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03-01-2009, 05:00 PM   #1
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How long is long enough? Bulb Setting

Hi, all. I finally got a chance to use my new K2000 yesterday, and in the process of exploring what it can do, I found the Bulb setting. Hallelujah! Remembering what fun I had using it on my K1000 and B&W film, I tried it a couple of times; no joy. Nothing but white on the LCD monitor. My question is this; seeing as how with color film you can experience that pesky reciprocity error if you have the shutter open too long, how long is long enough for the Bulb setting on a DSLR, and what is the optimal range for f-stops?

Thanks all.

03-01-2009, 05:56 PM   #2
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QuoteOriginally posted by Garlic Capital Newby Quote
how long is long enough for the Bulb setting on a DSLR, and what is the optimal range for f-stops?
It completely depends on what you're taking a picture of. Bulb generally implies that you're going to leave the shutter open for at least a few seconds, and it has to be pretty dark out in order to for an exposure that long not to completely wash out the image (like the "white" that you described).

Try using "bulb" outdoors at night (on a tripod, of course, otherwise you'll get nothing but blurriness). Start with a couple of seconds at the widest aperture (smallest f/number) your lens will accommodate. Review the picture and adjust the length of the bulb exposure and the aperture accordingly - use a longer exposure if the picture is too dark, or a shorter exposure and/or smaller aperture (larger f/number) if the picture is too bright.

Once you've got an exposure that works, you can double the time (ie, 4 seconds instead of 2) and use the next smaller f/stop (ie, f/5.6 instead of f/4) and get an image of the same brightness but with more blurriness of anything that's moving.
03-01-2009, 06:06 PM   #3
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This is really a question about light. You are letting in too much light for the conditions you are shooting under. Bulb mode needs to be used carefully and usually only in low light. In daylight you will need a neutral density filter such as ND400 and up to use bulb mode.( basically to reduce incoming light.) I would suggest you use the normal modes to start and then learn about aperture and other camera necessities before you play with bulb mode.

Cheers
Shang
03-01-2009, 07:09 PM   #4
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what everyone above said...

so to answer "How long is long enough?" : "Till you get a good picture" heh

03-01-2009, 08:09 PM   #5
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I don’t usually use bulb until I get past the 30sec that the camera can be set too.

As for reciprocity error technically it is still there in digital but you have more and better tools to deal with it. With film you could refer to some correction table for exposer time but with digital you can just take the photo and chimp to see if you need to correct exposer. AFAIK no one makes a correction table for digital. As it gets darker metering error and the points of light make other methods harder to use.

With color film the problem is each layer has a different reciprocity error so color balance could become difficult to impossible. In addition the color of the lights at night make the use of color temperature as a way to correct color balance impractical. If you shoot RAW and PP it can be much easier. Before it gets to dark look for something that is going to be in the frame that you can use to set the color and use that as your target to set the color balance. If you PP you also have better tools for dealing with noise in these long exposes.

What I have found is that when you take these longer photos is as important as how long the expose. Here are some links to some photos I took as the sun was setting. 2 are at 30sec but just a little later times and 1 is about 3 minutes (bulb) taken much later. The same target was used to set color balance in all 3 photos.

Flickr Photo Download: DAZ_3165

Flickr Photo Download: DAZ_3166

Flickr Photo Download: DAZ_3168


As the expose gets longer short frequencies wave noise (small waves) tend to smooth out leaving only the long frequencies wave noise making the water more “glass” looking.

DAZ
03-01-2009, 08:32 PM   #6
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QuoteOriginally posted by Garlic Capital Newby Quote
Hi, all. I finally got a chance to use my new K2000 yesterday, and in the process of exploring what it can do, I found the Bulb setting. Hallelujah! Remembering what fun I had using it on my K1000 and B&W film, I tried it a couple of times; no joy. Nothing but white on the LCD monitor. My question is this; seeing as how with color film you can experience that pesky reciprocity error if you have the shutter open too long,
I think it goes without saying but a digital imaging (in this case, CMOS chip) is not film and therefore, it does not suffer from reciprocity failure. As a side note, I had experimented with virtually eliminating reciprocity failure by way of gas hypering. It is oxygen molecules that actually help cause reciprocity failure. Between gas hypered film vs regular film, the differences were astounding!

Anyhow, with the CMOS imaging chip, you have something far more 'sinister' to deal with, that is, noise! The longer the exposure, the hotter the chip gets, and that introduces a lot of noise. Unfortunately, Pentax digital cameras are not as well suited for longer exposures as some other cameras. But pro (specially designed) cameras actually combat this heat by way of cooling systems. A properly cooled imager will keep collecting those meager photos happily for as long as they are turned on.

QuoteOriginally posted by Garlic Capital Newby Quote
how long is long enough for the Bulb setting on a DSLR, and what is the optimal range for f-stops?
I'm not sure how to answer this question. Long enough? Depends really on what you are photographing. One of the ways to combat noise, is to keep your exposures short but take many pictures. In post processing, using a method called stacking, one can achieve the results of a longer exposure.

