On April 9, 2016 10:16:32 PM PDT, Alan C <[email protected]> wrote: >Thanks for that erudite explanation, Larry. I found some more complex >explanations on the Web too. I'll give it a go with my M50/1.7 which is >the >fastest lens I have. Unfortunately the K7 will be quite noisy at ISO >1600.
What you need to explore is image stacking. > >Alan C > >-----Original Message----- >From: Larry Colen >Sent: Saturday, April 09, 2016 9:35 PM >To: Pentax-Discuss Mail List >Subject: Re: experimental geso Thunderhill at night > > > >Alan C wrote: >> I'm surprised there is virtually no lateral movement of the stars >> visible with a 10 sec. exposure. I suppose the short focal length >plays >> a part. In 1965 I photographed the Ikeya-Seki comet using a Super Tak >> 135/3.5, ASA 1250, 5 sec and slight movement was visible. > >20 seconds on the FA 31 is pushing the "rule of 600" that the exposure >time in seconds times the focal length of the lens needs to be under >600. Modified, of course, by the resolution of the sensor, how much >you >crop it down etc. > >In my case, when I'm stitching multiple exposures together then >downsizing for the web, my "effective focal length" for the rule of 600 >is much shorter than 31. When pixel peeping, you can see the stellar >blur, or even some doubling up of stars from the stitching. > >For example, this is one at 1440 wide, and if you look closely you can >see the blur >https://www.flickr.com/photos/ellarsee/26316993875/sizes/o > >The "original" is stitched to 6844 wide, so printed big, the blur is a >lot more noticeable. > >Note that 135 * 5 is 675, just slightly more than 31*20 (620), although >that can be effectively divided by 3 or 4 on some of the stitched >shots. -- Sent from my Android phone with K-9 Mail. Please excuse any swypos. http://red4est.com/lrc -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
