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Forum: Pentax SLR Lens Discussion
10-02-2009, 02:37 PM
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What, you don't eat off red Fiestaware?
Fiesta Ware (ca. 1930s)
Red Fiestaware, with a radiation rate of _20_ mrad/hr (20x that of Takumars -- plus you EAT OFF IT!), if you ate off it every day, is estimated to result in the consumption of .21 grams of uranium per year resulting in a dose of 40mrem per year. (Note that rem is like rad, only adjusted for how bad the particular kind of radiation is to humans. Not all radiation is created equal.)
The safety limit for humans is 5000 mrem per year. A single CT scan, which I had earlier this year, delivers a whopping 1200 mrem in one go.
Just for comparison, SMOKING a pack a day is estimated to deliver somewhere between 2000-5000 mrem per year.
So, considering that the lens is 1/20 what the dinnerplate is, I wouldn't worry too much. Just don't leave the lens in your pocket next to your testicles for 5 years running, ok?
As to electronics, if you can deliver about 5000 rads over a few minutes you can do long term damage, or if you exceed around 1Mrad. Since the lenses are 1mRad (1/1000 of a rad) in an hour, I don't think the camera will notice.
Put another way, background radiation is about 300 mrad per year, or about 1 mrad per day. So when your finger is touching the lens (What are you doing cleaning a lens with your finger?!), you are getting about 25x the rate as when you are not touching the lens.
Also, the rate of exposure is an important consideration. Your DNA has the ability to repair itself when damaged, if the damage is not too extensive. If you break off a single base, a repair molecule comes along and replaces it using the base's pair (each point on the DNA has a pair of bases) as a reference. Then the DNA is as good as new. If the rate of exposure is higher than the rate of your cells ability to repair themselves, or if you just get unlucky and get a full break, THEN you have a problem. If you received your entire lifetime dose of radiation all in half a second you'd probably be in a serious world of hurt, even though that same dose spread out is unlikely to cause problems.
The major danger from these lenses is not from using them, but from breaking them and then inhaling or ingesting radioactive dust. Don't do that. Now you are asking for trouble. The people who smashed the Takumar as a way to "fix" the lens were doing something stupid. I hope they didn't breath in too much of the resulting junk. http://www.hermes.net.au/bayling/repair.html step 3 = NO NO!
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Forum: Pentax SLR Lens Discussion
10-02-2009, 02:19 PM
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Wow, so glad to learn of this UV trick. Now I want some lenses.
Oh, btw, can we please tell everyone that the radiation is bad for them and they should avoid Takumars at all costs?
The prices for them are too high.
;)
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Forum: Pentax SLR Lens Discussion
09-30-2009, 06:50 PM
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I think that's part of the equation. I don't get auto-aperture either way, so that plus doesn't sway me.
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Forum: Pentax SLR Lens Discussion
09-30-2009, 05:48 PM
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Ok, I've purchased an M 50/1.7 and a mystery lens.
I paid a bit more for it than I probably should have (60$ after shipping), but the lister said it came with two lenses and described one of them as a "Sears 49mm PL". In the photo you see two lenses, about the same size, one is obviously the 50/1.7, and the other one is a little larger, but the lens area is completely dark and you can't see anything.
I racked my brains trying to figure out what kind of lens a Sears 49mm PL would be, and it finally dawned on me: he was reading what was written on the 49mm polarizing filter on the front of the lens, not the actual lens itself.
So, I figure, for an extra $20, why not take a shot and see what the other lens is? Maybe it's some junk lens, or maybe it's a nice 28mm. Who knows. It looks wide-angle-ish behind that dark mask. It looks like a piece of the lens is missing from the front, too. I thought maybe it was a teleconverter, but what kind of teleconverter takes 49mm polarizers and has what looks like f-stop writing on the side?
Anyway, next lens up is to find a good 35mm. I'd love to snag a 2.0, but they look really expensive.
I am also on the hunt for a decent ~50mm medium format lens to turn into a cheap DIY tilt, or perhaps I'll shell out for a nice eBay tilt adapter.
Total spent so far: $75 on lenses, $1950 on a new camera body. (Yikes!)
Right: 50mm/1.7, Left: A Sears 49mm PL?
