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 Post subject: Blurry moon - ideas?
PostPosted: Wed Oct 08, 2008 10:07 pm 
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The telescope arrived today. Been playing with it all evening :D Looks great through the eyepiece, but I'm having less luck with photographing from it.

First, let's go back a bit. I have the Sony A350, with the original Tamron 28-300 lens. My moon shots with this have never been sharp, even worse than my old Fuji S5700 at maximum digital zoom. I put it down to the lens, although now I'm not so sure. Later The Olympus E-510 came up used cheap with the 70-300 lens, so I snapped it up. This gave far better results than the Sony combo at 300mm.

Now, with the scope (1325mm f/13) shots of the moon fill most of the vertical frame. Again, it looks great through the eyepiece. I switch to camera, and using the viewfinder I similarly tune to focus. The images that come out look blurry. It isn't due to jpeg output, RAWs look same.

Example of A350+scope (100% crop):
Image

Example of E-510+70-300 (400% crop for similar size):
Image

While I can tweak the colours/contrast etc to improve the balance, fundamentally the Sony's output doesn't have any more useful detail.

Some considerations I'm wondering about:
I was using a static mount at the time, and the moon sure moved fast across the viewable area. I don't think this is the cause as it would only blur horizontally right? Exposure times were in ball park of 1/50s, using shorter didn't seem to help.
Mirror flip vibrations? But wouldn't this be in a vertical direction only? I did use cable release.
Combination of the above?
How much does air turbulence influence images? There was a little shimmering early on but it disappeared by the time I got those images.
Could it be simply the A350's software doesn't like this sort of image, where the Oly does better? I have a T-ring on order from China so it will be a little while before I can try that for comparison.
I have even tried focus bracketing. I'm quite sure it isn't the focus.

I can keep myself amused for quite a while yet just using my eye. Like camera stuffs, I got an itch for different eyepieces and maybe filters already... alas Jupiter become visible until quite a bit later, by which time it was already hiding behind some neighbouring trees :( Gonna have to find a quiet open spot to go out to I think.

_________________
Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 15-85 IS
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 150 macro, 120-300 f/2.8 OS, Celestron 1325/13
Tinies: Sony HX9V.


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 Post subject:
PostPosted: Wed Oct 08, 2008 11:12 pm 
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Hi popo,

1/50th of a second should be short enough to compensate for having an unguided set up if the Moon is just filling the frame. I would suspect that the problem is a combination of less than perfect seeing, slight misfocus and camera movement. Also bear in mind that at f/13 you are getting a little image softening due to diffraction.

My own experience has shown that getting a precisely focussed image is difficult. If the Moon just fills the frame at 1325mm focal length (it subtends just under 12mm) then it is covering, very roughly, 2000 pixels. If the camera sensor is just 1mm away from its correct position then this corresponds to a "blurriness" of around 1.5 pixels (2000/1325). I would also certainly try and use mirror lock-up and see if that helps.

You should be able to determine if it's a rigidity problem by using that technique and then taking a few shots at 1/50th of a second and then some more with as short an exposure as you can arrange by upping the ISO. Beware, though, of any image softening induced by the camera's high ISO noise reduction - it's probably best to turn that off and rely on noise reduction during post processing if needed.

Bob.

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Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


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 Post subject:
PostPosted: Thu Oct 09, 2008 1:08 pm 
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Weather looking good so far today so tonight I might have another chance.

Unfortunately the A350 doesn't have mirror lock up, so I can't do anything about that. I do note that if I take the telescope off the supplied mount, there is a hole where it can screw into a regular photographic tripod, so I might give that a try with some more weight on it.

Focus - I'll try bracketing some more when I can, but I'm fairly sure I covered enough range to rule this out, at least as the main cause. I was a little surprised how fine the adjustment was optically. The scope has a 25-turn knob (or so) for focusing, and the visually sharp band was equivalent to movement of maybe an hour or two on a clock face.

Can certainly try higher ISO/faster shutter, although if it's mirror shake that wont help and might even make it worse. Might have a go at the manual shutter method (long exposure, covered end except for when you want to expose). Not sure if I can move something out and in again at 1/50s though, so that might be one for when I get the motor running, although if I do that means I don't need short exposures for motion blur but it might still help if there's air wobbles?

From what I saw of lenses, I do wonder if it's the camera... the T-ring for the E510 is on its way from China so with a little luck I'll get that in a week or so and can answer that for sure. As great the live view on the A350 is for normal use, it isn't suited to this sort of work as there isn't a zoom function. Note to self, I do not need the 50D...

_________________
Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 15-85 IS
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 150 macro, 120-300 f/2.8 OS, Celestron 1325/13
Tinies: Sony HX9V.


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 Post subject:
PostPosted: Sun Oct 12, 2008 6:32 pm 
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I think I'm starting to appreciate how difficult this can be...

I had a few more goes at the moon over past nights, and all came out about the same. So today I tried some terrestrial imaging. Should be easy right? Lots of light, and I picked distant houses which in general don't move. The result? Blurry!

Again I tried a little focus bracketing to rule that out. It didn't help. I did try trading shutter speed and ISO for the same metering. Putting aside high ISO noise, the faster shots did seem a tiny bit sharper. I also did bursts of shots. Flicking between them, I could see distortion by the air. Different areas of each frame shifted slightly relative to each other.

But that's not the whole story. I finally figured out the diffraction calculator as previously linked. Print size isn't relevant but pixel size is, so I selected the tick box and can ignore the print values. All I have to vary is MP and f number. *if I'm reading it correctly* then for f/13 of the scope and the 14MP of the A350, it is diffraction limited to a size just over 3 output pixels. The diffraction limit is around f/8. Alternatively, sticking at f/13, the effective resolution where diffraction limiting sets in is 5MP! I might as well be using a D40...

Now, all the above still doesn't explain one thing. What I see through the eyepiece is far better than what I see in the photos. Is the eye+brain that much better at filtering, combined with better dynamic range? Ooh... that gives me an idea... moon HDR anyone? :D

And finally, I remembered to look for Jupiter tonight. It is now rising very early and is often blocked by trees near me as well as the evening light. Tonight I caught it just early enough to see. I got a while-ish blob and 4 moons clear to my eye. Photos gave similar difficulties as for the moon.

_________________
Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 15-85 IS
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 150 macro, 120-300 f/2.8 OS, Celestron 1325/13
Tinies: Sony HX9V.


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 Post subject:
PostPosted: Thu Oct 16, 2008 12:49 pm 
Did you manage to find out the reason your shots are blurry? Was it to do with diffraction?


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 Post subject:
PostPosted: Thu Oct 16, 2008 4:36 pm 
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Joined: Sun May 25, 2008 12:48 pm
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While diffraction is contributing in theory, I currently suspect that air movements are the biggest factor. In the short bursts I've tried, it can be seen that between each one the sharpness can vary. Tonight looks clear so far so I'll try a long sequence and see if that helps.

_________________
Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 15-85 IS
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 150 macro, 120-300 f/2.8 OS, Celestron 1325/13
Tinies: Sony HX9V.


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