In regards to f-stops... next to wide open. Stopping down a bit will help eliminate any edge lens distortion on many lenses. Again, depends on the subject.
03-01-2009, 08:44 PM   #7
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QuoteOriginally posted by DAZ Quote
I don’t usually use bulb until I get past the 30sec that the camera can be set too.

As for reciprocity error technically it is still there in digital but you have more and better tools to deal with it.
Not true. Reciprocity failure is an atomic level reaction that specifically takes place within the film's emulsion (photons reacting with the silver halide. The term cannot be used for anything but film. And besides, there is no similar reaction that takes place in a digital sensor.

BTW, nice photos (my back yard ).... I especially like the 3rd one.
03-01-2009, 09:10 PM   #8
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Pentaxmz you may be correct that digital has no reciprocity error (shrug) I am not a physicist. Here are 2 links that seem to indicate that digital can have reciprocity error, just a different kind.

http://en.wikipedia.org/wiki/Talk:Reciprocity_(photography)

Reciprocity

DAZ

Glad you like the photos, thanks.


03-01-2009, 10:47 PM   #9
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Great shots of the Seattle skyline, Daz.
03-01-2009, 10:48 PM   #10
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QuoteOriginally posted by Vylen Quote
what everyone above said...

so to answer "How long is long enough?" : "Till you get a good picture" heh
Ha! Ain't that the truth!
03-02-2009, 09:12 AM   #11
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QuoteOriginally posted by DAZ Quote
Pentaxmz you may be correct that digital has no reciprocity error (shrug) I am not a physicist. Here are 2 links that seem to indicate that digital can have reciprocity error, just a different kind.

http://en.wikipedia.org/wiki/Talk:Reciprocity_(photography)

Reciprocity
The wikipedia link wasn't available, but the other link was. I do not know what this guy is talking about, but it isn't the photographic reciprocity failure, which simply says, that the longer the exposition of film to light, the less linear the darkening action will be (a bit simplified). You explained reciprocity failure below quite well, especially with regard to the imminent colour shift - and digital will simply not do this - digital sensors are (within the technical limits) strictly linear.

Ben
03-02-2009, 02:24 PM   #12
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QuoteOriginally posted by pentaxmz Quote
Between gas hypered film vs regular film, the differences were astounding!
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.

Last edited by LeoTaylor; 03-02-2009 at 02:25 PM. Reason: typo
03-02-2009, 03:01 PM   #13
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QuoteOriginally posted by pentaxmz Quote
I think it goes without saying but a digital imaging (in this case, CMOS chip) is not film and therefore, it does not suffer from reciprocity failure. As a side note, I had experimented with virtually eliminating reciprocity failure by way of gas hypering. It is oxygen molecules that actually help cause reciprocity failure. Between gas hypered film vs regular film, the differences were astounding!
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
03-02-2009, 06:05 PM   #14
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First let me say that I am not an expert and only know what I have read so I could be wrong. I also don’t thing that reciprocity error is a problem in digital like it is in film.

I was trying to tell Garlic Capital Newby not to worry about it and just go out and take photos. I was trying to point out some other things that could be problems but that there were things to do about them so not to worry too much about them either. The part about the reciprocity error and the other stuff may have gotten a little mixed up and that would be my fault in not being clearer.

I was trying to be 120 percent correct as when I am only 110 percent I get called on it. I think that ship has sailed.

Again I don’t thing that reciprocity error is a problem in digital but in the extreme it is there. Now that I have said that someone will come out and say that they have a problem when they do XYZ so they have to do ABC so I am wrong. Digital is much more liner than film but in the extreme it is not and there it can give rise to reciprocity error. Day to day is this error impotent? I don’t thinks so but is there absolutely no reciprocity error in digital no. That is the 110 part.

One way that reciprocity error could accrue in digital is like this. As the photons are converted to electrons the electrons are stored as a charge in a capacitor on the chip. As soon as the charge starts to accumulate it also starts to bleed off. The longer it is held the more that leaks out. So in the extreme it is also like film in that it is not liner and can have reciprocity error. This is the 120 part.

Now I will go beck to something more fun like waiting for my new 77mm from B&H to arrive.

Thanks everyone for the kind words on the photos.

DAZ
03-03-2009, 12:29 AM   #15
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QuoteOriginally posted by DAZ Quote
Pentaxmz you may be correct that digital has no reciprocity error (shrug) I am not a physicist. Here are 2 links that seem to indicate that digital can have reciprocity error, just a different kind.

http://en.wikipedia.org/wiki/Talk:Reciprocity_(photography)

Reciprocity

DAZ

Glad you like the photos, thanks.
Ahh.... but we were talking about reciprocity failure, which is a problem uniquely associated with film.

On the other hand, natural reciprocity does affect digital imaging devices. The water bucket concept nicely explains reciprocity. But the film's silver halides don't always behave it this predictable manner during long exposures; hence the qualifier failure.

With film, there is a complex and little understood atomic and chemical interplay between discreet/sparse photons and silver halides. Anyhow, this issue is non-existent with digital imaging sensors.

Last edited by pentaxmz; 03-03-2009 at 01:32 AM.
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