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Forum: Pentax SLR Lens Discussion
09-29-2009, 11:44 AM
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Thanks for the great suggestions!
Next, I'm going to snag a 50mm f/1.7.
I've purchased a Vivitar 28/f2 (M11... really ridiculously cheaply!), and I'm going to keep a look out for a close focus version of it.
On the 35mm, do any of you own both the Takumar and the Pentax-K? Can you recommend one over the other or are they the same? As for -k or the -m, I thought the -m versions were specifically made to sacrifice IQ for compact size... are the -k versions sharper version?
gnaztee: I already have a zoom in that range that's f3.5 on the wide end, so I just can't see spending $200 on such a similar lens that's not much faster. My experience so far has been that cheap primes far surpass cheap zooms in IQ, too. But thanks for the suggestion, anyway! =)
-cwm9
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Forum: Pentax SLR Lens Discussion
09-29-2009, 04:07 AM
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My friend is getting married soon, and she is dead set on not hiring a professional photographer.
I used to shoot video weddings once upon a time, so she's asked me to shoot it for her. (No pressure, right? :lol:)
Anyway, I've been shooting with a slow Pentax zoom lens with my Canon that doesn't have the best IQ, and so I thought I'd get myself some primes, say f2.8 or better.
I don't care about auto-focus, auto-aperture, or even brand. (Adapters work great!) What I'd really like to know is what lenses have the best IQ in the $200 or less price range for 28mm, 35mm, and 50mm.
I have a Pentax-k 50mm f1.4, but seems a little fuzzy. It may just be a bad copy, or I may have just abused it too much as a kid. I was considering buying a Pentax-M 50mm f/1.4.
Any thoughts?
Thanks!
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Forum: Pentax SLR Lens Discussion
09-25-2009, 08:58 PM
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Oooh, thanks! Ok, I'll send a PM. Sorry about the profile not having a location. I live in Hawaii, so a first class stamp should do the trick! =)
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Forum: Pentax SLR Lens Discussion
09-25-2009, 06:22 PM
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Um... so... fix it yourself? If it just needs to be screwed back together, that's not hard. Worst case you break it and you buy a new one for $20 more than the repair?
Or, if that doesn't make you happy, you can always give it to me, and I'll try to fix it! :D
Just post it off to:
cwm9
PO Box 51042
Eleele, HI 96705
... and I promise you'll never have to think about it again! :lol:
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Forum: Pentax SLR Lens Discussion
09-25-2009, 04:57 PM
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Oops. Thread title was supposed to be M1.6X2MM, not M1.6X1.2MM... ugh!
Anyway, I'm not actually exactly sure how "long" it is. Some sites say to measure the threads only, others say measure tip to tip. Since this screw has an angled head, I'm guessing it's a 2mm. See http://www.mcfeelys.com/tech/dimensions.htm. If you measure threads only, it's 1.4mm.
My father bought a Pentax-K 50mm f/1.4 for his camera back around when I was born, and when I got older he gave the camera to me.
At some point, the lens stopped focusing to infinity, and being the up-and-coming physicist/curious teenager that I was, I attempted to take the lens apart when I was about 13.
Now, at that time, I was pretty lousy at taking things apart and didn't have many tools. I put a few scratches in the metal, not having any real lens wrenches, but didn't hurt the glass. I didn't get very far either, as I was never able to disassemble the lens without the wrench.
When I put it back together, I lost one of the screws that holds in the filter ring. It's not critical, but it does mean the filter ring is a little loose. Sadly, I even foolishly tried to force in a too-large screw from a Vivitar that had a "crunchy" zoom lens because of dirt (...that I ended up destroying..!) Luckily, though I managed to insert the oversized screw only though the filter ring retaining plate; I never did manage to force it into the lens body. :lol:
Now that I'm much older, I've decided I wanted to try the lens with my Canon 10D/7D (coming), so I took the lens apart again, remembered what a mess I made, cleaned everything up in an ultrasonic bath w/ethanol, and have reassembled the lens. I think I have the back focus problem fixed, too, but I won't know until my adapter ring comes. Apart from a few scuffs, everything else seems to be fine... filters still screw onto the lens just fine, too.
Anyway, I'm still missing this one M1.6x2MM machine screw.
