There are three types of guiding for astrophotography.
1.
No guiding2.
Manual guiding3.
Auto guiding which is the subject I want to touch . I jump start straight into astrophotgraphy. To old to dable with visual observation and to know the stars and constellation. But like all photography one must know the subject matter in this case the stars and what is up there. Then how and when to acquire their images and how to post process for gaga presentation. I sort of fill in these blanks as I go along.
Astrophotography too has got it magic hour. The rule of thumb is image when subject matter is close to zenith and like non captive or wild bird photography when in season they are in their photographic best. Ah ha I thought this was easy until I learn about meridian flip. Apparently only the most expensive mount or research grade ones don't have to be bothered with it.
There are urban legends in astrophotography too that came to me and that are still circulating. The one I have talk about is aperture. I was lost for when doing land photography the most important variable is f stop. In it you can control depth of field, blur, sharpness and with flash a sense of movement. Thus land photographers will go the extra mile to purchase the widest lense they can afford for the focal length. Focal length only matters when you can be in danger, the subject can be in danger or you are just too lazy to walk to the subject.
I now realise it too matters in astrophotography. They change the name to focal ratio and these low focal ratios are not call telescopes but astrographs. Very pricey and heavy and certainly not for the Tom, Dick and Henry and they come as refractors, newtonians and RC astrographs.
Also I was told when starting with autoguiding , a focal length of the guide scope is half that of the imaging scope’s focal length was a good choice. It was an educated guess that seemed to work based on experience. It works for I took or struggle to take the few that I managed in my three years of learning astrophotography.
This 'conventional' wisdom breaks down when amateurs start using their 9X50 finder scope of focal length 250mm as guide scope. They get round stars up with imaging scope to 1000mm. At first they thought that it was due to their newer more sensitive guide camera, this reduction of focal length of guide scope from 1/2 to 1/4.
Not according to this research / study results
here .
Focal ratio matters too.
You can read the complete paper
hereHis conclusion is we need a focal length of 136mm but at f/2.8 for the guide scope and for a faster f/number the star will be brighter and the focal length can be reduced.
Now need an EOS adapter for the QHY5 and when weather permits can field test.
cheers
