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Forum: Visitors' Center
04-30-2016, 04:38 PM
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UV light will discolor discolored lenses.. so to speak.. in other words clarify them.. how fast, how efficiently.. subject to trial.. UV lamps can be had in mineral prospecting stores etc...
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Forum: Visitors' Center
04-19-2016, 11:40 PM
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What the army says...
http://www.irpa.net/irpa3/cdrom/VOL.3B/W3B_13.PDF
More or less this says an eyepiece of thoriated glass will give you 10% of the alpha radiation it is capable of generating. And the lens in front of the camera body then, none by inference.
However the jury appears to be out so to speak. not much authoritative info about real exposures due to use of lenses other than anecdotal stuff.
Radioactive lenses
This looks like a fair study..
http://www.diva-portal.se/smash/get/diva2:652338/FULLTEXT01.pdf
"From the gamma spectra, it is clear that most camera objectives and the camera
houses rarely give higher intensities than 115% of the background radiation. Since
a simple Geiger meter was used to assist the choosing of which objectives to
measure more precisely, no objectives were chosen that gave off little or no
radiation. Thereby, the increase in activity - however slight - observed on all
measurements was expected."
"Here, is the radiation weighting factor which is equal to 1 for electrons.
Therefore, 2.77 μGy absorbed dose translates to 2.77 μSv equivalent dose. From
this, it is seen that the contribution to the annual maximum radiation dose to the
eye’s lens from this camera lens is 0.2 ‰.This is indeed a contribution, but a very
insignificant one. This amount of usage of the Carl Zeiss Tessar lens is therefore
deemed non hazardous in terms of beta radiation."
"In this case, the whole body is irradiated, meaning that the tissue weighting factor,
, is equal to 1. is given using the same calculation as in formula (9) with
. This gives an effective dose from gamma radiation from the Carl Zeiss
Tessar lens on the whole body of the photographer of 0.17 μSv. This, compared to
the standards set by the Swedish Radiation Protection Authority, is only 0.17‰ of
the maximum allowed dose."
-- my two ill educated cents in this scientific question is that given the most stringent standards the thoriated lense of the type in question do not pose a hazard..
-- if one desires perfect safety then don't come out of one's lead lined, air filtered cave until civilization is over (u might have a decent chance of surviving that long), and forage for food at night, using ir goggles and blowing your air horn to scare off what nocturnal predators that have survived.
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Forum: Visitors' Center
04-16-2016, 08:38 PM
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Thorium is not very radioactive in its natural state, compared to Uranium oxide. Gas Mantle globes were made of thorium and they were deemed safe for decades. Most radiation can only penetrate about 2 cm of air. I doubt that the gamma rays of the small amount of Thoria in the lens have enough energy to escape the glass. Over time the lens will yellow, from radiation however.
You probably get a lot more radiation from building bricks and granite counter tops. They will make a scintillometer scream. Counts of granite slabs can be 6,000 per minute, while background is about 40 counts.
"Thoria is a material for heat-resistant ceramics, as used in high-temperature laboratory crucibles. When added to glass, it helps increase refractive index and decrease dispersion. Such glass finds application in high-quality lenses for cameras and scientific instruments. The radiation from these lenses can darken them and turn them yellow over a period of years and degrade film, but the health risks are minimal. Yellowed lenses may be restored to their original colorless state with lengthy exposure to intense ultraviolet radiation."
Just don't sleep with the lens in your underwear. You should be fine.
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Forum: Post Your Photos!
04-16-2016, 10:19 AM
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Forum: Monthly Photo Contests
04-16-2016, 10:13 AM
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They are all stand outs. The most difficult which captured unaffected mood and moment in action -- is 8. Can't beat the cute factor. Followed closely by 14.
Compelling character studies are found in 4, 6, 7, 11, 12, 15. 15 grabs you the most character wise as it is eye on, but 12 is fairly good, and good light study..
Portrait Light composition excellence are in 2, 9, and 12.
Tough choice. It's all pro quality.
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Forum: Pentax DSLR Discussion
04-16-2016, 09:00 AM
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I guess you can reset exposure compensation whence you find out what the screen does to exposure. +/- button-back wheel is a tad awkward on K50.. but it does work.
The Katzeye I gather, now officially TU, or OoB was the shizzle with the brighter screen and now -- it appears to the Taiwanese choice. i.e. focusingscreen.com
(Few business rescue terms are ever that palatable.. lotsa sharks in that biz and can't say I blame their nature )
c'est domage as the fr. say.
So the burning question iz: who has undeniable quality in manual dead on German quality 45-degree-line large enuff split image with fresnel screen bright enuff focus screen thingie? I guess Taiwan will do but far from perfect for now..
Again I criticize without hands on as I am going on vids and forums and feel..
---------- Post added 04-16-16 at 09:18 AM ----------
I have to ask what "it" is. Katzeye or focusingscreen.com ?
i.e. The "it" that made your metering better..
---------- Post added 04-16-16 at 09:20 AM ----------
Sorry I see you were speaking about Katzeye, the now defunct, TU, burnt, dead, no longer shipping, don't even bother company..
geez...
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Forum: Pentax DSLR Discussion
04-12-2016, 05:37 PM
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This guy tested the Taiwanese focusing screen made for Pentax.. also made for other models. horizontal split image with microprism. They have many different styles. About $85 US, $15 shipping.
You Tube
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src="https://www.youtube.com/embed/Sq3TbZGsH3U?controls=1" allowfullscreen>
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Not in this youtube link but in other info they are not as bright as katzeye, ALL focusing screen aftermarket installs affect metering. The one in the video above was pretty much useless after F11. (in what kind of light I might ask) The solution is to to do open aperture focusing or focus in Auto aperture mode of lens? I don't know from this test if it affects spot metering at all. I aver from Katzeye's literature and the thread herein that these screens DO affect metering and this can be a bit..
However the video maker did say it really improved his focus experience and improved accuracy... This might be the pay off.
Cons: dark, affects metering, have to play with shim sets to get focusing accurate.. it seems that not all cameras have micro prism and diagonal split prism available (Nikon K3 style).. have to ask company. Instructions have to be followed carefully. English is conjectural type.
Plus: better manual focus. increased precision fewer bad shots.. major video makers says.. a Model available to fit a plethora of cameras including it seems jut about all Pentax models.
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Forum: Pentax K-30 & K-50
04-12-2016, 03:32 PM
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Don't know if this helps 4 months later.. taiwanese firm Focusing Screen
Bad Englich -- products seem ok in presentation, although a little pricey.. K10D is mentioned and K50.
Haven't tried yet. Different styles, angled split prism, horizontal, cross. My preference is for a fresnel ring with 45 degree split prism, as found on the old German cameras of the film days.
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