Orquid "Phoenix"

Orquid "Phoenix"

by ceinmart

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My Sony NEX-3 (first model) does not have the Electronic First Curtain Shutter feature, so when I use it for Moon photos, the close, open/close, open cycle of the focal plane shutter always adds shake to my pictures, even for 3-in-a-row actuated after a self-timer countdown. Is there a recommended way with this camera to get the effect of an EFCS-type vibration-free start of an exposure? Moon photos with an f/16 scope are about 1/25sec, so the "hat trick" is hard to do reliably. I suspect that beanbags draped over the camera and telescope are the best option short of upgrading to the EFCS-equipped NEX-5 series.

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Does camera shake occur even with a tripod? It isn't clear since you indicate you used bean bags on the camera. –  Peng Tuck Kwok Feb 19 '13 at 3:19
    
Also f/16 is a bit steep for moon photos. Depth of field isn't an issue! So you can open that up and get a faster shutter speed which might help a little. Plus you won't have any diffraction issues. –  ElendilTheTall Feb 19 '13 at 7:47
    
@ElendilTheTall it's not about depth of field, f/16 will be the maximum aperture of the telescope. –  Matt Grum Feb 19 '13 at 11:11
    
Ah, sorry, missed the scope part. Proceed! –  ElendilTheTall Feb 19 '13 at 12:08
    
NEX was never made for this kind of photography. It's simply too fragile camera to work well when you need perfectly-stable shots. Think about Alpha instead (eg. comming A58), it'll do far better job than any NEX for your type of photography (just switch camera to MF and remove mirror, 30 seconds job). Remember also that tiny body of NEX means that the sensor isn't cooled as well as it is in Alpha what increases noise in long exposure photographs. So I'd strongly recommend staying away from mirrorless for astrophotography. –  MarcinWolny Feb 19 '13 at 12:19
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1 Answer

up vote 1 down vote accepted

Are you getting proper exposures at 1/25? I think your blur may be more from overexposure than motion. Is the blur uniform (as if it were out of focus), directional along one axis (as if you were panning), or multi-directional (as if you were shaking the camera)?

  • If it is the first, you are overexposing.
  • If it is the second, the Moon's motion is causing the blur (actually the Earth's rotation that makes it look like the moon is moving that fast).
  • If it is the third, the cause is either the shutter motion you suspect or vibrations from your scope's motor drive. The weak link might also be the stability of your T-mount adapter.

I am assuming you have the motor drive on the scope engaged, but it may be introducing more vibration than the sky motion it is eliminating for the short Tv you are using. Even at 1900mm and with your APS-C size sensor any Tv over 1/5 second or so should be acceptable without the motor drive engaged.

I normally shoot the moon @ ISO 200, f/8, and 1/125. And that is using an EF 70-200mm lens (plus 2X converter) with only a 77mm objective on an APS-C body. Keep in mind telescope and camera lens nomenclature are different. A 1900mm, f/15 telescope does not necessarily correspond to a 1900mm camera lens stopped down to f/16. In a telescope the f ratio has more to do with the scope's field of View while the aperture is the diameter of the objective. Your camera's view through the Meade 125-EX should be much brighter than mine through the EF-70-200. How much the T-mount adapter chokes out some of the light from the scope is an additional variable, though.


Links to NEX-3 Moon Shots

http://www.flickr.com/photos/ofaic/5729178928/

http://www.flickr.com/photos/jbolland/8486471565/

http://www.flickr.com/photos/jbolland/8489887743/in/photostream/

http://www.flickr.com/search/?q=NEX-3%20moon

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My first round of pictures are not available to look at. But from a similar telescope the same day, I see that the proper exposure was actually 1/800 at ASA1600 on an f/11 prime focus refractor. It had the same vibration effect (slightly directional), which is good--the issue is not about the imaging system but about the first-curtain motion. At this point, if MarcinWolny could post his comment as an answer, it has the information that I'd select as the best answer so far: the camera simply lacks the right provisions for shake-free first-curtain operation, which would fix the fatal shake. –  Don Day Feb 20 '13 at 22:05
    
Why shoot the moon at ISO 1600? It is bright enough to shoot at much lower ISO. Remember, the telescope's f-ratio is not an expression of its aperture in the same way a camera's lens is, but of its field of view. It is certainly possible to get a good photo of the moon with your NEX-3. See the links I've attached to my answer. –  Michael Clark Feb 20 '13 at 23:51
    
Your pictures are compelling, Michael. The net for me is that even though I cannot eliminate shutter shake due to the mechanical first curtain actuation, careful management of ASA level can enable short enough exposures to minimize some of that shake. Thanks for following through. –  Don Day Feb 22 '13 at 15:28
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