I thought maybe one of you might have one lying around in a junk box from a trashed lens and would consider sending it to me via 1st class snail mail... I can send you $1 via pay pal to cover the postage.
Thanks!
-cwm9
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Forum: Pentax SLR Lens Discussion
09-24-2009, 06:00 PM
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Scam? Nah, my guess is he's guilty of fee-avoidance by selling lenses to customers outside of eBay/paypal and doesn't want to get caught by eBay via repeated listing cancellations. So instead, when he sells a lens, he changes the title and ups the price to something ridiculous so no-one will bid, with a bonus of free advertising. Who knows, maybe he's just after the free advertising, but I don't know what advertising a sold item does for you, except to excite curiosity and get people to check out your other items. Personally, I'd be worried it would turn people off by making them think you were a scammer.... (!) If you look at his other listings, you'll see there's a "Leica 39mm UVa SOLD" too ($9999.94), as well as many other listings with more reasonable prices. If you've looked at his feedback history, you'll see he's sold many camera items with good feedback.
As for the shipping cost, he probably uses listing software and it probably automatically calculates shipping cost by price. (You know, $10 for less than $100, $20 for less than $500, etc, etc.) Or maybe he just changes it to something random and expensive too. Anyway to avoid paying eBay fees, I guess.
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Forum: Pentax SLR Lens Discussion
09-23-2009, 10:16 PM
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AAAHH! :o Brain fart.
I MEANT the Pentax-M 28mm F2 and the Pentax-M 28mm F2.8. :)
Yeah, that is a lot of pictures to take and a lot of glass to use! Still, it'd be pretty cool to have resolution test shots from each lens... Sounds like way to much work for anyone sane, especially me! :D
The reviews of the Pentax A 28/2.8 were a bit... lackluster? So I'm glad you prefer the vivitar over it. I can't wait to get my copy in the mail. I hope it works out of the box and doesn't need the aperture fixed.
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Forum: Pentax SLR Lens Discussion
09-23-2009, 11:53 AM
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Was it ever determined what the relative performance is of these Vivitar lenses vs. their Pentax-M 28mm F2 or Pentax-M 28mm F2.8 (edited from 35mm, stupid me!) counterparts?
I just bought an M11 Kino/Kiron copy. I thought I was buying a K12 because the SN was long and the bestiary listed the M11 SN as No. 22xxx, which I took to mean it was shorter than the K12, but that turns out not to be the case.
I bought the lens for my 1.6x crop camera for use at a wedding. I looked like it needed cleanup, but that's easy enough and the price was right: $22.50 shipped.
I wish there was a standardized test of each of these lenses to find out which ones are the good ones! I guess the series-1 are probably the best.
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Forum: Pentax SLR Lens Discussion
09-21-2009, 06:05 PM
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If it's like my K-series 50/1.4, I think that piece just screws on, but I'm not quite certain. It should be easy enough to fix (if it's not truly broken). I don't even think you need any special tools to do it.
If you break it, you buy it, but if it were me I'd just take it apart and try to fix it. Besides, you'll learn something about your lens and have a better idea of what it will take to get it repair professionally if you can't do it yourself.
Go down to Costco or some other store and buy yourself a box of Nitrile exam gloves (plain, without powder!), or, if you are really paranoid, get some anti-static ones from eBay.
Then take a screwdriver and disassemble the back. If you find you have to unscrew a lens, or if that lens needs to be screwed in with a special tool (i.e., two notches on either side of a metal ring), then you need a lens wrench which can be picked up off of eBay for $16-$20...
I've yet to take apart a lens with electronics, but I don't imagine it's that much harder.
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Forum: Pentax SLR Lens Discussion
09-21-2009, 12:24 PM
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Hi! It's my first post.
I already have a 50/f1.4 SMC-K lens, and I'm wondering, does anyone have both the SMC-K and SMC-M versions? I'm wondering if there is any difference, and if so, which one is better.
Also, I want to buy a 35MM f/2, but I see there are many different versions. In particular, the M42 SMC Takumar seems to have a much larger front element in the photos I've seen than the Pentax-M, but the Pentax-M is newer... Does anyone know which of these lenses is the better one?
Thanks!
-cwm
50/f1.4 SMC-K + Canon 10D: unmounted/handheld w/lens tilt
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