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kypfer
Joined: 27 Sep 2017 Posts: 514 Location: Jersey C.I.
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Posted: Tue Aug 28, 2018 7:00 am Post subject: Optomax 300mm f/5.6 |
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kypfer wrote:
I picked up this T2-mount lens this morning for £1, so no great loss if it can't be fixed, but if possible I'd like to separate the rear lens group as there's haze/fogging between the elements.
I've figured out that the rear end of the lens assembly unscrews behind the aperture, so I can get at both sides of the rear group, but there doesn't appear to be any slots or other means of unscrewing the internal lenses.
The aperture has 13 blades, so it might be a nice lens to use on occasion, but at the moment it's just a little too soft
I realise there should be a tripod mount, but for the price I couldn't really complain
Any help would be gratefully received
Last edited by kypfer on Fri Sep 14, 2018 10:02 pm; edited 1 time in total |
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SkedAddled
Joined: 19 Oct 2008 Posts: 1426 Location: Michigan, USA
Expire: 2021-08-12
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Posted: Tue Aug 28, 2018 7:49 pm Post subject: |
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SkedAddled wrote:
It'll be easy enough to clamp a tripod-mount ring on it,
Can't offer anything on disassembly though, sorry. _________________ Craig
Of course I'm all right! Why? What have you heard!?
Canon Digital EOS 5D Mk IV, EOS 50D, Powershot S3 iS
Vivitar 28 f/2.8 OM - Zuiko 50 f/1.8 OM - Tamron SP 28-80 f/3.5 AD2[Favorite!] - Hanimar 135 f/3.5 M42 - Soligor 135 f/2.8 T4 - Tamron SP 60-300 f/3.8 AD2 - Soligor 75-260 f/4.5 M42 - Soligor 400 f/6.3 T4 - Soligor 500 f/8 T2 Cat + Matched 2X TC - Addiction Growing!
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marcusBMG
Joined: 07 Dec 2012 Posts: 1304 Location: Conwy N Wales
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Posted: Tue Aug 28, 2018 10:18 pm Post subject: |
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marcusBMG wrote:
Haze on the rear group of many these presets (300mm f5.6's; 400mm f6.3's; 500mm f8's etc) is bad news - it's usually deterioration of the glass, can't be cleaned.
http://forum.mflenses.com/hazy-lens-element-not-responding-to-normal-cleaning-methods-t66075.html _________________ pentax ME super (retired)
Pentax K3-ii; pentax K-S2; Samsung NX 20; Lumix G1 + adapters;
Adaptall collection (proliferating!) inc 200-500mm 31A, 300mm f2.8, 400mm f4.
Primes: takumar 55mm; smc 28mm, 50mm; kino/komine 28mm f2's, helios 58mm, Tamron Nestar 400mm, novoflex 400mm, Vivitar 135mm close focus, 105mm macro; Jupiter 11A; CZJ 135mm.
A classic zoom or two: VS1 (komine), Kiron Zoomlock... |
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kypfer
Joined: 27 Sep 2017 Posts: 514 Location: Jersey C.I.
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Posted: Tue Aug 28, 2018 10:59 pm Post subject: |
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kypfer wrote:
marcusBMG wrote: |
Haze on the rear group of many these presets (300mm f5.6's; 400mm f6.3's; 500mm f8's etc) is bad news - it's usually deterioration of the glass, can't be cleaned. |
Thanks ... not what I was hoping to hear
Unfortunately, without knowing how to disassemble the rear group I can't test the haze for solubility or "cleanability". Given that the group appears sealed, whatever caused the problem was probably put there at assembly time. I'd guess either degraded optical coating, though I'd expect to see that on all surfaces if that were the case, or deposit from evaporated locking sealant or maybe even the paint.
Here's hoping for bit more information |
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kypfer
Joined: 27 Sep 2017 Posts: 514 Location: Jersey C.I.
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Posted: Fri Sep 14, 2018 6:10 pm Post subject: |
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kypfer wrote:
Well, failing any other information and working on the principle that "as it's already broke I can't hurt it", I got brutal and managed to partially disassembled the rear group.
With the T2 mount removed, the retaining ring inside the rear of the lens proved to be plastic, which actually unscrewed easily once I'd drilled a couple of holes in it to get a purchase with a pair of needle-nose pliers!
With that loosened the rear element was loose and could be removed. The plastic ring won't actually come out of the rear tube, but it will rotate longitudinally to allow the rear element to be extricated. There is a spacer that may also fall out at this point ... don't lose it!
The mistiness/fogginess proved to be only on the inner (flat) surface of this rear element and would appear to be degraded optical coating. It won't wash off with alcohol or acetone, but, as it's a flat surface, it's practical to re-polish the surface with some metal polish. Several minutes later there was an obvious improvement in the clarity of the element so the whole has been reassembled (with a bit of fiddling to get the lens and spacer aligned).
At the next opportunity I'll make a few tests to see how it performs. It probably won't be outstanding, it's only a 3-element lens after all, but I think it's clear enough to be usable and that multi-blade aperture does look enticing |
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luisalegria
Joined: 07 Mar 2008 Posts: 6627 Location: San Francisco, USA
Expire: 2018-01-18
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Posted: Fri Sep 14, 2018 10:27 pm Post subject: |
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luisalegria wrote:
I finally found my post on a very similar lens I have (somewhere, in a box in the garage)
http://forum.mflenses.com/rubica-300-5-6-what-the-heck-is-that-t6798,highlight,%2Brubica.html
A "Rubica" brand on mine, otherwise the front barrel styling seems updated on your Optomax, with a rubber grip and a "step" in the barrel, probably because the maker reduced the barrel dimension for the sake of the new grip. Less material and machining without the knurled portion, etc.
Its probably also a three element lens.
Please ignore my comments on it, this was in my more speculative days!
The shots were taken at 6mp on a Pentax K100D and the lens is quite sharp on that sensor at f/8, not quite so at f/5.6 - see the bird. _________________ I like Pentax DSLR's, Exaktas, M42 bodies of all kinds, strange and cheap Japanese lenses, and am dabbling in medium format/Speed Graphic work. |
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kypfer
Joined: 27 Sep 2017 Posts: 514 Location: Jersey C.I.
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Posted: Sat Sep 15, 2018 7:38 am Post subject: |
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kypfer wrote:
Thanks for the link If the results from my lens are anything like as good as yours I'll be well pleased ... even if I too rely on the Shake Reduction in my Pentax |
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