Even with the same FOV value, the displayed image can differ significantly depending on the shape of the window.

[hiro1616hiro]

I wanted to discuss this in the Discussions section, but since there were no responses, I'm reposting it in the Issues section.

Aladin Lite was updated in February 2026, but after the update, there's an issue where the displayed object image differs significantly depending on the window shape, even with the same FOV (Field of View) value.

Before the update, it seems that the same size image was displayed regardless of the window shape.

The images below show examples of display in vertical and horizontal windows when "fov=0.54" is specified.

Both windows have almost the same area with "field of view=0.54," but the object in the vertical window is extremely small.

Before the update, objects in vertical windows were displayed at the same size as objects in horizontal windows.

This is thought to be because the size of the object is now determined by the width of the window.

It's more logical and user-friendly to fix the display to an absolute value and operate zoom in/out using the "+" and "-" buttons in the lower left corner of the window.

I sincerely hope that the specifications will be reverted to those before the February update.

[tboch]

Dear hiro1616hiro, thank you for your feedback.
I have the feeling that the new behaviour is the correct one. Field of view is kept constant (horizontally), whatever the window size is. Are you saying we should keep the vertical FoV constant?

May I ask what issue this causes to your tool/application? Windows resizing actions by the users are not frequent.

[hiro1616hiro]

Thank you for your reply.

For example, when you obtain the address of an arbitrary region using Aladin Lite's "Get view URL," it includes the Fov value.

If you send this to someone else, the image they see will depend on the shape of the window they have open.

This increases the likelihood that they will see an image unintended by the sender.

Regarding why I raised this issue,
I've actually been creating a list of target galaxies for about two years now,
and I've pasted the address obtained using Aladin Lite's "Get view URL" as a link to each object.

I had prepared vertical and horizontal windows to match the shape of the CMOS camera, so that the same field of view as the captured image would be reproduced.

Before the February 2026 version update, if the Fov value was the same, the object could be displayed at the same scale regardless of the window shape.

However, after the version update, even with the same Fov value, the size of the object changes significantly depending on whether the window is vertical or horizontal.

So, as tboch mentioned, the horizontal reference point has changed, is that correct?

These are the points I find inconvenient about the February version update.

Were there any problems with the previous specifications?

While I understand this specification change was made for a reason, for someone like me who uses Aladin Lite, the shift in the reference point is quite shocking.

I would appreciate it if you could let me know your outlook on whether this specification change will be continued in the future.

Incidentally, the galaxy list has already accumulated to around 3,000 entries, but it is expected to take another two years to complete.

After completion, I plan to distribute it to others who share my hobby of astrophotography.

(Please excuse any potentially offensive phrasing, as this is a translation from Japanese to English.)

[hiro1616hiro]

P.S.
After further consideration, I still believe that the Aladin Lite update released in February 2026 introduced an unreasonable change.
Before the update, the FOV value behaved consistently and remained fixed regardless of the browser window’s aspect ratio. I think this previous behavior was more logical and predictable.

tboch asked me, “Are you saying that the vertical field of view should be kept constant?”
Yes — that is exactly my point. Keeping the vertical FOV constant would avoid the issues that are now occurring.

For example, the images of targets embedded in DeepSky Corner vary significantly depending on the user’s browser window shape. This means that even when the same FOV value is specified, different users may see very different representations of the same object. This undermines the reliability of shared view URLs.

I would greatly appreciate it if you could reconsider whether the current behavior is truly the best approach, and whether restoring the previous specification might be more appropriate for users who rely on consistent FOV scaling.

[hiro1616hiro]

P.S.
In my previous comment, I said that “the vertical field of view should be kept constant,” but that was not entirely accurate.
The real issue is this: before the February 2026 update, Aladin Lite seemed to display the sky using an absolute scale corresponding directly to the FOV value, whereas the current version uses a relative scale that depends on the browser window’s shape.

With the current method—where the horizontal width of the window determines the scaling—I believe this will cause problems in many situations, such as small embedded Aladin Lite windows on websites.