quick snapshots pics with NEX 5N and the lens with degraded coating.





Wide open until about F2.8, the lens is glowy. At F2.8 onwards, contrast and sharpness starts to improve significantly.

Regarding the lens formula, i can report that it consists of a total of 6 elements in 2 main groups. Front group consist of 4 elements - 2 separate front elements and a fused 2-element group in front of the diaphragm. Rear group consist of 2 elements fused together.

[luisalegria]

In the usual convention, your lens would be called 6 elements in 4 groups. A "group" would be any unit of glass, whether it is made of one, two or three cemented pieces.

This lens therefore, because it has four groups, has eight coated surfaces.
Which surface is bad, and in what way ?
Bad coating wont created a "glow" - which seems like typical spherical aberration, which should be expected on a lens with a simple formula but large aperture.
Bad coating may reduce contrast, but one out of eight should not be very noticeable.

[Velectron]

Yes I agree with you. The glow is not because of the damaged coatings but because of spherical aberrations. It is present in all 3 lenses.

The coating is damaged on the front surface of the 3rd group from the front, i.e., the 2 fused elements in front of the diaphragm. If you look through the lens, it looks a bit like fungus (pale, slightly whitish) but is not fungus. Not that obvious when viewed from front but more obvious when viewed from the rear.

[luisalegria]

Have you tried cleaning it ?

I can't tell from the picture, but it looks like the problem could be condensate deposits.
Its also possible that it is signs of separation.

You should be able to tell if you can open the lens and get to this surface.

[Velectron]

Yup, tried cleaning and polishing. Helped a little but not too much. Looks like some etching had took place.

Its on the outer surface, definitely not separation.