How do I tell if a lens is coated?

[Colin D]

I've posted about my 305mm f4.5 Ross Xpres on here before but not about its coating. I assumed it wasn't coated but someone has posted one on fleabay, exact same lens, with lower serial number say it is coated.

Serial Number of my lens is 244752.

Link to competitors lens on fleabay is here: http://www.ebay.com.au/itm/ROSS-LONDON-XPRES-12INCH-305MM-f-4-5-FOR-SINAR-CAMBO-TOYO-FREE-SHIPP-330-/151007093140?pt=Camera_Lenses&hash=item2328b96194#ht_1574wt_1028

BTW, I am in the process of selling it to upgrade other equip't, this may make a difference.

Photos attached.

113149

113150

The very front element has a 3mm transparent mark I took to be a bubble on the outside of the glass, but I'm not so sure now. It is an oblong shape, if you run a finger over it there is a very fine even depth indentation, like a small piece of film has come off, is this an indication of coating?

[Colin D]

Just had a look under lights from the side, the front element reflection has a slight bluish tinge, the back element is greenish.

[goamules]

It's probably not factory coated, too old. Some lenses will get a "bloom" of color from atmospheric things, given enough decades. And some companies would coat older lenses, after the fact. But yours looks uncoated.

[Dan Fromm]

Garrett, on the one hand in the images posted the lens doesn't look coated. On the other, per P-H Pont's Ross chronology the lens dates from the late 1940s (the VM's chronology puts it closer to 1960) and the VM says that Ross started coating around 1946. In addition, in post #2 the OP reports what sounds like coating.

[goamules]

Good research. Well, it just may be an early single coating. Hard to tell from photos, and I didn't look up the serial numbers. Being brass, not black, I was assuming it was from the 1920s. But Cooke and maybe other British makers didn't always go "modern black" with their lenses.

[Colin D]

Thanks guys.

Garrett, the black paint has been removed by a previous owner, there are still traces of it in tight corners around the front ring.

[Steven Tribe]

I am a bit nervous about:


It is an oblong shape, if you run a finger over it there is a very fine even depth indentation

Now the finger is a very fine instrument, but we are talking about very, very thin coatings which should not be detected by this tactile method. Unless early coatings were different?

[Roger Hesketh]

In my, albeit limited experience, I have not handled that many Ross lenses. Just the small number I own. My experience is that if a Ross lens is coated. It as marked as such. With 'Ross Coated lenses' marked on the barrel. Could of course just be the ones I have.

[Colin D]

I am a bit nervous about:

Now the finger is a very fine instrument, but we are talking about very, very thin coatings which should not be detected by this tactile method. Unless early coatings were different?

Actually it was my fingernail, I dared not run a pin over it. I'm not talking in millimetres, it is micro fine and transparent. If it was a bubble I would have expected some rounding of the edge smoothing it out after the polishing process.