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Photography Question 
Lyndon Guy
 

How can I make a 1/10 sec. exposure?


So. I'm trying to shoot the moon, as it were. I'm using a Fuji S1 pro set at ASA 320 with a Mead 1000mm f/11 mirror lens. With this combination, I need an exposure time of somewhere around 1/10 to 1/4 second. Can't do it without getting all sorts of shake from the mirror going up and the shuttter opening. So I was trying to do some variation of the hat trick, where you cover the lens with something dark and opaque, open the shutter, wait for the shake to stop, yank the cover away, put it back, close the shutter. Works after a fashion, but it takes me too long to get my "hat" back over the lens - I overexpose every time! Any body got any great ideas how to unblock and reblock the lens fast but without shake?


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6/28/2001 4:48:42 PM

 
Ken Pang   What about a large piece of card with a rectangle cut in the middle?

Start at the top (which blocks the lens) then move the cardboard up, past the hole (which allows the light through) and finally to the bottom of the card, which covers up the light again. Same concept as the two curtains in a shutter...

Alternatively, you could just buy a ND filter :)

Seriously, I didn't even know that digital SLRS had a shutter... I just thought it had a mirror you could lock up prior to the CCD taking a reading. I suppose CCD circuitry isn't fast enough to get quick shutter speed.


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6/29/2001 2:53:53 AM

 
Lyndon Guy   Well, strictly speaking, I assume there's a shutter back there - the Fuji S1 Pro is built around a Nikon N60 body and it certainly behaves, sounds and pretends to have a real shutter. So I assume there's one back there. At any rate, I'll give your suggestion a try. THANKS!!


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6/29/2001 9:07:44 AM

 
Jeff S. Kennedy   Well first of all you need to refigure your exposure. If you are trying to "shoot the moon" 1/10 @ f11 is going to give you an overexposed moon every time no matter how you trip the shutter. The moon, like every other sunlit object, is subject to the Sunny 16 rule. Some use f11 as a rule of thumb for moon shots as well. You should be pretty safe shooting at f11 with a shutter speed the inverse of your ISO rating.


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6/29/2001 12:02:29 PM

 
John A. Lind
BetterPhoto Member Since: 9/27/2001
  Regarding exposure:
Be careful of using longer exposures when photographing the moon unless you have an accurate tracking system on the telescope set for its ephemeris. The combination of Earth rotation and Moon orbit will cause blurring at slower shutter speeds; the effect gets worse with increased magnification. Exposure for full Moon is less than required for a crescent Moon which is side lit by the Sun (by about a stop??).

Regarding camera shake:
Most astronomy film shooters use mirror lockup and aperture "prefire" (stopdown) when making photographs. Sadly, most current film SLR's lack both these features. Both of these can and will vibrate the camera/telescope combination. Adding a camera body to most telescopes does increase the susceptibility to vibration. I've done moon shots with a 600mm lens on a very sturdy tripod (set up on a concrete pad). The slightest vibration from even moving a very fexible cable release around can be seen through the viewfinder. Tripping the shutter release using a self-timer can help as it allows vibrations to dampen before the shutter opens.

-- John


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6/30/2001 11:54:36 AM

 
Ken Pang   John,

I have a custom function that allows a button on my camera to do a 10 second DOF preview. DO you think if I hit this button, it will close down the aperture for the shot, allowing me 10 seconds to take the shot?

Kind regards,

Ken


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6/30/2001 11:30:48 PM

 
John A. Lind
BetterPhoto Member Since: 9/27/2001
  Ken,
Sorry, I don't know enough about your camera body to tell you if it will work or not. One way to find out though is to try it (perhaps without film) and see if the lens aperture stays stopped down while you release the shutter.

Sources of vibration:
The first order effect is mirror slap. Second order effect is the lens stopdown. "Down in the weeds" at third order is the opening curtain hitting end of travel. If your viewfinder immediately goes black when you trip the shutter release using the self timer, then it prefires the mirror (possibly also the aperture stopdown). One of my camera bodies has a mirror lockup and the other two do not. However, the self timer prefires the mirror and aperture stopdown on them. Some time when there's no film in the body, check out the self timer to see what happens with yours.

-- John


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7/1/2001 1:19:36 AM

 
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