Is there a way to have SS5 calculate the star trail length for a given exposure time within the active FOV(s)? It is a simple calculation for SS once exposure time is specified by user, but tedious to do manually because it varies by the altitude and azimuth of the scope line of sight.
If "no", which I think is the case, could it be considered?
It is an extremely helpful thing to know for astrophotography or EAA with an AltAz mount.
We have generally been reluctant to add features specifically for astrophotography. It opens the door to a "slippery slope" of general support for astrophotography.
Nevertheless, we will keep it in mind for future upgrades.
Why do you need the specific length of the trail? You can simply advance time by the amount of the exposure and see where the star in question advances to.
It isn't really that simple, I don't think? In altaz mode, the mount is tracking the movement of the center of the FOV. But field rotation causes stars that are not in the center of the FOV to trail in proportion to the distance from the center. I can't think of a way to simulate this in SS5. I welcome suggestions, however!
To answer your question why I want to know: so that I can either choose objects that are positioned favorably for altaz tracking, or to estimate the longest safe exposure time. I would want to limit the trail length to approx. the pixel scale.
I think I misunderstood what you wanted. I though you were talking about star trails obtained by using a non-tracking mount and pointing it near Polaris and opening the shutter for a while. I seem you are talking about star trail cause by field rotation on a tracking Alt/Az mount. I agree my suggestion wouldn't be useful for the latter.
So, then, you will add this feature? ;-)
I wrote a spreadsheet to do the field rotation calc's for my use. I noticed that each item needed for input to the spreadsheet was already readily available in SS5, with the lone exception of exposure time. But even exposure time would not need to be provided to SS5 by the user, as it would be useful to know the stair trail length in "microns per second of exposure."
If you decide to look into this further, I'll be happy to forward a reference to the simple equation that estimates the stair trail length based on these parameters already known to SS5:
I don't see this as restricted to astrophotography applications. It also directly relates to EAA on alt/az mounts, which is becoming very popular.
Jim
I think it is pretty unlikely we will add this anytime soon but I will add it to the list of requested features.
"It also directly relates to EAA on alt/az mounts"
What is EAA?
Electronic Assisted Astronomy. Typically, a video camera that provides near realtime stacked images. Can also be done with DSLR and other digital imaging cameras. Very powerful tool for deep sky observing in light polluted areas.
And why does one need to know about the length of star trails due to field rotation for this?
In order to plan observing sessions:
For instance, assume use of Nikon D7200 and CPC 800 (with f/6.3 reducer) for near realtime electronic observing (EAA). Software used would be BackyardNikon and AstroToaster for capture and imaging, SS5 for observing plan and telescope control. The CPC 800 will perform altaz tracking pretty well, but cannot compensate for field rotation.
Say I would like to view M82 at 9:00 pm tonight. From SS5 I know it will be positioned at 26.2 / 46.3 az/alt coordinates (unfavorable location). According to my spreadsheet, exposure time of 5 seconds should give me stair trails of 5.3 microns in the corners of the sensor. If I want a view without noticeable trails in the corners, I would need to keep the exposure time below 5 seconds for each frame.
However, if instead I choose to view M95 in Leo, positioned at 92.8 / 22.7 az/alt (favorable location), my spreadsheet says I can expose for more than 90 seconds before the stair trail length exceeds the width of a pixel (3.9 microns) on my sensor.
This shows how sensitive the length of the star trail lengths is relative to object position. Being able to quantify this information while planning a session using SS5 would be very handy.
For using things like MallinCams, I just don't see this as an issue. The stars are generally somewhat bloated anyway. If you see objectionable trailing, shorten the exposure time.
I'm sorry, but you haven't convinced me that this is not mainly an astrophotography feature. I don't see us adding this any time soon.