Make Eyepices with different FoV show objects with constant size


first, thx for your awesome site, it’s really pleasent to use :)!!

One thing that’s currently strange in the telescope-simulator for eyepices is the handling of different FoV for eyepices.
Eg. for a 100 deg. eyepice the image actually get’s a lot smaller compared to looking through the real eyepice, instead of showing more.
That’s because the green ring does not change in size, when IMHO in reality for eyepices 50deg. vs 100deg. the size of the green FoV area should be increased and not the bigger FoV scaled down and fitted in the same FoV actually making the image apear much smaller than it really is.

I hope i could describe the problem with the current handling of FoV that it’s understandable, if not maybe this image helps:


Are you comparing eyepieces of the same focal length? For example are all of these 12mm eye pieces at different F.O.Vs? or are they different focal lenghts (12, 15, 9, etc…) with different Field of Views?

Hi Gebi, welcome to the forum!

Yes, I get what you mean. Two eyepieces with identical focal length but different FOVs should display objects the same size, but the bigger FOV show more surroundings. Am I correct?

This difference is also evident with binoculars, same principle applies. If you check the binoculars section you’l notice you don’t have a focal length or magnification inputs - only the FOV. If you change the FOV enough, the background zooms in/out as needed, to display the green circle as big as possible. The rationale is you’ll probably not want to have a small circle but be able to see as much as possible. This is only a problem when you are trying to compare different optics.

The good news is I have an item in the roadmap to update the Telescope Simulator in a way that you’ll be able to “add framings” to what you see. This way you’ll be able to compare different camera/eyepice/binocular framings, as well as zoom in/out as you please when the framing is in place.

I’m still a few months away of being able to do this, but hopefully that’ll take care of this issue :slight_smile:

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Partly, it’s noticeable when using the telescope simulator to compare eyepieces or when trying to frame really large FoV eyepieces because it shows the content much smaller than it really is, so people might get the wrong impression about them.

I read about your feature work on this in another forum thread and thought that might fit nicely.

A different possible simpler fix might be to use the current circle size for 68 degree eyepieces and simply paint a bigger circle (even not fully fitting into the sky map) for up to 120 degree eyepieces, because that’s kinda how it feels using such an eyepiece.
You have a wider FoV of the sky but you don’t get to see the whole 120 degree but you can look around without moving the telescope, so in a way just increasing the circle size would nicely match the behaviour.

Something like this? (not live yet)

This won’t change the fact that we need to zoom out to show bigger FOVs in their entirety, but this would certainly give you a very visual comparison of different FOVs.

By the way, this is going live shortly, as an option inside the eyepieces section :slight_smile:

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