Across:
8 Americans dismiss sin (‘Americans’ dismiss ‘sin’ = amerca = CAMERA) of one producing the pictures? (CAMERA),
9 Advertisement (AD = A-D) about soldier (-GI-) museum (-TATE- museum) (AGITATED) in a state (AGITATED),
10 To be lovesick (yearn) with no sweetheart (‘swEet’ heart = ‘e’) (‘yearn’ without ‘e’ = yarn = YARN) is a long drawn-out story (YARN),
11 Check out (eye = EYE) court (-CT-) indoors (in doors = DO-ORS) (EYE DOCTORS) for those who want a better view (EYE DOCTORS),
12 Car (model T-) is no trouble (-EASE-) in fourth gear (fourth ‘geaR’ = -R) (TEASER) – work that one out? (TEASER),
14 The Centaur (HORSEMAN) or similarly one of those in 13 down (similarly to one of the ‘stable lads’ = HORSEMAN),
15 Ethics (MORAL PHILOSOPHY) of most of (s) those in 21 down (‘morals’ without ‘s’ = MORAL) and 22 across (‘philosophy’ = PHILOSOPHY) (MORAL PHILOSOPHY),
18 Underworld (= HELL-) is crooked (-BENT) (HELL-BENT) and determined to achieve at all costs (HELL-BENT),
20 Japanese runner (TATAMI) reflected (= reverse indicator) in Hiroshima tattoo (in ‘hiroshIMA TATtoo’ = imatat = TATAMI),
22 Ideology (PHILOSOPHY) of holy Popish (holy Popish) structure (= anagram indicator) (holy Popish = PHILOSOPHY),
24 Challenge (DARE) to serve up (= reversal indicator) sample of horseradish (sample of ‘horsERADish’ = erad = DARE),
25 Guy (MAN-) on dole (dole) briefly (e) (‘dole’ without ‘e’ = -DOL-) popular (-IN) (MANDOLIN) with one of those employed by musician (MANDOLIN),
26 Old one (old one = NOODLE) suspects (= anagram indicator) the local fool (NOODLE).
Down:
1 Tear to pieces (SAVAGE) in wild (SAVAGE),
2 Check an Arabian (horse) (REIN) writing (from the 3Rs = R-) to a German (‘a’ German = -EIN) (REIN),
3 Try to impress others with whom you know (NAME-DROP) with big cheese (NAME-) from 24 down (‘drop’ = -DROP) (NAME-DROP)
4 Celebrity (NAME) going around in national costume (going around in ‘NAtional costuME’ = NAME),
5 Hardship (RIGOUR) of most of (t) the outfit (‘rigout’ without ‘t’ = RIGOU-) from regiment (-R) (RIGOUR),
6 Place to holiday before Day of Judgement (LAST RESORT) – only to be used if all else fails (LAST RESORT),
7 Get to (RE-ACH) cover short business-like (professional = -PRO-) (REPROACH) lecture (lecture/reprimand = REPROACH),
13 Employed by Stockholders’ (stock holders = stables) (stables employ STABLE LADS) Board (-TABLE) to find the French (the = LA-) diamonds (-D) in ship (SS = S- -S) (STABLE LADS),
14 Provide lift (HOIST) for pal leaving hospital (‘pal’ leaving ‘hospital’ = hosit = HOIST),
16 Catch (catch/overhear = OVERHEAR) report (= homophone) of GIs in Britain during the war, as the saying goes (comedian Tommy Trinder’s catchphrase: “overpaid, oversexed, overfed and over here” = “over here” = “OVERHEAR”),
17 Trip (outing = OUT-ING) around heartless (a) place (lay) (‘lay’ without ‘a’ = -LY-) (OUTLYING) that’s remote (OUTLYING),
19 Leases (leases) complex (= anagram indicator) (leases = EASELS) for art supporters (EASELS),
21 The rights and wrongs (MORALS) of manuscript (ms = M-S) about examination (-ORAL- examination) (MORALS),
23 Needles mates (PINS and needles) to take out of snake pit (‘take’ out of ‘snake pit’ = snpi = PINS),
24 A Bandon (‘a Bandon’ = ‘abandon’ = DROP) developer ignores levee (‘developer’ ignores ‘levee’ = dopr = DROP).