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Forum: Pentax K-70 05-31-2017, 06:22 PM  
Interval shooting oddity?
Posted By gifthorse
Replies: 14
Views: 1,643
You're quite welcome. There are many of us here who are glad to show off help out. I have an OGPS-1 and I like it for certain applications but it does have some limitations you need to know about. First, it needs to be calibrated whenever you use it and for long photo sessions it may need several re calibrations throughout the night. How well you do the calibration will affect how well the gps works. There are a number of calibration tutorials online. Second, it is also affected by large or nearby metal objects. (too close to a car, large metal buildings, etc) Third, is that "max of 5 minutes" thing. That usable duration will vary with the focal length of the lens. The shorter the focal length, the longer the usable exposure time. You won't get 5 minutes exposure time with a 300mm lens. From my experience, you should cut the recommended exposure time in half. Finally, star trails are caused by the star's motion relative to the earth (That includes the camera and it's sensor.) The OGPS-1 works by calculating and moving the camera's sensor in relation to the motion of the stars. If the camera sensor remains fixed relative to the stars , the sensor will be moving relative to the earth. You will get a blurred foreground. You can get around that by taking a second identical exposure without using the gps and then cut and paste that foreground over the blurred foreground. The OGPS-1 was one of the reasons I chose Pentax but if you aren't aware of the limitations and work within them, you'd wind up frustrated.
Forum: Pentax K-70 05-31-2017, 10:48 AM  
Interval shooting oddity?
Posted By gifthorse
Replies: 14
Views: 1,643
I believe that the object in your image is an Iridium flare. Satellite flare - Wikipedia There is a website that predicts them and other night sky objects such as the ISS at Heavens Above. Heavens-Above Simply enter your viewing location and it will show when they're visible at your location. If there's nothing showing in the table it just means that there is nothing visible during that time period. The website will also provide magnitude (brightness) and show a map of the object's path overhead. For the ISS and Iridium flares a single frame will give a better image. Multiple frames produce gaps in the arc. The shutter closed between frames creates gaps in the trail. The ISS and Iridium flares are bright enough and the duration short enough that a single frame is preferable. For meteor showers use Manual mode and interval shooting. The interval you choose is the time from the beginning of one frame until the beginning of the next frame. It isn't the time from the end of one frame until the beginning of the next frame. The interval you select must be longer than the exposure. i.e. if you're are shooting 25 second exposures, the interval must be at least 26 seconds. If you set 10 second exposures, the interval you set must be at least 11 seconds. If you wanted 25 second exposures with 5 seconds between each image, you would set the exposure for 25 seconds and then add 5 seconds to get an interval setting of 30 seconds. You also need to turn off the high iso and long exposure noise reduction. They double your interval. In other words, if you are making 25 second exposures with the noise reduction on, your interval will have to be 51 seconds or more. (25 second exposure + 25 second noise reduction + 1 second or more because interval must be greater than exposure time.) Noise reduction does a dark frame subtraction for each image. You can do a dark frame subtraction with a single dark frame in PP. Just do a web search for dark frame subtraction.
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