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View Full Version : Newton or rainbow rings on a 60cm Apo-Skopar?



Hugo Zhang
18-Jul-2006, 12:58
I have just bought a 60cm apo-skopar lens from an antique store from internet. It has rainbow rings on both front and back eleements. The rings on the rear are about 1/4" around the edge, the front ones cover almost 1/3 of the lens, pretty bad. I know this means lens seperation and I also know from what I read from here that this problem is common with this lens. I have never used lenses with seperations before. I bought this lens for my 10x20 banquet camera and wanted to use it in barrel and contact print only. My question is: Is this lens is usable? My instinct is to retrun the lens, but I think I will get some advice from those of you who know better. Thanks.

Arne Croell
18-Jul-2006, 13:32
I have just bought a 60cm apo-skopar lens from an antique store from internet. It has rainbow rings on both front and back eleements. The rings on the rear are about 1/4" around the edge, the front ones cover almost 1/3 of the lens, pretty bad. I know this means lens seperation and I also know from what I read from here that this problem is common with this lens. I have never used lenses with seperations before. I bought this lens for my 10x20 banquet camera and wanted to use it in barrel and contact print only. My question is: Is this lens is usable? My instinct is to retrun the lens, but I think I will get some advice from those of you who know better. Thanks.

It will be useable - there might be some extra flare due to the additional partial surfaces. The correction of the lens should not be affected, as the distance of the elements has only increased by a few hundred nanometers - as shown by the interference colors. Of course have an eye on the front element in case it decides to separate fully. I don't know what you paid, but the main effect might be on resale value, and the price should have been low.

Hugo Zhang
18-Jul-2006, 17:26
Arne,

Thank you so much for your reply. Here are two pictures of the lens. I paid $315 and the flange got damaged during the shipment. It seperated from the lens body and badly bent. What a pity!

Dan Fromm
18-Jul-2006, 17:55
Hugo, I'm sorry but those rainbows are Newton's rings and a classic manifestation of separation. I don't agree with Arne that they're harmless.

I have a Kodak 25-15 converter for my 25/1.4 Cine Ektar II that manifests the same rings. They're visible on my Beaulieu's ground glass and on film shot with lens plus converter.

I hope yours are harmless, but you'd best check. Hang the lens on a camera, focus it, and see how the image on the GG looks.

Regrets, good luck,

Dan

Arne Croell
18-Jul-2006, 23:28
Arne,

Thank you so much for your reply. Here are two pictures of the lens. I paid $315 and the flange got damaged during the shipment. It seperated from the lens body and badly bent. What a pity!
Hugo, I think that price was definitely too high given the degree of separation. An unseparated one would probably go for $600-800 on ebay as comparison. Flare would certainly be an issue given the area. Whether one can "see" the separation on film as in Dans experience, will probably depend on how close they are to the focus area. I have a 150mm Apo-Skopar which has separation in the front lens a little over 50% of the area, as well as an unseparated one, and couldn't detect any sharpness difference between them or an "image" of the separated area.

Emmanuel BIGLER
19-Jul-2006, 01:50
Agreed with Arne ; but Dan F. has extremely sharp eyes, he is able to see Newtons' rings very far from where they are supposed to be localized i.e. on glass... but depends on focusing distance and DOF of course;-)

Reminds me the Tintin story "The Shooting Star" where a spider is creeping across the entrance lens element of a telescope, Tintin is able to see sharp both the the spider on glass and the meteorite located at a few hundred thousand kilometers from Earth ! ;-);-)

Not kidding, too bad that the apo-skopar is supposed to be a heliar-type 5 elements / 3 groups, hence with cemented doublets, one in front and one at the back...

The problem of lens separation would not occur with a classical dialyte, apo-repro 4/4 design !!

Dan Fromm
19-Jul-2006, 04:40
Emmanuel, the 25-15 converter's rings act like a striped filter. The effect is striking and quite horrid. I wish it were invisible.

Cheers,

Dan

Steve Hamley
19-Jul-2006, 07:42
Hugo,

Maybe not too high a price although I'd certainly ask for some compensation. BTW, I have a 30cm Apo-Skopar with the same problem.

Anyway, John Van Stelton at Focal Point will recement at $180 per "joint", so you'd be looking at $360 more to get the lens fixed with a proper cement. That would put you "into" the lens at about $675 which is in the range Arne mentioned.

Steve

Hugo Zhang
19-Jul-2006, 08:19
Steve,

"Anyway, John Van Stelton at Focal Point will recement at $180 per "joint", so you'd be looking at $360 more to get the lens fixed with a proper cement. That would put you "into" the lens at about $675 which is in the range Arne mentioned."

Thanks. I know John. He fixed the Newton's rings on my Trigor for $700. Quality job and expensive.

I will see if I can put it on a lensboard to see the picture on the ground glass. I don't know if I can find a board with the exact hole for it. I have a 24" RD Artar in shutter. I really don't "need" this lens. I will see what I will do with it in the next few days.

Steve Hamley
19-Jul-2006, 10:01
Hugo,

Yeah, I have a recementing job on a Dagor cell and a recoating on a Heliar surface that my wallet isn't looking forward to.

And $600+ is a bit steep for a barrel lens unless it's otherwise pretty much perfect and it has some image quality or characteristic you want. You'd have to compare (financially) another $700 for shutter mounting ($1,300 total) against a new Fuji 600C in a shutter with standard filter threads or a really nice used 24" Artar in shutter for about the same price.

Steve