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Forum: Photographic Technique
09-21-2015, 11:18 AM
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On an APS-C sensor camera (K50, K3, etc) the recommended exposure time is 360 divided by the focal length of the lens. So for a 50mm lens, it would be 360/50 = 7.2 seconds. With the GPS attached and in astrotracer mode, you can go longer than the recommended time....around 20 seconds to about 4 minutes for some reports depending on focal length (exposure time inversely proportional to FL).
---------- Post added 09-21-15 at 02:22 PM ----------
Thanks. My last session was a bust. I don't think I aligned the mini-equatorial mount correctly (latitude setting as well as polar alignment). The small mount did not have a polar alignment scope and I had to eyeball it with the camera on the mount (note to self: not a good idea). Also, the latitude setting scale came off so I glued it back - I must not not done it correctly.
Sigh.
I'll be going back in a week or so lugging the larger equatorial mount AND the telescope (it has a polar alignment scope on it, and I just bought a dual-axis motor) with the T-mount adapter. Milky Way is essentially gone for the season (per your earlier posting) but I'll try to get some DSOs from the Messier catalog.
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Forum: Photographic Technique
08-19-2015, 05:25 AM
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Forum: Photographic Technique
08-18-2015, 06:04 AM
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Just to clarify, you should be able to take several 20-sec exposures within a 5 minutes or whatever time span than the astrotracer function recommends, right?
You could of course go longer with a motorized equatorial mount, but not having that, the astrotracer should work for compensating for movement along the ecliptic and taking multiple exposures for a short time for stacking, no?
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Forum: Photographic Technique
08-15-2015, 07:45 PM
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Wow, lot of super informative tips. Thanks guys and gals! I'll give it a shot at the next dark sky opportunity. I have a 28mm f3.5 manual lens, will give that a shot after figuring out its sharpest infinity. I have been using a carbon fiber travel tripod, next time I'll take the alt-az mount that is a good 18 lbs.
After that once I am sure everything is figured out with the camera I'll hook up the camera to my f/12 Mak-Cass telescope (probably can't get more than a few seconds exposure on that, but should be interesting).
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Forum: Photographic Technique
08-14-2015, 11:56 AM
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Holy crap - those are great images! Interesting technique too, stitching different shots together like that.
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Forum: Photographic Technique
08-14-2015, 11:22 AM
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Shoot, I didn't pay attention to the elevation angle...something to track for next time. The other difference, of course, is part of the sky. The bearings: first image is 69-deg and the second one 4-deg, per the image data on the LCD screen (from true North, I think). Would the detailed EXIF data (extracted from exiftool) show elevation angle?
Neither are cropped.
Thanks for tip about 45-degrees straight-up, I believe I may have been doing that. Lower than 45-deg would probably have showed trees. This was at a Silver Dark Sky site near Cleveland, Ohio - so close to neither the equator nor the poles (even the Earth and Sun consider us 'flyover states'!). Does that mean no matter what I do, stars will trail even with 30 second exposures?
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Forum: Photographic Technique
08-14-2015, 10:33 AM
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Forum: Photographic Technique
08-14-2015, 10:27 AM
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Yup. Just posted one. I should've posted an image in the opening post to begin with. I'll upload some more.
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Forum: Photographic Technique
08-14-2015, 10:19 AM
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Here's one I took on Wednesday on the K-3....
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Forum: Photographic Technique
08-14-2015, 09:26 AM
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I tried different combinations, K3 and K-50; 35mm prime, 50 mm prime, 18-135mm; 240 secs, 90 secs, 30 secs. I performed 'precision calibration' on the O-GPS1. I also tested if the sensors are indeed moving - they are (captured a long-distance object on the ground and the resulting images showed movement blur).
Process: I put the cameras in bulb mode, enabled 'Astrotracer' function in the cameras, performed 'precise calibration' in both cameras, set timed exposure, and used both 2 secs timer and cable release (one after another).
What are some things I could be doing wrong? Other things to try to get pin point stars?
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