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03-03-2009, 01:12 AM   #16
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QuoteOriginally posted by LeoTaylor Quote
Pentaxmz: Perchance you are an astrophotographer? I used to see the ads for hypering kits in Sky & Telescope. My wife didn't mind that I kept my K1000 film in the refrigerator, she gave the the camera. Being a chemist she put her foot down when it came to ordering hydrogen tanks.

Garlic Capitol: I've been to Gilroy! Since you used bulb exposure with film you must recall you could not set the K1000 in bright daylight and open the shutter manually. I used film for astrophotos for a few years and you soon learn what length exposures to use for what target.
Yes... or um... I used to be. But since moving to a big city, this hobby has been put on hold for a few years now. Once I can convince my wife that living outside the city isn't so bad... we will do this.

It looks like like your wife is too smart for your own good.

But good news! Helium also works in gas hypering. In my great experiments back in the early 80's, I found that it was really all about replacing the oxygen molecules with something else. Hydrogen appeared to exhibit to have the longest term effect, but helium worked as well. I wrote my engineering theses on this subject. Good times.

03-03-2009, 01:30 AM   #17
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QuoteOriginally posted by Ben_Edict Quote
I stayed with the Kodak 103series of films, which already hade a reciprocity exponent of >0.92. Later the humble Kodak Pro Gold 400 had a reciprocity exponent of >0.9. Unfortunately this film was in production only for a short period (I still have some packs of 120...) Hypering was always something, I was too lazy to do seriously...

Ben
It takes a bit of work to set up but the results are amazing. I started this experimenting in high school and was *very* fortunate to meet a very curious science teacher that supported my hobby. He helped be obtain the gas cylinders and gases (I used different mixtures but settled upon a hydrogen/nitrogen mixture), I used a PVC tube (big enough to stack several 35mm film developer spools), gas pressure meters, a small heater made from an electric blanket, homemade copper thermal heat exchanger (a better reaction occurred when the film was heated).

Simple tip:
Of course, all this is unnecessary, the point is to remove the oxygen from the film. One way or another is still better than nothing at all (e.g. place the film in a vacuum using one of those kitchen vacuum jars). It's not nearly as effective as gas hypering but the effects are still noticeable.

Here is an interesting calculator for estimated exposure times:
Exposures Custom
03-03-2009, 10:54 AM   #18
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Can one damage the sensor with extended exposure

All,
To date, i've only used exposures up to 30 seconds on the Manual mode, K10.

With the heating problem discussed above, is it possible to damage the sensor with exposures up to a few minutes. Not thinking of getting really extreme with exposure length, but i can see myself eventually getting beyond 30 seconds for some situations.

Just wouldn't want to damage the great sensor i;ve got now.

thanks, Phil
03-03-2009, 10:58 AM   #19
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QuoteOriginally posted by philbaum Quote
All,
To date, i've only used exposures up to 30 seconds on the Manual mode, K10.

With the heating problem discussed above, is it possible to damage the sensor with exposures up to a few minutes. Not thinking of getting really extreme with exposure length, but i can see myself eventually getting beyond 30 seconds for some situations.

Just wouldn't want to damage the great sensor i;ve got now.

thanks, Phil
No sensor damage with 20 minute exposures at -10 to -25C ambient temperatures here in winter. Haven't tried yet in summer. Will let you know how it goes in a few months.

Jack

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