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Which is better?
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PostPosted: Wed Mar 30, 2011 2:37 am    Post subject: Which is better? Reply with quote
Which is a better lens? The SX has a lip that prohibits me from adjusting the aperture on my cam. The non-SX has a yellowish tint to it, making it give slightly yellowish pictures. I am wondering if both are bad. Sad


PostPosted: Wed Mar 30, 2011 7:24 am    Post subject: Reply with quote
Do you use digital? If so, the tint shouldn't be a problem. You could always file the lip as well Smile

Either way, you've already got the lenses, so test them yourself Laughing


PostPosted: Wed Mar 30, 2011 1:58 pm    Post subject: Reply with quote
I want someone to tell me which one to keep or neither to keep. I simply don't know how to decide. How do I test it objectively?


PostPosted: Wed Mar 30, 2011 2:37 pm    Post subject: Reply with quote
The yellowing is probably from the lanthanum in the glass. Stick it in the sunlight on a windowsill for a couple of weeks and it will go away.

It's the UV in sunlight which fixes the yellowing.

If you wanted to fix it fast, sticking it under a UV lamp for a few hours should do it, maybe you know someone who keeps reptiles? They use UV lamps, or someone with a sunbed?


PostPosted: Wed Mar 30, 2011 2:49 pm    Post subject: Reply with quote
As Graham said before, you should test it by yourself with your cam and your type of photography.

Use a tripod, the selftimer and make the same shots with your 2 lenses. A wall for sharpness for example, or to test the CA try to find strong contrast etc.

As said before, the yellow colour is not a great problem.

Wink


PostPosted: Wed Mar 30, 2011 3:01 pm    Post subject: Reply with quote
Both are good lenses with excellent reputations and seem to be working as designed.

The yellow glass can be easily fixed as Ian says. This lens is an earlier type that used lanthanum glass. Many classic and valuable lenses have the same quirk, notably all the 50/1.4 Takumars. It is not a defect or poor quality.

The SX lens was designed with a modified M42 mount for a certain series of Mamiya cameras (MX, MSX, DSX) with open aperture metering. It also fits well on all other old M42 cameras. The mount is, as you see, not completely compatible with M42 adapters on DSLR's. There is no fix for that without making a modification to the mount - grinding off the extra lip on the aperture ring.

Personally, I would keep the Auto and sell the SX, because I don't like making such modifications.


PostPosted: Wed Mar 30, 2011 3:14 pm    Post subject: Reply with quote
Thanks! You guys are all awesome and totally make my day! I took some shots with my other Mamiya the other day and was happy with them. I will stick the non-SX in the sunlight. If anyone wants the SX lens, pm me.

Why is the non-SX lens so much heavier? Does it have more glass/elements in it? I think they shoot about the same. The SX may shoot slightly better, though.


PostPosted: Wed Mar 30, 2011 4:40 pm    Post subject: Reply with quote
I'd like to try that SX and modifications are fine with me. I'll PM you.

If anyone knows what wavelengths of UV are needed to reverse the lanthanum yellowing please let me know because I could make a simple cheap LED light that fitted in the lens cap specifically for fixing lenses, would be useful for all the Takumar owners I suppose and could be made very cheaply if you don't mind some soldering.


PostPosted: Wed Mar 30, 2011 5:11 pm    Post subject: Reply with quote
Quote:
If anyone knows what wavelengths of UV are needed to reverse the lanthanum yellowing please let me know


I just used a common 15-watt cylindrical fluorescent-type UV light to de-yellow a 50mm f/1.4 S-M-C Takumar. The Takumar probably uses Thorium rather than Lanthanum, though, since the radiation level was very dramatic on a Geiger counter.

You don't need exotic shortwave or germicidal lamps, as long as you're wiling to treat the lens for 8 days or more. I probably should have tried it for 16 days to see if the lens got any clearer.

more info: http://www.flickr.com/photos/s58y/sets/72157623430609256/


PostPosted: Wed Mar 30, 2011 6:31 pm    Post subject: Reply with quote
Quote:
If anyone knows what wavelengths of UV are needed to reverse the lanthanum yellowing please let me know.

