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Objective Thread Corrosion
Posted: Sun Oct 10, 2021 10:41 am
by LouiseScot
Can anyone suggest what the likely cause of this apparent corrosion or wear on the end of an objective thread might be due to?
- PlanFluorImg.JPG (16.94 KiB) Viewed 3964 times
Thanks for any ideas!
Louise
Re: Objective Thread Corrosion
Posted: Sun Oct 10, 2021 12:08 pm
by Hobbyst46
Just had a look at a very similar 40X Nikon objective. The blunt end surface (top surface when the objective is vertically held with the front lens down) is blackened. I believe it is blackened brass. So the black coating might have spilled to the rim, and formed a ring of width <0.5mm, and not very uniform. In other words, perhaps what you see is not corrosion, but either marginal black coating - or maybe peeled off coating ?
BTW, I have noticed that the color marks on the objective barrel (color code ring, printed specs etc) are easily removed with organic solvents. Yet another score in favor of Ye Olde engraved barrels of objectives from decades ago...
Re: Objective Thread Corrosion
Posted: Sun Oct 10, 2021 2:07 pm
by LouiseScot
Hobbyst46 wrote: ↑Sun Oct 10, 2021 12:08 pm
Just had a look at a very similar 40X Nikon objective. The blunt end surface (top surface when the objective is vertically held with the front lens down) is blackened. I believe it is blackened brass. So the black coating might have spilled to the rim, and formed a ring of width <0.5mm, and not very uniform. In other words, perhaps what you see is not corrosion, but either marginal black coating - or maybe peeled off coating ?
BTW, I have noticed that the color marks on the objective barrel (color code ring, printed specs etc) are easily removed with organic solvents. Yet another score in favor of Ye Olde engraved barrels of objectives from decades ago...
Thanks - I was wondering what likely caused the problem as I'd say it was actual damage of some sort. It's a Nikon CFI60 plan fluor. I was thinking of buying it (Ebay) but the seller is offering it for less than a CFI 20x plan achro he has. So was a bit suspicious, though it otherwise looks ok.
Here's another view:
- PlanFluorImg2.JPG (23.83 KiB) Viewed 3933 times
Louise
Re: Objective Thread Corrosion
Posted: Sun Oct 10, 2021 2:20 pm
by Hobbyst46
Ah OK - the objective I held in my hand is indeed a Plan Fluor 40x0.75 infinity /0.17 DIC.
Its top blunt metal surface is jet black.
Although I know little about Nikon in general, I believe that 40X0.75 objectives are ubiquitous, so should cost less (on the average) than 20x of the same set.
And the 60x dry is less useful than both. Just my personal opinion.
Re: Objective Thread Corrosion
Posted: Sun Oct 10, 2021 3:28 pm
by LouiseScot
Hobbyst46 wrote: ↑Sun Oct 10, 2021 2:20 pm
Ah OK - the objective I held in my hand is indeed a Plan Fluor 40x0.75 infinity /0.17 DIC.
Its top blunt metal surface is jet black.
Although I know little about Nikon in general, I believe that 40X0.75 objectives are ubiquitous, so should cost less (on the average) than 20x of the same set.
And the 60x dry is less useful than both. Just my personal opinion.
Hmm... the CFI60 Plan Fluors don't seem to be that common. I've seen a couple for sale in the States but they are quite a bit more expensive than this one.
Here is top view with some contrast enhancement:
- PlanFluorImg3.JPG (24.92 KiB) Viewed 3917 times
There looks to be some liquid around the circumference of the lens? Maybe oil?
I'll ask the seller but he'll probably just say it's 'as seen' - it's been up for sale for a while now.
Thanks
Louise
Re: Objective Thread Corrosion
Posted: Sun Oct 10, 2021 3:45 pm
by Scarodactyl
Looking at the original those appear to be jpeg artifacts around the inmer surface of the lens.
Re: Objective Thread Corrosion
Posted: Sun Oct 10, 2021 4:07 pm
by LouiseScot
Scarodactyl wrote: ↑Sun Oct 10, 2021 3:45 pm
Looking at the original those appear to be jpeg artifacts around the inmer surface of the lens.
Maybe, but I'm not convinced! I think I've now convinced myself there must be something wrong with it! Otherwise, why is it still for sale? (even discounted a little). I've asked the seller if it's oil so will see what he says!
Louise
Re: Objective Thread Corrosion
Posted: Sun Oct 10, 2021 4:38 pm
by PeteM
I'd be suspicious of the front element as well, perhaps oil intrusion or some other defect. However, if it is listed as "used" on eBay and ends up cloudy you should be able to return it.
