Show arcseconds/pixel in ocular plugin

Please write one real reason for using of arcseconds/pixel data (it will be depend on telescope)

Yes, arcsec/pixel data, like FOV data, depends on the selected telescope, sensor and barlow/reducer.
While using a guidescope with PHD2, one must adhear to rules related to the angular resolution of the guidescope with its sensor and the angular resolution of the scope used for photography and its sensor. In this context the display of horizontal and vertical angular resolution would be as helpfull as the FOV-frame already is for taking pictures.

A new feature has been added as revision 9103 of the trunk branch in Stellarium's Bazaar repository at Launchpad: http://bazaar.launchpad.net/~stellarium/stellarium/trunk/revision/9103

Please check this issue on version 0.90.0.9115: https://launchpad.net/stellarium/trunk/0.90.0

Solution works for me, but:

For a given sensor the published horizontal and vertical pixel sizes, resolutions und sensor dimensions leave room for interpretation. Cannon published for it's EOS600D sensor:
Chip size: 22,3 x 14,9
Resolution: 5184 x 3456
Pixel size: 4,3 x 4,3
Resolution times pixel size does not accurately match the chip size.

Proposal:
Calculate exact chip sizes from resolutions and pixel sizes.
Calculate FOV and arcsec/pixel from exact chip sizes.
Present results in Stellarium rounded to 1 digit after comma (more are meaningless).

This assures that square pixels have equal h-scales and v-scales.

My opinion to the last proposal: in one side you are right and we can automatic calculate it, in other side user can calculate it yourself. Any automatic calculation may introduce non-obvious errors in this tool and I be preferred do not add automatic calculation.

I recomment fill the last proposal as separate bug (feature request), which requires more discussion.