I just used a common 15-watt cylindrical fluorescent-type UV light to de-yellow a 50mm f/1.4 S-M-C Takumar. The Takumar probably uses Thorium rather than Lanthanum, though, since the radiation level was very dramatic on a Geiger counter.





1. Are you saying that the lanthanum makes the lens radioactive? Just one more radioactive lens to add to my collection, after picking one up from Japan last week. Wink Is this radioactivity dangerous?

2. I have a GE CFL black light. Does this emit enough UV to de-color the lens?


PostPosted: Wed Mar 30, 2011 7:05 pm    Post subject: Reply with quote
newton wrote:
I want someone to tell me which one to keep or neither to keep. I simply don't know how to decide. How do I test it objectively?


Tripod shots at all apertures. Use a well lit bank note as the subject. They show up resolution problems really well Smile


PostPosted: Wed Mar 30, 2011 7:15 pm    Post subject: Reply with quote
martyn_bannister wrote:
newton wrote:
I want someone to tell me which one to keep or neither to keep. I simply don't know how to decide. How do I test it objectively?


Tripod shots at all apertures. Use a well lit bank note as the subject. They show up resolution problems really well Smile


Hmm, good idea, I think I will have to start doing my lens tests this way.


PostPosted: Wed Mar 30, 2011 7:16 pm    Post subject: Reply with quote
s58y wrote:
Quote:
If anyone knows what wavelengths of UV are needed to reverse the lanthanum yellowing please let me know


I just used a common 15-watt cylindrical fluorescent-type UV light to de-yellow a 50mm f/1.4 S-M-C Takumar. The Takumar probably uses Thorium rather than Lanthanum, though, since the radiation level was very dramatic on a Geiger counter.

You don't need exotic shortwave or germicidal lamps, as long as you're wiling to treat the lens for 8 days or more. I probably should have tried it for 16 days to see if the lens got any clearer.

more info: http://www.flickr.com/photos/s58y/sets/72157623430609256/


I just wondered if 380-400nm UVA would do the job because I have loads of LEDs in that wavelength range.


PostPosted: Wed Mar 30, 2011 10:26 pm    Post subject: Reply with quote
Quote:
Are you saying that the lanthanum makes the lens radioactive?


Someone said the Mamiya lens contains Lanthanum, and that turned the lens yellow, and that UV could be used to bleach out the lens. I claimed that I bleached out an old Takumar with UV, supposedly containing radioactive Thorium rather than Lanthanum.

Lanthanum itself may be slightly radioactive, but I doubt you could measure it without a very fancy radiation detector. IIRC, it's about 10000x less radioactive than Thorium. Sometimes it's claimed that Lanthanum can be contaminated with other radioactive elements in lenses, and maybe this gives rise to slight measurable radiation? I have no idea myself.

If a Thorium lens gives 30000 CPM on a pancake probe, an equivalent (uncontaminated) lanthanum lens might give 3 CPM, depending on how well the radioactivity escapes the lens. This 3 CPM would be swamped by the normal background count, and would be pretty much unmeasurable with a simple geiger counter. I do have one slightly radioactive lens (Nikon 200mm Micro-Nikkor), and maybe it has contaminated lanthanum? Maybe it's just potassium-containing glass? I think the Nikkor is about as radioactive as a Waterford Crystal butter dish I measured. Perhaps some lens experts could chime in here?


PostPosted: Wed Mar 30, 2011 10:51 pm    Post subject: Reply with quote
I don't know exactly what the Mamiya lens uses, for all I know it could be thorium glass like the Takumars. As I understand it some glass formulas used both thorium and lanthanum.

http://www.orau.org/ptp/collection/consumer%20products/cameralens.htm

Either way, the yellowing is a typical mark of some sort of radioactive glass.
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