One possible cause of the darker area at the very end is atmospheric corrosion, much as happens over time with copper and brass. If the lens is mounted in a turret, the brass in the threaded parts is relatively protected. The bit sticking through at the end, not so much. The apparent problem at the front may not be related to the bit of blackening at the back.
Re: Objective Thread Corrosion
Posted: Sun Oct 10, 2021 5:09 pm
by LouiseScot
PeteM wrote: ↑Sun Oct 10, 2021 4:38 pm
I'd be suspicious of the front element as well, perhaps oil intrusion or some other defect. However, if it is listed as "used" on eBay and ends up cloudy you should be able to return it.
One possible cause of the darker area at the very end is atmospheric corrosion, much as happens over time with copper and brass. If the lens is mounted in a turret, the brass in the threaded parts is relatively protected. The bit sticking through at the end, not so much. The apparent problem at the front may not be related to the bit of blackening at the back.
I'll wait and see what the seller says. The corrosion could be linked to high humidity: it's from Japan so I think the summers there are quite humid. Mind you, I've bought several other objectives from Japan with no problem. Sometimes objectives are used in inverted microscopes so that might be a factor if it's been frequently and erroneously used with oil.
Louise
Re: Objective Thread Corrosion
Posted: Sun Oct 10, 2021 8:20 pm
by Hobbyst46
AFAIK corroded copper/brass is blue or turquoise. Not black.
Re: Objective Thread Corrosion
Posted: Sun Oct 10, 2021 10:11 pm
by LouiseScot
Hobbyst46 wrote: ↑Sun Oct 10, 2021 8:20 pm
AFAIK corroded copper/brass is blue or turquoise. Not black.
It might be from Fukushima!
Re: Objective Thread Corrosion
Posted: Tue Oct 12, 2021 12:51 pm
by LouiseScot
Oh well, I hummed and I harred and in the end I pressed the buy button! My previous experiences of buying from Japan have been positive. Fingers crossed! Hopefully, I should get it by the end of the month
Hope I can get away without paying any import charges
Still, if it's ok, it should be better quality than the equivalent Amscope one.
Probably the price of second hand objectives, and everything else, will be going up up up from now
Louise
Re: Objective Thread Corrosion
Posted: Thu Oct 14, 2021 9:15 am
by LouiseScot
LouiseScot wrote: ↑Tue Oct 12, 2021 12:51 pm
Oh well, I hummed and I harred and in the end I pressed the buy button! My previous experiences of buying from Japan have been positive. Fingers crossed! Hopefully, I should get it by the end of the month
Hope I can get away without paying any import charges
Alas, it's been shipped by DHL who have billed me £78 for VAT - boo
Re: Objective Thread Corrosion
Posted: Mon Oct 18, 2021 10:56 am
by LouiseScot
I received the 40x Plan Fluor today! The objective seems ok. However, looking through it by naked eye, I can see the same aberrations around the lens rim as in the photo. So not a jpeg artefact. I'm hoping it's of no consequence but won't know for sure until I get around to using it in anger. Looking through it via an eyepiece, it seems ok.
Louise
Re: Objective Thread Corrosion
Posted: Mon Oct 18, 2021 11:11 am
by viktor j nilsson
Would be interesting to see better photos of these defects! I don't think I am alone in spending quite a bit of time trying to figure out what objectives really look like based on crappy photos from online auctions. So I would be very interested in learning what the defects seen in the photo above really are.
Re: Objective Thread Corrosion
Posted: Mon Oct 18, 2021 11:54 am
by LouiseScot
viktor j nilsson wrote: ↑Mon Oct 18, 2021 11:11 am
Would be interesting to see better photos of these defects! I don't think I am alone in spending quite a bit of time trying to figure out what objectives really look like based on crappy photos from online auctions. So I would be very interested in learning what the defects seen in the photo above really are.
I'll try and take some images through it, and of it, a bit later. The 'corrosion' doesn't seem to be anything to worry about but it's hard to say what actually is the cause of the dark edge. A microscope objective expert would probably know!
Louise
Re: Objective Thread Corrosion
Posted: Mon Oct 18, 2021 3:34 pm
by Hobbyst46
Of more concern IMHO is the periphery of the glass.
Re: Objective Thread Corrosion
Posted: Mon Oct 18, 2021 5:16 pm
by LouiseScot
Hobbyst46 wrote: ↑Mon Oct 18, 2021 3:34 pm
Of more concern IMHO is the periphery of the glass.
I'll try it out tomorrow - not quite managed it today (where does all the time go?!). I've made a holder for it to use it on my rail setup. Although I could see exactly what is in the image above looking through it, I couldn't see the apparent aberrations when using a lens without. But I'll have to try it out properly.
Louise