This is a faint emission nebula about 10000 light years away in constellation Cepheus.

Quite some more nebulae from Lynd‘s catalogue of bright nebula (LBN) can be identified (LBN 486, LBN 489, LBN 490, LBN 491, LBN 492, LBN 493) in this field. Open star cluster NGC7261 is fairly recognizable on the right side due to the enormous number of stars in this field. It is closer to us and about 5500 light years distant.
The OIII signal in Sh2-135 is very faint and could barely become visible in this image.

Borg 90FL
1.08 Flattener
ZWO OAG
ASI 2600MM Pro
ZWO EFW
Baader Ultra-Narrowband 3.5/4nm and RGB filters
H: 36x300s
OIII: 36x300s
SII: 36x300s
R/G/B: 20x60s each
Total Integration: 10h over 4 nights
Bortle 4-5

PixInsight
GraXpert